# Nitro V8



## michaelj199 (Aug 7, 2012)

I have been working on designing a V8 two stroke glow engine with a .5in bore and stroke. I plan on starting work on this engine as directed project for collage.
since i don't know much cause I'm just starting out in the machining world, i thought id run it buy you guys for your advice. i know i shouldn't be attempting a V8 but what can i say...







It's a very simple (for the most part) design. I'm not going for pretty I'm hope for running. 

The engine is Two stroke based off a Detroit diesel. therefor a supercharger. im going with a rotary valve setup for "simplicity". the crank is modular steel discs and drill rod held together by square holes.

more details to come...


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## kutzdibutz (Aug 7, 2012)

Hi Michael,

well, best of luck with your project. A V8 is quite someting to start off with. Ambitious I would say and however I can totally understand the 'what can I say...' from you (I would be the same  ), it maybe would be better to start and learn from a single piston, get this to run and then scale up. A V8 has LOTS of parts (and lots of duplicate parts) so error seeking and correction can be quite frustrating...
On the other hand if you have some guidance which I'm sure you can get around here (and directed project means some guidance on the shop floor as well?) that will be achievable. Just dont lose your motivation  between all the parts... 

Cheers, Karsten


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## michaelj199 (Aug 7, 2012)

I've done one air motor. also of my own design. also not pretty but ran like a champ. as for duplicate parts and what not, hopefully a lot of it will be CNC as that is what we are focusing on this semester


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## skyline1 (Aug 7, 2012)

Hi Michael

Pretty ambitious for a first attempt but it looks like a nice design.

I can see those supercharger rotors being a bit tricky though they would definitely be a C.N.C. job. Very awkward shape to do by manual machining.

Nice bit of C.A.D. work BTW what program did you use

Regards Mark


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## michaelj199 (Aug 7, 2012)

all modeling has been on solidworks

so lets start with the block






i figured id mill the water pump hole then mill each deck surface and cut water passages including cross ports. then press in cylinder sleeves and then drill intake holes through block and sleeve. mill the deck surfaces again to insure sleeve flushness. using v-blocks mill the valley then flip it over and mill crank pockets 






heads






i figured id use cast iron for its high temp characteristics. im using rotary valves which will get quite hot. drilling the long holes the 3.25in through the head with any precision worries me. the .25in hole is for the rotary valve ( figuring out port size for timing took a lot more then i expected) the .125in hole is for cooling there will be a plug at each end. water will travel along the deck and above the valve (hopefully helping keep it cool). head bolts are 4-40
also if some one can give me the length of the threaded part of a standard glow plug i would be greatfull.


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## michaelj199 (Aug 7, 2012)

valves






the valves are .25in drill rod drilled down the center .125. they rotate at crank speed. the exhaust holes (in and out) are offset for timing and to hopefully limit blow by. 

any advise of rotary valves would be appreciated. tolerances and friction limiting. i'm kinda hoping ether there's enough blow by on the compression stroke to get lubrication from fuel/oil or maybe using neolube but i don't know how blow by would effect it.

crank






steel discs with two holes which will be square broached to .125. main bearing and throws will be machined to have square ends. main bearings and connecting rods will be installed before press fitting it all together.


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## warranator (Aug 7, 2012)

I have made a two cylinder air rotary valve motor and the biggest problem I had was the leakage between the cylinders blowing past the rotary valve. Mine was all made on CNC so precision was very good, I sorted mine out by putting O rings on the rotary shaft in between the cylinders. How are you going to drill holes in the drill rod?


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## michaelj199 (Aug 7, 2012)

ok so why i came to my valve design. with some trial and error, math, and a lot of letting it float around in the back of my head i came up with a timing equation. 

circumference of rotary valve / 360 * degrees you want the valve open / turning ratio (2 for half crank speed) / 2 = diameter of exhaust port

therefor port size is severely limited. if i went at half crank speed so i could just have a through hole id be limited to .054in exhaust port which is a no go. if i run at crank speed my exhaust port can be .108in which i can live with but requires me to offset my exhaust intake and output of the cam. i tried to figure out a way to drill it at an angle to make a through hole but my cross sectional area was to small and restricted flow. so i came to a tube. off the shelf tubular material can't really be trusted that much for roundness. so i will drill the center out of drill rod with a lathe. half way from one side half from the other. then plug the ends.


