KB Claimer pistons

[Kdub]

I'm putting together a SBC 388 for a 1 ton tow truck and thought I might use KB Claimer pistons. After reading a bunch of really old internet post that claim they crack, tops pop off, ring lands breaking and piston pin hole not being centered got me wondering. Are these pistons really this bad? Most all the info. I could find was old web forum stuff from about 2004 to 2010, so I'm wondering if maybe KB finally started manufacturing them properly or what...

[BillK]

I think it is all in the tune up. The guys at the local dirt track were using them and not having problems. I have seen them with broken ring lands but not sure what the cause was. You have to run a real big top ring gap and I dont think they do well with detonation but what piston does.

If I was going to do a cast hypereutectic piston I would prefer the Sealed Power ones myself.

[k-star]

No they are not that bad. I used these pistons since they came out. I never had one break where something out side did not break them. Incorrect ring gap, detonation etc. I had half dozen customers spray them with a 200 shot, not one broken piston.

Keith

[piston guy]

"User abuse" is the most common reason for cast piston failure. Cars and trucks have used cast aluminum pistons for trillions of miles since the switch from cast iron almost 100 years ago. Castings are more brittle than forgings which does make them more failure prone when abused. Treated with respect , cast pistons "usually" outlast the piston ring's ability to seal compression.

[cardo0]

Piston speed is to high for uetectics with 3.75" stroke. Maybe in a truck keeping rpms below 5000 they would live a long life but I think you are gambling. uetechtics are stronger than cast and plenty of cast pistons in truck motors. But increasing compression and running at higher rpms will test them.

I think safe piston speed is 4000 fpm and that's about 6300rpms for a 3.75" stroke.

Hope this can help.

[PackardV8]

Piston speed is to high for uetectics with 3.75" stroke. Maybe in a truck keeping rpms below 5000 they would live a long life but I think you are gambling. uetechtics are stronger than cast and plenty of cast pistons in truck motors. But increasing compression and running at higher rpms will test them.

I think safe piston speed is 4000 fpm and that's about 6300rpms for a 3.75" stroke.

Hope this can help.

We'll have to agree to disagree on this one. FWIW, I've never seen a hypereutectic cast piston fail from anything attributable to piston speed. The old school "4000 FPM safe piston speed" dates back to the dark ages of ICE technology. 21st century production engines with warranties operate well beyond that. The Lamborghini Gallardo/Audi R8 5.2-liter V10 has the one of the higher mean piston speed for any production car, 5295 FPM (26.9 m/s); a 92.8 mm stroke and 8700-rpm redline. The Ford Voodoo V8 has a 93mm stroke and an 8250 RPM redline. The Honda F20C has a 9,000 RPM redline; a mean piston speed of 4,965 FPM, or 24.6 m/s.

[Mark O'Neal]

Parts are almost never the issue when an engine fails. It's almost always either the genius tuner or the operator.

And I fail to see why a 1 ton tow truck would be operated at over 5,000 RPM.

[Kdub]

Ok I'm glad to see that there are no issues with the KB Claimer pistons so I'll go ahead and order them. That will save me a little money.

I have used KB hyperutetic pistons in several motors and they always worked well for me. I built one 402 BBC with KB hyperutetics for a drag car that shifts at 7500 rpm and probably has over 200 passes on it.

I really can't see the Claimer pistons being as bad as some of those old post in those old forums without there being a lot of PO'd roundy round guys over the last 20 years or so.

[rustbucket79]

Hmmm. "Tow truck" to me means high load/lugging/high combustion temperature/likelihood of detonation.

Claimer pistons-marketed as a budget lightweight (arguably) race piston, with higher top ring locations and thinner piston lids. Kind of asking for trouble in my opinion. I would stick with a heavier option like an FM or silvolite stock replacement, cast or hypereutectic.

If you're going for the claimers, add lots of top ring gap.

[econo racer]

Just follow the manufactures instructions about min ring gaps. I use 27-28 top for 125 HP nitrous. Most people bash there pistons because they never read the instructions on ring gap. Good product for the price and quality IMO.

[F-BIRD'88]

Only ever busted 1 piston ever. Was a FM hyper not a KB..
Motor had 12.65:1 cr, tried to run pump gas forget to dial back the spark. Hone 1 new piston bearings rod resize back in business. You have to try to break a KB hyper piston..
It Always means that you did something WRONG.

[Lizardracing]

The thing about hypers is they tend to explode and break up into tiny pieces and the loose end of the rod destroys the block while the bits of piston reek havoc elsewhere while a forged piston will be much less likely take out everything else.

KB's are sensitive to top ring gap like said above. Read the directions and I haven't had any issues to date.

[F-BIRD'88]

Had a bud who did break a KB piston . was 13.5:1 cr methanol. River racer. Was playing with carb jetting and timing and got z bit carried away (lean) . Again straight r&r 1 piston repair. Never a problem after., 6800 rpm WOT steady running.

[piston guy]

Common theme here . All the failures were as Mark and I have both said. owner tuner abuse/lack of respect. WHY do people who "cheap out" in the begining ALWAYS seem to have the money to REPAIR instead of SPEND ONCE in the begining? How is that saving?????

[F-BIRD'88]

A more expensive forged piston would not have survived these mishaps. . While they won't break they still fail by scuffing the cylinder wall . Still may run but the ring seal is destroyed. The repair is the same.