R51/3 what oil

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Darryl.Richman
Posts: 2087
Joined: Fri Oct 27, 2006 3:00 am

R51/3 what oil

Post by Darryl.Richman »

Oh, oh. Now you've done it, you've gone and openned up the wintertime "oil thread".

If you haven't changed the seals in the final drive and transmission, then 30 weight engine oil is recommended. If you have changed the seals in the last 40 years, then you can use GL-4 or, perhaps, GL-5 gear lube. There is a certain amount of controversy about whether the formulation of GL-5 will attack the "yellow metal" -- brass or bronze -- parts.

For the motor, there is endless controversy about whether you should use a) straight weight low or non detergent oils (30 weight summer, 20 weight winter); or b) modern multiweight (20W50) motorcycle or SG rated auto oil; or c) any modern 20W50 oil.

Having laid out the possibilities, I will let others argue for their particular choices.
--Darryl Richman

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schrader7032
Posts: 7254
Joined: Fri Oct 27, 2006 3:00 am

R51/3 what oil

Post by schrader7032 »

As Darryl has said, this is a controversial subject. As for engine oils, I initially have been using BMW 20w40 in my R69S, but I think I'm going to 20w50 next time around. My reasons are several: I live in South Texas and it doesn't get that cold. Also mutli-viscosity oils are strange animals. My latest reading/understanding is that the 20w part is the base oil with "bits" added to allow it to behave up to a 50w oil under the right conditions. However, as time goes by, the additives get sheared/reduced and the oil might be able to change to only 45w or 40w. I really want the 40w feature and if I start with a 20w40, the 40w part will degrade over time. So, I think I'm going to start with the 20w50 and it fals back toward the 40w.

The BMW oil is rated at SG. This rating ensures that it still have a fair amount of ZDDP, a zinc-phosphate combination which provides good anti-friction qualities. However, a seem to recall an issue with our engines having roller bearings as opposed to the later bearings which do more sliding. I haven't quite figured that one out yet...maybe someone can enlighten us.

Use a quality oil and change it often...that's what it comes down to.

Kurt in S.A.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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VBMWMO
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Joined: Sun Aug 23, 2009 7:49 pm

R51/3 what oil

Post by VBMWMO »

do i use in my 1951 R51/3 engine/ gearbox/ bevel drive please?
Dedicated to the Preservation of Classic and Antique BMW Motorcycles.

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