71 R75/5 engine refresh - not sure what I should look for

To clarify, my motor is leaking like a sieve and I plan to pull it this winter and replace all the gaskets. In fact, the whole bike needs a really thorough going over and refresh. It's been a rider for the last 35 years. But it's a nice running riding bike, so no obvious mechanical issues. Always starts, and purrs along beautifully.

Here's the loose plan so far - (keep in mind, I'm a shade tree mechanic. I've been wrenching on bikes for decades and know enough to get by, but no real BMW specific skills other than the basics, valve adjust, clutch adjust, etc)

Pull motor/trans, pull heads and ship off to have the valves converted to unleaded.

Take engine apart to replace all soft gaskets - especially the oil pan gasket. It's leaking a lot. All the other seams show signs of weeping.

Sympathetically clean everything up. Not trying to make the motor look new - just get rid of the oxidation and grime.

Take a hard look at the clutch and rear main seal. I'm guessing the seal needs to be replaced and the clutch may need to be reworked - take up is at the very last millimeter of the lever. I've had to adjust it to keep it from slipping but I think I'm running out of adjustment - not 100% sure.

So really, I'm wondering about the pitfalls of disassembly as well as the while your in there's of a motor with 40k miles on it.

I'm also wondering if there is a Go-To gasket kit, like from Bob's. I'll call and ask.

Any and all feedback appreciated.

I'd work with Tom Cutter at RubberChickenRacingGarage to purchase the gasket kits. He will know exactly what you need and can also help you with any tips. Be sure and share!!

Whereabouts in WI. I'm up in Cedarburg and my brother and his son are in Waukesha. We have three BMW's in the stable currently. Pushrod seals are most likely the reason for the leaking. Not too difficult of a job. PM and I would be happy to share some of the recent knowledge obtained recently with our refurbs we are doing on our bikes.

GO for it. I recommend Ted Porter in CA for the head/valve work. Get a copy of Oak's top-end manual if you can.

No need to pull the motor for the work you describe. Oak's Top End Manual is a wonderful suggestion. Be sure to block the crankshaft from the alternator end before removing the flywheel.

Airheads are known for leaking from split pushrod tube seals. The neutral switch is another item that often leaks. Before I pulled the whole engine apart, I'd clean up the bottom of the motor and see what's really leaking. The heads and barrels of a BWM can be removed and reinstalled without pulling the engine and if a top end refresh is all that's needed, you have saved yourself a lot of work.

Don't make a mountain out of a mole hill!

Keep it simple, "beemerphile" has it spot on. Leave the motor in the frame and work on it there. The less you take apart the quicker and easier the project goes, all the resealing, refreshing and cleanup you mentioned can be done with the motor still mounted in the frame.

Basic first step is to look up your local "airhead" club and reach out to that resource.

Don't pull the fly wheel unless you have researched that procedure and blocked the crank shaft.

20774 said:

I'd work with Tom Cutter at RubberChickenRacingGarage to purchase the gasket kits. He will know exactly what you need and can also help you with any tips. Be sure and share!!

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I've heard good things - I'll do just that. Thank you.

bmwscott said:

Whereabouts in WI. I'm up in Cedarburg and my brother and his son are in Waukesha. We have three BMW's in the stable currently. Pushrod seals are most likely the reason for the leaking. Not too difficult of a job. PM and I would be happy to share some of the recent knowledge obtained recently with our refurbs we are doing on our bikes.

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I'm in the Sussex area - a wee bit closer to Waukesha, but not far from Cedarburg. I'll send out a PM shortly - thank you.

ebeeby said:

GO for it. I recommend Ted Porter in CA for the head/valve work. Get a copy of Oak's top-end manual if you can.

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I've heard good things about Ted as well. I'll give him a call. I'm also a member of Airheads and enjoy the tech section by Oak (sadly posthumously). Would I source that manual there? Thank you.

beemerphile said:

No need to pull the motor for the work you describe. Oak's Top End Manual is a wonderful suggestion. Be sure to block the crankshaft from the alternator end before removing the flywheel.

