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Discussion Starter #1
High guys, just wondering how far the ring can stick out past the piston. Just had a set of BBC Diamond pistons made with piston ring groove depths of .190" top , .200" second and .190" oil.
They supplied a Hastings ring pack with .203" top , .186" second and oil .195". Obviously the top is what I have my main concern with. Piston ring land diameter is around .050" smaller than the skirt diameter.
 

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High guys, just wondering how far the ring can stick out past the piston. Just had a set of BBC Diamond pistons made with piston ring groove depths of .190" top , .200" second and .190" oil.
They supplied a Hastings ring pack with .203" top , .186" second and oil .195". Obviously the top is what I have my main concern with. Piston ring land diameter is around .050" smaller than the skirt diameter.
Call Diamond and tell them what’s up
 

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Idiot Savant
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It used to be so simple when everything was D Wall rings. Now the ring manufacturers are all over the where.
 

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Discussion Starter #6
Things seen to getting harder now a days. No one seems to give a shit about anything any more. Get a set of custom pistons and ask for them to supply rings to suit and they still cant get it right. In future, I'll have to give them the ring groove depths to suit my rings I suppose. I thinking they will change the rings with something that will have a lot of back clearance. Is there a max. amount of back clearance?
I remember talking to some one in Total Seal and I complained that they supplied a ring with .165" radial going into a .220" deep groove in the piston and they said that it means shit and has no effect. I always like to see minimum back clearance. Thoughts?
 

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Idiot Savant
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Things seen to getting harder now a days. No one seems to give a shit about anything any more. Get a set of custom pistons and ask for them to supply rings to suit and they still cant get it right. In future, I'll have to give them the ring groove depths to suit my rings I suppose. I thinking they will change the rings with something that will have a lot of back clearance. Is there a max. amount of back clearance?
I remember talking to some one in Total Seal and I complained that they supplied a ring with .165" radial going into a .220" deep groove in the piston and they said that it means shit and has no effect. I always like to see minimum back clearance. Thoughts?
Most of the business I do is piston sets. I get the ring set radials before I lay them out on all the custom ones. OTS is a bit of a guess. Total Seal has their numbers, Hastings has theirs, NPR has theirs...and they aren't shy about changing them.

It's always better to have a tight back clearance, but it really isn't the end of the world if it's loose. Guys used to back cut the D-Wall rings back in the day, and they worked fine.

Also, you're right, the land diameter is .040 smaller, the top land might be stepped or tapered .010 smaller than that. It you have it sticking out a few thou, it will never cause a problem. If the lands hit the cylinder walls, the rings are the least of your issues. .013 is a bit much though.
 

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Like Mark stated in post #5, life was much easier for all of us when all ring manufacturers followed the SAE 'D' wall specifications. Now everyone (ring manufacturers) has several radial widths available for most applications. I always recommend that the piston manufacturer be consulted for the specific brand and size of rings that they recommend for use with their pistons. Most current high performance pistons are being built with very exacting groove thickness and finish, BUT there is slight variation in the ring thickness offered by the ring manufacturers. This means that one brand of ring might have .0010" to .0015" side clearance in the groove and another manufacturer's ring might have less than .0010" side clearance which could lead to major problems.
 

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FYI - If you did not know it, they sell shim stock which can be placed behind the ring if there is too much radial clearance. Just so you know it’s not the end of the world if that becomes an issue. May give you more options with rings found locally?
 

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Discussion Starter #13

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Idiot Savant
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No...but I'll see if I can get them for you.


If the pistons were cut for a standard "D" wall ring, the depth would be .212. (Bore size/22 - .005) I have no idea what they were thinking.
 

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Regardless of what ANY ring or piston manufacturers bulletins may say, or what their tech people may say, excessive top ring to top groove back clearance wail ALWAYS be a detriment to performance.
 

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Excess crevice volume above or behind the top ring is never good.
.25cc in a NASCAR Ford was 5 hp
 
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