# Designing an engine



## Metal_slicer

Hello guys,

I have been designing a two cylinder engine but I may need a little help with cam design. Right now the intake and exhaust center lines are 30 deg. apart I did a search on google and can't find what I am looking for. I did find a chart but was not able to make sense of all the angles and degrees.

Here is what I have so far. I have not yet made the cylinder block.


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## BronxFigs

Looks great.  Very interesting to see the design process. Wish I could help you, but with no experience in engine design....I can't.

Is there a reason why you couldn't duplicate/borrow the timing events/cam profiles from a proven model engine design?  Maybe that will at least get you close to a solution.  I'm sure with some very slight modifications to the lobe design you'll have a working camshaft.

Just thinking out loud...can you make the camshaft by sliding on each individual cam-lobe/profile, so they can be rotated into different timing positions?  Then, you wouldn't have to re-machine the complete camshaft if a  specific cam didn't work as planned.  I think in the "Gemini" 2-cylinder gas engine, the builder used add-on cams to a shaft.

I can't wait for the rest of this design to show up on the forum.  It's nice to read about and see how designs evolve.  Thanks for the interesting subject.


Frank


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## petertha

Perhaps this past post of mine will get you started. I had similar questions. Note the gas vs methanol comments regarding timing, not sure what you had in mind there but I suspect that will factor in too.

http://www.homemodelenginemachinist.com/f26/valve-timing-4-stroke-glow-17093/

Actually, I'm in the process of drawing up a single cylinder design for myself as a starter IC project. A while back I cooked up an Excel spreadsheet to allow input of Inlet/Exhaust open/close values typically referenced on designs Then it spits out resultant cam phasing values, overlap, visual plot etc. I'm posting some screen caps for now because I need to go back & double-check the (late night spare time) math. But I'm just about to cross this bridge for my own project so hopefully can offer a tool if everything pans out.

In the interim, if you go to this awesome site & type 'camcalc' in the search box, it will go to a cam profiling tool app. Running it was kinda hit & miss for me in the past, but probably a function of my PC or OS.

http://www.modelenginenews.org/


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## stevehuckss396

Metal_slicer said:


> Hello guys,
> 
> I have been designing a two cylinder engine but I may need a little help with cam design.




It depends on the configuration of your crankshaft. If both pistons oppose each other things will be different than if both pistons go up and down together. Also the direction of rotation of the cam would be needed.

What info would you be looking for specifically?  

I typically make mine with about 280 duration and 110 degrees lobe separation for ease of machining. 5 degree increments works good with my method of machining.

Tell us what you need and i'm sure you will get as much help as you will need.


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## Metal_slicer

Thanks Guys,

I am going to have the pistons opposing each other, one TDC and one BDC. The bore is going to be .9" and stroke 1". I have read an article on cam design and they discussed factors like fuel to be used, RPM ranges and even valve float all are taken in to consideration in the design of the cam. Since I'm not making a racing engine, all I would need is a simple cam design that would allow me to run the engine and rev it a few times. Fuel I'm not sure about, what ever is recommended for model engines that is cheap and available everywhere.


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## BronxFigs

Just throwing out some general question:

Since this engine is being designed from scratch, is there a way to design an engine for use on propane?  Or, is it just a matter of converting a conventionally designed _gas engine_, to be run on propane, by using the correct mixing demand valves, etc?  And, what about running an engine like this on Coleman's lantern fuel, instead of pump gasoline?

It would seem that barbeque propane is always available, cheap, less fumey, safer to carry, and easier on the engine parts.  It seems that running an engine on propane is always either a conversion, or, an afterthought.  At least, I do not remember ever seeing any model engines designed specifically, to be run on propane, but then again, I'm usually wrong.

I'm really curious about this design-from-scratch process, and the choices that are available.

Thanks,


Frank


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## dman

BronxFigs said:


> Just throwing out some general question:
> 
> Since this engine is being designed from scratch, is there a way to design an engine for use on propane?  Or, is it just a matter of converting a conventionally designed _gas engine_, to be run on propane, by using the correct mixing demand valves, etc?  And, what about running an engine like this on Coleman's lantern fuel, instead of pump gasoline?
> 
> It would seem that barbeque propane is always available, cheap, less fumey, safer to carry, and easier on the engine parts.  It seems that running an engine on propane is always either a conversion, or, an afterthought.  At least, I do not remember ever seeing any model engines designed specifically, to be run on propane, but then again, I'm usually wrong.
> 
> I'm really curious about this design-from-scratch process, and the choices that are available.
> 
> Thanks,
> 
> 
> Frank



gasoline engines run fine on propane but there may be a loss of power. gas fuels are light and displace a lot of air so there is less air and fuel mass per stroke. 

you can raise the compression with a propane engine and there is less need for velocity i nthe ports to keep the fuel atomized so propane engine sometimes have large ports and high compression, but if you want maximum torque there is an ideal velocity and valve timing. that also depends on how fast you want the engine to spin.  

cam design has a lot to do with airflow and rpm goals. what are your goals for the engine?

also are you going for even firing order? or will the pistons try to counter ballance each other to some extent? 