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I'm taking the bike down to it's core components and figured the motor removal wouldn't be that big of a deal. The center stand is off, so I want to put that back on. And I wanted to inspect the frame and, if necessary, touch up the paint here and there. I've done a few motor swaps on vintage Hondas, so I figured this would be fairly straightforward. Do you feel removing the motor is inadvisable unless absolutely necessary? Thank you.

Anyname said:

Airheads are known for leaking from split pushrod tube seals. The neutral switch is another item that often leaks. Before I pulled the whole engine apart, I'd clean up the bottom of the motor and see what's really leaking. The heads and barrels of a BWM can be removed and reinstalled without pulling the engine and if a top end refresh is all that's needed, you have saved yourself a lot of work.

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I've cleaned it up somewhat and it seems that whatever fluid it is, is gathering beneath the transmission in that well, which I assume is the top of the oil pan. I need to get a closer look. I have it on the lift and I'll take pics. Thank you.

69zeff65 said:

Keep it simple, "beemerphile" has it spot on. Leave the motor in the frame and work on it there. The less you take apart the quicker and easier the project goes, all the resealing, refreshing and cleanup you mentioned can be done with the motor still mounted in the frame.

Basic first step is to look up your local "airhead" club and reach out to that resource.

Don't pull the fly wheel unless you have researched that procedure and blocked the crank shaft.

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Sound advice. I'll do my homework. Much of that has been reading snowbum's tech articles. I'll do a few youtube videos as well and try to source Oak's top end manual. I definitely do not want to waste time, or worse, create an avoidable situation. Thank you.

Right side isn't too bad. I cleaned this a month ago.



Not as good here though.



Left side is much worse. I didn't clean this.





From the back - this is where it really is bad. That area below the rubber part fills up with oil and then drips a LOT.

Front isn't great



left side

nevada72 said:

I'm taking the bike down to it's core components and figured the motor removal wouldn't be that big of a deal. The center stand is off, so I want to put that back on. And I wanted to inspect the frame and, if necessary, touch up the paint here and there. I've done a few motor swaps on vintage Hondas, so I figured this would be fairly straightforward. Do you feel removing the motor is inadvisable unless absolutely necessary?

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No, it is not hard to do, but it is not necessary to do for what work you are needing to do. This is unlike a Honda 350 where you can't get the head off without removing the engine. But there is nothing to fear in doing it. The biggest fear is losing the shim out of the crankshaft, thus all of the "block the crankshaft" advice.

My thinking is that if you have a true 40,000 miles on the od, you probably only need a freshening up on the valves and seats. I've done hundreds of Airheads in a past life as a head specialist. If those parts are in reasonably good shape a light cut on the seats and a light grind on the valves and their probably good for another 50 to 75,000 miles of use. Save yourself the bucks and put that money on parts you really need. New valves guides are probably a must. Top ends on Airheads are usually good for 75 to 100,000 miles. Good luck with your project.

My R 90/6 looked like that when I go it

In fact it was worse, it came with a fresh filter and oil change when I got it so I rode it and monitored the oil level for a year or so before I addressed the leaks. It took a long weekend to replace the rear main seal, oil pump O-ring, oil pan gasket, cam shaft seal, oil pressure switch and I lapped matted the valve covers to the heads for a better seal. Transmission was sitting there so I replace the neutral switch, transmission input and shift lever shaft seals. Its been dry as a bone since that long weekend of wrenching and cleaning.

Lessons learned: If it ain't broke don't fix it, after 40 years even those good German seals leak a little and damb that little run-off from little leaks keeps rust and corrosion from forming.

Keep it simple, keep it within a budget, learn about the bike and enjoy the ride.

Zeff

BLOCK THE CRANK SHAFT BEFORE YOU PULL THE FLY WHEEL. Set it to TDC before you start.

