# My First Engine Build



## c_mario (Aug 20, 2018)

Hi,
I discovered this forum while searching for projects to build with my lathe. I purchase a lathe around 4 months ago. I have never used a lathe before but wanted to make an IC engine. First I just made some simple bushes, Kurled knobs, ornaments and a Gyroscope..
I found the MP3.2 plans on this site so decided to make it.
I have attached a photo.

I was wondering what the starting technique was.
I have not been able to make it run for more than a few seconds. At first I had very little compression so I grew the cast iron piston by heating then quenching in oil, then tempering. It grew so it no longer fit into the bore. I then lapped it to get a push fit to the top of the bore.
It seems to have good compression now from what I can remember from my RC flying days when I was in my 20's.

I get it to fire but it only runs for a few seconds maybe 5 or so at what sounds like an old 4 stroke idling.

One thing I didn't do was the little ledge on the backplate I circled in the attached 2nd image.
Mainly because I didn't understand what it was for, it did not seem to be needed for piston clearance.
Whats it for?
Anyway I was hoping I could get it to run at least once.
Thanks for Reading.


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## minh-thanh (Aug 20, 2018)

maybe ...help you 
https://www.homemodelenginemachinist.com/threads/glow-engine.30315/


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## natalefr (Aug 20, 2018)

Check the carburettor, often you have problems with fuel flow, if the needle has too pronounced taper you can have a too delicate and critical adjustment, which taper has the carburetor needle? Do you have the constructive design of the carburetor?


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## c_mario (Aug 20, 2018)

natalefr said:


> Check the carburettor, often you have problems with fuel flow, if the needle has too pronounced taper you can have a too delicate and critical adjustment, which taper has the carburetor needle? Do you have the constructive design of the carburetor?


I followed the plans for needle taper as best I could.
How many turns out should I start with?


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## natalefr (Aug 20, 2018)

Normally for airplane engine IMHO try to start and 1 and half if the motor start quickly and stop open more
For my Hupshur horizontal four stroke (example) the needle taper was 16° and the motor was critical, now the taper is 3° and is better


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## c_mario (Sep 6, 2018)

Still struggleing to get this to run. I remade the cylinder liner as I missread the plan and cut the transfer ports too high. The new liner has the transfer ports at the correct height. I have good glow on the plug, i see fuel is getting to the combustion chamber, I get it to fire on almost every flick of the prop but it just wont continue. I made gaskets to seal the backplate and front crank housing better.
There seems to be good compression. I tried different needle positions changeing slowly about a 1/4 turn at a time. What can I try next?


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## minh-thanh (Sep 6, 2018)

If you put plug into head and flip prop counter clockwise,did you feel resistance by compressed air and hear popping sound?


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## c_mario (Sep 6, 2018)

Hello minh, 
Absolutly, there is resistance and popping sound. The engine also fires when igniter is connected.


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## minh-thanh (Sep 7, 2018)

You should check the carburetor and adjust little by little,
Lock the carburetor, then open it   very little, very little and start the engine, little by little you will have the best position.
And the carburetor must follow the plan. (I made a mistake when make it did not follow the plan )


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## Cogsy (Sep 7, 2018)

Depending on the taper of your needle, 1/4 of a turn might be too much - some are incredibly touchy and go from too lean to too rich that quickly. If you've got an electric starter/drill on it just get it spinning and creep the needle open, listening for changes in the noise to show you if you're getting closer or further away. If you're hand flipping the thing I'd guess your arm is getting sore by this point...


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## c_mario (Sep 7, 2018)

Hi Cogsy,
I followed the plans and the needle taper is as drawn, and yes I am hand flipping the engine.
So if I start from a dry engine, should I prime it at all. When I was in my 20's I flew RC planes. Priming was open throttle, needle 1.5 turns out, block carb air intake, flip prop several times to prime. Open carb intake, attached igniter , flip by hand till start. Didnt take long at all.
So I should try closing needle, no prime? open say 1/16 turn flip a few times, open another 1/16 flip and repeat?


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## Cogsy (Sep 7, 2018)

When I flew RC I had pretty much the same starting technique as you describe, but that was with well-known engines. I would say you would still want some prime with yours, but the unknown is how much needle you need and how 'touchy' your needle adjustment is, which can vary between home-made engines even using the same plans. Even with production engines sometimes I'd flood mine and need to close the needle and spin it for a while to clear the issue or it just wouldn't fire.
If I was you I'd be setting up some sort of electric start driver (probably just an electric drill with a drive hub) so you could prime it, then drive it constantly while slowly adjusting the needle to figure out where it needs to be. It takes a lot of the guess work out of it. I'm sure you'll get to the point where you can had start it when it's tuned properly but it could be tough to get to that point with hand-flipping.


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## GailInNM (Sep 8, 2018)

A few things you might check. These might sound silly, but they are things that I have seen others or my own engines.

Check that the spray bar is clean on the inside. I have seen an instance where there was a chip inside that prevented the needle from closing all the way resulting in too rich a mixture even when it felt  like the needle was all the way closed. You can also hook a piece of fuel line to the fuel inlet and suck or blow to make sure that the needle is actually closing all the way.

Look down the air inlet and make sure that you can NOT see the cross hole in the spray bar.  It is easy to have the spray bar rotate when it is being tightened. If you can see the hole it will not draw fuel when running, but will draw fuel when you choke the the engine when blocking the air inlet and turning the engine over to prime the engine.

While looking  down the air inlet check that the crankshaft valve hole is just opening just after bottom dead center and closes just before top dead center when turning the engine in the normal run direction.  I have seen one engine that had the valve hole was in the right absolute angular position relative to the crank pin, but on the wrong side.  The engine would run fine in reverse direction, but would not run in the correct direction..

If the cylinder sleeve is rotated 180 degrees so the exhaust port and the transfer passages are reversed the engine will not run ofter the prime is used up.  Not likely in your case because the ports are very different visually, but still worth a quick look look.

Not so easy to check is the location of the transfer ports relative to the exhaust ports.  As you already know it is easy to get them in the wrong place.  With the the 45 degree bevel they are hard to machine and even harder to measure them.  Still, with proper lighting you may be able to see the piston close the transfer ports while the exhaust port is still 1mm open.

Last, make sure the two crankcase gaskets are in good condition. Any air leakage into the crankcase will drastically change the fuel/air induction.

Gail in NM


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## c_mario (Sep 9, 2018)

Thanks for all the info GaillnNM and Cogsy. I have almost given up hope. I can confirm spray bar facing correct direction and blowing down fuel hose with needle closed shows it is truely seated. Ports are facing correct direction  and transfer ports close before exhaust port. Will check crankshaft valve hole (open just after BDC and close just before TDC).
I am going to rebuild another crankshaft housing and try to get closer tolerances as I can see fuel coming from the front of the crankshaft. I made a bronze bushing for it but ruined the alignment so have to start again.
I do see on the down stroke that there is enough pressure in the crankcase that I can hear a leak, fuel will bubble up between the sleeve and the cylinder before the transfer port opens. With all the in and out and pulling apart and checking , if I make it too tight I wont get it out again. Is it meant to be a push in never get out again fit?
Regards
Mario.