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## skyline1 (Aug 8, 2012)

Hi Michael

Looking at your crankshaft drawing, that's a lot of square holes and press fits. It will be difficult to get them all perfectly accurate and square and should a big end bearing fail they would be difficult to replace. some small motorcycle engines use this type of construction and a big end failure is a technical and expensive job to fix even on a single cylinder engine (I know, I had one !) It will also make assembling the engine hard, sliding all 8 pistons (with rings if you decide to use them) into their cylinders at the same whilst supporting both ends of the crankshaft sounds like a job for your pet octopus. 
You might consider split bearings this will make crankshaft construction and engine maintenance much easier. On steam turbines I use plain cast iron bearings running in Silver Steel (Drill Rod) shafts, I know it sounds mad but they run really smoothly  and at high speeds ( up to 30,000 R.P.M. in my case)  they don't score the shaft and they have a really long life, in fact they can outlive ball races.

I have made a couple of steam engine crankshafts by a similar method. but they were only single throw ones. 

What I did was to make the main shaft in one piece initially. fit the webs and crankpin(s) to it a tight wringing fit then silver solder the whole thing together. You could of course cross pin it if the webs are thick enough or I have even heard of high strength loctite being used. Next step is to finish the main journals to size using very fine gentle cuts in the lathe. I then sawed out the bit(s) of main shaft between the webs and again using very fine cuts machine the crankpins by offsetting the job in the lathe by the radius of the crank throw. you can use two distance pieces for this with a centre hole and a hole the size of the main shaft spaced the crank throw away in your case  they will be a sort of crucifix or disc as your crankpins are at 90 Deg to each other.

It might also be possible to use this offset turning method to machine the entire thing out of solid indeed full size crankshafts are usually made this way but of course they are usually made from forgings rather than solid billets.

With a 4 Axis C.N.C. this sort of offset machining could be quite easily accomplished. I am as much a beginner as you with C.N.C.
But I think If you were to mount the job in the 4th (Rotary) axis rotate it slowly and arrange for Y and Z axis to describe a circular path around the crankpin centre .reduce the size of the circle on successive cuts. small endmill in the spindle and voila instant crankpins. Well that's the theory anyway something for you to think about.

Regards Mark


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## michaelj199 (Aug 8, 2012)

cast iron bearings... interesting. that would solve a worry i had about using sintered bronze and the the worry about my rotary valves. id like more info on how you prepared these bearings please.

my multi piece crank was for ease of making but i do worry about its strength. if i one piece it my connecting rods will need end caps. end caps need screws so i would need to widen my connecting rods to around .140 to allow for clearance foe 2-56 socket head cap screws. which would mean id need to widen the offset of my block... grr and hope there's enough clearance for them spinning around down below.

the multi piece is made of drill rod which is good steel and a nice surface for bearings. i was going to make a jig for punching the square holes so they would all be the same. but then again this is roughly 1/8th scale and normal main bearings are around 2-2.5in which would be .25 to .3125 and they are currently .1875.

a lot to think about...


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## Jasonb (Aug 8, 2012)

If you want those square holes to all be true and accurate then get them spark erroded, if you have CNC at your college then I would assume you also have EDM. Punching will distort the webs too much.

J


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## michaelj199 (Aug 8, 2012)

its a small collage. our edm is cobbled together just big enough for tap removal it would take a day per hole. the broach i have works basically works by pushing a tapered square file through a pre drilled hole hopefully this wont distort the web to much

as for a one piece crank i didn't leave enough room for two piece connecting rods.


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## kutzdibutz (Aug 8, 2012)

Hi Michael, 
when it comes to a built crankshaft I find the Schillings-approach quite an interesting idea. Needs some space for the bearings though. But maybe woth considering.
Have a look here- the text is in german, but I think the pictures say enough.

http://www.cncmarc.ch/reihenmotor.htm

Cheers, Karsten


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## michaelj199 (Aug 8, 2012)

wow that's a really cool crank design. with how compact this engine design is i can't impalement anything like that but that's definitely something to store away for later pondering.


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## michaelj199 (Aug 8, 2012)

piston and connecting rod






i am using piston rings and unless 0-80 screws will hold the connecting rod end caps on i see no way to make two piece connecting rods that will fit in my block.
i modeled using 2-56 screws but the connecting rod would hit the bock and opposite side piston sleeve. i know it will be a pain to install but i see now way around the trade offs for making such a small engine. i mean it's 3.25in long.
i hope you guys are not saying my crank is doomed to fail cause i don't really know how to fix it without a complete engine redesign.

and the the supercharger






the vanes i tried to make like the real thing. to model this i had to draw 4 equation lines using equations for an epicycloid and a hypocycloid. then spline them together and extrude it. this will be cut top down using CNC. the case is fairly straight forward but is going to be a nightmare to set up. i have not made the rear bearing case but the front one includes the gears. 

the pulleys for running everything are going to be .080" (MXL) timing belts from SDP/SI. the belts are 3/16th inch wide.


