It's been a while since I've posted...still on my quest to build up my rocket block and am still working on specifying parts for the beast...
Anyway, my question is regarding pistons with high wrist pin locations that intersect the oil ring. I cannot seem to find any drawings or descriptions of how the oil rail support works. It sounds like it is an extra piece which fits onto the piston somehow to bridge the gap that is necessary to fit the pin in place, but I can't seem to picture how this works...
So perhaps you wise engine gurus will help me understand how this works.
It's just another thin oil ring basically, very similar to the one's that come with the oil control rings. The only difference is that they have a raised dimple which keeps it located so that the support ring ends are not over the wrist pin. These support rings come with the pistons if they are required and the oil control ring groove will be machined a little wider to accomodate the additional support ring.
Okay, I think I'm starting to see how that works...
I did see an image where a pin had been placed in the oil ring groove so that the oil ring gap fit over the pin and kept it there. If the oil rail support has a dimple that acts to locate the oil ring, how does the support stay located??
The raised dimple prevents the oil support ring from rotating. The oil support ring is installed so that the raised dimple is located over the piston pin bore. With the dimple facing down into the piston pin bore, it cannot rotate past the edge of the piston pin bore where it intersects the oil ring groove. It's an interference fit. This keeps the end gap of the oil support ring from ever becoming located above the piston pin bore, thus providing support for the oil control rings and allowing them to rotate normally.
That is not the ONLY way it's done, but Monty is correct in stating that what is needed will be supplied by the piston manufacturer. If in doubt, ASK, when you place your piston order. Good luck, and...
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Piston Oil Rail Question...