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## vederstein (Sep 9, 2018)

_... At first I had very little compression so I grew the cast iron piston by heating then quenching in oil, then tempering..._

I didn't know of this technique.  I may use it for my PITA stirling I'm working on.

Can you point me to or write up a short procedure?

Thanks,

...Ved.


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## c_mario (Sep 10, 2018)

vederstein said:


> _... At first I had very little compression so I grew the cast iron piston by heating then quenching in oil, then tempering..._
> 
> I didn't know of this technique.  I may use it for my PITA stirling I'm working on.
> 
> ...


Hello Ved,
I found some info on a web site somewhere but cant remember which one. It works with Cast Iron so all you do is heat the piston till its glowing red hot, mine was almost orange then quench it in oil. I just used motor oil. Do it outside and drop completely in the oil otherwise you can cause the oil to catch fire ( yes that happened to me) and the smoke and smell was pretty bad. Outside was no problem, I've actually done it twice. I think it expanded about .07mm. After quench and cooled, heat it again till just a straw colour and then let it cool in air , I am told this takes the brittleness out of it.


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## Aerostar55 (Sep 13, 2018)

c_mario said:


> Hi,
> I discovered this forum while searching for projects to build with my lathe. I purchase a lathe around 4 months ago. I have never used a lathe before but wanted to make an IC engine. First I just made some simple bushes, Kurled knobs, ornaments and a Gyroscope..
> I found the MP3.2 plans on this site so decided to make it.
> I have attached a photo.
> ...


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## Aerostar55 (Sep 13, 2018)

That flat on the top of the back plate is for piston clearance.  If you didn't need it, I would suspect that 
your piston might be too small, or the wrist pin might be in the wrong place.  Either of which would affect porting and thus the ability of the engine to pull fuel.  Make sure that the crank case has a good seal. ( front bearing, Back plate cover and bypass)  Do you feel a slight pop or pull on the down stroke?  This is the air "force' that pushes the fuel up over the piston through the bypass. It's critical in any two stroke.  Other than that check the dimensions on your venturi tube, needle valve. The spray bar hole must be accurate and turned in the correct orientation to the intake. Try extending the length of the intake tube with a temporary tube, or partially blocking the intake (choking).  That said many glow plugs these days
are just defective.   Try several different or new ones.


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## c_mario (Sep 13, 2018)

Aerostar55 said:


> That flat on the top of the back plate is for piston clearance.  If you didn't need it, I would suspect that
> your piston might be too small, or the wrist pin might be in the wrong place.  Either of which would affect porting and thus the ability of the engine to pull fuel.  Make sure that the crank case has a good seal. ( front bearing, Back plate cover and bypass)  Do you feel a slight pop or pull on the down stroke?  This is the air "force' that pushes the fuel up over the piston through the bypass. It's critical in any two stroke.  Other than that check the dimensions on your venturi tube, needle valve. The spray bar hole must be accurate and turned in the correct orientation to the intake. Try extending the length of the intake tube with a temporary tube, or partially blocking the intake (choking).  That said many glow plugs these days
> are just defective.   Try several different or new ones.



Thanks for the info. I will check the piston size again but I did follow the drawings. I certainly feel a pull on the downstroke. 
When you say bypass, whats that? Is it the vertical channels in the cylinder wall that transfer fuel from the crankcask to the combustion chamber?.
I will remake the front bearing housing and try to get a better crankshaft to housing fit and install a bronze bush at the very front of the housing.
I was seeing fuel coming out the front of the engine.


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## Aerostar55 (Sep 13, 2018)

Yes 


c_mario said:


> Thanks for the info. I will check the piston size again but I did follow the drawings. I certainly feel a pull on the downstroke.
> When you say bypass, whats that? Is it the vertical channels in the cylinder wall that transfer fuel from the crankcask to the combustion chamber?.
> I will remake the front bearing housing and try to get a better crankshaft to housing fit and install a bronze bush at the very front of the housing.
> I was seeing fuel coming out the front of the engine.


the bypass is the passage that allows the fuel charge to “bypass“ the piston.  If you are seeing fuel coming out of the front bearing it should be going up over the piston. It’s normal to get a little during running as this helps to lubricate the crank shaft.


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## minh-thanh (Sep 13, 2018)

c_mario said:


> Hello minh,
> Absolutly, there is resistance and popping sound. The engine also fires when igniter is connected.





c_mario said:


> . I will check the piston size again but I did follow the drawings. I certainly feel a pull on the downstroke.
> .


Hi c_mario !
When you assemble piston and cylinder, it is dry and clean ? With my little experience of do  it is: keep the piston and cylinder dry and clean, and then make it easy to determine whether it is sealed or not .


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## c_mario (Sep 21, 2018)

Well, I have checked the piston, remade the front housing for crankshaft , remade venturi, remade cylinder liner to lower the transfer ports, sealed front housing and backplate with gasket sealant, made gasket for cylinder to crankcase yet I still cannot get it to keep running. It will fire almost every time I flick it but just wont keep running. I see the glow plug glowing through the exhaust port so I know its lit, I've checked that the needle closes completely by trying to blow through the fuel tube while slowly opening the needle valve and it definitely cuts off flow. I've primed by choking and flicking over the engine and via a syringe directly into cylinder through glow plug hole. Always get same result, engine fires a couple of times on each flick but will not keep running. I tried a drill to start it but I don't have a spinner on the prop so the nut tends to undo trying to start it. It seems a little excessive to go buy a starter and spinner at this stage just to try to start it, but I may do this out of frustration.


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## Cogsy (Sep 21, 2018)

A plastic spinner shouldn't cost much and you can whip up a spinner driver to fit your electric drill I'm sure, just a bit of turned aluminium and maybe some rubber from an old bike/car inner tube should do it. I remember from my RC days that a visibly glowing glow plug isn't a completely foolproof test. If the glow plug battery is a little low, the plug will glow nicely in the air/engine but the cold fuel cools it down very rapidly. A couple of times at the field having starting problems, changing plugs, etc. and then borrow a fresh glow driver and it would fire straight up. Might not be your issue but is something to remember.


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## Mechanicboy (Sep 26, 2018)

First of all: Is compression good? When you are turning the crankshaft, it must not be leakage past piston and you feel resistant to turn the crankshaft.

The engine with good compression will start easy.

Is the ratio of compression right? The glowplug engine can have a ratio of compression from 1:8 to 1:10. too low ratio of compression make it difficult to run the engine without battery connected to glow plug.

