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Author Topic: M91 Crankcase oiling  (Read 135 times)


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M91 Crankcase oiling
« on: August 27, 2019, 02:19:59 pm »
How are folks oiling the crankshaft mains and rod bearings - if at all? 

I'm had another observation about this new engine - I've noticed quite a lot of crankcase air pumping and/or windage coming from the vented cap on the crankcase.  I'm wondering if that is the source of the increased engine heating that the M91 has shown over the M90.  I'm thinking this engine may run much cooler with a properly vent crankcase - maybe just removing that cap would be enough.  I just had an additional thought - I wonder if the pressure in the crankcase (resulting from the downstroke of the piston) could be the causing of some of the piston 0-ring issues that have been reported.....


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Re: M91 Crankcase oiling
« Reply #1 on: August 29, 2019, 01:10:49 pm »
Good thoughts on the ventiation. I have been thinking similr and will try leaving the cap off. I have also been thinking about cutting some larger openings into the crank case area.

As for the main bearings, they are needle bearings. I find that when I place a drop of synthetic clock oil next to them on them outside, it is wicked in immediately... at least when it isn't running. I believe this also works while it is running.

Running them slower and with plenty of oil in the fuel also goes a long way toward keeping them cool. WD40 is not a good lubricant.


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