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Discussion Starter #1 (Edited)
I hit 158k and then had a misfire code for cylinder 3, and I drove it and drove it and got to 166k and she died. It was a failed ring that ate up the piston and cylinder wall.
I honed the block .020", did a full clean and rebuild and put her back together and it ran great... for 300 miles. Then it started smoking. I did my oil change at 500 miles and it stopped smoking, I figured the rings are seating, no big deal. Then the misfires came back on cylinder 3.
I just checked it with a borescope and 3 is getting chewed up. Probably another failed ring, WTF would cause such a thing?

TLDR: at 166k miles, svt died because ring in #3 broke. Rebuilt motor, now 700 miles later, ring in #3 broke again, WTF!?
 

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I hit 158k and then had a misfire code for cylinder 3, and I drove it and drove it and got to 166k and she died. It was a failed ring that ate up the piston and cylinder wall.
I honed it .020" and put her back together and it ran great... for 300 miles. Then it started smoking. I did my oil change at 500 miles and it stopped smoking, I figured the rings are seating, no big deal. Then the misfires came back on cylinder 3.
I just checked it with a borescope and 3 is getting chewed up. Probably another failed ring, WTF would cause such a thing
TLDR: at 166k miles, svt died because ring in #3 broke. Rebuilt motor, now 700 miles later, ring in #3 broke again, WTF!?
Sounds like a lower rotating assembly issue. Possibly worn out of balance? Did you replace crank & rod bearings, and/or check crank journals for wear? May have a bad crank. 150k is a short life for a good crank, but may have had an issue from the Frod factory that never got noticed. Just my $.02
 

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Discussion Starter #3
I had the crank ground .010/.010 for good measure, but only because there was a small ring that was detectable with your fingernail on a rod journal.
The crank was in balanced perfectly when I checked it. And I balanced everything within 2 grams when matching each rod assembly.
 

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How on earth did you hone .020"? Did the piston size get changed? Because it dang sure better have, and then how did you balance that one to the others?

More questions abound, there are reasons for what happened there.

'Lower rotating assembly', that's a good one.........
 

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Discussion Starter #5 (Edited)
I honed each cylinder .020, think I should have only honed the bad one and not the others?
 

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Pennies apiece, balance is the obvious issue.

And yes there is a "lower rotating assembly", the crank, rods, pistons, and pins. Just as there is an upper rotating assembly, the camshaft and valvetrain...I have been building engines for 3 decades...you?
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To begin with you MUST use oversize pistons with that big an increase in bore and you DON'T hone that big, it would take a day to a cylinder doing it. You BORE most of the distance and then hone the last couple of thousandths or so. You never hone over say .005" and even more so if not using say a Sunnen CK machine to do it. The hone stones will severely overload with anything like that much material being hogged out. AS well you never bore/hone one cylinder bigger than the others (other than the most minimal amount), it won't work.

Maybe a decimal error there and only honed .002" which is doable and no pistons needed for that. But .002" will not remove spit as far as wall damage goes.

Any four that was out of balance would shake worse, they do it even in perfect form. When you specialty balance you generally balance to within 1 gram not 2. A dollar bill is typically used to check weight there, it being that weight.

If the hone job was not done to the correct RMS or crosshatch angle for the ring type then the rings get eaten alive. If the pistons changed then the rings may well have needed to be sized to the bore and not doing it tears them and cylinder walls up when the ring ends butt.

You have no idea how many engines I've built, I don't even know, it has been that many. I was playing with 800 hp. AMC engines in the mid '70s. When I ridiculed the lower rotating assembly thing it was in terms of it being a balance issue.
 

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Discussion Starter #10
Yes, I used a Sunnen hone and it was .020 (.50mm), the crank was checked on a Sunned crank balancer and the 2 grams was a function of the little end of the rod.
It spun to high rpm (6800) very smoothly when it was put back together, it spun better than any stock SVT that Id had apart before.
 

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You still have not answered the piston oversize question. They MUST be oversize to service that big a hole. And Sunnen by itself means nothing, they make cheap crap hand hones as well, say you used the machine to do it. Still incompetent, you would have balled the honing stones up to not get correct wall finish at that much honing, NOBODY does that. Honing at that much begins to drift off the true bore center as well, why you bore first to establish a solid straight hole on center then slightly hone it to perfection.

'When I ridiculed the lower rotating assembly thing it was in terms of it being a balance issue.'

By that I meant the issue had nothing to do with the balancing.
 

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.020 would require a new set of pistons , with a .020 bore and stock pistons you would have crazy piston slap

What was your air fuel ? could be running lean , bad Inj

What was your timing doing

Tom
 

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Bet your oil squirters are plugged on #3 or blocked by new bearings. Overheated pistons will crack rings. The whole overbore fight is fing ridiculous I owned a 78 m2 with a 2.3l an punched it .030 no problem 1 pass with a finishing hone and ran perfect. Dont care how long someone has been doing somthing that could just mean you have 40 years of doing it wrong. Junkyard mechanics are a dime a dozen.
 
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