Is the compression in crankcase good? You will hear "poof" from transferport when you are turning the crankshaft without cylinder head.  If no "Poof" there means leakage one place in the crankcase to example leakage via gasket or from crankshaft/bearing if the tolerance is fault.


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## Mechanicboy (Sep 26, 2018)

Minh-Thanh wrote this: When you assemble piston and cylinder, it is dry and clean ? With my little experience of do it is: keep the piston and cylinder dry and clean, and then make it easy to determine whether it is sealed or not .

I will correct the fault explained by Minh-Thanh: 

With dry piston and cylinder --> the piston feel tight in cylinder -- > OK
With oiled piston and cylinder--> The piston is loose in bottom of cylinder and feel tight in top of cylinder (tapered cylinder) --> OK

If the cylinder is not tapered, the engine will lose compression when working temperature is raise due the cylinder is expanding by heat.

With tapered compression make engine easy to start up and keep cylinder parallel when the engine is running under working temperature without loose compression.


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## c_mario (Sep 26, 2018)

Mechanicboy said:


> Minh-Thanh wrote this: When you assemble piston and cylinder, it is dry and clean ? With my little experience of do it is: keep the piston and cylinder dry and clean, and then make it easy to determine whether it is sealed or not .
> 
> I will correct the fault explained by Minh-Thanh:
> 
> ...


HI,
Thanks for your responses. I do understand the principals you explain and I have built the engine according to plans on this site so if the compression ratio is whatever the design produced. I do understand what you mean by 'poof' sound from transfer port opening and I believe I get this however it is hard to check with cylinder head off because the cylinder bolts hold down both the head and the cylinder together as one. I have looked for any leaks in the crankcase and the last thing I can think of before I give up is the fit between the cylinder liner and the cylinder wall. If there is leakage between them I guess that will be a problem. How to seal that? This is the second cylinder liner I have made but it is not a hard fit, i can remove it by hand. If I use a sealant what should it be?
Thanks.


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## Mechanicboy (Sep 27, 2018)

You can listen there is "poof" from cylinder when the glow plug is removed.

No need to make a new cylinder every time it fails. Relap again until the cylinder is parallel. Make a new piston and lap. Try to fit the piston into cylinder until it stop a half way into the cylinder --> Stop, no more lap the piston.

Smear the piston with chrome polishing paste (I am using the Autosol Solvol Chrome Polish) and press light into in the cylinder in same time you are rotating the piston into the cylinder until the piston is stuck in the cylinder. Remove piston from cylinder and clean both piston and cylinder carefully free for polishing paste. Take a test fit and check as i wrote in early post. If the piston do not stop up to TDC, repeat again to lap the piston into cylinder and take a test fit after cleaning is done. Also the cylinder must be tapered created by piston under lapping and the piston feel tight near TDC when you are pushing the piston into the cylinder.

Cylinder of high tensile steel from drive shaft or old wrist pin from piston (must be annealed if to hard to machine the steel, unnecessary to rehardening since alloy steel is hard enough).

Piston of cast iron as you can find in the old cam shaft made of cast iron (the cam is impossible to machine, between cams is soft and machinable) or thick brake disc (without ventilated disc).


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## c_mario (Sep 27, 2018)

Mechanicboy said:


> You can listen there is "poof" from cylinder when the glow plug is removed.
> 
> No need to make a new cylinder every time it fails. Relap again until the cylinder is parallel. Make a new piston and lap. Try to fit the piston into cylinder until it stop a half way into the cylinder --> Stop, no more lap the piston.
> 
> ...



Hi Mechanicboy,
The piston to cylinder liner fit is as you described. I have done the lapping job as described.
What I was saying was that the cylinder liner fitting into the aluminium cylinder/crankcase is not a very tight fit.
I think if it leaks between the steel liner and the aluminium that is bad right?
I can pull it out by hand.
Should it be a tight permanent fit?
should I use some sort of sealing material like a gasket cement ?
Thanks.


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## Mechanicboy (Sep 27, 2018)

c_mario said:


> Hi Mechanicboy,
> What I was saying was that the cylinder liner fitting into the aluminium cylinder/crankcase is not a very tight fit.
> I think if it leaks between the steel liner and the aluminium that is bad right?
> I can pull it out by hand.
> ...



It must be light press fit due heat of expansion and keep tight against leakage.


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## f2cf1g (Oct 2, 2018)

Hi c_mario and forum, I haven't posted before.  Apologies if I have contravened forum etiquette by posting here first.  I see you have re-made most of the motor without success and it occurred to me the one thing you haven't tried changing is the compression ratio.  I have done a few Nelson head conversions and I find that getting the head volume right is important.  If it is too low you can get the symptoms you described, i.e. hard to start then run for a while then stop.  It needs to be 10:1 or a bit more, as a previous posted has said, especially using fuel without nitro.  Alternatively it could be the head joint leaking, this could have a similar effect.  Maybe machine say 0.2mm off the top of the liner and adjust CR with brass shims if this is not how it is already set up, the shims also provide a better seal.  This only applies if it's not flooding off due to excessive needle opening or leaning off with not enough fuel.  Hope this might helps.  Good luck.


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## c_mario (Oct 7, 2018)

The plans I went from say the compression ratio is 8.3 :1.
I have teflon seal at cylinder base and aluminium foil at head. I cannot see leaks.
After weeks of trying the best I get is a 2 second run. See if the video sound gives anyone a clue what might be wrong.


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## Mechanicboy (Oct 7, 2018)

Enough fuel? Turn the fuel needle 1.5-2 turns from closed. Too much fuel out of exhaust port = too much fuel.


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## c_mario (Oct 7, 2018)

Mechanicboy said:


> Enough fuel? Turn the fuel needle 1.5-2 turns from closed. Too much fuel out of exhaust port = too much fuel.


I have tried infinite fuel needle positions. The needle was 1/4 turn from closed in this case. It does not seem to make any difference. I can even disconnect the fuel line, close the needle, prime with direct inject into venturi and it will run like that off the prime alone. I made a new needle assembly as well , this time by choosing a sewing needle as suggested in some other text's I've read. f2cf1g spoke of compression ratios , I could make a new head to increase that. I too thought fuel air mix. Now maybe fuel itself, but this is a new bottle of fuel I purchased only 3 weeks ago.