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## agmachado (Aug 8, 2012)

Hi Michael,

Very interesting your project... and the design is very good !!!

th_wwp please!!!

Cheers,

Alexandre


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## michaelj199 (Aug 9, 2012)

My engine will have two carbs and Steve Huck has graciously allowed me to use his carb design from the Demon V8. Now the Question is carb sizing and whether or not to offset them in a way so the second carb acts like a secondary. would that allow me to more easily control mid range air/fuel ratio or would it just add headache? i want this to be high revving and id like to but a load on it... maybe one day put it in an 1/8th scale pickup. ;D


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## skyline1 (Aug 9, 2012)

Cast iron bearings can be made just like bronze shell bearings. porous bronze is the ideal material for high load low speed bearings but at high speeds a peculiar effect sets in which I have seen in practice. They tend to score the shafts even very hard well lubricated ones. In fact they don't just score them they can actually eat them away in no time. The idea is that the bronze being softer wears before the hard steel and when it does you simply adjust the bearing (thinner shim) or replace the bronze bush.

At high speeds like 10,000 R.P.M+ (Depending on the bearing design)  the exact opposite occurs. It is quite a well known effect (ask any maintenance engineer) but exactly why I don't know.

Cast iron bearings don't do this, it is something to do with the free graphite particles in the iron forming a surface barrier. I came across this when I built my first model steam turbine and was having exactly this problem. I was discussing it with various model engineers and  had a chance conversation with somone who used to work for Maclaren. According to him they were using C.I. big end bushes in full size racing engines. He probably shouldn't have told me but it was some time ago

As your little V8 is likely to be very much in the high speed category cast iron bearings sound worth a try. I know it sounds bonkers, I didn't believe at first but they work great.

As for your Crankshaft would it be possible to simply make the crankpins a little longer and the webs slightly thinner to make room for the bolts and you could fit studs to the bearing caps and nuts on the inside of the conrod end. this would leave you a litlle more room in the crankcase. without needing to alter your cylinder centres.

I like you idea of a an R/C pickup truck with a proper V8 in it cool or what !

Regards Mark


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## skyline1 (Aug 9, 2012)

kutzdibutz said:


> Hi Michael,
> when it comes to a built crankshaft I find the Schillings-approach quite an interesting idea. Needs some space for the bearings though. But maybe woth considering.
> Have a look here- the text is in german, but I think the pictures say enough.
> 
> ...



Yes interesting it looks like the crankwebs are split and the inner bearing race actually forms part of them It has several advantages

It would be very rigid 

The bearing load would be reduced as they are bigger, although the linear speed would increase for a given R.P.M.

It would be easier to machine (no square holes) 

It would not need a major redesign just an enlargement of the main bearing seats.

Regards Mark


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## Jasonb (Aug 9, 2012)

Regarding your question about Glow plugs, the length of thread on a OS #8 plug is 4.5mm (0.177") and the thread is 1/4x32 UNEF.

Looking at your piston drawings do you think rings are really needed? Steel liners and CI pistons are quite common on Glow and diesel engines. I've just finished a glow motor with the plain CI piston lapped to the liner and thats good for 10,000rpm with a 10x6 prop

[ame]http://youtu.be/AvbnjyrHq8M[/ame]

J


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## waynes world (Aug 9, 2012)

Jasonb said:


> Regarding your question about Glow plugs, the length of thread on a OS #8 plug is 4.5mm (0.177") and the thread is 1/4x32 UNEF.
> 
> Looking at your piston drawings do you think rings are really needed? Steel liners and CI pistons are quite common on Glow and diesel engines. I've just finished a glow motor with the plain CI piston lapped to the liner and thats good for 10,000rpm with a 10x6 prop
> 
> ...


 or make use of the scorpion v8 plans that are already done sic issues.


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## trumpy81 (Aug 10, 2012)

michaelj199 said:


> its a small collage. our edm is cobbled together just big enough for tap removal it would take a day per hole. the broach i have works basically works by pushing a tapered square file through a pre drilled hole hopefully this wont distort the web to much
> 
> as for a one piece crank i didn't leave enough room for two piece connecting rods.



I would definitely consider the crank design shown in that link rather than your press fit crank. Although you may need to seal each pair of opposing cylinders from the rest to maintain some sort of crankcase pressure to aid in supplying each pair of cylinders with fuel.

The difficulty with your design will come when you try to press the pieces together. If you don't have perfect alignment in all planes at the time they are pressed together, it's game over, your crank will come out twisted in one way or another and attempting to correct it will most likely result in a weak joint. Not something you want in a crankshaft.