you can break things down into opening and closing events, or you can go with intake centerline, duration, and lobe separation which is more useful for manufacturing the cam.

every 180 degrees of the crank is a different stroke, the cam turns half the speed so the strokes are 90 cam degrees apart. because the valves need to open smooth and resembling sinusoidally to avoid stability problems, when the lobes are big enough there is too much overlap so they spread the lobes apart a bit more. lobe separation is usually between 100-120 degrees and the majority of them are somewhere close to the center of that range. 

the intake center line is measured in crank degrees and the lobe centers are measured in cam degrees so the numbers are usually pretty close. you should be able to balance the cam in the overlap period with the springs of the intake and exhaust valves with the crank at tdc and the engine should run. remember to check for piston clearance. the valves often move faster than the piston and if you don't have the lobe separation and clearance right things can crash.


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## BronxFigs

dman:

Thanks for the great answer.  Now, I have to think about all the important points that are outlined in your answer.  I appreciate the time and thoughts, and for your help.


Frank


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## Metal_slicer

My plan is to go with some sort of liquid fuel. I don't mind even using r/c nitro fule.


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## Metal_slicer

Did some more work on the cad design. It's quite a challenge especially when my laptop crashes when I try to do to much. I have included a wire frame picture so that you can see the various parts inside. I created the crankshaft, rods, and pistons. I have started working on the lower portion of the block and I need to make several changes. This design will likely change several times, but here is what i have at the moment.


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## Henry

That looks really nice!!!. About your crashing problems, normally it will be the memory, if the crash got worse when the model become more complex, that will be the problem, It is really cheap now and you will be able to buy 4 Gb for like 40 or 50 $, cheaper look how many programs are using the memory now and you will be able to stop a few of them.


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## Metal_slicer

I had to start over with the design. I was able to re-use some of the parts from the previous design though. Here is a picture of it. I'm almost ready to start machining. Still need to figure out if I can improve the spark plug clearance which is very close to the valve spring. I'm afraid it may rub on the spring. There is not much room when you add the screws and intake/exhaust ports. I am going to try to experiment cutting an angle for the sparkplug.


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## Metal_slicer

*The individual parts...*
Still a work in progress, not all the parts are shown.


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## gbritnell

Don't take what I'm about to say as anything but helpful information. Others on this board know that I am one of the most helpful when it comes to information giving so let me start. 
I would like to start off by asking what your modeling background is? By that I mean have you ever built an I.C. engine of any sort? Most of us here started by making a simple hit and miss engine or something like that so we could learn how all the pieces interact and what elements are required for a functioning engine. 
My background is extensive. I grew up in an era when people worked on their cars and hot rods, everything from simple spark plug changing to complete engine and transmission rebuilds. Added to that is my background in machining. I started in my teens and then worked at it for 40 some odd years, not counting my home shop work. I have designed and built quite a few model engines, steam, aircraft, automotive and motorcycle to name a few. This was not an overnight process. 
While I applaud your interest in designing and possibly building it's not just a matter of drawing pieces and parts. Your question about cam design prompted this reply. A couple of the fellows gave you information on cam design and characteristics which are essential for the proper operation of an engine. Knowing the difference between mild cam timing and radical timing and how they affect the performance of an engine are basic to understanding any engine's operation. 
There are so many other questions that need to be answered when designing and building:
What type of material are the parts to be made from?
What compression ratio are you going to use?
How big should the valves and stems be?
What size porting and manifold should you use?
What are you going to use for a carburetor?
What type of ignition will it have, points or electronic?
How are you going to trigger the ignition, from the cam or through a distributor.
All the above and more have to be taken into consideration when designing and building and engine.


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## BronxFigs

Thought provoking comments.  

To watch an engine being designed and be "built" on a computer screen is very interesting.  

I'm staying around for the real build that I hope will follow.  Good luck Metal Slicer.


Frank


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## Metal_slicer

gbritnell said:


> What type of material are the parts to be made from?
> What compression ratio are you going to use?
> How big should the valves and stems be?
> What size porting and manifold should you use?
> What are you going to use for a carburetor?
> What type of ignition will it have, points or electronic?
> How are you going to trigger the ignition, from the cam or through a distributor.
> All the above and more have to be taken into consideration when designing and building and engine.



My modeling experience is self taught. I am using Viacad 2d/3d which is a non professional software program. I have used it to design robot parts and have made several items with it. I realize most have started off with a hit-n-miss engine but I don't really have an interest in this engine. 

I have graduated from a trade school with a diploma in automotive and diesel technology back in 1989 and worked in an automotive shop for 3 years before changing my profession to the electronics manufacturing arena. I understand learning to turn a wrench vs. designing an engine are two very different things, but my goal here is not to make a running engine although I would  like it to be able to run for a few seconds, and even better a few minutes. I have an interest designing something and then making it. Because I am not an engineer, I don't expect it to actually run. 

