Piston Ring Failure Diagnosis

[Rick Finsta]

BTW I deburred the bottom of the cylinder - looks like that hadn't been done when I assembled it. The littler metal boogers (technical term) seemed to line up with the scuffing on the piston and cylinder wall... I'm checking the other cylinders as well. I figure I'll just re-ring the whole thing while I've got it apart. I won't hone the other cylinders at all - I will just hit them with scotch brite, clean them, and then apply the quick seat powder for good measure.

Rings should be here today and then the thrash starts to get the car back on the road by Thursday. Amazon made me forget how awful it is to wait for parts!

[Rick Finsta]

Just to update I got the engine re-ringed and I also tossed in new rod bearings. If you want to be scared get a stretch gauge - with the same lubricant on burnished rod bolts/nuts I saw a range of 0.0045-0.0075" stretch at 45ft./lbs. and had to go anywhere from 42-50ft./lbs. to get them all in range (0.006-0.0065"). I get that the bolts are stronger than these rods by a good deal (stock rods) but that was eye-opening as I've never had the stretch gauge before.

Fired the motor last night, heated it up, and everything seems to be okay; I'll be taking it for a rather spirited drive this afternoon after work to make sure the rings are properly seated and then I should probably check leakdown right away, but part of me wants to not worry about it and just see what it does at the track.

[Chris1]

Good luck - hope it is all good now.

I'd guess by the description you gave that you had more of a valve sealing issue than a ring issue. As noted earlier the wider wear pattern at the gap is typical. Greater wear/gap on the top ring is also typical - it's doing the lion share of combustion sealing. When/If you re-leak test be sure to listen where the air is escaping to. At 45% leak you will easily be able to hear whether it's escaping back up the intake, out the exhaust pipe, or out the crankcase breather. I don't know that MAP review is going to give you the answer - I see engines that'll leak a fairly high percentage at the valves still show the same MAP, or darn close to it. When I see the MAP drop off measurably the valve seal is so shot the engine freewheels from lack of compression when you shut it off... and leaks in the 80% range.

[wyrmrider]

quick seat powder?
scotchbright?
get thee behind me Satan

[MadBill]

Just to update I got the engine re-ringed and I also tossed in new rod bearings. If you want to be scared get a stretch gauge - with the same lubricant on burnished rod bolts/nuts I saw a range of 0.0045-0.0075" stretch at 45ft./lbs. and had to go anywhere from 42-50ft./lbs. to get them all in range (0.006-0.0065"). I get that the bolts are stronger than these rods by a good deal (stock rods) but that was eye-opening as I've never had the stretch gauge before.

Fired the motor last night, heated it up, and everything seems to be okay; I'll be taking it for a rather spirited drive this afternoon after work to make sure the rings are properly seated and then I should probably check leakdown right away, but part of me wants to not worry about it and just see what it does at the track.

I recently changed out the forty five year old Carrillo bolts in my "Rip Van Winkle" BBC project for ARP2000s. Initially there was quite a lot of variation in the torque to minimum stretch, but after 3 or four re 'n re cycles, they settled down at only +/- 2 lb.ft. torque to hit the mid point of the stretch range.