Restoring a 1973 BMW R75/5 Motorcycle

July 15, 2007

Can I get a mulligan?

Filed under: /5, 1973, airhead, BMW motorcycle, motorcycle, motorcycle restoration, R75, R75/5 — Penforhire @ 12:50 pm

As several of you pointed out, I really needed to get that beadblast grit out of my engine before assembling. Al called me up and suggested hot-tanking the engine. Not another outside service!? Hrmph! Well, I told myself I’d consider that if I was unhappy with what I could do in the garage. I popped the oil pan off. Not so easy to do since I followed the repair manual’s recommendation to use sealant on the gasket.


Looks familiar. Gosh I was hoping to never see it again.

I was thinking of using kerosene or “odorless” mineral spirits. Gary suggested Stoddard solvent, which I think is a similar petroleum distilate that used to be a drycleaning fluid. Joe had a great idea to apply whichever I chose with a $10 garden sprayer.


I used mineral spirits mostly because of the low odor (and low flammability compared to, say, alcohol) and after considerable spraying, rotating the engine, and collecting runoff I was satisfied I had gotten enough grit out. As Bob mentioned, if you do this be careful to avoid any open flame or sparks while spraying or in the area while it slowly evaporates. My gas hot water heater and clothes dryer are both in the garage so I picked a time when I could leave the door open for hours and kept a fan running.

After the engine stopped dripping I immediately sloshed motor oil around the interior. The solvent should have gotten all the bearings oil-dry and they would be quickly damaged if they move without lubricant. I dripped oil down the connecting rods and hand-applied oil to pushrod lifters and cam surfaces. The loose parts all moved smoothly. Okay, one more of my goofs rectified.

Here is the setup I used to load the engine back in the frame.


That is a single 2×4, covered by a soft rag, on top of two jacks that barely fit around the centerstand. The 2×4 hits the centerstand upper crosspiece when the rear engine bolt is in but it is not needed to mount that rear engine bolt. The center of gravity is forward enough to rotate the engine with one hand around the front engine bolt after it is through. Or you could be smarter and use two pieces of wood, front and rear, to clear the centerstand.

I wrestled the engine onto the 2×4. I wasn’t too worried about the frame paint since it was powder coated but I still managed a scratch. So, uh, remember to cover the lower frame rails with tape or rags, just like it says in the manuals. I made some educated guesses about the spring mounts and spacers. The manuals are incredibly weak on the exact exploded view of which pieces goes where and in what orientation. Heck, Hammersley’s on-line fiche system had a better view! Make sure your sidestand is in place before you load the engine since it blocks the pivot.


Woo-hoo, engine is in! Now I want my mulligan.

Did you know the transmission doesn’t want to slip in behind the engine right now? I didn’t, obviously, but I found out when I went to load it after greasing its input splines. Oh, I didn’t give up before forming a few more light scratches on the frame. Joe mentioned pivoting the rear sub-frame out of the way but, staring at it, that is no easier than Clymers’ technique of putting the jacks back under, removing those engine crossbolts, and sliding the whole engine temporarily forward. Grrr. I’m too pissed about not anticipating this to undo my work right now.

And thanks to several readers who told me the offset peg lengths are correct. I forgot the cylinders are not exactly in-line. That offset is matched by the footpegs for shin-to-carb clearance. I managed to get the new rubber on the footpegs. I tried using WD-40 as lubricant. That is what I always use on handgrips since it is temporarily lubricious and then disappears. But that didn’t work so well on the pegs. Too much rubber expansion and associated friction. Joe suggested wire lube, used by electricians to “fish” wire through conduit more easily and also designed to evaporate. He also likes to mount the rubber with the pegs on the bike, using its weight to hold them.


The $5 bottle of clear goo I got at Home Depot is reminiscent of something more X-rated but, yep, worked like a charm. As you can tell, I have extra if you need some.

I got an update from my engine shop, Motor Works. They went to hone the cylinders and discovered the pitting is too deep. So we’re doing a real overbore, I don’t know which of the standard sizes yet, and getting new pistons. I don’t have a firm date for delivery yet but I figure another couple of weeks at least. That also raises the total cost of head-and-cylinder work close to near $1,000 ! Makes me wish I had bid a bit more on those supposedly refurbished heads that popped up on e-bay a few months ago. I look at it this way, this rebuild should last my lifetime and I’ll have confidence in it. And before some of you jokers comment on this, I know full well I could up-size the engine significantly (R80 or R90) for nearly the same cost plus minor carb modifications. But this is a real R75/5 and it is staying a R75/5.

What time is it? That’s right. Time for another episode of Homo Two-Wheelis! Sunday was the “Just for the Hell of it Ride” put on by the Brotherhood of the Third Wheel. Think I’m kidding?


These guys are for real. I think their club may be a bit understaffed but I do seem to see more trikes these days.

BMW Joe and I started off at Huntington Beach Honda and the ride was up over Glendora Mountain & Glendora Ridge roads to a checkpoint at Buckhorn Lodge on Mount Baldy road.


What a great day for a ride! It was hot but I was prepared with a Chilly Mate misting bottle. See for this item in the Aerostitch catalog. I found mine, the exact same unit, at Walmart for less than 1/3rd their price. Load it in the tank bag, aim the nozzle up at your chest, and you’ve got swamp cooling on the go. Oh yeah, I had one of these around my neck too —, again found much cheaper at Walmart. And don’t get all over me for shopping at Walmart. In this case the goods were identical.

Here’s a picture of Karyn and her monster Wing (the big fellow rode a modern Triumph Bonneville, forgot his name).


I still can’t believe she rides that beast.

Oh yeah, more proof the BTW exists —

Speaking of Aerostitch, don’t forget that this Wednesday is “Ride to Work” day, started in 1992 by Andy Goldfine. The date is always the 3rd Wednesday in July. See

That’s all for this week. Can I get that mulligan?


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