Cast Iron / stainless steel - what would you use for cylinders?

[Metal Mickey]

I have a separate post running on my building a pair of Seal engines (Edgar T Westbury design 15cc 4 cylinder petrol engines) and have gotten to the stage where next week hopefully, I will make the cylinders. Now I am tempted to go two different routes. One set of 4 cylinders in Cast Iron and the second set of 4 in stainless steel. What would you do?

The pistons are made from aluminium and have two rings at the top. The cylinders are 5/8" internal diameter and 1 9/32" long.

A second question relates to some bar stock I have and whether it is phosphor bronze or no? It is very red and certainly not just copper. I have received different colours in the past and always mark on the bar what it was supposed to be but this long length isn't marked (don't know how that happened......must have been the wife!)
All contributions welcome!

MM

 

[Tin Falcon]

MM:
IIRC stanless is pretty much a no no for any application with a sliding fit. Stainless tends to gall. CI would be the preferred material here.
There are others here with more CI experience than I have (NONE) the high carbon content of CI tend to be partially self lubricating.
Tin

 

[Metal Mickey]

Many thanks Tin, didn't realise that about stainless steel. I was going to use if for the valves as well. ARethink needed now..............

 

[Mo deller]

Many thanks Tin, didn't realise that about stainless steel. I was going to use if for the valves as well. ARethink needed now..............

I think stainless is ok for valves. The spec for my glowplug Vega is for stainless valves and I dont think a sparky would be any different.

Mo.

 

[Stan]

Is there an easy way to calculate the clearance on an aluminum piston in a CI cylinder to compensate for the difference in expansion with heat?

 

[Artie]

The accepted automotive standard is 1.5 thou per inch of bore diameter. Im not sure if this is applicable in micro engines.

Rob

p.s. I think I should clarify that last point. The std is for CI cylinder and ali piston BUT it takes into consideration controlled piston expansion by using steel gudgeon inserts cast into the piston and/or cam grinding of the skirt (they arent round when cold but become round when hot).

 

[deverett]

A second question relates to some bar stock I have and whether it is phosphor bronze or no? It is very red and certainly not just copper. I have received different colours in the past and always mark on the bar what it was supposed to be but this long length isn't marked (don't know how that happened......must have been the wife!)
All contributions welcome!

MM

I think you are right about the reddish metal being phosphor bronze. I have some that I thought would be good for some bearing bushings. It was the very devil to machine. Very slow speed - I soon learned that bit - and very sharp tools seem to be the way to go.

Dave
The Eemerald Isle

 

[JMI]

MM:
IIRC stanless is pretty much a no no for any application with a sliding fit. Stainless tends to gall.

There may be some truth to the above but that has not stopped the manufacture of many self-loading (semi-automatic) pistols with stainless steel slides and frames.

Jim

 

[Metal Mickey]

Many thanks so far. I have ordered some more cast iron just in case........Thanks Jim and Dave

 

[Kermit]

On the subject of 'galling'. We have a pressure testing set we make for trouble-shooting jet engines, which uses more 304 stainless SAE 37 deg flair fittings than you've ever seen in one place before. Having inspected way too many of these things, I can authoritatively state; surface finish can predict whether a fittings threads will gall on the first fitting. Any sign what-so-ever, of any surface imperfections in the fittings int. and ext. threaded parts, and the fitting will gall badly the first time it is loosened and then retightened. A perfect surface finish and the parts will not gall until after the second tightening down.

Whether that will hold true outside of a fifty foot radius around my body remains to be seen. ;D

 

[Jadecy]

Have you thought about using 4130 (chromoly) as a cylinder liner? I've never used it myself but have seen it at model enginerering shows in kits and running engines.