I noted that you said you didn't leave room for 2-56 SHCS, have you got room for 0-80 SHCS which are a bit smaller than the 2-56's? You could also go smaller, 00-90 for example, if you don't mind using jewellers screwdrivers to tighten them up 

Also, why the rotary valves? why not just use cylinder porting like most commercial two stroke aero engines? It'd be a lot less complicated and easier to make?

Sorry, don't mean to sound negative, just a few questions I have is all. I do like the concept though 

When using valves as in a four stroke you use one intake valve diameter as a guide for the carburettor opening. The venturi would be slightly smaller.

I have no idea how to apply that rule of thumb to a two stroke though ...


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## skyline1 (Aug 10, 2012)

trumpy81 said:


> The difficulty with your design will come when you try to press the pieces together. If you don't have perfect alignment in all planes at the time they are pressed together, it's game over, your crank will come out twisted in one way or another and attempting to correct it will most likely result in a weak joint. Not something you want in a crankshaft.
> 
> I noted that you said you didn't leave room for 2-56 SHCS, have you got room for 0-80 SHCS which are a bit smaller than the 2-56's? You could also go smaller, 00-90 for example, if you don't mind using jewellers screwdrivers to tighten them up
> 
> ...



Yes I was thinking along the same lines and unless you put a small radius on the corners of the square spigots at either end of the crankpins and the square holes in the Webs as is standard practice with aerospace components. you will get stress raisers at the corners. which could lead to fatigue cracks. especially in a small high revving engine like this.

I'm not saying it can't be done and the theory is sound given the caveat above but it would probably need a precise jig to be made to ensure all the press fits are spot on. If you were mass producing them this would be the way to go but for a one off you would probably spend much more time designing and making the jig than the actual crankshaft.

Regards Mark


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## michaelj199 (Aug 10, 2012)

Skyline1
C.I. bearing do they work at low speed (idle) with no forced oil. 

trumpy81
I don't need to seal the different cylinders because I'm using a supercharger. That is also why I'm using the rotary valve, so i can build boost. also i cant use the bearing crank cause it would get into my cylinder walls and crash my pistons.

as for the crank, for rotational alignment, as long as all the webs and drill rods are the same it should all line up.(i would think at least with 90 degree offsets to me throws) for sticking a square block in a square hole I had thought it would self align. 

If I made the main bearings and webs one piece and added the throw would something like that work better? I'll also do some modeling to see if 0-80 screws might work for rod caps.


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## michaelj199 (Aug 10, 2012)

ok then I increased my deck height and increased my con rod length. as long as you think 0-80 shcs will hold up i can use a solid crank. now to contemplate this new can-o-worms. since its going to be a softer metal what bearing material should i use?


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## skyline1 (Aug 11, 2012)

Hi Michael 

Yes C.I. bearings can be used at slow speeds I have used them on oscillating engines. (wobblers). like this one I estimate it's speed at about 400 to 500 R.P.M.











Lubrication would be a bit of a problem but C.I. is at least partially self lubricating. This is due to the free graphite in the iron. You will soon know about this when you have to machine some (your hands will be black in no time). As I have never run them completely "Dry" I could not be sure but I doubt they will need force lubrication. How do you intend to lubricate the bottom end by the way

The crankpin in this one is (I think) Mild steel and it seems to run pretty smoothly. So plain mild steel may be a suitable material for your crankshaft if it is rigid enough  You could still use Drill rod as it can be softened (Annealed) as well as hardened. It is a little pricey in larger sizes though.

When this engine approaches construction I can provide you with some Cast Iron Bar for making bearings for the cost of the postage. It shouldn't cost too much to ship a small piece to the States

These are by-products of my little foundry (casting sprues) and is the material I use myself it's soft grey iron and machines really easily. It can be made into really thin bushes and shells. The crankpin Dia. on the little oscillator is 1/8" so you can see how thin it can be turned.

Regards Mark


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## trumpy81 (Aug 11, 2012)

michaelj199 said:


> Skyline1
> C.I. bearing do they work at low speed (idle) with no forced oil.
> 
> trumpy81
> ...



That makes more sense, for some reason I thought you were using the rotary valves for the exhausts .... doh!

In that case the supercharger plus rotary valve should work, but you'll need to isolate each cylinder from the other along the valve to prevent fuel from leaking into other cylinders at the wrong time. A plain lapped valve might work but under pressure, albeit small, from the supercharger it could easily force a small amount of fuel past any clearances you may have in the valve, not to mention reducing crankcase pressure which would have the opposite effect. a few O-rings should solve that problem but getting the grooves just right so that there is little drag but full sealing at full operating temperature will be tricky to say the least. 

The 0-80 SHCS will work no problem at all. The only purpose of the rod cap is to stop the rod from flapping about, there is no real load on the cap itself.