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## f2cf1g (Oct 7, 2018)

The motor sounds good and I'm sure is ready to run.  However, 8.3:1 is low and may well be the problem whatever the designer says.  Don't forget that the teflon and aluminium washers are both reducing the compression ratio.  We are talking tenths of a mm here.  No need for a new head, just put the one you have back in the chuck, skim 0.2mm off the area which seals against the head and see what difference that makes.  But before you do that:
1. Check that the crankcase is not full of fuel, that could cause the symptoms you are seeing because the liquid fuel douses the plug or causes a hydraulic lock preventing the engine from turning over.  Upright engines are very easy to flood and difficult to empty when mounted on a bench (turn upside down and encourage to drain into the cylinder through the transfer ports then turn on one side to empty through the exhaust.
2. When/if the crankcase is empty, close the needle completely or disconnect the fuel line and prime it though the exhaust port by splashing fuel against the closed piston, open the exhaust port and let the fuel trickle into the cylinder.  Then flick and see if it will run on the prime.  When it does, reconnect the fuel line, open the needle a turn or so and try again.
3. Make sure the plug is glowing orange and set the tank so that the fuel is level with the spraybar.


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## Mechanicboy (Oct 7, 2018)

Read capter five.. https://rclibrary.co.uk/files_titles/1996/Engine_Encyclopedia_RonMoulton_partA.pdf

And the other part of book if you want the complete book  
https://rclibrary.co.uk/files_titles/1996/Engine_Encyclopedia_RonMoulton_partB.pdf


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## Mechanicboy (Oct 7, 2018)

With 8:1 compression ratio you need hot glowplug. 

How to measure compression ratio in your model engine.. 
http://adriansmodelaeroengines.com/catalog/main.php?cat_id=153


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## c_mario (Oct 7, 2018)

Thank you Mechanicboy and f2cf1g. I read the documents that were pointed out to me , thanks for that. I will try all the suggestions mentioned.
I am using a hot glow plug.
I may be experiencing the hydraulic lock mentioned as sometimes after it fires the prop stops/locks on the down stroke.
This certainly is a learning experience.
Thanks I will let you know what happens.


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## c_mario (Oct 12, 2018)

Hi,
As suggested by f2cf1g I drained the crankcase, I splashed fuel as suggested, It ran on prime, I reconnected fuel hose opened 1.5 turns continued to fire a few times as before.
So I did the skimming to increase the compression ratio. Still the same result no matter what I do. Glow plug is glowing orange.
I know fuel is good, plug is good technique is good because I found my 35 year old OS max 40 that's been sitting in a box for probably 20 years and got it started in less than a minute.
Thanks for all your info but at this point I think I will give it a rest for now since its just too frustrating and disappointing, i really hate giving up on anything.
Failure here discourages me from further projects.


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## minh-thanh (Oct 12, 2018)

I think  it ran but the fuel was leaking when the piston went to the TDC, and leakage of fuel, though very small, would make it hard to run or it does not keep running - check for leaks.
With compression, it should be really good - check the cylinder and the piston. My first engine, I unfix it and adjusted the cylinder and make new the piston more than 10 times


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## f2cf1g (Oct 13, 2018)

I'm sorry to hear that you have no success but it must be fixable, just have to find the cause.  For example, I have recently completed an Atom Minor.  Initially it wouldn't start without an electric starter, the symptoms were exactly as you describe.  I suspected the piston fit which was rather loose (made as recommended for a spark ignition motor by someone on a forum) so I cherry-bombed it to increase its size and re-lapped.  It now starts easily by hand.  Maybe that's the core of the problem but I know you have remade a lot of parts already.....  I recommend trying it on a starter if you can borrow or make one.


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## Mechanicboy (Oct 13, 2018)

From my own experience, it's best to make a big model engine with piston ring and these small engines that can be difficult for beginners since there is no supervisor present and teach the beginner to make a small model engine without piston ring.  A larger engine has less compression loss than a smaller engine and the engine should be easy to start and run.

Beginn with a 10 ccm engine or larger and get more pleasure from running the engine.


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## c_mario (Oct 15, 2018)

Thanks everyone for all the suggestions. Since I have tried everything I can think of and nothing makes any difference I can only think that my piston to cylinder liner fit is no good. I don't know what good compression should feel like. For comparison as I mentioned I have an OS Max 40 and it ran fine. Its compression felt no different to my engine when rotating by hand but it is a ringed engine. At this point I have had this apart so many times i'm starting to strip threads in the crankcase and now needing helicoils to repair. Its not fun now.
Mechanic boy, is there a 10cc engine plan you can recommend.


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## Mechanicboy (Oct 15, 2018)

C_Mario,.. here is the large 4 stroke engine with piston ring who is popular for newbeginners to create own engine..
http://www.machinistblog.com/free-plan-webster-engine-works-4-cycle-gas-engine/

10 ccm glow plug engine..
http://www.hemingwaykits.com/acatalog/Jones_605___Colin_Jones.html

The Sparey 5 cc engine is not difficult to build due the engine has long stroke and large length of piston who give less leakage than a short length of the piston and short stroke engine...
http://www.hemingwaykits.com/acatalog/The_Sparey_5cc_Engine___L_W_Sparey.html


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## f2cf1g (Oct 17, 2018)

If you suspect the piston seal (it should hold compression for several seconds when held at the top of stroke) and if the piston is made of cast iron you can make it fit more tightly by "cherry bombing".  First expand the piston by heating with a gas torch until it is glowing bright red then plunging into oil to cool it quickly.  You should find that it has grown and will no longer fit into the cylinder.  Re-lap to fit, taking care not to go too far.  As you lap, keep checking by cleaning the piston thoroughly then sliding into the cylinder which should be tapered towards the top. Stop lapping when the piston gets about half way up, between the top of the exhaust and top dead centre.  Assemble the engine and check that it will turn over.  If too tight lap a bit more and try again.

Fitting the piston to the cylinder is the most difficult and critical process in two stroke building so you should not feel that you have failed if you have to try again.  I had to make four pistons the first time I rebored a diesel.  This is much easier than starting again from scratch!  Goo luck.


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## c_mario (Oct 17, 2018)

Hi f2cf1g,
I have actually "grown" the piston 3 times now and relapped as you describe. The last time, yesterday, I did it and it expanded by .06mm and did not fit the bore.
I lapped it till it would go half way up the bore, then fitted it back into engine. It was hard to turn over but gradually became easier with lubrication and a fair few rotations.
Same result.


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## WOB (Oct 17, 2018)

Check to see if your piston is round. Sounds crazy, I know.  But unless you started with stress relieved cast iron blank, machining the interior to make room for the rod small end will allow the inherent stresses in a cast iron blank to be relieved and will distort the piston out of round.   Lapping does no good because the thin cast iron is flexible and simply bends under lap pressure.   A dead give-away is the lack of a uniform surface finish after lapping to fit the cylinder.   If your piston is out of round even by a couple of tenths, toss it and make a new one from a new blank that has been heated to about 1200 deg F ( dull red) for at least 30 seconds and cooled slowly.    Then you have a dead, inert material to machine and will hold shape despite being machined all over.    It is the only way to get good compression with a lapped piston assuming the cylinder shape and finish is proper.

