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Location:
Lost in the K hole
Registered:
May 2002
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 fly-cuts :: how deep to dig ??
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Sun, 27 October 2002 14:17
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im looking at a potentially machining 2 to 2.5mm deep flycuts into my pistons (which have samll flycuts in em already) to accomodate a nice lumpy cam...
anyone have an idea how to tell if this is too deep (thus compromising structural integrity of the piston) without sacrificing a piston and cutting it in half???
any general rules on flycutting i should know about?
rules of thumb for minimum clearance of valve to piston?
cheers
ed
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Location:
tallahassee FL usOFa
Registered:
May 2002
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Re: fly-cuts :: how deep to dig ??
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Sun, 27 October 2002 15:42
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is this just to keep it non-interference? even though it's only necessary for "floating exhausts" and/or big lift & duration, the manufacturers seem to cut'm for both. probably so the piston can go in both ways.
i don't know
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Location:
Eskilstuna, Sweden
Registered:
May 2002
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Re: fly-cuts :: how deep to dig ??
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Mon, 28 October 2002 00:06
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This may not help you too much, but here goes.
I doubt if there is anyone on this forum who can give you the definative answer, I certainly can't and as fly cutting of pistons etc is a exacting art form due to the nature of pistons and valves not liking to touch each other I WOULD strongly suggest getting an engineering shop to answer your question.
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Location:
Brisbane / Gold Coast
Registered:
May 2002
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Re: fly-cuts :: how deep to dig ??
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Mon, 28 October 2002 01:58
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Depends on the piston, ie, if it's forged then 2.5mm should be thick enough for the metal on the top to hang together, and if it's cast then 3mm would be better. If you're running boost, then add about 0.5mm to that.
You need a clearance of 0.060" minimum from valve-to-piston at all times.
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Location:
Lost in the K hole
Registered:
May 2002
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Location:
Lost in the K hole
Registered:
May 2002
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Re: fly-cuts :: how deep to dig ??
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Mon, 28 October 2002 11:04
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ok, how does this sound like for a plan:
#1- find spare piston and cut in profile where the existing flycuts are to see how much meat is in the piston crown.
#2- given they are cast, allow 3mm, and calculate max flycut depth
#3- install pison in block, rotate to TDC. install head on block, and set both intake and exhaust valves to required lift height (say 11mm).
#4- calculate how much material has to be taken out of pistons to allow above said 11mm valve lift plus an extra 1.5mm. compare to max depth as calulated in #2 and if ok, go machine it.
sound about right??
cheers
ed
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