There is another solution for the crank that I saw recently on Youtube. A Japanese gentleman used a bearing to hold two horizontally split sections of the crank together. It's more difficult to describe than it is to understand it when seen. I will try to find the video again although it may be difficult as the title was in Japanese 

Visualise this, each crank section features 2 webs, one on each side, plus the offset rod. Then each end of this section has a shaft that is machined in half to form a D shaped shaft. There are four of these assemblies with each pair of D shaped shafts mating together inside the ID of the bearing. They are then held together with a small bolt through the center of the two shaft sections and the bearing.

The video shows it much better .... ;D;D;D

For big end bearings, you could use some .005" phosphor bronze shim stock. You'll need to make a couple of dies to form and punch/drill for the cap screws but that's all part of model engineering


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## trumpy81 (Aug 11, 2012)

You're in Luck ... I found the video on Youtube;

[ame]http://www.youtube.com/watch?v=CJUwHoLreHk&feature=relmfu[/ame]


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## michaelj199 (Aug 11, 2012)

the rotary valve is for exhaust. air/fuel mix goes through the supercharger into the valley. the valley has ports leading to cylinder. as the piston moves down the cylinder the exhaust valve starts to open. at roughly  .125in from bdc the exhaust valve is completely open and the intake port is starting to be uncovered. at bdc the exhaust valve is closed and the intake port is fully uncovered. so the burnt gasses are pushed out the cylinder. 

I'm going to use a solid crank with C.I. bushings. i might make two different styles of crank. a 90 degree offset and a 180 degree offset crank. with a flat (180 degree offset) crank it would sound more like a 4 stroke V8. at least i would imagine it would. two cylinders would fire at the same time so there would be 4 pops per revolution like a 4 stoke. plus it might increase torque. lol

if i used a splash oil system would i need to worry about what oil i used. at tdc the intake ports are open to the crank case so fuel could get into the oil. i don't know if glow fuel will effect an oils lubricating ability.


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## skyline1 (Aug 12, 2012)

Hi Michael

In many engines a small percentage of oil is mixed with fuel (or the energy transfer medium like steam) for lubrication. displacement lubricators in Steam engines, the petroil system in two strokes and small gas turbines use it as well. In some gas turbines (mini jets) it serves a dual purpose of cooling the bearings as well.

The Nitro fuel you are intending to use probably has a small percentage of oil in it. (Castor oil I believe but I may be wrong).

As to whether reversing the mix i.e. getting a small percentage of fuel in the oil would be detrimental I couldn't be sure. But provided the oil is changed fairly often I don't think it will be a problem but I'm not an expert on this.

The Model Jet guys use a 4% mixture in the fuel of either turbine oil (Shell 500 I believe) or 2 stroke racing oil (like Castrol R which is Castor oil based).

If, as you say, fuel is admitted to the crankcase during part of the cycle, it might be possible to lubricate the whole engine this way.

Just a few thoughts, the model jet forums might be able to give you some advice too.

Regards Mark


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## skyline1 (Aug 12, 2012)

Hi Michael

In many engines a small percentage of oil is mixed with fuel (or the energy transfer medium like steam) for lubrication. displacement lubricators in Steam engines, the petroil system in two strokes and small gas turbines use it as well. In some gas turbines (mini jets) it serves a dual purpose of cooling the bearings as well.

The Nitro fuel you are intending to use probably has a small percentage of oil in it. (Castor oil I believe but I may be wrong).

As to whether reversing the mix i.e. getting a small percentage of fuel in the oil would be detrimental I couldn't be sure. But provided the oil is changed fairly often I don't think it will be a problem but I'm not an expert on this.

The Model Jet guys use a 4% mixture in the fuel of either turbine oil (Shell 500 I believe) or 2 stroke racing oil (like Castrol R which is Castor oil based).

If, as you say, fuel is admitted to the crankcase during part of the cycle, it might be possible to lubricate the whole engine this way.

Just a few thoughts, the model jet forums might be able to give you some advice too.

Regards Mark


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## Jasonb (Aug 12, 2012)

Glow or nitro fuel has 15-20% oil so if you are feeding the air/fuel mix via the crankcase then you won't need additional oil. 

If your inlet ports are not open to the crankcase then you will need some means of oiling the lower end in which case the same castor or synthetic oil that is in your fuel would be best as any drawn into the cylinder will just burn off.


