Piston clearance, help needed!

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360duster

360duster

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Hi Guys,

i had a machine shop bore and hone my block .030". I gave them the Piston set (KB356 hypers) supplied with my stroker kit.

Now it´s time to start the assembly, i measured everything. Found out that one piston from the set is smaller in diameter than the other 7, this creates the correct clearance (.0020") at 7 Pistons and around .0043" at 1 Piston. It seems that these f**ing idiots measured not all pistons and finish the bores all with the same diameter.

Now i´m a little concerned if this will work on the street or if i will have wear / Oil use problems. I know from the KB specs that they suggest up to .0050" clearance for some kind of engine, so it seems that the pistons will live a while.

from the shop i have no reply at the moment, i think he´s in the same boat as i and does not have an idea (i know, he should have...:angry7:).

Please let me know what you think!

Thanks in advance

Michael
 
In my opinion, there are two screwups. That much difference in the size of the pistons is unacceptable. I would contact KB about getting a replacement piston. Then there is the machine shop. They should have caught it before doing the bore. Sleeving that one bore is an option, but the shop should eat the cost.
 
I would imagine KB can send you a replacement piston, so long as you are not in a mad rush... That would be my first suggestion. If it's been mounted (as in pressed on) then scrap the idea of sending it back... Chances are they won't accept it anyway. In that case, I'd just run it. As you say, they do have applications where the pistons are run loose, and I don't think you'll have too much to worry about with .0025 extra clearance there. You have a short piston anyway because of the longer stroke so the ring wear is going to be much faster than a factory displacement.
 
Your machinist finish honed the bores without measuring each piston first?!? Assuming he uses a CV-616 or similar, its the same work (programming CNC) to finish each bore to it's piston and have uniform clearance.
 
LOL, KB Hyper pistons............ The same quality was put into making them as to sizing them....

LOL

And everyone keeps buying them because they are "cheaper" than a forged, and "better" than a stock cast.....

LOLOLOLOLOL


Pistons are like politics...........
 
Ive read a few articles out there testing hypers and various bore clearences. Basically from those readings they can be run from .002 to .006 without any noticeable damage or hp loss from the extra clearance. I was running my speed-pro hypers at .0045, they never chattered when cold and didnt have any skirt problems when pulled.
 
send it back.

btw I've run them just teetering away in the bore before, probably had 8 thou , no issue.


Check all the quench pad/chamber 'quench distance' clearance's.
 
If KB won't take it back measure all 8 cylinders and put the bastard piston in the smallest hole. I'm sure when they honed the cylinders they did not get all 8 at exactly the same I.D. + - .000 and they probably had a .0005-.001" finished I.D. tolerance.
 
LOL, yeah, use the oddball piston...........

Sheesh!

The things you hyper KB guys do to use them...........

Wild is right, .080 is actually pretty cool, sound like a diesel and run like stink!

I have had "machinists" tell me a SBchubby I built with .060 would make it ten minutes, funny how that car has been running low 11's for 8 years now! Gotta love the first high nickel 350 chubbies.... best worst motor ever built.......

I would ask for a new piston, for sure, at least....
 
Ok, i´ll contact KB to check if they can supply a single piston that fits. Gonna wait til monday if this dumb machinist will give me a feedback or not - no chance that i will give engine parts to him again. It seems very hard to find a shop you can trust over here.

Thank you guys for your input, positive or negative - i´m more relaxed now. If it´s not possible to get another piston i´ll run it as it is.

Michael
 
360duster said:
Ok, i´ll contact KB to check if they can supply a single piston that fits. Gonna wait til monday if this dumb machinist will give me a feedback or not - no chance that i will give engine parts to him again. It seems very hard to find a shop you can trust over here.

Thank you guys for your input, positive or negative - i´m more relaxed now. If it´s not possible to get another piston i´ll run it as it is.

Michael
Click to expand...

they will sell a single piston, but you will have to go through a dealer...or KB might just have to give to you for free.

they sponsored me a free piston.
 
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