Attention, here comes a bit of smart kit - a BMW R86. This isn't a typo, but a bit of clever mix 'n' match game. So what we started out with here was a BMW R45, which in its first stages of life grew to a much more healthy R65. As you surely know, a R65 runs a 82 x 61.5 mm bore and stroke combination. Now there isn't much wrong with that. It's a bit bland in stock configuration, the phrase "not quite a powerhouse" springs to mind, but it's a very decent commuter.
Let's just say there's no replacement for displacement and we have a little gander at what else BMW has got on the shelves. A BMW R100S runs a bore and stroke combo of 94 x 70.6 mm. I say I wonder if that could be made to fit... (As this is a blog post on the conversion you obviously know the answer already!)
To be fair, there's a German company who sells it as a kit for such a compelling price that I haven't even bothered putting the same kit together myself.
Four nuts holding the rockers on plus two more holding the cylinders to the heads.
The pushrod-tube-seals were well and true past their prime. They hadn't started leaking (yet), but honestly it would only have been a matter of time.
Splitting heads and cylinders is easy as there are studs poking out, which only take a gentle tap and then release the lot.
BMW gudgeon pin clips are probably made from the toughest and most springy steel known to man, but other than that, there's not much to installing those pistons and cylinders.
Only a smear of sealant around the two top studs is required, the rest relies on the o-ring. Let's see if this is going to leak.
Nice thing about this job, there's only one actual special tool required and that's a special spanner for the exhaust nut.
Fire the old girl up...
... and run her in gently. 😏
A bit of rejetting and some other carb-work might be due, as it originally had fouled one plug, because of a certain lack of synchronization.
And another shot of the bike as I am actually quite fond of it, but don't let Chris now or he'll take the piss of me forever for that statement.
So what's my verdict: if you already have a high-mileage R45/65 said kit is well smart and if the pushrod tubes are leaking, well not that much extra work to do. I admit with the engine being rather short stroked, it would benefit tremendously from a free flowing exhaust and different carbs and if you wanted it a bit more sporty, you'd probably throw in the right kind of cam and then end up with a nasty backroad-scratcher until the cylinders touch the ground. I admit I have just been checking ebay and some other sites for one of those unloved Dutch army R65 GSes... luckily there aren't any for a reasonable price at the moment.
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