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## michaelj199 (Aug 12, 2012)

can anyone tell me the carb barrel port size on a .12ci/2cc nitro engine? given the effective displacement ~.137ci and the fact that i have two intake ports open at a time I think 2 carbs of roughly .12 size would be a good place to start for carb sizing. i got the effective displacement by multiplying one cylinders displacement .098ci by boosted pressure ratio (14.7+6)/14.7=1.4 

I would also like your input on tolerancing the rotary valves. i was thinking .0015-.002. The valve is going to be hot and i don't want it seizing or to loose to much compression to blowby.


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## trumpy81 (Aug 12, 2012)

michaelj199 said:


> the rotary valve is for exhaust. air/fuel mix goes through the supercharger into the valley. the valley has ports leading to cylinder. as the piston moves down the cylinder the exhaust valve starts to open. at roughly  .125in from bdc the exhaust valve is completely open and the intake port is starting to be uncovered. at bdc the exhaust valve is closed and the intake port is fully uncovered. so the burnt gasses are pushed out the cylinder.
> 
> I'm going to use a solid crank with C.I. bushings. i might make two different styles of crank. a 90 degree offset and a 180 degree offset crank. with a flat (180 degree offset) crank it would sound more like a 4 stroke V8. at least i would imagine it would. two cylinders would fire at the same time so there would be 4 pops per revolution like a 4 stoke. plus it might increase torque. lol
> 
> if i used a splash oil system would i need to worry about what oil i used. at tdc the intake ports are open to the crank case so fuel could get into the oil. i don't know if glow fuel will effect an oils lubricating ability.



So I was thinking on the right path to begin with re: rotary valve.

OK, with your crankcase pressurised there is a very real possibility that you will get fuel being forced into the cylinders past the piston, whether you have rings or not. You have to remember that you will need clearance between the piston and the cylinder wall. How much clearance depends on material choice but you will need clearance!

It would be better if the rotary valve controls the intake and use ports for the exhaust, that way you could control the fuel intake more effectively. Of course that will mean you need lubricate the bottom end with a few drops of oil before any running, but with the blow by past the piston, the fuel/oil mix will maintain the lubrication of the bottom end.

As for C.I. versus Bronze for plain bearings, it makes little difference provided the plain bearing has been designed correctly to begin with. A poorly designed plain bearing will gall the shaft and itself regardless of the material used.

You'll find some useful information about plain bearing design here:
http://wikihelp.autodesk.com/Invent...ineer1994/2105-Bearings2105/2122-Plain_Be2122

There is also a plain bearing calculator available somewhere on the net, I used it when designing my V8. Here's the address to one calculator, but it's not the one I used:
http://www.vesconite.com/design/bush/entry_alldesigns2.htm

You'll find the calculator that I used here:
http://www.metalstop.com/


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## michaelj199 (Aug 13, 2012)

re: rotary valves
no i cannot use the valve for intake. first having an exhaust port means that the port is open equal time on both the down and up stroke. I don't want this. I want the exhaust to open before the intake to relieve pressure. then open for a period of time with the intake to allow exhaust gasses to be forced out. then the intake to be open by itself to allow the cylinder to be brought up to boost pressure. My current configuration allows for this. It also helps keep the piston cool. This configuration is based of the two stroke Detroit diesel.


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## trumpy81 (Aug 14, 2012)

michaelj199 said:


> re: rotary valves
> no i cannot use the valve for intake. first having an exhaust port means that the port is open equal time on both the down and up stroke. I don't want this. I want the exhaust to open before the intake to relieve pressure. then open for a period of time with the intake to allow exhaust gasses to be forced out. then the intake to be open by itself to allow the cylinder to be brought up to boost pressure. My current configuration allows for this. It also helps keep the piston cool. This configuration is based of the two stroke Detroit diesel.



First off, the Detroit diesel injects fuel directly into the combustion chamber it does NOT pressurise the crankcase and then force fuel past the pistons into the combustion chamber. 

Forcing fuel past the piston will alter the intake timing when compared to direct injection also.

To replicate the Detroit diesel, you will need to have the blower feed fuel/air directly into the combustion chamber. For that to work you would then need another rotary valve or a piston controlled port. That is why I suggested the intake be controlled by the rotary valve and the exhaust be controlled by port. The exhaust cycle is less critical than the intake cycle in terms of the needed duration, as the gas pressure after combustion, helps to expel the gases. Theoretically, the more gas pressure, the less duration that is needed. 

Remember that it is the height of the port opening that controls both the opening and closing timing events and depending on where the port is placed in relation to the piston travel, will determine the actual timing events.

This is a design limitation of ported two stroke engines and it's also why companies such as Yamaha developed slide valves (YPVS) in order to alter the port timing of their two stroke engines.

Also, if you wish to see piston blow by at work, take a close look at a Cox .049 engine.


