9 second bagger?
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From: poway
I think he's thinking cylinder spigots which also needs to be trimmed.. George mentions cutting the rear cylinder piston for the pistons to clear each other.. NO need to cut the front.
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If you cut only one piston the cut has to be much larger and really unbalances the one piston futher. As for the spigots they both have to be cut short and the pistons pull out of the bottom more and more as the bore sizes increase. There is just no other way around it, plus the two case alignment dowels get in the way!
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From: poway
If you cut only one piston the cut has to be much larger and really unbalances the one piston futher. As for the spigots they both have to be cut short and the pistons pull out of the bottom more and more as the bore sizes increase. There is just no other way around it, plus the two case alignment dowels get in the way!
Not really that much more material. The brow part of the cut at the edge of the skirt is the same. The angle back is different. The single piston cut is 45 degrees while the 2 piston cut is 22.5 deg each. You cut the rear cylinder as the thrust side is not cut.. Cutting the front piston removes thrust side skirt. The 116 SnS TC kit I had only had the rear piston cut. My 113 SnS Evo motor is the same way.
Make a thicker dowel, smaller hole and bore one side of it out. The early TCs had an O ring on that dowel. Later TCs and M8 don't but they use the same dowel.. It's 9/16 in diameter with about a 0.4" hole.
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As for remaking the dowels it doesn't do any good when the support material for the dowel is gone! Now you could press plugs in and weld in place then rebore for a smaller dowel. That means you plug both case halves and remachine both halves, which no one is currently doing. Problem with that is now you are restricting the oil return from the heads, so it's easier to just put solid dowels in place them drill the heads and run external oil return lines down to the camchest,
While all this can be done it makes for a bunch of one off special parts.
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From: Lake Geneva WI
the moonshine hp guys were talking about this. never would have thought of something like that.
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Both sides of the pistons are thrust sides! One side has a little more but due to the rod angles and the 45 degree spacing both sides see plenty of wear. So, IMHO cutting one piston all out, and the major imbalance that causes to the piston and ring package is worse than cutting much smaller amounts from each piston. In either case, it's not for a long life engine to begin with.
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From: poway
Both sides of the pistons are thrust sides! One side has a little more but due to the rod angles and the 45 degree spacing both sides see plenty of wear. So, IMHO cutting one piston all out, and the major imbalance that causes to the piston and ring package is worse than cutting much smaller amounts from each piston. In either case, it's not for a long life engine to begin with.
4 1/4 bore pistons from wiseco..
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It not just cylinder pressure at work here! The rod angle has a major effect on it. This is why we shift the pin center line in the pistons, to help balance the pistons but most people now days want to make one piston work in both cylinders and you cannot do it with a shifted pin location. If the pressure was 5000 psi spread across the piston it would travel straight down the middle with even pressure on both sides if it were not for rod angle! Also the M8 pistons are shorter to begin with than most TC pistons like you pictured due to the engine layout. When the piston it allowed to twist in the cylinder with too short of skirts, ring wear is greatly increased! With the shorter cylinder REQUIRED for a 4.600" bore more of the piston skirt is hanging out of the cylinder bottom with nothing but air supporting it, allowing the piston to twist and cause contact with the cylinder in areas it is not design for as well.
Last edited by Steve Cole; Sep 29, 2022 at 07:30 PM.