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Old 12-30-2009, 04:00 PM
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383 Piston to Crank Clearance

Was working on assembling my SBC 383. I have a Scat crank, scat 5.7 rods, and speed pro hypereutectic pistons.

I had checked all of the clearances and ground the rods as required as well as checking the block clearances. Never thought to check the piston to crank clearance as this was set up for a 383...just never crossed my mind.



I just put the first piston in the bore and only have about .045" of clearance from the piston to the crank. Is this enough? I'm guessing uh...no. I'm thinking I need about .050 at least.

The rotating assy is already balanced, but I think if I do grind the skirts just a bit(speed pro had ground the skirts a little in that area, but evidently just shy of enough)...anyway, if I just grind another .010 off of the skirts right where it gets close, I don't think I'll have to rebalance it...

So, what is everyones opinions. ???

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Old 12-30-2009, 04:49 PM
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Yep, .050 is the recommeded minimum clearance.
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Old 12-30-2009, 04:54 PM
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Yah...I checked it, its more like .030 clearance.

I pulled the piston back out and have a sandpaper roll queau'd up to hit all of the pistons with.

I looked closer at those speed pro pistons and they didn't grind in the area my crank is close(the chamfer on the edge of the counterweight to the radius of the skirt relief if that makes any sense). Some have a smidge of casting flash there that isn't helping things any. At least I found it now rather than after I had it running and I knocked a skirt off a piston.
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Old 12-30-2009, 05:49 PM
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You're using 383 pistons, with the pin relocated for 5.7 rods right? I've built several 383's and never had any clearance issues with the skirts on the 5.7 engines.
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Old 12-30-2009, 07:16 PM
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Yep. Everything is right. I have .017 deck clearance. I researched the part numbers and made sure it was right.

Near as I can tell, Speed Pro pistons are made in India(yah think they put INDIA really big on them as they are proud of them or because they are rubbing it in our faces?). Good 'quality' Indian castings. I think they got a bit sloppy on the skirts. I didn't realize they were made in India until after I bought them. Speed pro, I thought 'USA'.

Anyway, I hit them with the sandpaper roll and they cleared right up and now I have a good .055 of clearance. I'll have to do that with all of them I expect.
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