rear main seal

[JJH]

1979 R65.  I have a lot of leakage from the shelf under the gearbox.  After a ride (10-20 miles), it will leak out I estimate 5 ml or so.  It does not smell like gear oil, so I am pretty confident it is motor oil.  So the question is what is the danger of keep running this for the summer/ fall.  Obviously I will have to keep an eye on the oil level, but what danger is it to having it leak? 

I know it is time to replace seal and o-ring, but the weather is nice, and unfortunately I am out of cash for the tools/ parts that will be required.  Getting a few more months will help my finance and more importantly mental situation.  I find that a 20-30 minute ride in the countryside works much better than any pill the pharma industry can come up with

Thanks,

John

[Barry]

As long as that oil doesn't accumulate so much that it gets onto the rear wheel then no particular danger if the oil level is monitored.  Even though you will be keen to not let the oil level run below the  minimum mark I would still avoid filling up to the full mark because that will increase crankcase compression which won't help with the oil leak.  I would fill to half way and monitor it regularly.   

A 79 has limited air space in the crankcase so filling to the full mark should always be avoided in any case. BMW in a service bulletin even recommended that you shouldn't fill it above half way.  In acknowledgement that air space was tight, R65's got a bigger sump in 81 which had both more oil volume and more airspace.

You didn't mention recent usage of the bike. If by chance it's been stood unused for a time then there is a possibility that the  seal may well improve on it's own.

[Bob_Roller]

What kind of oil are you using ?
Regular oil, or synthetic ?

[JJH]

Barry,

The bike has not had much use lately as I have been working on some pushrod tube seal issues.  I would guess only about 500 miles this year, maybe 100 since changing out the tube seals.  The oil level usually finds its own level at below 1/2.  If more is put in, it would normally just leak from the "breather?" holes in the middle of the crankcase.  I did just change the oil (with the pushrod seals), so it was near the full mark.

Bob,  I just use Castrol dino 20W50 for motorcycles.

[Barry]

If needed I'd take some oil out to adjust it down to the half way mark and then just ride it while you monitor the situation with the seal.  A 79 really shouldn't ever be run at the full mark.

Does it by any chance have the "turkey gobble honk"  which is attributable to crankcase compression and breather/seal issues.

[Justin B.]

Most of these models "prefer" to run about half-way between marks and will barf out what they don't want.

[Barry]

I agree everyone should run at the halfway mark but for the early model it's even more important.  To put it in perspective the 78-80 models have the same air space at the half way mark as the 81-84 models do when run at the full mark.

[JJH]

Barry et al.
A very depressing tale.  Bob had asked what type of oil I used, but I lied.  I normally use Castol, but they were out so I used Valvoline 20W50 (vr1).  An interesting thing about the Valvoline bottles (and most others) is that the 20W50 bottle looks identical to the 50 weight bottle.  I picked the first bottle (20w50) and then picked up the 2 bottles behind them.  So fast forward, I put 2 bottles of 50 weight and about 1/2 of 20W50.  It was only luck that the empty bottles were still sitting in my dustbin.  This is what I have been riding with for ~100 miles. 

So I drained the old oil, filled with new oil 20w50 for sure!  Unfortunately after this I started the motorcycle, instead of a small seep at the pushrod seal, it was now spurting and bubbling oil.  I didn't really bother with checking how the main seal was, at this point I am too embarrassed and angry with myself to investigate.  I ordered new pushrod tube seals and O-rings.  Once they are in I will evaluate the main seal leaking.

Even with all this I am very grateful for all the help this forum has provided me.

John

[Justin B.]

I may be totally off-base but I wouldn't think that straight 50W in an air-cooled motorcycle, in Missouri, in the summertime, would be harmful.  Maybe International Falls, MN, in Jan?

[JJH]

I'm not the oil guy, I am just going on the excess pressure from heavier weight oil?  But you are correct, it is hot (for Missouri).

[Barry]

At 100 Deg C  Valvoline straight 50 is as near as damn it exactly the same viscosity as 20W50.  It is a lot thicker when cold so the oil pressure would be much higher regardless of the relief valve. Even then I don't see how it would cause pushrod tube seals to leak or the rear main seal to leak as neither are under oil pressure.

http://content.valvoline.com/pdf/vr1_racing.pdf

[Bob_Roller]

The bike is about 38 years old and most likely the seals are factory  original .

Rubber hardens with age and heat .

It's about time to change them, this is not uncommon on older vehicles, you've probably never operated a vehicle this old before, I know this is new to me as well, I've done work on my '81 R65, that I have never done on any other vehicle and I usually keep them 20-25 years .

I'm the original owner, the '81 was manufactured in 09/80 and I've owned it since 01/81 .

Plus 24 years of desert heat operation .

[mrclubike]

You didn't hurt anything with the 50w
Do check the gallery plugs on the left side of the engine
When they leak the oil runs back off of the rear  and it looks like it is coming out of the rear of the engine 
Mine does it

[Tony Smith]

I may be totally off-base but I wouldn't think that straight 50W in an air-cooled motorcycle, in Missouri, in the summertime, would be harmful. 

Well it is winter now in Australia and last weekend I drained the 20W/60 weight oil and replaced it with my "winter" oil - 20W/60

Ok, so we have a somewhat warm climate and very mild winters, I just couldn't help myself.

[peteremc]

Tony, thanks for reminding me that:

(a) it's winter at this time of year
(b) maybe I also need to replace my 20W/60 with fresh 20W/60

OK, I couldn't help myself too. Nice (most of the time) to live in the tropics.

(From someone who lives almost around the corner from Tony)