Piston skirt protrusion at BDC

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4spod
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Piston skirt protrusion at BDC

Post by 4spod »

How much can a piston skirt exit the bottom of cylinder bore on a sbc be considered safe, even though the gauge point of skirt remains inside cylinder.Thanks Marc.
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Re: Piston skirt protrusion at BDC

Post by rebelyell »

WAG
what matters most is relationship of lowest part of pin bore to the highest part of bore liner at 90* to pin bore at BDC.

perhaps reveal here what you're working with ? --- might yield more cogent answer.
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Re: Piston skirt protrusion at BDC

Post by Walter R. Malik »

4spod wrote: Tue Nov 29, 2022 6:10 pm How much can a piston skirt exit the bottom of cylinder bore on a sbc be considered safe, even though the gauge point of skirt remains inside cylinder.Thanks Marc.
It really depends upon the skirt used on the piston and where the actual "fat" part of that skirt is located.
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Re: Piston skirt protrusion at BDC

Post by Tom Walker »

If you are working with the “880” roller block SBC, most if not all have a little bit shorter cylinder length.
Usually only becomes an issue if doing a 383 with the 3.75 stroke and many 383s have been done using that block

Believe there where even GM 383 crate engines that used that block.
There is a lot online about the “880” short cylinders. Good luck with whatever you do.
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Re: Piston skirt protrusion at BDC

Post by 4spod »

rebelyell wrote: Tue Nov 29, 2022 6:25 pm WAG
what matters most is relationship of lowest part of pin bore to the highest part of bore liner at 90* to pin bore at BDC.

perhaps reveal here what you're working with ? --- might yield more cogent answer.

The bottom end 3.75 x 6.0 x 1.125 CH SRP. 1974 010 block.Just thinking more piston rock in the cylinder barrel ?
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Re: Piston skirt protrusion at BDC

Post by rebelyell »

As TOM W said, the much newer 880 blocks have a shorter liner than your old 74-era block.
Wise choice that short 1.125" CH. It'll probably be fine ... probably. Again, to be certain, suggest you measure YOUR block versus pin bore etc.

And yes, GM did & does market a 383 using 880 block, even longer 3.800" stroke, relatively short 5.7" rods and pistons having those old-fashioned thick-wide ringpak ... all those things which push the pin bore closer to bottom of its relatively short liner. It's a good motor but it has never been OE in any series production vehicle; strictly aftermarket.
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Re: Piston skirt protrusion at BDC

Post by steve cowan »

I have nearly finished a 383 - 880 roller block, I believe the issue can be the oil ring can come out the bottom.
I went for a cp piston short skirt and thin/ tighter ring pack
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Re: Piston skirt protrusion at BDC

Post by Greenlight »

Check the amount of piston "rock" at BDC on the lowest point on the piston skirt. If it is in the range of 0.050" or more, you may have ring seal issues and oil usage..
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