ryanpilot

My Feedback: (4)

I tried to find the answer to this question with no luck so here it is. I am sure someone has the answer.

A club member brought me an Itilian G75 that will not run consistantily. I tore it apart and inspected. Looks worn out. Does any one have the proper measurements for Piston Ring End Gap as well as max bore on cyl and min dia on piston?

Any help would be apreciated.

Bax

My Feedback: (11)

The specs you are looking for just don't exist. Usually, the ring gap can be as small as a few thousandths when the engine is warm, but we don't have specs on max liner diameter and min piston diameter. Those are usually quite inconsequential. You can usually tell that the piston/ring/liner fit is too loose if the engine will not idle and accelerate. You should be able to lean the engine to get a good top end.

The fuel you are using, along with the propeller will be more telling. They can dramatically influence how the engine runs. Your engine may not have ever been properly broken in, and so may just need more rich running for it to "come in".

ryanpilot

My Feedback: (4)

Thanks for the info. I have been a mechanic for ever and did not realize that there was no tech spec for theses plane engines. I would venture to guess by the wear in the sleeve and the varnish build up that the engine is just worn out. The guy it belongs to has no history as it was used when he got it. He was turning a 13x6 prop and using 15% with 18% oil.
The problem is that we can get the engine tuned and running realitivly good and after a few minutes, when the engine is hot, then all settings go away and the engine will not transition or will just quit running. Several of us have tweeked this engine with no sucess and those of us that have tried have been in the sport for many years. I am the fortunate one to have volunteered to check out the engine.
From my experiance, and with no tech specs, I think it is just plain worn out.

Thanks for the help

Bax

My Feedback: (11)

Yes, it does sound like a worn engine. You should be able to get a consistent high-speed needle setting once the engine's warmed up. However, once you've found a good high-speed needle setting, it should be "good" for the rest of the flying session. It should not change at all if nothing else changes. An inconsistent needle is one sign of a worn engine. Another sign is a reasonably-good top end, but lousy idle and acceleration, assuming it once had a good idle and acceleration.