[swampyclark]

Has anyone ever measured it with a scale or similar? Here is why I ask. I have a 290 that has a high oil usage Im working on.

I am thinking that the oil ring tension is to low to effectively wipe the barrel by being worn. I am guessing 20-25 lbs would be a good number but I don’t know. I have sourced an aftermarket ring set that should fit but not sure untill i install and check the gaps. Cant find parts or new heads so stuck in a repair mindset

Full story below

Thanks

Mike

Quick history. New to me with no real paperwork do to loss of previous owner. Airframe Log book shows sent for overhaul and reinstalled about 250 hours ago for what its worth. Being a 290 parts are an issue

Engine was treated as experimental so really not sure of level of overhaul

That being said.
Oil consumption out of limits

Engine making close to rated power based on lycoming eng manual chart(map and rpm). . -120 hp at 3k. (140hp *(1-3x.03). Envelope math 125hp

1,3,4 bone dry plugs. Last 2 conditionals mid low 70 on 1,3,4 80 on 2. Zero oil in catch can. No significant oil residue in split exhaust system to confirm but wet plug in 2 and scope of standing oil post flight and higher compression had me really thinking #2 for the win.
Pulled the jug and inlet guide was a little out of spec but not bad. Replaced and reamed in new guide. Top ring slight wear middle almost none. Oil ring could not really tell.

Only minimal blow by discoloration and no build up in the glands.

Bore had some corrosion but not too bad.

Couldn’t find a ring set and its a p10 to boot

Not even sure if the current rings are actually lycoming. They are keystone chrome but have a relief groove on one side and no part numbers Never seen a real one if anyone can confirm this ??

Due to that went with a light deglaze and clean up and put it back together. I did not measure the oil ring tension unfortunately

Ran it for about 3 hours. Can’t tell if compression is still good from oil in the cylinder or the fact i cleaned and lapped the valves also but the plug is still wet. Oil consumption better but still high

With dry plugs elsewhere and no oil on the belly Im still thinking its confided to#2 but the other 3 do have some corrosion just not convinced enough to pull the other 3 yet to look for a possible broken ring. No metal in filter or screen too btw
Thanks for reading. Appreciate any ideas

 

[KeithO]

Sir, with all due respect, given its an old engine with scarce parts, one should not assume anything when one has a problem with an individual cylinder. Is the cylinder round ? Depending on how it was honed one cannot assume it is round. Take it to a cylinder shop with micrometer adjustable holes and then you will quickly see if it is round or not. Very little material need be removed to see if there is any ovality or grooving present. The same would go for taper. if the cylinder is in fact not round and the rings have been run in it for some time, they will tend to wear into the local features but couldnt be expected to seal properly. Cylinders can be recovered by Nikasil or chrome plating so there is that option, but it relies on you having cast iron rings to run in the new bore. Hard bore will need soft rings. The bore diameter may be reduced if needed if std size pistons and rings are available. Not sure where you should start. Obviously for balance all pistons need to match from a diameter and weight point of view.