The materials I plan to use are free machining steel, stainless steel, and brass. The size of the valves and ports are based on tool sizes available, example, 1/8" for the valve stems because 1/8" is a common size for a drill bit. Any smaller than 1/8" and the strength becomes less and its harder to machine on the lathe. Ignition is going to be electronic triggered by the cam shaft. The cam design I may need help with the lobe design but I will worry about that when I cross that bridge. I'm not going to be over critical about Exact port size, the perfect size valve stem, or compression ratio. 

I want to design this engine and learn as I build it. I will enjoy this project even if in the end the engine wont run.


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## Metal_slicer

Material question:

Should the cylinder and piston rings both use the same cast iron material?


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## stevehuckss396

Metal_slicer said:


> Material question:
> 
> Should the cylinder and piston rings both use the same cast iron material?



Dont have to. You can use Steel liners with the cast rings. 

Cast cylinders, cast pistons, cast rings
Steel cylinder, cast piston, cast rings
steel cylinder, aluminum piston, cast rings

I like the last one personally.


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## Metal_slicer

stevehuckss396 said:


> Dont have to. You can use Steel liners with the cast rings.
> 
> Cast cylinders, cast pistons, cast rings
> Steel cylinder, cast piston, cast rings
> steel cylinder, aluminum piston, cast rings
> 
> I like the last one personally.



Yes I like the last option also. Steel cylinders, 6061-t6 pistons, and cast iron rings.


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## stevehuckss396

Metal_slicer said:


> Yes I like the last option also. Steel cylinders, 6061-t6 pistons, and cast iron rings.



I use 12L14 for my liners. It's a leaded steel so it machines like a dream. I have made liners for 4 engines now with no second thoughts. 

If your feeling a little froggy, make the bottom of your cylinder smaller than the top by a few thou. Then size your liner to the top and bottom and undercut the center. This way even a 2+ inch long liner will only need to be pressed in the last 1/2 inch or so. Much easier than pressing the entire length of the liner. A little more work making liners but they go in easy and undamaged so i think it's worth it.








Liner drops right in to here and almost lines it self up for pressing.


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## Metal_slicer

Here is the underside of the cylinder head. The chambers are cut 0.1" deep. The intake and exhaust ports are 0.25" O.D. with a 45Deg bevel. Valve stems are cut or I should say will be cut 1/8" The valves will be machined out of free machining T-303 stainless. I was thinking of making the entire head out of brass but I may try to use 6061-t6 instead.


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## stevehuckss396

Metal_slicer said:


> Yes I like the last option also. Steel cylinders, 6061-t6 pistons, and cast iron rings.




I have used both 6061 and 7075

6061 go .001 - .00125 under bore  or 1 to 1-1/4

7075 go .00075 - .001 under bore  or 3/4 to 1

Cast go .0005   Bob Shutt built his Peewee V4 so tight he still has not put rings in it and it runs great.


This is just what I do and others may advise differently.


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## stevehuckss396

Metal_slicer said:


> Here is the underside of the cylinder head. The chambers are cut 0.1" deep. The intake and exhaust ports are 0.25" O.D. with a 45Deg bevel. Valve stems are cut or I should say will be cut 1/8" The valves will be machined out of free machining T-303 stainless. I was thinking of making the entire head out of brass but I may try to use 6061-t6 instead.





Looks good!

Compression ratio?


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## Metal_slicer

stevehuckss396 said:


> Looks good!
> 
> Compression ratio?



I don't know ;D I'm using eyeball engineering . I could send you the .igs file if you want to see it. Let me know if you are interested.


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## stevehuckss396

Metal_slicer said:


> I don't know ;D I'm using eyeball engineering . I could send you the .igs file if you want to see it. Let me know if you are interested.



Well your going to want to get that one right or you will cause your self problems. I shoot for 5 to 6 to one. Good idle and easy to turn over to start.

Peewee is 5.25:1

Demon is 5.5:1

If you need help with that one PM me and ill lend a hand. Might want to nail down the CR early because the chamber design will effect the length of the valves and things like that.


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## Metal_slicer

stevehuckss396 said:


> Well your going to want to get that one right or you will cause your self problems. I shoot for 5 to 6 to one. Good idle and easy to turn over to start.
> 
> Peewee is 5.25:1
> 
> Demon is 5.5:1
> 
> If you need help with that one PM me and ill lend a hand. Might want to nail down the CR early because the chamber design will effect the length of the valves and things like that.



I found a web calculator that I was able to find out the CR. The current chamber design as it stands right now I am getting 18.5 : 1 

CC one cylinder is 0.573

I'm going to need to cut a deeper chamber or dish out the piston.... Working on it now to see if I can get it lower.


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## Metal_slicer

Ok I got it down to 6.07 : 1 by leaving the entire chamber cut .1" deep the full diameter of the cylinder. In other words, it will be like a Hemi type combustion chamber. I'm off to bed, got to work tomorrow.


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## Metal_slicer

Hello   guys,

I want to start machining the engine block but I have a question about the crank journals. Do I drill the hole undersize to ream later? Or do I mill them out using a ball mill? Got any pointers?


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## stevehuckss396

Personally I drill under and then finish with a boring head in the mill. You need the bore as straight as it can be.

If your drill wanders the reamer cannot correct it but the boring bar will.


