Boxerworks.com

Gidday Fellas,

Got the new seals, gaskets, clips, o-rings plus every other bloody thing laid out on the workbench ready to go, yep the heads and pots are coming off the 81 this Saturday as I have weeping push rob tub seals myself..

Keen to get into it and sort this thing....

I forgot to ask a question from my original post.

I am putting in new seals on this 1975 R90s. The BMW fiche lists two part numbers.

11-32-1-262-995
11-32-1-250-267

I believe the 267 number is up to 1975 and the 995 number is for '75 and later.

Do I need to know the serial number to determine which one? What would be the difference between them? Would installing the wrong one be an issue with leakage?

thanks,

jimmyg

Using the VIN on something like RealOEM is probably the best to ensure the right part. It's also good to know the build date of the bike. Putting in your VIN on RealOEM will show you the build date. The -995 number is for the '76 models (the fiche says from 8/1975). I think the reason for the change is that for the '76 models, the engine spigot opening was increased to 99mm...it had been 97mm. So, likely the change in opening necessitated some kind of change for the pushrod tubes and/or seals.

Kurt in S.A.

thanks Kurt, makes sense.

Now, the dumb follow up question, for valve cover gaskets, oil pan gasket, no sealant, right? And the gasket has printing on it that is to be oriented towards the engine? Something about one side of the gasket is treated to react with the heat from the engine to seal correctly?

thanks again,

jimmyg

Both the valve cover gaskets and the oil pan gasket can be installed only one way. They can NOT be flipped and installed backwards. I have used a thin layer of silicone sealant (or grease when I didn't have any) on paper gaskets in the past. It makes removing them so much easier down the road.

The way I remember it is to install the gasket so you can see the printing. In this case, the valve cover gasket printing would be away from the engine. And to date, I've never used any sealant on any gaskets that I've had to replace. There are some that need or could use it, but I haven't been there yet.

Kurt in S.A.

grant81rs wrote:Got the new seals, gaskets, clips, o-rings plus every other bloody thing laid out on the workbench ready to go, yep the heads and pots are coming off the 81 this Saturday as I have weeping push rob tub seals myself..

Not sure if your laid out parts include the cyl. head gaskets. For changing the pushrod tube rubber grommets, it isn't neccessary to separate the heads from the barrels; if you back off the torque on all six cyl head bolts, but only remove the nuts from the studs going into the crankcase, you can pull off the heads & barrels as one unit. And then push the gudgeon pin out to allow you to pull the head+barrel assembly off the piston. If doing so you can save your new cyl head gaskets for a later job.

tsa -

Are you pulling the cylinder/head completely off the studs or just enough to replace the seals? I'd be concerned about the two small O-rings and getting them pinched going back together.

Be sure and thoroughly clean the mating surfaces, then apply a thin layer of sealant. I would find it difficult to clean these surfaces with everything still hanging on to the long studs.

Kurt in S.A.

jimmyg wrote:II am putting in new seals on this 1975 R90s. The BMW fiche lists two part numbers.
. . .
I believe the 267 number is up to 1975 and the 995 number is for '75 and later.

Do I need to know the serial number to determine which one? What would be the difference between them? Would installing the wrong one be an issue with leakage?

For the crankcases with 97 mm cylinder holes, the pushrod tube diameters were smaller than those used for the 99 mm crankcase hole engines. ISTR 14 mm vs 18 mm. Measure te outer diameter of your pushrod tubes, this will show you which version rubber grommets you'll need. If you install the 18 mm grommets on 14 mm tubes, you are most likely to see oil leakage; for the other combination, you won't get the PRTs into the grommets. The holes in the crankcase (for the PRT rubber grommets) remained the same pre and post 1975.

Kurt in S.A. wrote:tsa -
Are you pulling the cylinder/head completely off the studs or just enough to replace the seals?

Yes, for the reason you mentioned; to clean every mating surface until its spotless. Wrt the small O-rings around the upper cylinder studs, they were not used on the (, or at least not my late '73 model) /5. For later engines that uses those small O-rings, you obviously can't replace them without pulling the head+barrel assembly completely off the studs. Same goes for later engines that uses the big O-ring around the cylinder base; the barrel (with or without the head attached) will have to be pulled off fully to allow replacement.