Author Topic: Rear Main Seal on a 1993 BMW K75S  (Read 812 times)

Offline stokester

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Rear Main Seal on a 1993 BMW K75S
« on: February 05, 2019, 06:33:55 PM »
I've finally gotten around to taking care of that nagging small oil leak and am pulling the transmission on my BMW K75S.

The final drive is out and the next step is to pull the transmission.  As with most vehicles with over 75K miles and especially motorcycles this one needs other things as well.  I found a fuel return line with cracks and will be replacing other known items such as the fan and fuel pump damper which because of ethanol (thanks feds) breaks down and destroys an expensive pump.  After all the new parts it should be good for another 75K+ :)

Stay tuned for updates!
Nick
Yorktown, VA

Offline DeadNutz

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #1 on: February 05, 2019, 06:42:26 PM »
Can you buy ethanol free gas in your area? That is all that I run in my truck and small engines. Truck gets much better mileage and the carbs on all the small engines stay in good shape.

Offline jabberwoki

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #2 on: February 05, 2019, 07:19:13 PM »
Yeah that ethanol is the Devils juice. I run real gas in the duke.
Is the need enough? or does the want suffice?

Offline stokester

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #3 on: February 05, 2019, 07:26:36 PM »
To be honest the cracking on the fuel line is from age but the expected deterioration of the damper is certainly from the corn juice in the fuel. 

Alas there are no convenient nor easily available places for non-corn fuel for me. 
Nick
Yorktown, VA

Offline slip knot

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #4 on: February 05, 2019, 08:40:41 PM »
I found ethanol free at the fuel supplier. even sells it at a somewhat reasonable $2.68/ gallon. With 5 gasoline tractors, 2 mowers 3 onans and 2 welders ethanol fuel is a real pain for me.


75K on a motorcycle is almost unheard of around here.

Offline Matt_T

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #5 on: February 05, 2019, 09:38:06 PM »
Paid $2.25 for ethanol free regular yesterday. A bunch of gas stations around here carry it which probably keeps the price down.

Offline DeadNutz

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #6 on: February 06, 2019, 10:00:02 AM »
Paid $2.25 for ethanol free regular yesterday. A bunch of gas stations around here carry it which probably keeps the price down.

Lucky you as that is a great price for clear gas. I can get 87 octane clear up in Carson City for about .30/gal more than regular. In Gardnerville I can get 91 octane for about .40/gal more than regular. For the increased mileage and smoother idling on the truck I consider it a wash.

Offline bmwrd0

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #7 on: February 06, 2019, 10:51:47 AM »
I did this on my old R100/7 but ended up having to do it twice as I forgot to change the o-ring for the oil pump. The only thing really hard about that was you needed a special socket to pull the swing arm bolts.

Offline Matt_T

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #8 on: February 06, 2019, 12:08:57 PM »
Lucky you as that is a great price for clear gas. I can get 87 octane clear up in Carson City for about .30/gal more than regular. In Gardnerville I can get 91 octane for about .40/gal more than regular. For the increased mileage and smoother idling on the truck I consider it a wash.

You're actually getting a better deal at 30 cents over. The E-10 was $1.90. Ethanol free normally costs 30 to 60 cents higher around here depending on when you catch it.

I am lucky in that I don't have to go out of my way to buy it though. Even the little country store closest to my place carries it.

Offline stokester

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #9 on: February 06, 2019, 12:09:38 PM »
I did this on my old R100/7 but ended up having to do it twice as I forgot to change the o-ring for the oil pump. The only thing really hard about that was you needed a special socket to pull the swing arm bolts.
Like this
Nick
Yorktown, VA

Offline stokester

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #10 on: February 06, 2019, 06:08:39 PM »
Removed the transmission/swing arm today along with the clutch assembly to gain access to the leaky seal.

The new seal needed to be installed .5mm proud of the engine case according to a TSB which could be a problem without a proper installer.  Thanks to the fine work of Ray, AKA goodfellow it was set to the proper depth.

Not sure if I'm going replace the clutch assembly, the friction disc still has plenty of life and the pressure plate looks good.
Nick
Yorktown, VA

Online goodfellow

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Re: Rear Main Seal on a 1993 BMW K75S
« Reply #11 on: February 06, 2019, 07:20:45 PM »
Thanks for the pics Nick -- great project!!