'79 BMW R80/7 Rebuild - Crank Shaft Advice

Hey All,

I bought a 1979 BMW RE80/7 with 65k miles up on it last year with the goal of stripping it down to each individual component and rebuilding it again. I've been a long time BMW owner but this is my first airhead and the first project of this magnitude I've ever taken on. Really excited about this rebuild




I'm at the point where I'm starting to rebuild and I have a couple of questions for some of the experts out there (@brook reams if you have time?) The first step is installing the crank shaft back into the case but before I do, I'd like some advice about checking the main journals for wear in order to figure out which main bush bearings to order. Looking at the journals there are some linear markings but feel smooth and seem "good enough" to my untrained eyes but could someone with a better eye please have a look and see what you think?




I've also got some photographs of the connecting rod journals. Definitely lots of small nicks there, but hoping again they're "good enough" to get by without a regrind. What do you think - a little buffing good enough for these?




My main concern of all is with the wear on the main journal diameters. See the diagram, but I am basically getting a taper of >0.2mm on the Alternator end. From reading my Clymer manual I believe this means its time to grind down a size to level everything out, but wondering if anyone has experience with this? The bushing is in a terrible state (see photo).




Any advice would be much appreciated on all of this. It's the first step in the build for me and I want to do things right. If you have any advice - or you recommend that I ship it off to an expert, please add a reference. I live in California

Thanks in advance folks.

Beardy

Beardy -

Welcome to the forum! Hopefully Brook might have some advice. In NorCal, Ted Porter has a shop The Beemer Shop...he might be a resource for you.

beardyobeards said:

Hey All,

I bought a 1979 BMW RE80/7 with 65k miles up on it last year with the goal of stripping it down to each individual component and rebuilding it again. I've been a long time BMW owner but this is my first airhead and the first project of this magnitude I've ever taken on. Really excited about this rebuild

[snip ...]

I'm at the point where I'm starting to rebuild and I have a couple of questions for some of the experts out there (@brook reams if you have time?) The first step is installing the crank shaft back into the case but before I do, I'd like some advice about checking the main journals for wear in order to figure out which main bush bearings to order. Looking at the journals there are some linear markings but feel smooth and seem "good enough" to my untrained eyes but could someone with a better eye please have a look and see what you think?

[snip ,,,]

Any advice would be much appreciated on all of this. It's the first step in the build for me and I want to do things right. If you have any advice - or you recommend that I ship it off to an expert, please add a reference. I live in California

Thanks in advance folks.

Beardy

Click to expand...

Hi Beardy,

I don't want to rain on your parade, but I would never recommend a first timer tackle the crankshaft. It is not for the first timer as it is very easy to destroy it with unpleasant consequences.

I did publish material on my latest build, 1983 R100RS, where I did remove the crankshaft. This is my fourth complete rebuild in over 10 years and the first time I felt I might have enough experience to take this on.

That said, I took the crankshaft and engine block with bearings installed to Matt Parkhouse for his personal inspection and opinion. Based on that, he replaced the rear main bearing, which is the easier one to replace.

The front main bearing requires pinning of the bearing and that's a very precise and delicate operation that I still am not confident I would tackle on my own. Any mistake in that work is catastrophic to the engine.

Installing the crank and getting the correct end float is critical to not damaging the crankshaft. I do show how I did that work here. It took me several attempts to get it right. That said, I haven't done a first engine start on this motor yet, so I can't confirm all went back together correctly.

--> 11 BMW 1983 R100RS Install Crankshaft, Adjust End Float, Install Camshaft


So my advice is to take your engine block and crank to an experienced airhead mechanic for an expert opinion on it's serviceability. You might try Ted Porter at the Beemer Shop who is an experienced airhead mechanic in CA.

I hope that helps.

Best.
Brook Reams.

Totally agree with Brook! You wouldn't want to perform brain surgery after reading about how to do it from a slide show presentation......