Piston pin looks to far off center.. 454 build might need more compression ?? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-10-2013, 01:19 PM
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Piston pin looks to far off center.. 454 build might need more compression ??

Gen 6 454 roller block.
.030 over
flat top pistons -5cc and .004 below deck
stock crank .030/.030
stock rods
ZZ502 cam
Bowtie heads 98cc chamber
Bowtie intake.

This motor started off as a truck motor with a rebuild of 6k miles on it. already bored .030 over. Once i got it and disassembled it- Block was cleaned, brass freeze plugs, cam bearings , deck squared, tq plate honed.

I cleaned the pistons real good yesterday and noticed that 2 of the pins are way off centered in the piston with the rod centered. Is this an easy fix? Will the pin hold its place if it gets pressed in farther.

Or Can this be run this way? its been running this way for 6,000 miles already..

My other question is about my deck clearance. Piston is .004 in the hole at tdc.. I was told that i need atleast 9.8 compression to benefit from this cam in a 454. Right now I am at 9.28 compression. With a 1.625 compression height. If i went with new pistons to bump up compression. I would only be able to get a 1.640 compression height in a dome piston and that would put my pistons at .011 above deck, and less then .030 quench..

Is this even an option?

Really considered trying to just keep what i got and go forced induction later on with the low compression..

Thanks
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Old 03-10-2013, 02:05 PM
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As long as the pin is in good contact with the piston pin bore at its working spec. Assemble the piston in bore and you will see that the rod/pin is not always centered in the piston.

Just looked at pics. The pin needs to be moved. That is a bit too far off.

The pin can be moved with a fixture and a press. If the rod eye is at proper ID spec. the pin will not in move in normal operation.

Deck height problem can be remedied with a thicker head gasket. BBC gaskets can be had fron about .020" thru around .060" from common sources or use a Fel Pro head shim at .020" and a regular gasket.

Factory BBC tall deck 366-427 used to have a common problem back in the day. The rod eye would get finished a bit too big at production and in operation the pin would slide over and wear on the cylinder wall. Some all the way to coolant. Others just massive oil use.
I did many bore/sleeve jobs on those engines.
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Old 03-10-2013, 03:21 PM
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9.28:1 isn't considered low compression when it comes to boosting a motor, especially going the roots route. You could do it, but at low boost levels, maybe 5 pounds, mostly a poser thing. Turbo is a little more forgiving, but there are limits. Static of 9.5:1 will give you an effective c.r. of 13.4:1 at 6 pounds of boost.
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Old 03-10-2013, 06:04 PM
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Just installed the two offset pistons and they slide over to where there is even less pin on one side. Also checked my deck height and piston is .018 in the hole so I can go to a 10.5cc dome piston to get 10.3:1 and still have the piston .003 in the hole.
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Old 03-11-2013, 12:13 AM
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Where on the pistons are you checking the deck?
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Old 03-11-2013, 08:10 PM
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I checked top, middle and bottom of piston in cylinders 1,2,7,8 . When I asked the guys at the shop they said the pistons should be .004 in the hole but they are .018. I figured this out After I checked it Yesterday to see how far offset the pin was..

I didnt think i could get new dome pistons without them sticking .010 out of the deck, since they have a 1.640 compression height . Guess I can with that extra .018 ??

Last edited by dually502; 03-11-2013 at 08:18 PM.
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Old 03-11-2013, 09:05 PM
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Yes, the pistons you have now are rebuilders replacement pistond. Usually .020 short. That would put the 1.640 compression pistons close to the deck. The quench could then done with the proper gasket combo.
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Old 03-16-2013, 12:36 PM
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What is the highest compression u guys recommend for the zz502 cam, aluminum Bowtie heads and EFI setup on my 454? I was thinking 10.5 to 11 on pump gas ?

Opinions?

Thanks everyone.
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Old 03-31-2013, 09:01 PM
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Quote:
Originally Posted by dually502 View Post
I checked top, middle and bottom of piston in cylinders 1,2,7,8 . When I asked the guys at the shop they said the pistons should be .004 in the hole but they are .018. I figured this out After I checked it Yesterday to see how far offset the pin was..

I didnt think i could get new dome pistons without them sticking .010 out of the deck, since they have a 1.640 compression height . Guess I can with that extra .018 ??
When checking the deck height it is best to use a dial indicator
and a bridge. Find top dead center of the piston, then using a straight edge and a set of feeler gauges measure to the top of the piston parallel with piston pin.
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