I'm using less oil! I changed the main & rod bearings on my 1980 slant back in June. Prior, I was getting about 600 miles to a quart. Now I'm getting 1500 miles. Rod bearing clearance was in the range of 0.0035 - 0.0040. The new bearings clearanced at between 0.0015 & 0.0020. So tighter clearances = better oil control: less oil is being thrown on to the cylinder walls. If I didn't have an oil leak at my oil cooler adapter, I guess I'd get maybe 2500 - 3000 miles/quart. 150,000 and running strong! 80% running time at 60-70 mph.

Mitch

Cool ! Did you replace the bearings with the engine in-chassis ? What did your crank journals look like?

Did you use stock bearing size or undersize?


De Soto Frank
(driving the 1964 Valiant Signet 200 convertible, known around town as "the Blue Cloud".... )

Hello Frank, in -chassis. Journals looked very good, although I did not mike them. Bearings were standard.

Mitch

I also have an '80 cast crank motor which has excessive oil consumption. I measured the compression on each cyndiner at 170lbs, with very little variation. It does not make sense that the motor would use so much oil unless too much oil is being thrown unto the cylinder walls.

What was your oil pressure before and after the crank swap?

My oil pressure before & after was/is about 52 highway/35 idle, but I had long ago installed a TRW high volume pump. New, the engine used maybe 1/4 quart between 2500 mile oil changes. Compression then and now - before milling my head, was about 145-150. If you're not losing oil through the valve guides/seals and not leaking it out of the engine, then it's going past the rings. It is possible to have good compression together with poor oil control, but if your rod bearings have excessive clearance - as did mine, then this - by itself, will increase your oil consumption. What is the mileage and oil consumption on your engine?

Mitch

My motor is an '81+ hydrualic motor, I don't know what it came out of. I have not meaured oil pressure. I also found another cast crank motor with clean bores and worn crank, someone had replaced its oil pump. Other than the bearings being a little more narrow I don't know of a reason that cast crank bottom ends might wear faster. A little STP helps, keeping the highway speed down also seems to help. I think I'll keep driving it as is. Until I learn otherwise, I'll try to rebuild only steel crank motors.