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Old 08-23-2011, 09:05 AM
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Pistons hit heads on 454 w 25.5cc dome

I have asked before about this motor but now I wanted to check my valve to piston clearance I found I need push rods and the piston hits the head close to the spark plug hole. How and how much can I remove from piston? are the valves going to hit as well? what push rods? I have KB 25.5cc dome pistons.Pro Comp 320cc heads W/ 115cc chambers. Lunnati 722 lift roller cam Please has anyone run this combo? what do I do now?

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Old 08-23-2011, 09:15 AM
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Being a blower motor guy, I don't get into dome pistons much, but can't imagine them hitting the head in a 115 cc chamber, but anythings possible. Looking at the obvious, are the pistons installed/oriented correctly? I'd be leery of removing too much of the dome and compromising the piston head thickness.

As far as valve clearance, which pistons are they, single, double valve reliefs?
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Old 08-23-2011, 09:38 AM
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KB257 Pistons. Cam is solid roller Lunati 50226LUN.rockers are crower 1.7 rollers. Heads are Pro Comps as said before seam like they just bairly hit it will spin and only 2 piston have a mark #s.5&6 . I searched and found very little info. I found this is not so un common as brodex has a little info about it. They say to clearamce the piston. They also say it will not bother my ballance because its above the piston pin? Is this true? will this work? there is a notch in the piston that seams to be for this but its off a little one way I will try to post a pic later

Last edited by TonkaYJ; 08-23-2011 at 10:01 AM. Reason: Add pic
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Old 08-23-2011, 10:13 AM
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bump for pic
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Old 08-23-2011, 10:26 AM
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it "will" affect the balance of the piston. But its gonna be negligible because of the distance from the pins center plane. That said, how thick is the piston at that point?

Id take a little material from both the head and the piston before i took of a fair amount from one.

Throw that sucka on a mill and start cuttin...
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Old 08-23-2011, 11:23 AM
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Its is required to verify any non stock dome to non stock had on any BBC build. Verify .050" minimum clearance at all points not just the parts that are hitting now. .050" clearance. Use modeling putty on the dome.

You can grind the dome or grind the chamber. No the balance won;t get messed up.

VTP clearacne must be checked and with that big a cam piston notching for valve clearance will most likely be required
.100" intake .100" ex
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Old 08-23-2011, 02:44 PM
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Check the stroke of the crank on the 5 and 6 pin.
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Old 08-23-2011, 03:14 PM
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Is it just an illusion or is that piston out of the hole, above the deck?
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Old 08-23-2011, 03:46 PM
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Quote:
Originally Posted by lmsport
Check the stroke of the crank on the 5 and 6 pin.
crank was checked by 2 good engine shops
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Old 08-23-2011, 03:47 PM
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Quote:
Originally Posted by 68NovaSS
Is it just an illusion or is that piston out of the hole, above the deck?
Just the dome is
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Old 08-23-2011, 04:24 PM
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Quote:
Originally Posted by TonkaYJ
crank was checked by 2 good engine shops
Thats an unusually random problem. Did you use the same head to check both sides?
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Old 08-23-2011, 04:38 PM
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Use clay and check ALL the chambers. Just not seeing a mark on the piston doesn't mean the other domes couldn't be just a hair away from touching. Mark the heads "left" and "right" and keep them in the same position.
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Old 08-23-2011, 05:17 PM
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Quote:
Originally Posted by cobalt327
Use clay and check ALL the chambers. Just not seeing a mark on the piston doesn't mean the other domes couldn't be just a hair away from touching. Mark the heads "left" and "right" and keep them in the same position.
I sent everything to a machine shop that builds a lot of race motors around here I asked him to make it fit and degree the cam and figure out what push rods I need so we shall see what he says
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Old 08-23-2011, 05:27 PM
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Quote:
Originally Posted by TonkaYJ
I sent everything to a machine shop that builds a lot of race motors around here I asked him to make it fit and degree the cam and figure out what push rods I need so we shall see what he says
Thanks for the update- that's sure one way to deal w/it! lol

Keep us posted...
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Old 08-24-2011, 08:08 AM
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I will let ya all know what they do. I am just wanting to get it running and at this point I figured let a pro look at it
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