WOB


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## WOB (Oct 17, 2018)

Removed duplicate post

WOB


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## c_mario (Oct 17, 2018)

Hi Wob,
After lapping I measured the piston in multiple locations and the measurements where all 16.021 to 16.022 mm.
The piston finish appeared uniform after lapping, i.e. no spots duller or shiner than any other.
I believe I machined the centre first before machining the piston to initial size before lapping. 
When you say tenths, do you mean tenths of an inch or tenths of a millimetre?


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## WOB (Oct 18, 2018)

It appears that your piston is round.  That leaves the head gasket and even the glow plug/gasket  as possible leak points.    I should have been more specific about tenths:  I meant 1/10 of a thousandth of an inch: 0.0001" or 0.0025 mm

WOB


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## Billitmotors (Oct 19, 2018)

As Aerostar said the flat on the backplate is for piston clearance first turn the crankshaft through bottom dead centre and see if you can feel if the piston is binding on the backplate or even better machine the flat on the backplate as designed . Also check that there is no leakage on any of your joints on the crankcase. the easiest way is to pour fuel on the joints one at a time and flick the engine over   while watching for air bubbles, any leakage can be enough to reduce the crankcase pressure and stop the engine from continuing to run.
Also you said that when the engine does fire it sounds like a fourstroke.  Do you mean it is running roughly? If so this could be because the piston skirt is just bottoming  out on the backplate. You could also simply look at the backplate adjacent to the piston and see if there are any marks on it.
If you have built it as per the plan and your fits are good it really should run. My bet is still on leakage around the crankcase joints.
I hope this helps.
Rob Jenkins.


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## c_mario (Oct 21, 2018)

Hi Billitmotors.
I did put the flat into the backplate as in the plans. You can hear the engine in my little video clip in this thread, sounds rich or what the guys at the model club I was in 30 years ago called four stroking. I have looked for leaks and used sealant on all surfaces. Best run is about 4 seconds.


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## Mechanicboy (Oct 21, 2018)

4 second running before stop can be caused by expansion by heat then the cylinder do not keep tight around the piston.  As normal when the piston/cylinder is ready to use when the piston must stop 2-3 mm before TDC, also tight and more tight until the piston stop a bit before TDC when you are pushing the piston into cylinder after you has lapped the cylinder/piston. You can't distort the fit of piston/cylinder when you are flipping the propeller with fuel into the engine.  Running-in the engine will improve the tolerance between piston/cylinder who are impossible to create on tools.


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## f2cf1g (Oct 23, 2018)

After you mentioned it in your last post I watched your video (not sure why I didn't see it before).  The motor appears to be oscillating not fully rotating.  I've not seen this on a glow before but in a diesel it is caused either by too high compression ratio or too much fuel causing too much comp.  Either way, backing off the compression lever allows the motor to turn over and run.   I wonder if too much comp is the problem?  A bigger prop with more inertia might help starting.


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## KenC (Nov 19, 2018)

Your cylinder liner needs to be a very good fit in the crankcase because if not you will get the leaks that you have already seen. The liner should need a firm push by hand to get it into the case, it should certainly not just drop in. My view is that all the comments about the needle and settings are just a red herring. Take the plug out and flick over the engine. This should give a definate pop due to crankcase compression, though not as definate as the pop you hear when the plug is in place. If there are crankcase leaks you will not have enough suction to pull fuel in, nor enough pressure to transfer it up the transfer ports into the cylinder. If the engine runs for a few seconds it is probably just using up any fuel that is in the crankcase. Oh, you are using proper glow fuel I assume!
A further point as already mentioned, is that the ledge on the top of the rear cover is so that the piston does not hit the rear cover as it approaches bottom dead centre. If you did not make that ledge and if your piston does not hit the rear cover, there are some errors in your construction of the engine. I would start off by a detailed check of all your dimensions and correct those that are not as they should be. Hope all this helps.
Ken Croft
See my own engines at
www.flickr.com/photos/kcemb/albums/
And then find the album called Model Aircraft Engines.


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## c_mario (Nov 20, 2018)

Hello Ken,
Thanks for the detailed reply. At this stage I have gone backwards. I have made two cylinders and grown the cast iron piston several times in an attempt to get a better fit. I just kept getting the same result. I then decided to make a ringed piston. Cast iron Piston Cast Iron ring. Thought this might be better. Actually worse, engine has not fired since. As for the pop when flicking over the engine without plug I believe I get that but again, never seeing one that is correct I don't know what a pop should should sound like. Yes I am using Glow fuel, It was purchased recently. I made the ledge in the cover and checked my measurements also. I made new cylinder head that reduced the distance from the top of the piston to the glow plug also to I guess increase compression.  I've taken a break from this now since I clearly don't have the skill to get it right. I may build another engine if I find a suitable plan and simply concentrate first on getting a good Piston to Cylinder fit.
I wonder why most plans are diesel engines. I don't even know if hobby shops here sell the fuel for them.


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## minh-thanh (Nov 20, 2018)

Hi c_mario !
I think you should try with the flywheel, the same way I do in this thread:

https://www.homemodelenginemachinist.com/threads/glow-engine.30315/page-3
That's how I do it, because with the first engine I do not know how right, exactly ...
It will be easier to run.
And when it has run with the flywheel you continue to adjust the cylinder, piston ....


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## ixb1 (Nov 20, 2018)

Hi C-mario
I read your problems with engine starting.If you make needle valve as in plan (needle taper and fine 4mm thread) you need open at full 4 turn to run rich (if i remember corectly).
If you put about 1/2ml of fuel into carb,few times flick and connect igniter.Engine will run.Do not put fuel into cylinder,it causes violent kick back and loosing prop.


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## KenC (Nov 20, 2018)

I didn't know you put up a video, but I just warched it. I would say that the engine has too much fuel. It is flooded and does not clear the excess fuel. There is of course still the possibility of an error in your build somewhere. I say this because if a normal engine has the fuel shut off and runs just on fuel sitting in the case, it will lean out and run fast as the fuel is used up. It will not splutter to a stop as yours does. When you connect the fuel line, put your finger over the carb and turn the engine over, can you see fuel (or air bubbles) being pulled along the fuel line? If you then shut the needle fully then repeat with your finger over the carb, does it still pull fuel along the line. If it does, your needle is not shutting off the fuel. As for the design, if  I can find the drawings I will run the dimensions through a little prog I have to check timing events, as it may simply be a design fault. Oh, a final thought. Have you tried attempting to run it clockwise as it is a simple mistake to misread the position of the port in the crankshaft!


