Q: When an engine with chromed cylinders comes into a shop with oil leaks and the source has been identified as thru bolts and cylinder base o-rings, how should the cylinder removal and reinstallation be handled? Also, is there any wisdom in turning the oil scraper ring upside down in chromed cylinder to help control oil consumption?
JAMES FINLAYSON, via email
A: James, I’m somewhat at a loss with your question simply because of the lack of information. However, I’ll try my best to answer what I can, which may assist you with your situation.
First of all, if we are talking about a Lycoming O-235-C series engine, which has a scraper ring, the proper position for the ring is so that it scrapes up the cylinder barrel.
Since Lycoming has not produced an engine using chrome cylinders since probably the 1960s, it’s difficult for me to guess what may have been done with the cylinders you are speaking about. It’s more than likely that they have been refurbished by some field facility that specializes in chrome repaired cylinders and which also provide the associated parts. My recommendation would be for you to make contact with that facility and ask them for advice regarding proper ring installation.
With regard to the removal and reinstallation of the cylinders, it’s all quite standard on all Lycoming engine models.
I can’t say that I ever recall hearing of leaking thru-bolts on an O-235-C series engine, but then again, maybe you aren’t working on that engine model. Crankcase thru-bolt leaks do occur on some of the newer higher horsepower models, usually high time or overhauled, wide cylinder flange or wide-deck configured engines. Lycoming covers the proper repair in Service Instruction 1290F, which is the latest revision of that particular publication.
However, there are no, nor have there ever been, any wide-deck O-235-C series engines.
The only other reason I can think of that may cause a cylinder to leak oil at the cylinder base “O” ring would be a lack of proper torque on the cylinder base hold-down nuts. This condition may show indications of fretting on the crankcase/cylinder mating service, which would definitely be a concern. Possible damage to the bevel on the crankcase where the “O” ring seats and/or possibly a twisted or damaged “O” ring may also cause an oil leak in this area.
I realize I keep going back and referring to the Lycoming O-235-C series because it’s the only engine, except for various 6-cylinder Lycoming engines, that incorporate a scraper ring. The 6-cylinder models that use that piston configuration have been out of production for many years. Even if Lycoming has continued to provide replacement cylinder, piston and ring assembly kits in order to continue supporting those models, none of them, to my knowledge, use pistons with scraper rings.
If my memory continues to serve me well, I believe the reason for using a scraper ring in a chrome cylinder was because chrome was not a wettable surface. The chrome process was actually known as channel chrome, where the oil traveled the cylinder bore through channels. Scraping the oil up the barrel by the scraper ring provided better lubrication on the cylinder walls.
