Posted by Vaughn [172.68.189.136] on Monday, January 14, 2019 at 14:15:24 :
In Reply to: Re: Good Grief! posted by Andrew in MI [162.158.74.66] on Sunday, January 13, 2019 at 16:56:35 :
Ok, pistons on the older-style, long-stroke, small-bore engines were generally the full-skirt type due to angle in connecting rod during strokes (minimize piston wear). Then, as lower hood lines and oversquare engines (where bore dia. is larger than stroke lgh.) became popular, the semislipper and fullslipper pistons (reduced skirts) came into use. On these pistons, the number of rings were reduced to two compression rings and one oil-control ring. One reason for designing a slipper piston for use on the short stroke oversquare engine, the piston skirt had to be cut away to make room for the counterweights on the crankshaft. The slipper piston is also lighter reducing inertia load on the engine bearings making a more responsive engine. None of this is due to new metal applied in engine development although new metal developments were a product of redesigns and applied but styling re-designs in vehicles.
On the older style engine, 4 rings are used, 2 for oil due to the length of skirt and length of stroke to control the buildup of oil between piston skirt and cylinder wall. When I look at the design of the piston and the two oil control rings, the oil assembly ring seems to be best for the 4th groove. Ring manufacturers may recommend the 3rd groove for some reason, but to me placing the assembly in the 3rd groove creates a
“bottle neck” in the oil removal process. The cast iron oil ring slots are not that great to remove large amounts of oil and placing them in the 4th groove defeats their purpose, whereas the oil assembly rings are designed to move large amounts of oil and placing them in the 3rd groove defeats their purpose.
The rings in my engine are two cast iron oil control rings that came with the pistons I installed (Military). It works and I’m sure more oil is getting past the rings to the combustion chamber that will add to carbon build up, the engine doesn’t smoke, so I am ok with it, however it’s not my preference. All I can say is go with what you are comfortable doing, contact the manufacturer maybe there is a compelling reason, talk to mechanics, there are variety of opinions out there, and for me, I’ll still go with the assembly in the 4th groove dictated by design.
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