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## KenC (Nov 20, 2018)

I have just looked at the drawings and I have just a few comments. It has quite difficult transfer ports for a first engine, though I doubt small errors in the build who have much effect. What is quite apparent is that sealing the cylinder liner to the case will not be easy, particularly because of the very small distance between the top of the exhaust hole in the case, and the top of the case. If your cylinder is a drop-in fit in the case it will never seal. The cylinder needs to be a firm "thumb press" fit in the case if it is to have any chance of good crankcase compression; no amount of gaskets anywhere will compensate for a slack liner fit. If you cannot get the engine to pull in fuel with your finger on the carb inlet, a liner/case bad fit is the most likely reason.
I am full of admiration for your tackling this build as a first engine. It is not a design that I would recommend as a first, something like the Boll Aero which is another bar-stock engine would be much more appropriate. 
And as a final comment, disregard anyone who advises you to lap a piston to a cylinder by lapping the two together, what ever lapping medium they use. I use solvol autosol as a final polish to both piston and cylinder, but never with the piston in the cylinder. That is simply a recipe for failure; the only thing that should come between a piston and a cylinder is oil. Trust me, I have in excess of 50 engine builds behind me of more than 40 different designs.


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## c_mario (Nov 20, 2018)

Hi Ken,
Thanks for the detailed responses. 
Firstly , when I open the needle and place a finger over the carb inlet and turn the prop  fuel is definitely pulled up the fuel hose. If I close the needle valve and do the same procedure fuel will not be drawn up the hose. I know this for sure because I also made a second carb and it did not seal at all.
Second, I do think the cylinder to case fit is not good. I have made two cylinders and I still see fuel bubbling up between the bottom of the exhaust port and the cylinder liner.
I have tried sealants but could not seem to stop it even though I felt that the cylinder was a tight push fit into the case.
I did not lap the piston inside the bore, I lapped it with a lap I made.
The piston in it now has a Ring on it, but I did not lap the ring because I don't know how or if I should.
I did try running it clockwise but it made no difference.


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## Mechanicboy (Nov 20, 2018)

KenC said:


> I use solvol autosol as a final polish to both piston and cylinder, but never with the piston in the cylinder. That is simply a recipe for failure; the only thing that should come between a piston and a cylinder is oil. Trust me, I have in excess of 50 engine builds behind me of more than 40 different designs.



I have never had trouble to lap the piston straight into the cylinder and compression is still good as before for several years in my model engines. The method I learned from Jan David-Andersen (model engine maker who produced these D-A engines) when I received the book about model engine construction authored by Jan David-Andersen. The main problem is that there is no practical training of younger generations to lap the piston / cylinder and lap the piston into the cylinder.

Download and read this book who are translated from norwegian to english  https://www.google.no/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwiLkYK9kOTeAhUHiiwKHYLGA08Qjhx6BAgBEAI&url=http://adriansmodelaeroengines.com/catalog/attachments/Jan%20David-Andersen%20Diesel%20Motor.pdf&psig=AOvVaw2WvPUWuEUXUmX55vXsP3Sa&ust=1542843069001768

And the history about these D-A engines.. http://blhf.org/DA-motorer


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## minh-thanh (Nov 21, 2018)

WOB said:


> Check to see if your piston is round. Sounds crazy, I know.  WOB


 And check if your cylinder is round. ?? check it with light. 
I did some pistons in accordance with the not round cylinder 
Some changes when I make font-bearing and crankshaft, I think it will be more closed.


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## KenC (Nov 21, 2018)

Forget using a ringed piston since there is a lot of science in the design and making of piston rings to get them to work properly. Modern engines of around 3cc never use piston rings as they are a source of difficulty and never necessary. 
From the fuel suction tests you have done I think fuel suction is not the problem, just so long as ALL the port positions in the cylinder and crank are as per the design. IF, and with all due respect to a first time builder, if all your dimensions are as per the drawings, all that is really left is your piston and cylinder fit. Ideally the bore should be slightly tapered, in your case half a thou from the bottom to the exhaust ports, then at the most a tenth or two from the ports to the top of the cylinder. I say "ideally" because a parallel bore will still allow an engine to run, just not at its best. The surface of the cylinder should have a mirror finish, use a wooden lap soaked in metal or chrome polish for the final shine. Forget all about the cross-hatched finish on commercial engines, this is the result of using a hning machine, and is of no importance. Mirror finish is better. The piston should be parallel, lapped to a similar mirror finish, and it should enter the cylinder up to just past the exhaust ports. An engine finished this way will be tight to turn over top dead centre, and when freed after a run, you should be able to turn it to dead centre, release it, and it should hold compression still at tdc without a leak for at least a few seconds. Just tap it from tdc and the piston should bounce down the cylinder under residual cylinder pressure. If you put your piston at tdc and it stays there for ever, even after you nudge it, the fit is too slack to run, even for a glow engine where piston seal is not so critical as with a diesel.
So, firstly, check, double check, then check again, that the engine is totally built to the dimensions on the plan. Yes, I know you have already done that, but do it again, or get a pal to do it for you.  When you have done that, put your ringed piston in the bin, re-finish the cylinder, and make a new piston. Do not ever, for any reason, enter the piston into the cylinder with anything other than a meticulous cleaning with acetone, and a sloshing of light oil. If all of that fails, send the engine to me and I will sort it out for you. Seriously.


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## justisla (Nov 21, 2018)

Fit a carb off another commercial engine. OS or Irvine- but do not use MDS they are useless carbs. You may have to make a sleeve adaptor to fit but make sure it is airtight. Then use an electric starter with a prop spinner on the prop.


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## Mechanicboy (Nov 21, 2018)

KenC said:


> Ideally the bore should be slightly tapered, in your case half a thou from the bottom to the exhaust ports, then at the most a tenth or two from the ports to the top of the cylinder. I say "ideally" because a parallel bore will still allow an engine to run, just not at its best. The surface of the cylinder should have a mirror finish, use a wooden lap soaked in metal or chrome polish for the final shine. Forget all about the cross-hatched finish on commercial engines, this is the result of using a hning machine, and is of no importance. Mirror finish is better. The piston should be parallel, lapped to a similar mirror finish, and it should enter the cylinder up to just past the exhaust ports. An engine finished this way will be tight to turn over top dead centre, and when freed after a run, you should be able to turn it to dead centre, release it, and it should hold compression still at tdc without a leak for at least a few seconds. Just tap it from tdc and the piston should bounce down the cylinder under residual cylinder pressure.



Funny to read your comments,.. not all is correct.. 

Mirror finish surface is not really good idea, we need oil pockets in the cylinder/piston surface to last long time. Also dull gray surface after lapping is done.  When the engine is assembled, it must be pinch when the piston is on way to TDC in the cylinder which means the cylinder is tapered. The tapered cylinder is created by the piston who is lapped into the cylinder at final stage, also push piston into in same time rotate the piston to create tapered cylinder.  Never use wood as lapping tool, better copper, brass or aluminium due the wood is too soft.  See at this link http://modelengineeringwebsite.com/Super_Tigre_12.html

In next post i am showing the unused engine in box with lapped cylinder/piston who are not mirror finished.


