I have an irvine 53 on a H-9 Aresti. I loved the engine all 6 flights. I had a 12X6 then a 12X4 then a 12.25X3.75.
The motor is now on it's way back to Sig. On the 7th flight it sagged bad just as I was landing and when I picked up the plane I noticed the motor felt odd(turning the prop). Upon inspection the connection between the piston rod & the cranshaft( is it the wristpin ?) was scared and there was black residue everywhere. also metal shaving visible.

I was worried that I hurt it with the 12.25X3.75 prop OR I leaned it out too much. I've had modeling friends( some I would call EXPERTS with decades of experience) tell me it had to be a problem with the engine.

What do you guys think & what probs if any have been experienced by others with this engine. The LHS guy said it was his 1st irvine to have any problem of any kind and he also said he didn't think the damage was from 1 lean run.

BTW I have a OS 46FX with problably 100 flights. I've used Fox 40's, Fox 50's, Fox 60's, Magnum 40, ASP40 and never had an engine failure before.

Thanks for listening while I vent frustrations and thanks for advice.I'll post Sig's reply when I hear from them if anyone's interested.