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## michaelj199 (Aug 14, 2012)

i have an intake port. its at the bottom of the stroke. its .125 in diameter routed directly from the intake valley. a pressurized crank case is a side effect. when the piston is at tdc, the intake port is uncovered by the piston allowing air/fuel into the crank case. i cannot increase the length of my piston to keep the port closed off from the crank case without causing interference problems in the lower end. if i could make room in the head for two rotary valves i would have made it four stroke. space is a commodity.

i am pretty set in this design aspect of my engine and if I've come off as to blunt or rude I apologize. i just thought i had made my design understood.


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## trumpy81 (Aug 15, 2012)

michaelj199 said:


> i have an intake port. its at the bottom of the stroke. its .125 in diameter routed directly from the intake valley. a pressurized crank case is a side effect. when the piston is at tdc, the intake port is uncovered by the piston allowing air/fuel into the crank case. i cannot increase the length of my piston to keep the port closed off from the crank case without causing interference problems in the lower end. if i could make room in the head for two rotary valves i would have made it four stroke. space is a commodity.
> 
> i am pretty set in this design aspect of my engine and if I've come off as to blunt or rude I apologize. i just thought i had made my design understood.



No need for apologies, I do understand where you are coming from.

I'm not trying to deter you in any way, just trying to point out a few facts of life that's all. I would like to see your engine work as much as you do, but clearly you have a lot more learning to do.

Something else for you to consider, a Detroit diesel runs with a maximum redline around 2500 RPM, your engine will be lucky if it idles under 3000 RPM simply because of it's size and inherent losses in efficiency when compared to a full scale engine. That, by necessity, will demand different port timing to start with.

Air and Fuel DO NOT scale. That is you can make the engine way smaller than it is already, but the properties of fuel and air do not change simply because you have made a smaller engine.

To my knowledge, I have only seen one successful multi-cylinder, two stroke model engine and that was based on the top ends of several Cox .049 engines. Mind you, I haven't actually seen this engine run, so it's open to interpretation as to whether or not it actually works. It does work on paper though ... lol

I have the plans for it floating around here somewhere if you'd like to see them.

At present, what are your port timings? That is, at what degree of crankshaft rotation will the intake open and when will it close and what will the duration be, likewise for the exhaust?

I asked, because I think you will find that the intake port will need to be a little higher than I imagine it to be at present. I'm just guessing though.

When you map out the intake port timing for all 8 cylinders you will see why you will need to at least seal the crankcase between each pair of opposing pistons. Then your current plans have some chance of success.

You'll also have to make some reasonable pressure with the supercharger to compensate for the reduced crankcase pressure of each pair of cylinders.

Each opposing cylinder pair will be pretty much moving in the same direction, IE: as one side goes up, the other side will be coming down, so there will be little or no pumping/pressurising action going on to help force the fuel in the direction it needs to go in, they will simply be moving the air from side to side. The supercharger should overcome that though.


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## michaelj199 (Aug 15, 2012)

port timing is:
intake 112.02-247.98 duration 135.96
exhaust 81.79-180 duration 98.21

pay attention to the left cylinder. the right valve is off timing.

[ame]http://youtu.be/_o1erbmHEIQ[/ame]

better view of intake port


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## trumpy81 (Aug 16, 2012)

> pay attention to the left cylinder. the right valve is off timing.


Not sure what you mean by that?

Do you mean that the exhaust valve timing is not correct?

I can see by the video that it isn't correct, as the valve opens with the piston at BDC and is closed before the piston starts moving up (about 20 degrees duration it would appear, but hey, the slide rule is downstairs ... ).

Like they say, a picture is worth a thousand words ... 

With the piston at TDC the intake port is uncovered which means that the crankcase will be filled with fuel/air as it will be under pressure from the supercharger. That fuel/air will eventually be forced past the piston and rings and into the combustion chambers of the other cylinder/s as the crankcase becomes more and more pressurised.

Personally, I think if you were to employ the rotary valve for the intake instead of exhaust without any other changes, you'd have much better results. There's no reason why you can't use a slot instead of a simple hole for your ports which would help with the timing. You'd also have less of a problem with the crankcase filling with fuel/air.

Your design is much better than I was picturing it though. Kudos!

