ring end gap
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Tourer
Joined: Nov 2007
Posts: 313
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From: Ontario,Canada
ring end gap
I have a set of 4.065 cp pistons ,the instructions with the pistons say to gap the top compression ring at bore x .005 and the 2nd compression ring at bore x .006 this is for motorcycles and atv's,this seems a little excessive to me was wondering what the engine builders on this site are gapping there cp pistons at? and also what the negative if any conseqences of excessive ring gap are.
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Tourer
Joined: Nov 2007
Posts: 313
Likes: 2
From: Ontario,Canada
OK thanks for the replies ,I just thought that maybe the piston manufacturers might put this spec. in there instructions to be on the safe side and avoid customer complaints if rings are gapped to narrow resulting in piston failure ,so I thought I would throw it out there and see what others have gapped there rings at,because I didn't want to have an oil burner when I put it back together,so yes I guess I shouldn't be trying to re invent the wheel and go by the instructions that came with the product they know it best.
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From: Hollis
OK thanks for the replies ,I just thought that maybe the piston manufacturers might put this spec. in there instructions to be on the safe side and avoid customer complaints if rings are gapped to narrow resulting in piston failure ,so I thought I would throw it out there and see what others have gapped there rings at,because I didn't want to have an oil burner when I put it back together,so yes I guess I shouldn't be trying to re invent the wheel and go by the instructions that came with the product they know it best.
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Tourer
Joined: Nov 2007
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From: Ontario,Canada
no doubt in my mind,thanks for the help.
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Banned
Joined: Mar 2007
Posts: 3,706
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From: Woodstock, Ont , Can
CDN. RG: The gaps are norm for these kind of aircooled setups. Ever wonder why the second ring has more gap than the top. Well, I did and found this expanation that I thought I'd pass along to those interested.
Thinking on piston ring gaps has also changed. In the old days, second ring gap specs were tighter than those for top rings because they didn’t see as much heat. But this didn’t account for inter-ring gas-pressure buildup between the top and second rings. If the pressure between these rings equals or exceeds the pressure above the top ring, it can cause the top ring to lift off the bottom of the piston ring groove and lose contact with the sealing surfaces. It also inhibits the ring’s ability to transfer heat from the piston. To keep inter-ring pressure from becoming a problem, the current trend is to create an easy escape path for the built-up pressure by gapping the second ring larger than the top ring. Another benefit is that because gas pressure is now directed downward towards the sump, any oil that has collected in the ring pack areas will go with it.
Ron
Thinking on piston ring gaps has also changed. In the old days, second ring gap specs were tighter than those for top rings because they didn’t see as much heat. But this didn’t account for inter-ring gas-pressure buildup between the top and second rings. If the pressure between these rings equals or exceeds the pressure above the top ring, it can cause the top ring to lift off the bottom of the piston ring groove and lose contact with the sealing surfaces. It also inhibits the ring’s ability to transfer heat from the piston. To keep inter-ring pressure from becoming a problem, the current trend is to create an easy escape path for the built-up pressure by gapping the second ring larger than the top ring. Another benefit is that because gas pressure is now directed downward towards the sump, any oil that has collected in the ring pack areas will go with it.
Ron
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