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## Metal_slicer

stevehuckss396 said:


> Personally I drill under and then finish with a boring head in the mill. You need the bore as straight as it can be.
> 
> If your drill wanders the reamer cannot correct it but the boring bar will.



Thanks, I didnt think about that. Another question I have been wondering about for the past week is do I drill then bore the journals after the main bearings are bolted in place? Because if I do this first then later try to make a matching main bearing, there are going to be issues with roundness.


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## stevehuckss396

Metal_slicer said:


> Thanks, I didnt think about that. Another question I have been wondering about for the past week is do I drill then bore the journals after the main bearings are bolted in place? Because if I do this first then later try to make a matching main bearing, there are going to be issues with roundness.



Nope!

Just bore the block with the caps installed and then make bearings to fit.


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## Metal_slicer

stevehuckss396 said:


> Nope!
> 
> Just bore the block with the caps installed and then make bearings to fit.



Thanks Steve!

I got some of my material in yesterday, annealed 303 stainless round rod and 6061-t6 round rod for the pistons. I made some practice cuts to test out my setup to get a feel for the material. I'm hoping to start machining the block this weekend if time permits. I fully expect many problems along the way, buy hey, that's ok! I'm doing this project to learn while having fun.

It seems I'm in need of a lot of tools. I need to grind me a tool for the piston ring grooves.


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## Metal_slicer

Some pictures to share of my shop, shop dog, tools and equipment...


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## stevehuckss396

stevehuckss396 said:


> Nope!
> 
> Just bore the block with the caps installed and then make bearings to fit.




Found the pictures. My oil pan also acts as the front and rear cap. Thats why you only see 3 caps.


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## maki2212

what all i need have to build v8 ? please


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## Metal_slicer

stevehuckss396 said:


> Found the pictures. My oil pan also acts as the front and rear cap. Thats why you only see 3 caps.



My design uses the oil pan as front and rear caps also. Thanks for sharing those images!


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## mu38&Bg#

Just a few comments. Just by looking at the image in post 13. The crankpins look small. The small end of the rod has little meat on it. The lower side of the wrist pin hole in the piston has little meat on it. These may or may not be deal breakers, but I would consider increasing crankpin size. It will make for a stronger crank less likely to bend in manufacture, and increase oil film shear for better lubrication. For clearances around things like plugs and valves, you want to be certain before you begin making parts. I can't tel from the image if the hole for the plug is drawn at major or minor diameter. If it's at the minor diameter, make sure it won't break through other features like the valve seats. Actual valve seats should be narrow, .010-.020".

Greg


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## Metal_slicer

dieselpilot said:


> Just a few comments. Just by looking at the image in post 13. The crankpins look small. The small end of the rod has little meat on it. The lower side of the wrist pin hole in the piston has little meat on it. These may or may not be deal breakers, but I would consider increasing crankpin size. It will make for a stronger crank less likely to bend in manufacture, and increase oil film shear for better lubrication. For clearances around things like plugs and valves, you want to be certain before you begin making parts. I can't tel from the image if the hole for the plug is drawn at major or minor diameter. If it's at the minor diameter, make sure it won't break through other features like the valve seats. Actual valve seats should be narrow, .010-.020".
> 
> Greg



Yeah I have the valve seats at .025", the crank pin is at .125" and I agree it is smaller than I would have liked. I would have liked the crank pins to be at least 3/16" I will try to see if I can change this, but it always makes me nervous making changes in CAD and risk loosing countless hours invested. The vale seats, intake, and exhaust ports and bolts are not intersecting. I had to angle the spark plug hole to allow for more valve spring clearance which is not shown in post #13. Another thing I didn't like about this design is the size of the pistons. I feel as though the pistons are to big, but I am not going to change this because it would cause to many changes, and it would be better to just start over.

Today I did a practice cut on a valve and I didn't like the quality of the finish of the valve stem. I am thinking of taking a longer piece long enough for two valves and center cutting the end and making two of the 1/8" stems using the live center in the tail stock and turning them down to .125" , cut them in half and then machine the thicker ends to the dimensions of the valve head for both valves. The problem I was having trying to cut one valve at a time was when the stem became smaller it was deflecting away from the cutter causing a tapered valve stem.


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## Metal_slicer

Practice 303 stainless valve I cut today. I did not part it off the bar stock, I just wanted to practice.


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## stevehuckss396

It's alot of fun when things go good.

That looks like about a .093 or .125 stem. You can get "E" clips to retain them if your interested. They are tiny so get a few extra. Make a little brass retainer that will hold it on when installed.

This one is .093 stem


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## mu38&Bg#

I would expect to see a 5.5-6.5mm crank in a ~10cc cylinder. If the engine will never see a load it may be strong enough, but still looks like it will be difficult to machine. Piston proportions look great for a model engine. This isn't a racing piston. Just keep a copy of your CAD. I have 6 versions I kept of a project I'm working on now. There are always new ideas, just after you commit to one.

Greg


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## Metal_slicer

My stems are .125"

Steve where did you get those springs? I have been looking but its a jungle out there!