Here's a Youtube video of a commercial 4 cylinder opposed 2 Stroke from the seventies. You'll notice the plenum that is employed for the intake:

[ame]http://www.youtube.com/watch?v=w-A5wvag224[/ame]


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## michaelj199 (Aug 16, 2012)

i believe the effective volume of the crank case will stay the same. while one piston is going up another is going down. the crank case pressure will only get as high as boost pressure and cylinder pressure will always be greater then or equal to boost pressure. therefor there should not be much if any air/fuel pushed up past the rings. there is only one point in time that the crank pressure could be higher then cylinder pressure and that's with the exhaust valve open right before the intake port is uncovered but that would be for only a very short period. with this V8 design and an open crank case ( not divided) there will always be an intake port open to the intake valley. so pressure increases caused by blow by of the rings will vent back into the intake valley. so there's no reason the crank case should become excessively pressurized.

i plan on running around 6-7 psi. this is a calculated figure so most likely closer to 5psi. my initial compression ratio is ~8 to 1 and after boost my effective compression ratio will be around 9 to 1. i plan on using brass chim stock for head gaskets so i can adjust compression ratio at will. timing can be controlled by the heat of the plug. i will start out with a medium and work from there.
~.78ci engine
~.88ci per rev supercharger
1.25 overdrive on pulleys
=~6-7 psi boost


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## trumpy81 (Aug 18, 2012)

That all sounds good Michael. I hope it all goes to plan for you. 

When do you plan to start building it?


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## michaelj199 (Aug 18, 2012)

school starts the 27th. I've got to batten down and double check all my parts. it's going slow considering i just started quitting smoking. my brains all fuzzy lol. every time i try concentrating i unconsciously get up and head out for a smoke. It's hell but it needs doing. lol


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## vcutajar (Aug 18, 2012)

Good luck with the build.  If you post it here I will surely be following.

Vince


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## trumpy81 (Aug 19, 2012)

michaelj199 said:


> school starts the 27th. I've got to batten down and double check all my parts. it's going slow considering i just started quitting smoking. my brains all fuzzy lol. every time i try concentrating i unconsciously get up and head out for a smoke. It's hell but it needs doing. lol



Well I wish you luck re: smoking. I wish I could give it up, but I lack the will power to even try ... lol

Right now I'm re-working my own V8 project. I found a few items that weren't quite finished and I decided to make some changes, so I know what your going through right now.

I hope you will keep us posted on your progress. This is an interesting project simply because it is a two stroke and there is not too many examples of multi-cylinder two strokes out there.


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## michaelj199 (Dec 18, 2012)

sorry for no updates between learning matercam and sharing machine time with other students things provided slower then expected. i was so caught up in trying to get parts done i didn't take picks. now that the semester is over  i took some of what i got done

the engine block was made using the 4th axis so it would be easer to set up the part. ie. not needing clever ways to set my part zeros. the first block was made in wax to verify tool paths. the second block was in aluminum and i had an oops when i forgot to update both banks bolt pattern when i made a change. the third was a success.





















the oil pan was cut out of the center of a piece of stock. pocketing out the inside then flipping it and contouring and parting it off.





the heads were also cut out of the center of the stock. top side first then bottom. then i used a radius tool down the sides of the top getting ride of the tabs for a bonus. then i stuck it in the vise on the side and did the exhaust side.





and some shots of what i have assembled


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## agmachado (Dec 18, 2012)

Very, very nice...

Congratulations!!!

Cheers,

Alexandre


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## stevehuckss396 (Dec 18, 2012)

I love it!!


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## trumpy81 (Dec 19, 2012)

Michael, that's looking really nice. I can't wait to see the finished article.


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## michaelj199 (Dec 19, 2012)

unfortunately i do not know when i will be able to work on it again. i do not own my own my own machines. and im finished with school.


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## trumpy81 (Dec 20, 2012)

Sorry to hear that Michael. If you were in my neck of the woods you'd be welcome to use my machines. I'm assuming that you are in the US?

I read, quite some time ago now, that there were places that you could hire certain amounts of time in an entire workshop. I don't know if these places exist or still exist but worth looking into?

Another possibility, a school workshop (community college I think they are sometimes called), with permission of course  Maybe you could approach the staff/administration at the school where you started the project?

Or post an ad in your local newspaper requesting the use of someones workshop, for a small fee of course. I'd hate to see this project go unfinished.

Anyhow, I wish you all the best with this project and I would like to extend the Seasons Greetings to you and I trust you will have a Happy New Year.


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## Herbiev (Dec 21, 2012)

I'm sorry to hear that too. If you are in South Australia you are welcome to use my facilities. Whatever you do dont go back on the cigarettes. I gave up 21 months ago but too late. 18 months ago I was diagnosed with emphysema, put on oxygen 24/7 and suffered 4 bouts of pneumonia. If only I could turn back time


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## michaelj199 (Dec 23, 2012)

thanks you guys. im in the process of applying and interviewing for jobs. after everything is settled down i have my eye on getting an sieg x3 mill. then hopefully work on getting the parts to cnc it. and since most of the stuff i work on is small i was contemplating building a jig to allow me to use the mill as a lath until i can afford one. thats my plan anyway will see how it goes


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