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Discussion Starter #1
If so ,
What tipped you off that it was broke ???? How did it feel running before you took it apart ????
 

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The engine suddenly had a misfire. Pulled the plugs and found one with the gap mashed shut. It was caused by the parts of top ring land that broke off. Opened the gap back up and the engine hit on all eight again but it was using the second ring to hold cylinder pressure and that doesn't work for long.
This happened twice... finally said 'screw it' and had a set of custom JE's made. No more problems.

HiTech
 

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I bought a wrecked car and found it had KB domed pistons in it, one of them with a chunk of the ring land missing, Im rebuilding the motor now and Ive thought about getting just one new piston but now after reading this Im thinking I should just get a new set of forged pistons. sounds like they are junk
 

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Yup had a set of KB break right on the top.
It was caused by the parts of top ring land that broke off.
How much HP were these engines pushing?

How many rpms?

Power adder or N/A?

I have a .040 bored 302 and need cheap pistons for a 350 hp or less application,with NO power adder.
 

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I ran KB's for a couple of seasons in 12.5 -1 circle track motors turning 7800-8200 with no problems. The upper ring gap is critical with these because the piston retains more heat. The only failures I've seen have been because the builder did not increase the top ring gap as instructed.
 

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Yep, I cracked a couple in the top ring land.

Then I got a new set of KB's, and one of them shattered....broke apart at the pin boss, and the rod did the rest. Lost a whole motor on only its second run...

Never again.

Toma
 

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i cracked one...but that was because it hit the concrete floor on the top corner. the ones in the motor are fine. like someone said earlier, it's all in the top ring gap! i have mine gapped around .035".
 

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The only reason the top ring land breaks is because of improper end ring gap. You MUST file your top ring to KB's recommended specifications. Stock ring end gap is 0.020". KB's minimum is 0.028". I'm running 0.036" so I can run NOS in the future. I haven't had any problems. My combo is putting out 335 rear wheel horsepower.
 

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The only reason the top ring land breaks is because of improper end ring gap. You MUST file your top ring to KB's recommended specifications.
Ok mine were filed to KB's specs. Specs were taken right off from their tech department. Didnt have any problem with the ring end gaps butting up against each other. So what cuased mine? I would like to know. KB will blame ring gap on any of their pistons that fail. If you are having that much of a problem with a pistons popping the tops off of em maybe they should look into their piston design.

I went with KB's cuase they were cheap but ended up costing me more in the long run. Thats why my new motor has the best parts I can afford and I wouldnt recomend KB's to a Chevy Owner.

Rex
 

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KB's seem to be VERY inconsistant. Of course i used the proper ring gaps.... .040" for my 460 on nitrous....problem is the damn things broke and I hadn't even sprayed yet.

Don't get me wrong, my very first set I sprayed with 250hp regularily for 2 years, and 7000 rpm with no problems, and then BAM, 2 bum sets in a row....

Russian roulette with those things...

Toma
 

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I thought it was my nitrous but it sounds like these pistons where junk I broke 2 pistons on one eng and 4 pistons and cracked the block in 2 different spots on my other eng now I have je pistons
 

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Discussion Starter #16
Thank You guys !!!
Most of the time people won't reply to my posts. How did you guys know that you had cracked a piston ???? I have this vibration in my car that I just can't find the source of. I have checked everything and all that I can conclude is that it is realated to engine RPM. It's not the trans, driveshaft, rearend or anything like that. The vibration does not start until 5000 rpm and continues from there. I really don't think it is the pistons but I have checked so much other stuff, I am just kind of lost. I talked to someone from a well known performance shop that builds alot of circle track motors for late models and he said that the KB pistons are junk. He won't even sell them if somone wants them. Thanks again for all the posts guys.... Any other ideas about this vibration are welcome......
 

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balancer probably slipped. it's not the pistons. how's the oil pressure?
 

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Discussion Starter #18
Thanks Fast 89,
I already checked the balancer by checking the timing, that was just fine. The vibration is definetly coming from the engine somewhere, I have chased this thing for about a month now and singled out the engine the oil pressure hasn't changed at all and the car runs just perfect other than this damn vibration so I don't know what the hell the deal is, I am lost....This stuff is never easy !!!!
 

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Whats the proper way to check ring end gap?, Ive got these pistons out of the engine right now and want to see if they were gapped properly or not, If they werent I may use them again just get one new one and make sure the top ring has the proper gap
 
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