My gen 6 502 (new in 2000) had metric rings and low tension oil rings and many others had these rings, nothing "BOGUS" about that. Mine burned 1-2 quarts of oil from brand new every 5-10 hours of run time, I had motor out and apart by 50 hours because of 45+% leak down in 2 cylinders, this was such a common problem that J/E made replacement srp pistons that were the same weight but .002 bigger in dia with American rings so guys could re-ring 502's and only have to have block honed, not re-bored or re-balanced, not sure at what point these 502 motors got these metric ringed pistons or if they all had them but I think it was the efi gen 5/6 ones that were metric low tension rings and the earlier carbed ones were not,, Smitty

Yeah, I know this is an old thread but I ve been doing a lot of research on B 1 drives & 502 issues. Very interested in this subject. Do u know if merc was doing warranty on any of these oil burners in 2000? I'm looking @ a 2000 w 502s in it. Low hour boat. So this falls into the year of my worst fears.
I read there are 2 or 3 formula factory guys that do nothing but help buyers on used purchase boat record info. I ll be checking into this depending on how the purchase goes.
I know my brothers 93sh 502 was a oil burner from day one & merc replaced it. He bought the boat new.

730hrs. on my twins, Still running strong. Just regular maintenance. They burn a little oil. Amount varies on how hard I run them.

I have one 2000 year 502MPI that just turned 1000 hours last time I ran it, other one has 860 in boat. 1000 hour motor did roast a piston last year from faulty fuel injector. Scabbed it back together with new/used piston and rings along with replace all 16 injectors with Racetronix flow-matched sets from Articfriends. He modified tunes in MEFI3's and added a bit more timing and bumped limiters up. Running premium fuel now. Gained noticeable mid-range punch afterwards and 2-3 mph top end. Was having oil consumption/blowby issues making mess in bilge last season afterwards. This spring I eliminated PCV breather system and installed catch-can breathers on motors. Haven't leaked or sprayed any oil out since and bilge is staying perfectly clean and I don't baby the motors either. Oil consumption has dropped dramatically. I also run 20-50 NAPA brand conventional with a full quart of Lucas stabilizer per motor. After doing this, oil pressures when hot evened back out to normal. Motor that was hurt always ran 10 psi lower than other. Now within a few PSI. I know for sure they are tired and on borrowed time, and full rebuilds are planned soon but still run dang good considering.

So, drumerjb, your real question is whether or not this was a bad-piston boat and whether or not it has been corrected. I doubt engines were done or prevent owner would have that info and been spouting it repeatedly. As to whether or not it was-is needed, a cheap borescope thru plug holes and you could most likely read the number on top of the pistons, at least some of them.

Friend just had his gone through with 800 hours on it. Believe it had a roller lifter that was on its last leg. There were other issues as well, just cant recall them. I think valve springs would be about shot by then as well.

Its a broker boat. Original owner purchased new. If warranty was done I'll find out through Formula. You re saying take a look inside for .010 oversized pistons?? Or a # that identifies a changed piston?

Where was the oil coming out of the engine that it made that much of a mess?

so much for that. The factory GM pistons have the part number stamped right on top. My 03 502 has no numbers on piston crowns. I just assumed they were there till I looked just now. I guess the JE pistons used in 502 dont. I was thinking we could research which piston numbers were the low tension metric ones. The broker would have the info on if engines were replaced and it would be highly touted by them. So my bet is orig engines. So the real question is, if it had the bad low tension ring Pistons originally, would they still be holding compression after 17 years even with low time running? And I thought we'd be able to answer that by the number on top of the piston.

Ah,got it. Great info,thanx. So the issue is weak tension oil rings & poor ring seat/blow by?
These engines have 160 hours on them. They should be like new IMOP provided regular maintenance. Or is it a craps shoot? Its not like a leak down test is going to tell you if a motor is burning a quart or 2 to 100 gallons of fuel especially if its doing it @ 4-5000 rpms of harder. I mean do compression tests & if you are 150 or better call it ok. @ what point do you suspect oil burn? Below 145psi??? I suppose it will show up when the plugs are pulled..Someone was saying they are to pig rich from merc,,but it would need to be pretty rich for washing.

A bird dealer/owner said they burn oil because of Siamese jugs that don t have proper water cooling/hot spots. Rings loose circle & tension.
Someone else said improper honing. I do not know. Maybe a little of everything & you got a oil burning 502.