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## KenC (Nov 21, 2018)

At the temperatures that our engines run at, do you really think oil will be retained in the grooves produced by a Delapena or Sunnen hone? Don't be so silly. And give me abreak, lapping a piston into a cylinder? I wonder what experience you have. Haveyou ever seen the surface finish on any of the high performance 2.5cc engines built in Russia for control line team racing? I guess not. They are polished using jewellers rouge to mirror finish. Likewise the tether car engines, the 1.5cc glows run at up to 48000rpm. Try that with your groovy finish. And I certainly never suggested to use wood as a lap, just wood soaked in metal polish for a final polish. If you do not have either the knowledge nor the experience of building high performance engines, it wouldbe better not to mislead novices with your imagined ideas. On the subject of cylinder taper, you are on the right lines.
I just read the link in the above post. He may be a competant engineer, but his piston/cylinder methods are not good. Honing bushes for a Quorn cutter sharpening machine are not the same as the requirements for honing a model diesel engine piston and cylinder. Is is all to easy to publish articles as if you are an expert. You would be better served to read my guidance on piston/cylinder fitting in the back issues of Model Engine World in my series on the construction of the Thaler diesel, or on our Motor Boys web site of MEW edited by my pal the late and much missed Ron Chernich.


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## Mechanicboy (Nov 21, 2018)

The proof is these photo of factory produced D-A engines produced by Jan David-Andersen --> The picture tell more than you can talk about mirror like surface in cylinder and piston. In fact there is cross hatched surface in the cylinder and the piston by lapping.  Did you not read Ron Chernich wrote in his homepage: The surface must be dull cray when the cylinder is ready lapped? As you see there is not mirror finished without cross hatch, the new piston has still marks of lapping while the used engine do not have more marks of lapping after the engine is running-in, also the piston has porous surface since the piston is cast iron and will remain oil inside to lubricate between cylinder and piston.  With other: We can't do it better with tools to keep all tight tolerance before the engine is adapted by running-in. Also "the mountains"  in the surface will be worned out to "the plateau mountains"  then the fit of piston/cylinder get correct tolerance under running-in. In case the surface is mirror like (without cross hatched/dull gray) and will be difficult to adapt the piston into the cylinder and create the tapered cylinder.  The ABC, ABL etc engines has cross hatched surface and porous aluminium piston as you can see  with magnifier of same reasons to keep cylinder and piston lubricated.  You can find the plan of D-A Satelitt in "Motor Boys International" book by Ron Chernich, there will you find my name.


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## Mechanicboy (Nov 21, 2018)

KenC,.. as i wrote in earlier post: Did you not read Ron Chernich wrote in his homepage: The surface must be dull cray when the cylinder is ready lapped? Also no mirror like surface...


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## minh-thanh (Nov 21, 2018)

Hi KenC !
I'm a new ,and still learning and I'm not sure I understand about it


KenC said:


> and it should enter the cylinder up to just past the exhaust ports. An engine finished this way will be tight to turn over top dead centre, and when freed after a run, you should be able to turn it to dead centre, release it, and it should hold compression still at tdc without a leak for at least a few seconds. Just tap it from tdc and the piston should bounce down the cylinder under residual cylinder pressure. If you put your piston at tdc and it stays there for ever, even after you nudge it, the fit is too slack to run, even for a glow engine where piston seal is not so critical as with a diesel.
> .


I have a question
If I remove the plug and turn the shaft,The piston moves freely in cylinder Or it will be a bit tight near TDC ?


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## Mechanicboy (Nov 21, 2018)

minh-thanh said:


> Hi KenC !
> I'm a new ,and still learning and I'm not sure I understand about it
> 
> I have a question
> If I remove the plug and turn the shaft,The piston moves freely in cylinder Or it will be a bit tight near TDC ?



Hi Minh-Thanh..

It must be tight near TDC  to keep compression. If the cylinder was parallel, the compresion will be lost when working temperature is rising..

Except case hardened steel cylinder and steel piston, there is not tapered cylinder due both expanding about the same size (you can push piston in both way in the cylinder without pinch in the Cox engine). The degree of hardness is not the same in the cylinder and the piston to prevent galling. The surface is more mirror like unlike from lapped steel cylinder/cast iron piston and need short running-in. It's difficult to make the steel cylinder and steel piston in home workshop and it cost too much to buy the special grinding/honing tools.


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## KenC (Nov 27, 2018)

Don't waste your time quoting Ron's wisdom to me. Ron was a computer prof at Brisbane university, and much of what he knew about engineering he learned from myself and the other motor boys. It is rather silly to quote Ron's website to me since I was a significant contibuter to the site. Ron was a great guy and missed by all of our group. His website will remain a good reference source for many in the model engine hobby. 
And the cross hatch pattern on cylinders is produced by the use of a Delapena or Sunnen hone (or similar machine) and is not a requirement, it just happens to be good enough. My own machine when I was engine building was a bench model Sunnen, but I always polished for the final finish after lapping.


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## c_mario (Nov 28, 2018)

Wow Guys,
Take it easy. I appreciate your differing points of view and your offer Ken.  Both of you obviously have had success in building engines and have your own techniques that work for you and that's great. I am convinced its the piston cylinder fit, so I will proceed down that path again. Will put ringed piston in bin and do cylinder and piston again. I do find it difficult to measure the cylinder taper thou. I do have those little telescoping bore measuring tools but I don't think I am using them correctly. Like these https://www.machineryhouse.com.au/Q618?gclid=EAIaIQobChMIk4Xdm7L23gIVyYRwCh2dDwFjEAQYAiABEgJeZ_D_BwE
Regards
Mario.


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## f2cf1g (Nov 28, 2018)

Those things are no use for the tolerances applicable to pistons and liners.  To have any hope of measuring taper accurately you need a bore gauge.  However, that's  not necessary provided you follow Ken's advice and lap the liner and the piston using the techniques described on Ron's site.  I too was a computer consultant but even so successfully  built an ML Midge diesel using that method.  Took five goes at the piston though.


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## KenC (Nov 29, 2018)

It is not really about different points of view. An engine finished with a dull grey appearance or a commercial cross-hatched pattern will clearly run and if done correctly, it will run very well. But it is just plain silly to say that it is a requirement for pistons and cylinders to be finished this way. It is also a bit pointless to quote texts written in 1945 by someone who eventually became a commercial engine builder, and to show examples of his vintage engines, and in so doing to ignore progress. It also pees me off to be told how I should have been building enigines over the last 20 years by someone who appears to have limited experience of engine building and modern techniques, and who goes on to quote the writings of Ron Chernich, who was one of our own group.
But to return to tapered cylinders. The telescopic gauges are not easy to use but can be of use if a direct reading bore comparator is not available. Basically any measuring kit is better than none at all. Interestingly I see that bore comparators from China are available on eBay for a fraction of the cost of the Mitutoyo versions that I used. For sure bore taper makes an engine run well, but a parallel bore will still work and allow an engine to actually run, which is surely all a beginner with his first engine build actually wants isn't it. It would be a naive first builder who though he was about to produce a high performane engine for his first attempt. I guess most first engines are destined to sit on a shelf after their first run, rather than destined to take to the air as did most of my own engine builds.
I joined this forum because as an experienced engine builder and one of the original members of the Motor Boys, I thought that even though no longer actively building engines, I had something I could contribute to the hobby. I now see that I was wrong to think that, and I shall bow out and quit banging my head against the wall. Life, mine at least, is far too short.


