Top bearing Yammie 40

[Burley_Boy]

When I pulled one of my engines downto check the electrics under the top flywheel, (Yammie 40 84 model), I found the top bearing on the crankshaft very dry and I put some grease there prior to putting the flywheel back. Having flicked through a general service manual it said after a complete head-job to oil this bearing ie not grease. I got to thinking if this is the case should this bearing be periodically oiled and if so .... how?
The workshop manual was inconclusive so I'd be interested in comments.

[aido]

the upper bearing is pretty important.
it's going to have a seal, i doubt you can grease
the bearing without getting the seal out first.
probably no harm done if you put some grease
on the shaft to seal area.
the actual bearing is probably oiled by the same method
as the other bearings. like the fuel/oil mix.
some motors have a dedicated oil line to the upper
bearing though.
good idea to change the seal when you get access to it.
any leaks there are bad and can lean out the top pot.

[NQCairns]

Yeah like aido says, on premix engines it is migrated oil from the adjacent cylinder crankcase that travels past thrust washers etc to the bearing, with up to 6000 pulses a minute enough oil gets there to do the job. New tec jobies (dfi and 4st)use pumped oil through galeries in the crank like a car or so I understand.nq

[Burley_Boy]

pulled apart another 40 today and I see what you mean. This bearing was dry as... on the Yammie.
I'll have to have a look at why. Buggered if I know why yet.

[NQCairns]

A bearing will flog out fairly fast if not lubricated enough, it will show signs of blueing that cannot be missed if stressed, if it is still in good condition then the system is working well enough, those bearings seem oversized I guess to account for the tough job they do.
Some engines run 100:1 premix and still the bearings last :o.

[Burley_Boy]

Can't tell how blue it is due to the black charred colour.... :o