I've cleaned it up somewhat and it seems that whatever fluid it is, is gathering beneath the transmission in that well, which I assume is the top of the oil pan. I need to get a closer look. I have it on the lift and I'll take pics. Thank you.

That's an indication of a rear main seal leak or the transmission input shaft seal. Tranny out and clutch and flywheel out for all that.

Greetings! I am your friendly state Airmarshal. There are quite a few Airheads in Wisconsin. Something to consider, if you have the time and inclination, is, after joining the Airheads, sponsor a tech session for the winter and get lots of help and meet a lot of new friends. We're here to keep the Airheads on the road.

MANICMECHANIC said:

Greetings! I am your friendly state Airmarshal. There are quite a few Airheads in Wisconsin. Something to consider, if you have the time and inclination, is, after joining the Airheads, sponsor a tech session for the winter and get lots of help and meet a lot of new friends. We're here to keep the Airheads on the road.

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Greetings! I am already an Airhead! I would love to sponsor such a session. Should I make arrangements through you?

1074 said:

That's an indication of a rear main seal leak or the transmission input shaft seal. Tranny out and clutch and flywheel out for all that.

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This seems like an "all of the above" case with the same Rx. Oil and gear lube can usu. be distinguished by smell. Hard to tell from the pics, but it also seems possible that the clutch arm rubber boot might be leaking. It is time for a general going-over. Might as well go for the prize and remove the front cam chain cover to check the chain and tensioner - plus it makes changing the cam and tachometer seals significantly easier.

beemerphile said:

This seems like an "all of the above" case with the same Rx. Oil and gear lube can usu. be distinguished by smell. Hard to tell from the pics, but it also seems possible that the clutch arm rubber boot might be leaking. It is time for a general going-over. Might as well go for the prize and remove the front cam chain cover to check the chain and tensioner - plus it makes changing the cam and tachometer seals significantly easier.

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Agreed. The bike has been on the road for decades, with periodic maintenance. The prior owner (2nd) basically rode it as a commuter for 34 years, which in Wisconsin means sporadically. He did a good job on upkeep because he needed it to be reliable. But it's still an old bike that is at a point in it's life where it needs some attention. So the title of this thread is a little misleading. It's not just the motor that I want to deal with, but everything. Which fortunately, on an old two wheeled German tractor like a /5, "everything" doesn't really add up to much.

But clearly the motor is the heart of the machine. I want to make sure I do it right. hence my thread. I will take your advice on the cam chain tensioner inspection and seal replacement.


So as an update, the bike went from this - (taken Saturday during beggars night - what better way to hand out candy than from the garage while working on bikes?)


To this...... -


....in fairly short order. Honestly, the bike is a pleasure to work on. Or take apart anyway.

I like your Dream.

Fixing things

nevada72 said:

Agreed. The bike has been on the road for decades, with periodic maintenance. The prior owner (2nd) basically rode it as a commuter for 34 years, which in Wisconsin means sporadically. He did a good job on upkeep because he needed it to be reliable. But it's still an old bike that is at a point in it's life where it needs some attention. So the title of this thread is a little misleading. It's not just the motor that I want to deal with, but everything. Which fortunately, on an old two wheeled German tractor like a /5, "everything" doesn't really add up to much.

But clearly the motor is the heart of the machine. I want to make sure I do it right. hence my thread. I will take your advice on the cam chain tensioner inspection and seal replacement.


So as an update, the bike went from this - (taken Saturday during beggars night - what better way to hand out candy than from the garage while working on bikes?)
View attachment 71424

To this...... -
View attachment 71425

....in fairly short order. Honestly, the bike is a pleasure to work on. Or take apart anyway.

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Handing out candy while working on bikes works well with a airhead tech day also, 12 oz bottles of liquid refreshment ( even if it’s beer ) will not hurt anybody’s feelings either