IC engine cylinder

[Schmitz08]

Hi
I have a question. I would like to make a small diesel engine. I have the plans of the ML Midge engine. Most IC engines have cast iron cylinders and pistons. Cast iron is difficult to find and buy.

Could the cylinder be made of a different material? I believe cast iron is used because it lubricates. Could, for instance, bronze be used?

Hans (Netherlands)

 

[bentprop]

hello,Hans.You could use bronze,or a brass liner in a steel cylinder.It depends what you use for the piston.As long as the two materials are different,you should be ok.Aluminium piston in a brass liner is the usual option.
Btw,where in nl are you?.I was born in Den Haag,and lived there till i was 18,then emigrated to new zealand.
another Hans.

 

[GailInNM]

Hans,
First off, welcome to HMEM. I invite you to make a post in the welcome section with a little bit about yourself and maybe some about your shop and interests.

On small engines, like the ML Midge, the piston and cylinder are lapped to very close fits to each other. Because of this the materials of the piston and cylinder must work well together from a sliding function and have a very similar coefficient of thermal expansion. Bronze against bronze does not work well from a sliding/wear standpoint. Bronzw slides and wears well with steel, but the coefficient of expansion of bronze is greater than steel and you will lose compression as the engine warms up. Cast iron works well from both points.

Another combination that is some times used is soft steel against hardened steel. In most cases the cylinder is left unhardened and the piston is hardened. With the difference in hardness they wear well together and the coefficient of thermal expansion will be near the same. Many commercial engines were built this way.

Best of luck with the Midge. It is a fine design and a good running sport engine.

Gail in NM

 

[Schmitz08]

Thank you Gail and Hans for your comments.

I now know that finding the right combinations of metals is the key. That makes sense

In the meanwhile I managed to find some cast iron bars at a gathering (http://www.stoomgroepzuid.nl/).
I will use them for my first attempt on the Midge.

And Hans, I work in Den Haag ;D

Greatings, Hans

 

[Marklubbock]

Hi all & thanks for the kind comments regarding 'my' little engine.
On the original, I used free cutting mild steel for the cylinder & cast iron from window sash weights for the piston. All of the original engines are still running today even after prolonged runs in R/C models, so wear does not seem to be a problem-hope this helps, you can save the expensive CI for pistons!

 

[ANIMATE]

Hi All
Iam making a simular engine Boll Airo and have made a mild steel liner (case hardened with kensit powder) and a cast iron piston i will try and keep you informed as to how it works
regards Gordy

 

[oops again]

Hi ANIMATE
I have built a Boll Aero and had some trouble with the cylindar, a lot really. I decided in my wisdom or lack of it to make the cylindar out of silver steel and harden and temper it. The problem is that the transfer ports are milled into the cylindar which causes some distortion when chilled. My first attempt was at least 2 thou out of round. I got plenty of lapping practice but binned it in the end and started again. The second time i made a sleeve to go over the cylinder and heated the lot up and chilled it in oil (cooking oil is best). The result wasn't perfect but the lapp sorted it out. Much to my surprise at the time the engine lept into life. If you go with the Kasinite case hardening, by the time you get it round again most of the case will be gone so wy bother with it. Beleave me there is less grief in machining up another cylindar and piston. But put the transfer ports in first and then bore it out, that way any internal stress is releaved before the final cut in the bore. with the benifit of hindsight cast iron is the smartest choice Dave

 

[ANIMATE]

Hi Dave
yes i did put all the ports in before i case harded it ,i i made a small steel box and put the cylinder and kensit and heated the hole thing and left it for about half a hour glowing cherry red and took it out and quenched it in cold water ,its lapped realy nice like a mirror in side with a very slight taper, i never thought about silver steel , maybe on the next one ? im working on a .3 Diesel i have made the die 2 part for the graverty fed mold ,i think i will try some silver steel for the cylinder in this when i get round to it mmmmmm food for thought thankzz mate
regards GORDY