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## Metal_slicer

dieselpilot said:


> I would expect to see a 5.5-6.5mm crank in a ~10cc cylinder. If the engine will never see a load it may be strong enough, but still looks like it will be difficult to machine. Piston proportions look great for a model engine. This isn't a racing piston. Just keep a copy of your CAD. I have 6 versions I kept of a project I'm working on now. There are always new ideas, just after you commit to one.
> 
> Greg



Thats a good idea. I will make a copy before I tear things up.


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## stevehuckss396

Metal_slicer said:


> My stems are .125"
> 
> Steve where did you get those springs? I have been looking but its a jungle out there!



Grainger lists a million of them. Worst case they have to get them from the warehouse and you wait a day.


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## Metal_slicer

Started on the engine block. The last image was taken seconds before a malfunction occurred. It bent the drill bit and caused slight damage to the hole just drilled. The problem was a set screw attaching the Z-Axis stepper motor coupling to the lead screw. It came loose, therefore, when backing the drill out of the hole it started to free spin leaving a portion of the drill bit still in the hole and then began to jog over to the next hole! I'm tempted to use some blue loctite on this screw, this is the second time this has happened.


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## Metal_slicer

Did some more work on the engine block. I milled the block to the proper dimensions today. I was able to fix that damaged hole after all. Turns out 1/8" is to tight for some of the push rods to move freely, so I drilled one size larger. I may need to create some sort of guide but I'm not sure yet. Here are the images of what I have so far.


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## Ryan

A shop dog to go with the lathe dogs...


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## barnesrickw

Metal_slicer said:


> Did some more work on the cad design. It's quite a challenge especially when my laptop crashes when I try to do to much. I have included a wire frame picture so that you can see the various parts inside. I created the crankshaft, rods, and pistons. I have started working on the lower portion of the block and I need to make several changes. This design will likely change several times, but here is what i have at the moment.



Is a brave man that uses CAD on a laptop.  My hat is off to you and your shared drivers.


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## barnesrickw

Ryan said:


> A shop dog to go with the lathe dogs...



Lost my shop dog a few years ago, and my shop cat recently.  Best shop accessories I've ever had.  Not a fan of small dogs until my daughter got a Yorkie,  Morkie actually. Trying to turn her into the new shop dog.  Daughter does not like the aluminum shavings in her coat.


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## Metal_slicer

A few more images of todays hour in the workshop. Bottom crank case features machined as well as the bolt holes.


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## Metal_slicer

Hello guys,

I have a question about making the crankshaft. Which would be easier? using round stock or flat bar? How can I accurately center drill the journal center lines for both ends? If I can get the center lines drilled correctly, I think I can do it.


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## stevehuckss396

You are going to want to use 1144 stress proof steel. It has very little stress internally so it won't warp as you remove metal. It also cuts very nice. It only comes round so I mill a small flat on the end of the bar so when I flip the bar to do side 2, I have a surface that I can run an indicator across.


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## Metal_slicer

stevehuckss396 said:


> You are going to want to use 1144 stress proof steel. It has very little stress internally so it won't warp as you remove metal. It also cuts very nice. It only comes round so I mill a small flat on the end of the bar so when I flip the bar to do side 2, I have a surface that I can run an indicator across.



Forgive me, but I don't understand what you are talking about. I understand you mill a flat on the end of the round stock, and I did this on some scrap 12L14 stock to explore using the edge as a reference but that is only good for the Y - Axis, I will need a reference for the X-Axis as well don't I? 

I don't have an indexer or any kind of turn table yet. Just my cnc mill and manual lathe.


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## Swifty

What Steve was getting at, is you mill the flat as a reference for a dial indicator when you flip the part for centre drilling. You will still have to indicate both ends to find the centre if the bar.

Paul.


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## kuhncw

Here is another way to line up the crank centers on a round bar, assuming you have a vee block that will hold your crank blank.  After indicating the bar and drilling centers on one end, flip the vee block (don't loosen or move the bar), indicate the other end, and drill.  

Hopefully the photo is attached properly.

Regards,

Chuck


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## Metal_slicer

kuhncw said:


> Here is another way to line up the crank centers on a round bar, assuming you have a vee block that will hold your crank blank.  After indicating the bar and drilling centers on one end, flip the vee block (don't loosen or move the bar), indicate the other end, and drill.
> 
> Hopefully the photo is attached properly.
> 
> Regards,
> 
> Chuck



Thanks for the example image! I like this idea a lot! This seems to be the easiest way to do this. Milling a flat on the round bar and using a dial indicator is still not very clear to me because I don't know what orientation the bar is. horizontal? vertical? is a mill used? how is the part held, etc... I'm sure I may frustrate some of you but I just cant picture in my mind how a dial indicator is used for this particular method. I'm not a machinist, everything I know is 100% self taught.


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## stevehuckss396

Metal_slicer said:


> I understand you mill a flat on the end of the round stock, and I did this on some scrap 12L14 stock to explore using the edge as a reference but that is only good for the Y - Axis



After you flip the stock, the flat will be at the bottom. Align the flat along Y and indicate so it is perfectly along Y. Once done you have rotated 180 and are back in alignment with side one.


