At first glance, the story is quite simple: I'm looking for rings for a Lyco O-290 G, pistons 62719P10, CR 1:6.5.
Then it starts really: all the shops I contacted are telling the same
: this engine (O-290) is out of production for decades, I will have extreme difficulties to source the ring sets, and, cherry on the cake, even more in P10 state (rebored + 0.010'').Starting from there, one option I'm looking at (don't yell at me now, I'm just looking
) is to seek for O-320 rings and cut them to get the proper gapping. The bore difference is 5.125-4.885 = 0.240", which gives a circumference difference of .750'' approx lengh to cut on the ring. I have then several questions:
1/I am at ease on engines, and would go ahead for that solution (cut bigger bore rings) on a bike or car engine without problem. Has somebody on the forum already done it on a aircraft engine, especially a O-290????
2/ how do I recognize half-wedge and full wedge rings? Mines are trapezoïdal shaped, with both faces of piston groove (top and bottom) unparallel to the top piston face. In short, the ring section looks like a V-belt with a much weaker angle. Does "half wedge" mean one face parallel to top piston face, or is it a matter of difference of angle, "full" meaning bigger angle than "half"???
3/Indeed, the compression rings are still within the manufacturer's tolerances, I just really need to replace the oil regulating rings (one broken during cleaning, don't tell me, I know
). Obviously, as everything is opened, I would prefer to replace the full set of rings, but facing my sourcing problem, box up with the actual compression rings would delay a little bit my trouble. So, same question as in 1/, but only on oil regulating rings?3/ If someone have on a shelf, picking dust, some sets of rings for a O-290, I would be very glad to make an offer for them...I am not sure of the reference, possibly compression 62916P10 or 68115P10, oil regulating 67540P10.
4/ for the O-320 rings option, does the plain/nitride/chrome cylinder makes a difference? In other words, I belive my barrels are "plain" if I find a set of rings for nitride or chrome barrels, are they suitable? I guess the answer is "NO", I need some expert confirmation or explanation.
5/ Does any owner of a O-290 solved this kind of problem, is there an option I did not think about? Change full pistons+rings? If so, is an "upgrade" with 1:7.5 (O-290D2 pistons) or 1:9.5 (O-435 6 cyl. pistons, same bore) makes sense (my crankshaft is a strong O-320 one)? Would it be "acceptable" for LAA? Will I need to change the prop for a coarser one?
6/I am reluctant for second hand spares or a second hand engine for obvious history tracability reasons. Am I right or are the Lyco parts beyond my fears and undestructible, as long as they meet the manufacturer tolerances?
Plenty questions, I know, but many thanks already for comments and ideas to move a little bit forward in my troubles.
Bertrand