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#1
01-27-2009, 09:07 PM
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wrong pistons for my 4.25 crank/6.8rods?
Just mocked up piston #1, and this is what I've got. The piston sticks .169" out of the hole! I am using an Eagle 4.25 crank and Eagle 6.8 BBC rods. I measured the rods and they're 6.8", if I'm doing my math right. I don't know how to measure the crank, but I have to assume its the correct one. I don't know how to confirm my pistons are correct, however. Its got to be the pistons, right? The block is a virgin '76 with 87K miles. The machine shop is waiting for my order as far as how much to deck.
I got the forged Ross flattops from Butler. The spec sheet says 66997 on the top (job card #). Dome height =0 pin diam=.980 bore 4.181 CH 1.495 CAM J
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greg 1976 SE 455 twin turbo austin, tx |
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#2
01-27-2009, 09:22 PM
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sounds like that piston is for a 6.625 rod, if you use that stroke crank. 6.8" - 6.625"= .175" Would put you .006" in the hole. About right.
If you wanted you could swap rods or pistons, if they had a 6.625 rod with a bbc crank pin.
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 1963 Cat SD Clone (old school) streeter 1964 GTO post coupe, tripower, 4speed (build) 1965 GTO 389 tripower, 4 speed, driver 1966 GTO dragcar 1966 GTO Ragtop 1969 Tempest ET clone street/strip 1969 GTO Judge RA lll, auto 1969 GTO limelight Conv. 4speed go and show (sold) 1970 GP SSJ 1970 GTO barn find..TLB…390 horse?….yeh, 390 1972 GTO 455 HO, 4 speed, (build) 1973 Grand Safari wagon, 700hp stoplight sleeper 525ci DCI & 609ci LM V head builds Last edited by J.C.you; 01-27-2009 at 09:38 PM. |
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#3
01-27-2009, 09:33 PM
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It is absolutily the wrong piston. C/H should be around 1.295.
Ace
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Am I glad I got out of the business I was in? HELL YEAH!!! |
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#4
01-27-2009, 10:00 PM
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Thanks.
That what I thought, but Butler was already closed when I found the problem. I'll give them a call tomorrow to exchange them.
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greg 1976 SE 455 twin turbo austin, tx |
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#5
01-28-2009, 06:27 AM
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FWIW:
What is the pin diameter of those 6.8 rods?
That is a 455 piston for a stock length 6.625 rod with a stock type Pontiac .980 pin. |
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#6
01-28-2009, 07:52 AM
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Wrong Pistons
I'm just curious about 2 items?
First, what pin did you use for the "mock-up"? And second, was this purchased as a "balanced" rotating ass'y or does it need to be balanced still! If it's the former, already balanced, you may have other issues for sure! Thanks, Gary in N.Y. P.S. You may want to check the damper "press-fit" on the Eagle shaft beforehand also!! There are many undersize "snouts" in the marketplace on their "cast" pieces on the Chevy platform? |
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