I'm in the process of building my 347 with KB pistons...What's your combo and what makes you think you broke one??? I have a buddy that built a 383ci chev. with KB's 10:1 C.R. Ran it for a few miles and parked it for the winter....spring came and out he went and got on the thottle hard....old gas,,,Detonation...top chunk of piston broke off and bent valves,one rod,and cracked the cylinder....He sleeved the block, never run old gas and never broke any more KB's...I'm told that they are tough pistons, just don't detonate them and follow the instructions for installation...just my 2 cents Russ....
347,10.1comp,dart snr's,comp cams 294s,quad webers,scat h beams,scat crank,kb hypers,it was at the dyno today to tune the webers,and whilst running it started to fume out of both breathers on the rocker covers,they stopped the engine removed all the plugs and found number 4 plug black and very small what looks like iron filings on the plug and the rest of the plugs perfect condition,so i assumed that the compression is blowing past the piston and into the oil to create the fuming out of the breathers.......does that sound like it could be true??
KB hyper pistons require tons of ring gap... more than stock sets usually provide. What usually happens when one of those pistons fail, is the top ring butts at TDC and sticks in the bore. When the connecting rod tries to pull it back down, the top ring land is pulled off.
Checking the ring gap is MANDATORY with these pistons. Even standard (non-file fit) rings often need to be ground to fit.
I was warned about them also when building my 351C 4V, if you go to their web sight they will tell you about the gap and how important it is, then they show you a picture of what happens to the top. I talked to the rep over there and he told me they run them with blowers and / or Nos all day long with no problems. So far no problems for me.
'56 f-100, '72 Torino clip, 351C 4V quench, C6, 9" 3.70 gears, got her running last night, and wow did she run.....
I had no problems with my dome KBs in my 12:1 351W shifting at 7800 and using nitrous. I broke a set of Ross pistons which I got to upgrade from the KBs without leaving the driveway bumping the nitrous from idle out of gear. I put the KBs back in and ran another year with them until I got a set of Wiesco pistons which broke without nitrous driving to the track. Both the Ross and Wiesco pistons broke around the ring lands but the KBs never broke with the same tune-up, timing, and nitrous. I love KBs!
I've used them in several engines with great results. The biggest problem that I see is that people don't read the instructions that come with them.
They have stood up to all of the abuse that I can throw at them. You guys should quit blaming the pistons as the problem. More than likley its because of some other part failure that would have taken the piston out anyway!
<font size=-1>[ This Message was edited by: 85Mike on 4/20/02 8:11am ]</font>
I've never used KBs but if I do I'll make sure to read the instructions and get ring gaps right.When we were kids the instuctions to the models/toys were thrown out because in our minds they weren't needed.I guess some things never change for some people. Me?I never grew up.Ha.
Any profession motor builder that failed to properly follow the KB instructions should eat all the re-rebuild costs and do something to compensate you for the remove and install ( I am assuming you did this part). The only reasons I have heard of the KB hypers failing is ring gap issues and detonation. Best Wishes.
the engine is out and the heads are off.number 4 piston has detonated on the edge of the fly cuts down to the first ring,and all other pistons are ok .i havent seen it yet but i will on monday,can some1 please explain how detonation happens?? and why only on 1 piston??does it have have something to do with the weber set up??
Measure that piston's ring gap, anyway. Good fuel is essential to avoid detonation. Lean fuel mixtures can also lead to detonation, especially if the fuel is borderline. Too much ignition advance also causes detonation.
As for one going before the others... someone has to go first.