# Cylinder liner material question



## Scota4570 (Jan 25, 2011)

I would like to make a model airplane engine from scratch. I fly giant scale RC. I have been doing lots of chainsaw and wacker conversion. I own a good lathe and mill. I would like to take it to the next leve and make the whole engine.

I am envisioning a single cylinder two stroke. I would be piston ported. The layout would be conventional with the crank supported by two bearings on the front. I would use a walbro carb. The case would be made from bar stock. The displacement would be around 30CC. It would run on gasoline. The spark would come from an auto advance ignition unit. 

The only thing that intimidates me is making the clyinder true, round and highly finished. I was thinking of a "shortcut". If I lined the aluminum cylinder with the steel tube from an automotive shock absorber. I could save lots of fussing? I would only have to make my aluminum piston and use one or two rings. The exterior of the cylinder would be heated and the liner frozen before assembly.


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## Lakc (Jan 25, 2011)

As you said you have a good mill, you only really need a boring head to make a cylinder. Your final finish, once its straight and true, is usually a simple ball hone or brake cylinder flex hone. 

 The best way to learn how to make a cylinder is screw up making a cylinder. If your honest with yourself, and can accurately assess (and measure) where you goofed, up you will soon think its one of the easier jobs to do. For me, most of the fun is in the learning.


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## jpeter (Jan 25, 2011)

Cast iron is the best choice for cylinders. You can get it from McMaster Carr, Mcmaster.com. After you bore it as straight as you can it no doubt will have some taper. You can't hone that out with a brake cylinder hone cuz that style of hone won't remove a taper. You can, in the home shop, lap it out or take it somewhere and have it honed straight with a Sunnen hone. Auto engine rebuilders will do this for you. Sounds like a fun project. Gonna be great to brag at the air field about having build your own engine.


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## GWRdriver (Jan 25, 2011)

This would depend upon the bore, but if it's large enough you might be lucky enough to find and adapt a ready-made aftermarket sleeve stock. I'm floored by the vast array of aftermarket sleeve stock available these days but if it's below the smallest available stock size - I couldn't find 1.625" bore sleeves - then it becomes special order and $$$$. Failing that, as recommended, I would go with continuous cast cast iron bar - say Grade 40, but I would also isit the I/C engine building boards to find out what other builders have been using. I also know that aero engines always had lapped pistons and cylinders. I've done internal honing and external lapping with success but I've never lapped a bore. As Jim says, you probably won't end up with a round and straight bore and a compensating hone or lapping will be needed. The problem with most automotive shops is they probabaly won't have a hone small enough to get into your bore (one of Murphy's Laws.) That isn't of much help to you but I know there are people building engines at home and they have learned how to do it right, all we have to do is find them.


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## Longboy (Jan 25, 2011)

.....Your shortcut is DOM tubing. There is no boring. Just cut to length and fit piston of same size to bore.


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## mu38&Bg# (Jan 25, 2011)

Any pressed in thin wall sleeve will take the form of bore it's going in to. It will likely still need to be honed for the kind of tolerance you'd like to see in an engine of that type if any significant amount of life is expected. Of course, there are many ways to skin a cat and OS's GT55 uses construction like a glow engine, while virtually all other gasoline engines of that size follow the typical utility engine design.

Don't be afraid to try whatever method comes to mind. In the very worst you'll learn one way NOT to do something.

Greg


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## kf2qd (Jan 26, 2011)

The easiest cylinder liner is going to be Cast Iron. Steel can be made to work, but you will have to heatreat and polish. I have made a cylinder lap out of a piece of steel bar with a slight taper away fro the area I want to use as the lap. Coat with some course and then fine lapping compound and I got nice straight bores. Then I made the piston to match the bore as that was easier than trying to match the bore to the pistons...

The engine in my avatar here was made this way. The plans for it are in the plans section as a .60 size 2 stroke. That one would run a consistent 10,000 RPM with a 10x6 prop and 5% nitro.


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## Scota4570 (Jan 26, 2011)

It is great to find a bunch of guys who understand what I am talking about and can give valid feedback. 

So to further refine my vision for the reader........It would be set up like a Brown Junior. The transfer port would be via a piece of channel silver soldered on the outside of the cylinder that connects two holes. Possibly two transfer ports? The intake and exhaust ports would be laid out like a chainsaw engine. 

I have read elswhere that running an aluminum piston in a steel cylinder with iron rings was the way it was done on prewar engines. If I make an iron cylinder, probably a tougher grade, then run rings with a more slippery grade of iron, is that good? How about cooling fins? There would be many thin fins. Will the iron stand up to that. Just use my parting tool? Boring the cylinder? Lathe, Or do it on the mill with a flycutter? 

Hey, I just called a machinist friend. He has a bunch of D-2 Tool steel in it's anealed state. It is 1 1/4" ID and 2 1/16 OD. It is seamless and he guesses it to about 38 rockwell. This stuff is for making bearing races and such. He says it cuts nicely. Any opinion of this as a material?  

Thanks for the great feedback.


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## jpeter (Jan 27, 2011)

The nice thing about cast iron is it's porous enough to hold some oil and it's easy to machine. Regarding honing, autoshops can use the wrist pin hones for small holes.


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