It could have been done at the time the piston was installed back into the block,,,like ring compressor slipping off the rings there on the bottom
Are you the person that installed the pistons in the block? coz thats where the land got broken..bottom oil ring hung on the cyl wall and piston was knocked in the hole anyway...Want to bet???
No... Thankfully I did not assemble it. It has multiple cracks (4~5)between top and second, and second and oil control rings
Detonation (pinging). Had it in a couple early 60's Pontiacs w/4 spd hydros. They shift too soon, bogging the motor and with the hi comp of the day and today's shit octanes, it really rattles the ring lands to death.
What kind of pistons? Cast, hyper or forged? Seen that a bunch on hyper pistons. They need a lot more end gap on the rings or they will break ring lands clear off. SPark
Here is where I would have to plead ignorance... never learned how to tell'em apart if it wasn't written on the box
One piston or several in the set? Several would probably mean that the ring gaps were way too tight while one may mean rough handling during piston installation Since the piston is broken anyhow I'd see if I could get the ring (s) out in one piece and check the end gaps. I'm inclined to agree with the rough handling with a big hammer (handle end) during piston installation with the ring compressor slipping off too though. when the crank em tight band style ring compressors get worn a bit the slip pretty easily especially when you or the shop is doing the same size piston over and over during installations. One more thing that came to mind that I have seen is: does the block still have a wear ridge from before it was redone? Years ago I had an engine brought to me that some guys had done a home re-ring job on and they didn't use a ridge reamer to cut the ridges out of the block and the new rings hit the wear ridge and broke the pistons.
I would also vote for ridge at top of cylinder wall not being properly removed during rebuild. Top ring will then bang against the ridge on top dead center and cause stress on piston between ring lands.
Eliminated that idea then. that leaves detonation, rough handling or tight rings. On the tight ring idea, guys reads a couple of engine building stories in the rags that have build your own high performance engines in them and one or two say that the hot lick engine builder uses rings that are .010 larger than the bore of the engine and then custom fits each ring to the individual bores. He then proceeds to buy rings that are .010 larger than his pistons but doesn't cut the to fit the bores with the exact ring gaps he needs. Photos of broken ring lands show up on the HAMB from the guy who ended up with that engine.
Detonation bangs on the pistons harder than most anything you can imagine. The wrist pin pushes up thru the down force of pre mature combustion. The piston is along for that ride having to deal with those two forces arguing.
Got any history on this engine? Kolbenschmidt is pretty specific on pages 36 and 37 here - http://www.ms-motorservice.com/fileadmin/media/msi/News/ks_piston_damage_50003973-02_web.pdf
I'm listenin' to you... but in every other case of detonation I'v ever seen there has some pretty severe skirt and bore damage, with metal transfer and surface pits popped out of the crown, and sometimes some ugly discoloration from heat. In this case the ring face isn't even scratched. I might have thought that he sucked up some water, but there is no visible bend or twist in the rods. I'm not tryin' to start arrangement... I'm just stumped.
That's an excellent link and pages 36 and 37 lay it out. One of the conditions to look for this damage on page 36 or 37 is "no metal transfer of signs of over heating) See figure 3 on page 37.
I say detonation as well. This is the common place where hyper pathetics bust when guys attempt nos on them with a sloppy tune. i.e. detonation damage and/or weak casting for the suddenly larger dose of cylinder pressure.
Are these out of a Pontiac motor? My buddy pulled down 3 pontiacs from the 60's and all 3 had the same cracks. Non of the 3 cars had been ran since about 1970-1972 Makes me wonder if it is a pontiac thing. I used to work in a machine shop and every 302 ford I ever tore down, had the bottoms of the skirts broke off. It never hurt the way the motor ran. You would find them laying in the oil pan.
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