Posts
674
Joined
1/1/2008
Location
Hampden, MA
US
Fantasy
2530th
Edited Date/Time
1/28/2019 2:25am
As the title suggests, how important and what is the purpose of positioning the oil ring gap as shown in this screenshot from a KXF manual?
I’ve always done it this way, but it’s a pain to get the end gaps aligned in these positions. Let alone trying to get the gaps to stay in place when compressing the rings & slide the cylinder on. When I broke down a brand new KXF, I made it a point to see how the expansion ring and the two oil rings were oriented. They were NOT positioned as shown in the manual. I’m not talking about the top ring, that one is easy to get right.
I’m just curious if I really need to stress this for future builds. Thanks in advance.
I’ve always done it this way, but it’s a pain to get the end gaps aligned in these positions. Let alone trying to get the gaps to stay in place when compressing the rings & slide the cylinder on. When I broke down a brand new KXF, I made it a point to see how the expansion ring and the two oil rings were oriented. They were NOT positioned as shown in the manual. I’m not talking about the top ring, that one is easy to get right.
I’m just curious if I really need to stress this for future builds. Thanks in advance.
.
The reason for rings facing forward and rear is because they also tell you not to align them with the wrist pin bores.
That is incorrect, the ring gap size does not change with upstroke or down stroke. It only changes with heat.
Every other ring and spring expander ring should have the gap 180 degrees different. Thus you get the longest distance from one gap to the next,
This is mainly relevant on the oil ring set.
Never align ring gaps to the wrist pins as the piston is smaller in this area and the gap more exposed to blow-by and oil.
"unless there is a pin to locate the rings, they will constantly rotate on the piston."
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The Shop
Anyway, having built engines for all sorts of racing (even supercharged land speed stuff) and testing engines on a very accurate Schenck dyno, measuring power output at the crank, I do find that it does matter where the ring gaps are.
Yesterday I bent the edge of one of the oil rings closest to the gap when trying to slide the cylinder on. I’m glad I could tell something was wrong, it required more force than usual for the piston to slide into the bore. If I didn’t notice I’m sure it would have trashed the cylinder.
Not when they rotate on the piston. The only way to guarantee a ring will never rotate on a piston is to put a pin in the ring land.
I would not reuse it.
https://www.highpowermedia.com/blog/3954/rotation-of-piston-rings
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