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## ShopShoe (Nov 29, 2018)

f2cf1g,

I would say that I agree with you on bore gages.

But, FYI for c_mario and others (me included), I think the video below provides a very good tutorial on how to successfully make use of the telescope gages. My accuracy improved a lot once I used the techniques Abom presents.



Just trying to be helpful,

--ShopShoe


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## KenC (Nov 29, 2018)

His technique is exactly how I do it but I have a further comment. I have expensive telescopics by Moore and Wright, and some cheaper chinesebudget ones. If I lightly snug the clamp, rock it in the bore and then withdraw it, I like to tighten it a bit more to make sure it does not change when using the mike to measure it. When I do this with the Moore and Wright, it holds its setting. When I do this second tighten with the cheaper gauges, the setting changes. So beware if you use cheap gauges.


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## Mechanicboy (Nov 29, 2018)

KenC said:


> It is not really about different points of view. An engine finished with a dull grey appearance or a commercial cross-hatched pattern will clearly run and if done correctly, it will run very well. But it is just plain silly to say that it is a requirement for pistons and cylinders to be finished this way. It is also a bit pointless to quote texts written in 1945 by someone who eventually became a commercial engine builder, and to show examples of his vintage engines, and in so doing to ignore progress.



Yes, you (KenC) wrote without to try it self with your own model engines after the method from 1945, it's not important to speak about to compare these engines either it's vintage or modern. Jan David-Andersen wrote the book in 1945 and you can't ignore how he wrote who was easy to create and lap the piston/cylinder without problems who are explained in the book. I did as he explained in his book how to create and lap the cylinder/piston, never had problem with my model engines when i created and lapped the cylinder/piston. Then you can not continue to bombard and ignoring all that I have shown and written in previous comments.  
See at this link, Jan David-Andersen is a true engine enthusiast.  After he stopped making engines for sale from 1950 to 1964, he continued to make engines for his own use.  Here he shows one of his recent creations in 9/14-2015, see this movie after the MOV.file is downloaded..
http://blhf.org/sites/b/blhf.org/files/688d5caaa75f923139f1443bdb631288.MOV

About measure the cylinder with measuring tools, use cylindrical plug gauge or steel ball in right bore size  (with brass shaft soldered on the steel ball to hold with fingers) to control the size and check taper since not all home machinist has expensive measuring tools such as bore comparator.


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## minh-thanh (Nov 29, 2018)

Hi c_mario !
I have advice for you
Although I have made two engines with   cylinder diameter 16mm and a engine with cylinder diameter   13.3mm , I just want to find out: how it works, everything, .... I have to say is really I hate do   it again. Do not waste time with it. It does not prove anything. 
If you want to challenge the ability : OK, let's continue ,But  It does not prove anything. 
Otherwise, make the engine different with a larger diameter cylinder.
Or converted it into a 2 stroke engine with ignition and flywheel (I did the same with all my  engines and it was easy to run) And enjoy the results .


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## Naiveambition (Nov 30, 2018)

Not meaning to hijack the thread , but I have a question on the bore gage use.  
How do you know that the guage is centered in the bore when you tighten.  When I was using them I had to adjust till it felt centered then tighten , even so it took me a few times to get a repeatable reading.  Now given they are a cheaply set and i do not expect much in accuracy. Do the more exspensive ones have tighter build  tolerance fits that would not allow side movement in the guage.


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## Mechanicboy (Nov 30, 2018)

Naiveambition said:


> Not meaning to hijack the thread , but I have a question on the bore gage use.
> How do you know that the guage is centered in the bore when you tighten.  When I was using them I had to adjust till it felt centered then tighten , even so it took me a few times to get a repeatable reading.  Now given they are a cheaply set and i do not expect much in accuracy. Do the more exspensive ones have tighter build  tolerance fits that would not allow side movement in the guage.



In really the bore diameter is never in 100% exact in measure in the home workshop. The important is the marks of tool is removed from the cylinder by lapping and the piston is adapted to cylinder under lapping operation. In fact the measuring tool to control the bore is rare used under lapping. In the mass production in the factory the bore gage is used to control the nominal measure in the bore under lapping operation.


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## ShopShoe (Nov 30, 2018)

Naiveambition,

What Mechanicboy says is correct.

The point I was making by posting the video is that if you use the telescope gages, you can be more accurate by careful practice and consistent use of good techniques. My funds are limited, so I may want bore gages, but I can afford the telescope gages and they can help me get the job done, but I have to understand the limitations of their use.

I started with a cheap set of telescope gages and those have a mediocre fit and finish and are a pain in the *** to use, so I got a smaller set of Starrett telescope gages when one of my suppliers had them on sale and they have a better "feel" than the cheap ones and are easier to use. (In my case, the cheap ones go up to 6 inches, the Starrett set I have stops at 4 inches, but I seldom measure 5 and 6 inch bores.)

The use of telescope gages depends on feel and experience, so better feel (for me) leads to more consistent results. 

I am also not in a production environment, so I can also make more than one measurement to double-check myself.

--ShopShoe

P.S.: For smaller bores, I sometimes turn up "go" and "no go" gages to help me make a bore to size. My best micrometer used to make those to size probably results in a more accurately sized bore than a telscope gage measured with any micrometer I own. (In my shop, with my tools, with my skills, anyway)

--SS


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## Mechanicboy (Nov 30, 2018)

Do not forget: Temperature.  In case the measure tool is on a warm place to example on the lathe and the cylinder is cold, then you get fault measure.  It same with the cylinder in warm hand and the cold piston is pushed to control the fit or taper to example, then you get fault measure. 
As rule: All parts and measure tools must be in same temperature who is standardized to be 20 degree celsius/68 Fahrenheit to get right result of measure.


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## Rocket Man (Nov 30, 2018)

Mechanicboy said:


> Hi Minh-Thanh..
> 
> It must be tight near TDC  to keep compression. If the cylinder was parallel, the compresion will be lost when working temperature is rising..
> 
> ...



I fly model airplanes all the engines these day have a tapers sleeve.  I had a bad sleeve so I made a new one from pre heat treated 4150.  I machined it straight through .0005" small.  Then I put a .001" taper from bottom to the exhaust port.  It worked great.   People on the model airplane forum said that is how it is done so that is how I made it.


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