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## Looper7

Photo of set up



Hope that helps


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## Metal_slicer

Thanks Looper7,

I was considering using flat bar, but I wanted to try using round bar instead. I like the idea of using a v-block to clamp on to the round stock and I will likely use this method. My goal is to have crescent shaped counter weights which would be easier to achieve using round stock.


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## Metal_slicer

Ok! it's been a while. It's going to be a long process because I need to buy several new tools to do the various jobs. I have taped the head bolts, side inspection cover bolts and oil pan bolts which will double as front and rear crank bearings as well. I bought the A2Z QCTP so now I can swap out tools fast. I got the much needed cut off tool so now I can part off my work pieces. I still need to buy a 4 jaw chuck, indexer,  turn table, index boring head, and boring bar. Oh and I will need a v-block, parallel set.... I think I need some aspirin now. 

Sorry I don't have any pictures yet. I will try to take some this weekend and share with you all.

A have a question: What would make a light press fit .001" undersized? I'm thinking ahead when its time to machine the cylinder sleeves.


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## Fabrickator

If you're dropping a steel cylinder into an aluminum block, you will need at least .004" interference fit. Aluminum expands at 7 times the rate of steel and anything less could become loose when/if the block heats up. You would heat the block slowly to 375* and then drop the cylinder in it.


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## mu38&Bg#

You'll want to double check your figures for thermal expansion coefficients. 6061 aluminum is about 23um/m-°C and 1018 steel is about 12um/m-°C. .004" press on a 1" bore is going to be a problem.

Model aircraft engines are built with steel liners in aluminum blocks with slip fits, but the liner has a flange which is clamped by the head. Do a search for press fits and work with that. Depending on how carefully you bored the block it may be tricky, tapers cause problems. Lapping would help fix problems. If you don't have a .0001" bore gage, you may want to make the liners to size then lap the bores to fit the liners. It will be hard to make liners to fit an unknown bore size when the fits need to be in the tenths range.


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## the_one

hey guys I was just wondering how to figure out the max PSI that would be in the combustion chamber


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## barnesrickw

That's a tough one.  Compression ratio and thermal expansion of whatever fuel, and the air to fuel ratio may come into play.


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## gbritnell

the-one,
Why would you need to know this?
Gbritnell


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## the_one

so i could run a FEA


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## Niels Abildgaard

Ricardo say peak pressure in psi is roughly 100 times compression ratio for a spark ignited with satisfactory valves.


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## the_one

Thank you Niels


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## gbritnell

Pardon my ignorance but what is FEA?
gbritnell


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## stevehuckss396

gbritnell said:


> Pardon my ignorance but what is FEA?
> gbritnell





Hello George!

I think its part of Solidworks where stress on parts is checked to make sure there is not going to be any failures.


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## Metal_slicer

Hello Guys,

I have been away for a long while. I have been busy looking at techniques and learning as much as I can. I have been looking into cam cutting and I think I have figured out how to do this using Cogsy description from another thread. It took me a few tries in Viacad, but I think I got it. See attached image:


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## Metal_slicer

Ok, I don't have much to share but I have included some pictures of my practice valves as well as a trial piston which I may remake because i'm not sure if the second ring groove will interfere with the wrist pin. 

I went to home depot today and bought a box of assorted springs for just over 4 bucks. I cut the springs to length and then ground the ends flat. I can always use the other springs for other projects or for the throttle linkage. I have also made a pair of stainless steel exhaust pipes to be soldered to a mounting bracket later.


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## gbritnell

I'm looking at the picture of the valve springs and at first glance they look waaaay too heavy. What is the diameter of the wire? You should be able to get away with a wire size of around .032-.036. 
gbritnell


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## Metal_slicer

gbritnell said:


> I'm looking at the picture of the valve springs and at first glance they look waaaay too heavy. What is the diameter of the wire? You should be able to get away with a wire size of around .032-.036.
> gbritnell



Not sure. I will have to get the calipers on them but my workshop is in the barn way out there and I kicked off my shoes for the night. I wanted to use a spring strong enough to prevent valve float and to keep the valves closed nice and tight.


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## Metal_slicer

Well you got me curious so I had to go take a look.  The springs in the picture measured .047" I have some .038" and .025" available. If I use the .047" springs, what would happen? To much resistance and wear?


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## Longboy

Your scale is close to what I build Metal. On my first gas scratch build, I first tried .031 springs and could feel the resistance on a hand turnover and engine would not run. Redid with .023 springs and my engine turned over easy. I don't believe you will have a chance with the "47's" on this displacement. You want enough spring to move the valves to a certain RPM without adding to the internal load of the sum of your engine's moving parts. Dave.


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## Metal_slicer

Hello Guys,

Ok I have 2 more sets of springs that I could use. 

.023 and .019 thick springs.

Which would I have the best luck with?


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## petertha

I'm no expert & maybe others can chime in if I'm off base.The engine I'm building from plans has wire dia = 0.8mm = 0.031" which is similar spring values & length layout as a commercial RC engine (OS-FS-61) at 0.027" & Edwards 5-cyl radial at 0.030". I was interested in how much force this arrangement translated into lifting the valve off its seat, ultimately driven by the cam ring & pushrods through the rocker assembly. I think the general method goes something like this:

- go to calculator website like link below (looks a bit different than at the time I took the screen grabs, but appears to yield the same values). 

