Re: Bore size vs piston diameter
[Re: DGS]
#2326169
06/24/17 06:10 PM
06/24/17 06:10 PM
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Joined: Oct 2007
Posts: 4,205 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,205
New York
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The piston manufacturer should be able to tell you the recco skirt clearance for that specific piston and your engine. It's going to vary considerably with the aluminum alloy, forged vs. cast, cooling system, somewhat with the pin boss and skirt design. Very important: the difference in width across the pin boss vs. across the thrust axis is the "cam grind" or profile. The most common cam profile is the standard Van Norman “C”. It compensates for the way the piston shape changes during hard use, and it's fixed during manufacture, and no correction for this can be made by changing the skirt clearance. Your guess may be correct, or far enough wrong to cost you $$$.
Boffin Emeritus
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Re: Bore size vs piston diameter
[Re: Moparteacher]
#2326179
06/24/17 06:42 PM
06/24/17 06:42 PM
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Joined: Jul 2005
Posts: 636 Graz, Austria
DGS
OP
mopar
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OP
mopar
Joined: Jul 2005
Posts: 636
Graz, Austria
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Where are you going to find a .010" over piston? Or, any 440 piston that doesn't start at .030" over? Custom? It's likely to cost more than a shelf piston. And what about rings for a 4.330 bore? They're available but I only see 5/64, 5/64, 3/16 oil.
A replacement std piston is the same cost as a .030" over piston, and the machine work is likely to cost the same whether .010" over or .030" over. Plus a quality piston in std is more difficult to acquire than a .030" over piston. Most manufacturers don't offer std. pistons anymore.
Measure the taper in the bore. It may come round and straight with a good power hone with just a few thousandths taken off. Then run a forged piston a little loose with file-to fit oversized std rings.
So lets say is needs .005 to get straight and round 4.325". A forged piston is likely to have .003" clearance machined into it at 4.317". You now have .008" clearance and it's still a std. bore. No boring bar needed, just a hone.
I would like to bore not more than needed to have as much wall thickness as possible. Racetec/Autotec pistons are available in custome sizes so the .010 over shouldn't be a problem. The rings seem to be the real problem at the moment as I coulnd't find any 010 over rings in 1/16"
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Re: Bore size vs piston diameter
[Re: polyspheric]
#2326180
06/24/17 06:43 PM
06/24/17 06:43 PM
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Joined: Jul 2005
Posts: 636 Graz, Austria
DGS
OP
mopar
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OP
mopar
Joined: Jul 2005
Posts: 636
Graz, Austria
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The piston manufacturer should be able to tell you the recco skirt clearance for that specific piston and your engine. It's going to vary considerably with the aluminum alloy, forged vs. cast, cooling system, somewhat with the pin boss and skirt design. Very important: the difference in width across the pin boss vs. across the thrust axis is the "cam grind" or profile. The most common cam profile is the standard Van Norman “C”. It compensates for the way the piston shape changes during hard use, and it's fixed during manufacture, and no correction for this can be made by changing the skirt clearance. Your guess may be correct, or far enough wrong to cost you $$$. Minimum clearance required is .0035 to .0045
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Re: Bore size vs piston diameter
[Re: DGS]
#2326233
06/24/17 10:34 PM
06/24/17 10:34 PM
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Joined: Oct 2007
Posts: 4,205 New York
polyspheric
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master
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Posts: 4,205
New York
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WRT file fit: remember the ring circumference is the bore X Pi, so +.010" ring set is -.031416" on the end gap. Even if you get it down there the radial tension is higher than you want.
Boffin Emeritus
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Re: Bore size vs piston diameter
[Re: Al_Alguire]
#2326859
06/26/17 11:12 AM
06/26/17 11:12 AM
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Joined: May 2005
Posts: 1,961 Apollo, PA.
B1MAXX
top fuel
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top fuel
Joined: May 2005
Posts: 1,961
Apollo, PA.
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[quote=Al_Alguire]Well I thought the same about a .030" overbore. Surely enough meat for that with our dragster. So I did not bother sonic checking the block. Well the end result was this. The cylinder wall was roughly 2X the thickness of a Pringle! This was a 69 HP 440 block. I too was more concerned with the mains than the wall thickness of the block. Apparently I should have checked the cylinder walls too. As for the question at hand. I would make sure you can get a good ring for the finished bore size. Pistons are the easy part, they will build the clearance into them when manufactured, provided the info you give them is accurate and the bores are round you should be good. That block was doomed at standard bore . boring it .030 was not the problem there. However that brings a great point A sonic check would go along way to total piece of mind. At .030 we are taking .015 of the radius of the bore If .015 puts wall thickness to critical tolerances than the block was no good from get go.
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Re: Bore size vs piston diameter
[Re: DGS]
#2326971
06/26/17 02:15 PM
06/26/17 02:15 PM
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Joined: Feb 2008
Posts: 714 Central TEXAS!!!!
sr4440
super stock
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super stock
Joined: Feb 2008
Posts: 714
Central TEXAS!!!!
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quick look at the hastings piston ring site and I found 25 rings in the 4.330 size. but you better know your width and thickness before you have the pistons made.
Without Data, you’re just another guy with an opinion.
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