A point came a while back where getting oily boots every time I took a ride on the R100RS was really beyond a joke. I took my usual course of action which was to park the errant bike in a corner of the garage and move on to something else that worked slightly better. A few months on having now broken that bike which I had moved on to and continued the cycle my attention turned back to the Beemer.
I placed an order for a top end gasket kit and sparkly brand new stainless pushrod tubes from Motobins. The parts arrived next day and then I sat on them for another couple of months. A few days ago with all the extra lockdown workshop time many of us have been experiencing of late I decided to knuckle down and do the job.
For some reason it seems like it might be useful to share the experience with others... Two points first though:
1. I take a perverse satisfaction from doing jobs on my bikes without workshop manuals and taking the time to work everything out for myself as I go along. I only refer to a manual if I get really stuck. So, if you are like me please feel free to read on and then ignore all to experiment for yourself.
2. This was a really easy and fairly quick job and I wish I had done it earlier rather than put up with an incontinent bike for quite so long.
First job should be to clean up the dirt and oil from all around the heads, barrels and base of the barrels. This should be before even ordering parts. If I had done it the correct way round I would have found out that my bike already had stainless pushrod tubes and I would not have then bought another set and then sat on them for several months - way too long to send back for a credit note
Next up remove the carb by undoing all the jubilee clips and wriggling it free. It's easiest if you take the carb to airbox connector tube off first. Remove the downpipe lock ring - easy if you always keep the threads lubed with copper grease. Valve cover off next then spark plug out.
Take the head off next, always just slightly loosen each holding nut before undoing any single one all the way.
Lay it all out on a clean cloth or sheet of paper in the order it comes off and in the right position.
Turn the motor manually so that the piston on the side you are working on is at top dead centre or thereabouts. Wiggle the barrel to free it off, give it a tap with a leather mallet if necessary. Someone has previously tapped the fins on my barrel in the wrong place and too hard.. Slide the barrel up to the skirt of the piston so that the gudgeon pin is exposed. The first side I did I exposed the rings which meant that I ended up taking the barrel all the way off and then had to remove the gudgeon pin and piston to re-assemble and get the rings back in the barrel safely. As I learnt (and would have surely known if I had used a manual!) there is no need to do this at all, it's perfectly easy to replace the seals with the barrel sitting as per the above picture. On the plus side I discovered that the bores on my bike are in very good health, far better than I had expected.
The old rubber seals for the pushrod tubes should come off easily. I cleaned the mating faces of the base of the barrel and crankcase and applied a smear of gasket sealant before re-assembly. In an ideal world you would replace the o rings on the upper studs but this is an extra complication I personally didn't want to bother with and in my mind isn't really necessary. If you really want to replace these o rings you can of course pull the barrel off altogether or remove the studs with the barrel in situ to fit new ones. Now put the new seals in place, make sure they are aligned (there should be an arrow to face downwards but even without the marker the alignment should be fairly obvious).
Slide the barrel back in - it wont go all the way until you get the head on and tighten it down a bit. The new seals need some pressure to seat themselves.
Now back on with the head and rockers.
For the head bolt torque settings and valve clearances there's a handy table for all 1970-85 models on the Horizons Unlimited site: https://www.horizonsunlimited.com/tech/R-1970-85-techspecs
Once again, I strongly recommend using copper grease on the exhaust ring thread.
Once all re-assembled move over to the other side and repeat.
And now you can go out for a test ride wearing your finest brogues.
Thank you forr this
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