- define a compression spring by: wire diameter + od + free length + number of coils. Of course it has to fit any dimensional constraints of your engine. Example spring OD sits semi submerged in a head hole or ID must clear valve cup stem diameter.

- the calculator spits out a tabular listing of force values for incremental compression lengths starting from zero force at uncompressed (free) length to max travel (solid) height. I plotted these for visual reference. 

- using the graph you can eyeball the corresponding forces at valve closed & valve open spring compression lengths. In this 0.028" dia wire example it might be ~2 pounds whereas a similar dimensioned 0.035" dia wire might be ~ 4 pounds. Now what is low or high or desirable relative to our little engines I will leave to others to comment on, but I think the forces themselves are in the ballpark. Of course you can achieve similar target forces with different combinations of lengths, coils, wire type etc. all as dictated by your own engine layout.

http://www.planetspring.com/pages/compression-spring-calculator-coil-calculator.php?id=compression


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## petertha

Edwards  & Ohrndorf radials, head/valve/spring examples


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## Metal_slicer

Hello Guys,

Started to machine the valve cover and nothing but disasters, well maybe more bad luck than disasters. I started to drill the bolt holes and noticed the drill bit screeching and then locked up. The chips got clogged. Restarted the CNC code and more problems with the drill bit clogging. Tried one more time then then the Z axis lead screw became loose so the bit stayed in the hole. I had to tear down the z part of the mill and fix the problem. When Finished I changed the drill bit to something sharper and then manually drilled the holes and was able to get through that operation. :wall:

The cheap china bits are ground horrible and the 6061 aluminum was sticking to the tip causing virtually no cutting action. A small bit at .112" needs to be sharp! I wasted so much time fixing the mill and setting up several times that 
I got tired of it all and called it the day. Tomorrow I will be back at it again.


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## petertha

I'm no expert but I found backing out & clearing chips often & WD40 makes for happier aluminum drilling. Crappy, dull, knockoff bits are a non-starter IMO.

Another thing I tried when faced with relatively deep & small diameter holes in aluminum is parabolic profile. Seem to work better than regular bits & straighter hole. I tried Titex brand HSS uncoated, so far so good. They are more spendy though.

http://blog.cnccookbook.com/2013/09/06/parabolic-vs-standard-flute-twist-drills/

I know some people regrind the lip angle for grabby materials & including brass apparently. I don't have those facilities so its a check-book solution.


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## mu38&Bg#

A common common problem with drilling is not feeding fast enough. What is your feed and speed? Drilling in aluminum needs .001-.002" per flute per rev. If spindle speed is high, feed rate can be pretty high. Peck drilling is need to clear chips. Without coolant you have to start pecking at maybe as little as 1.5-2 diameters deep. it really depends on what your chips look like. Sometimes chips clear nicely, other times they don't.  Bright HSS drills work best (until you step into carbide), any tialn or altin coating containing aluminum will want to stick. Cheap drills are a waste of time unless you can resharpen them well. Drills previously used in harder metals should be resharpened for best results in aluminum. I try to use four facet drills and resharpen them with four when being used for aluminum.

Greg


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## Metal_slicer

dieselpilot said:


> A common common problem with drilling is not feeding fast enough. What is your feed and speed? Drilling in aluminum needs .001-.002" per flute per rev. If spindle speed is high, feed rate can be pretty high. Peck drilling is need to clear chips. Without coolant you have to start pecking at maybe as little as 1.5-2 diameters deep. it really depends on what your chips look like. Sometimes chips clear nicely, other times they don't.  Bright HSS drills work best (until you step into carbide), any tialn or altin coating containing aluminum will want to stick. Cheap drills are a waste of time unless you can resharpen them well. Drills previously used in harder metals should be resharpened for best results in aluminum. I try to use four facet drills and resharpen them with four when being used for aluminum.
> 
> Greg



Thanks for the info Greg. I was break chip drilling after every 0.025" at 2800 rpm and the bit was coated I believe with tialn. I ended up manually drilling with a different bit making longer chips because I believe the smaller chips were building up and not able to clear out of the hole. Bottom line I did several things wrong here. 

The good news is that I was able to complete the operation and move on to the other CNC operations and was able to finish the entire bottom of the valve cover today. I need to flip over the cover and do the final operations. I took some pictures with my cell phone but it is so out of focus so I might have to wait until I am finished so I can take a picture with my DSLR camera. I don't want that camera anywhere near fling chips and oil.


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## Metal_slicer

Valve cover completed. I was not happy with he way the groves turned out. I used an 1/8" 4-flute end mill and used an engraving operation. Oil didn't make a difference. I will try to hand finish this to make it better. Any tips for the grooves?

For the most part everything else turned out ok.


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## petertha

Is the end mill slot raggy on one side but cleaner/better on the other? Might be a direction/rotation thing? (climb milling etc). Maybe just a finishing pass is required with this in mind?


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## Longboy

Those small diameter end mills flex and load up with chips easy galling the sides of a groove cut. You are into a hand finish now. I measured my 12inch single cut file and its .135in wide. You can drag it at an angle along the groove length to smooth somewhat or oversize the width with the end mill so you take only a one side cut and reverse to other side. A brass or steel wheel brush for electric drill can carve up some of the vertical wall mess and whatever horizontal top surface ends up with brush marks can be easily be sanded and polished out. Try a clean-up with a groove on some scrap aluminum.


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## Swifty

I always use WD40 on aluminium, a spray can is handy, but I recently bought a 4 litre bottle which I decant into a smaller container and use a brush to apply, stops aluminium from sticking to the cutter. A lot depends on the aluminium that you are using, normal extrusion is usually fairly soft and sticky, I'm a great fan of using structural plate aluminium, a harder grade and great for machining.

Paul.


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## Metal_slicer

I have a question about what to do for the valve guides? would drilling the guides be good enough or should I ream them? The cylinder head material is C360 brass.


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## Swifty

I would ream them, a close fit on the valve shaft is required. Imagine when the inlet valve is open, if there is too much clearance between the shaft and hole, it would suck in air, instead of the correct fuel mixture through the carby.

Paul.


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## Metal_slicer

Thanks Paul, I appreciate your input!


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## Metal_slicer

Things are starting to stack up... I really need to try to refinish the valve cover groves. The camera is giving it to much justice!

I still need to cut the valve seats and ream the valve guides which I will need to order. If I ream the guides for 1/8" what size drill do you recommend I use?


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## Swifty

I use a drill about .004" undersize before reaming 1/8" holes.

Paul.


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## Metal_slicer

Sorry guys I don't have any photos of my progress but here is what I have done the past few days.

1.) Drilled head bolts, rocker arm studs, push rod holes and valve guides
2.) Drilled camshaft bore. Still need to make a 5/16 flat drill to make the camshaft bearing pockets

I found an error with the valve cover. I did not account for head bolt clearance so I will need to re-machine the valve cover to fix this problem. Error with exhaust ports have mounting screws clipping the ports. Not to big of a deal, its good the intake ports are free from any screw holes. Last concern is the lack of head material left for the valve stems. I have about 1/8" thick brass for the valve stems. 

Pictures coming later...


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## Blogwitch

MC,
A little late I am afraid, but your problem with cutting slots is a very basic one.

If you want a decent finish and size for a slot or cutout, you never start off with the correct sized cutting tool, especially in the smaller sizes as they flex too much, and will usually cut oversized.

Say I was cutting a 1/8" (3.2mm) slot, I would use a 3mm slot drill to rough out first, leaving a couple of thou to remove on depth. Then, when you follow down with the correct sized cutter set to correct depth and running at fairly high speed the chip load is greatly reduced to almost nothing and you will end up with a perfect sized and smooth finish on the slot.
I know it takes twice the operations and time, but hey, we are not in a race to finish anything, and you would certainly appreciate the smoother finish, and you will pick up a lot of the time wasted by not having to do so much cleaning up work.

John


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## Metal_slicer

I did a practice valve seat cutter copy based on Steve's design. I did it with aluminum to run through the operations before trying tool steel. I'm not sure if it would be cost effective since I would need to get a torch outfit to harden the tool. It may be better if I buy a 45deg off the shelf cutter, however I like the valve stem guide pin on the custom design. No sure...


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## Metal_slicer

Here are some pictures of the cylinder head with all the holes drilled for valve cover, rocker studs, valves, and push rods. I didn't plan on making separate valve guides, but there is just not enough material in the head to serve as valve guides. I have not cut the seats yet either. I have a temporary aluminum retainer that does not have an e-clip, it is resting in the valve stem grove for the purpose of this photo shoot. I really didn't want to make any press fit parts but I might as well give it a shot. About how much of an interference fit will I need for the inserts? Comments welcome.


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## Swifty

There are various charts for different fits, but one thing you have to keep in mind, is that in a hole of lets say, 0.5000", a pin of the same diameter will be a tight fit. What I normally do is make the pin the same dia as the hole and put a drop of loctite on as well, more as a lubricant than to hold the pin in.

Paul.


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## Metal_slicer

I did some more work today. I cut the roller tip rockers out and parted off 4 303 stainless roller tips. I still need to mill the mid section of the rocker arm for the  1/4" bearing. I also need to hand finish the parted off roller tips. Here are some pictures of today's session in the workshop.


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## Metal_slicer

More work done on the engine.


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## Metal_slicer

Here are two more photos of the rockers mounted.  I am going to need to make valve guides because there is not enough support in the head the way it is now.


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## Metal_slicer

I made a trial valve guide today. This should be much better. I hope that I can get the press fit sizes right, I seem to always over shoot my dimensions when I get down to the last few thousands.


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## _wallace_

Hey mate,
its been a while since any posts have been made. Is the engine finished or has it been put up on the shelf for now?


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## Metal_slicer

Hello,

I have lost my job and I have put the project on the shelf. I need to get certain tools, and tools are expensive. I just don't have any extra money at the moment .


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