1) Help looks genuinely interested in the work, and yet small enough to take along should there be trouble on the road. We approve !

2) There are 2 piston seals. One does the pumping and one does the sealing to the outside world. Your issue area is small enough and far enough down the bore that that I would start with the rebuild kit. (You can mail me that saved $250 if you like. Or, you could take you new mechanic out for ice cream.)

3) You are correct on the piston. Once you break through the chrome plating it's toast. It will always have rust blooming from that point, which may keep the piston from doing "it's thing". A very uncertain result that is best rectified now.

4) DOT3 and DOT4 are the same except for the temperature rating. You want the higher rating. You can buy DOT4 locally at any good auto parts store. 2 small pint cans are better than 1 large can.

Now you're also going to need a new pump-type oil can and a short length (6") of 3/16 fuel line or battery breather hose. I like the clear hose so that you can inspect for air. The object of the exercise is to pump fluid into the bleed nipple, not air.

When you finish with the oil can, you'll need to completely disassemble and wash. The DOT4 will eat it up too if you're not really careful.

I finished the m/c (see photo) and then reassembled the front brakes on Friday. They seem to be working ... so thank you very much for your help!

Today was the Utah Airhead Fall Tech Day, and I hauled my bike up to DeVern’s place and got some great help with my carburetors (see photo). Thanks especially to DeVern and Phil for their help.

We also swapped out my old, dead battery for a new one, but no lights came on at all when I turned the key on. My brother and I had been able to jumpstart the bike with the old battery back in June, before I had it shipped out here, but now there is absolutely nothing coming on at all. The battery had about 12.4 V of charge, but something is keeping it from flowing. DeVern also noticed that the kill switch didn’t seem to be working correctly - it was moving back and forth smoothly. Not sure what the electrical issue is. I plan to return the battery I bought, since it doesn’t actually fit - it’s off-the-shelf from an auto parts store - I just bought it so I would have something for the tech day.

• I believe there is a standardized battery shape that is close to that of the BMW called a U1. Unfortunately, the terminals of the U1 are reversed from those of the OEM battery and the terminals are also taller which allow them to destroy the tool caddy. So you can't go by physical dimensions alone.

My answer has been the PC680 battery by Odyssey. This is an American-made AGM, and although a smaller size, packs all the punch of the larger OEM battery. And the terminals are on the correct side. This battery will fit comfortably in the rear of the stock battery holder, but you need to strap it in with long cable ties since the stock battery hold down is too big. There are dealers an Amazon selling these in the $115 range.

• Electrical issues of this type are best chased with a schematic and a 12V test lamp (or "probe"). You can walk through the various parts of the system starting at the battery and then moving from one connection point to the next in a logical sequence. The only thing to realize is that the OEM electrics don't have a "main fuse", which many American riders add. And so that fuse would not show up on your schematic. Most people place that fuse right at the battery, so you do have to use your eyes, as well as a good bit of common sense.

• You don't need to buy a battery to start testing your system, you can use your battery charger. You'd connect the Pos to Positive, and Neg to Negative and then start testing.

• A very common failure point is the OEM German fuses. Oxides formed over time prevent the fuses from making good connections. you'll either have two 8A fuses inside the headlamp shell, or in a frame-mounted black plastic box located just over the air filter box. I believe you have the first location, but I'm not sure about R80's.

Hope this helps.

Hi again,

I grabbed an Odyssey battery like you suggested, and a light probe. After studying the schematics and various websites on airhead electrics (and learning a lot ... which is great ... thanks to all those people for sharing their knowledge), I found that power made it to the ignition switch, but cut out completely once the switch was turned. I checked the fuses (which are in the headlamp), and they were sound. I figured might be a ground connection loose ... so I just started at the battery and worked my way forward with every connection.

There is a buzzer relay on the R80/7, and the connections were corroded and not fully connected - so I disconnected and cleaned it, and then reconnected it - but there was still no power. I disconnected and inspected the starter relay and the voltage regulator - and those connections were fine. Inside the headlamp there was a wire with some electrical tape over it - I unwound it, but it was just covering up an exposed wire/connector junction. I was despairing a bit at this point, since nothing else readily apparent seemed off - and I figured I was going to have to start diving deeper into the body of the bike. I tried the ignition again, not really hoping for much, and the lights all lit up. I pulled the plugs out and grounded them on the cylinder covers, just to see if there was any spark ... and it was good. Something I did fixed the ground.

I had my tank lined by a radiator shop in SLC - Ron at Bavarian in SLC had observed that the tank was rusting out by the petcocks. When I got it back and did a cleaning of the bottom of the tank, I noticed that what was really happening was that the white paint was flaming off down there and revealing the original paint ... which was a rust-red color. I think it’s okay. The lining will hopefully ensure there is no rusting through.

I was planning to rebuild the petcocks, but the covers won’t come off. As they are, they hit up against the knobs, and there is no room for them to swing off around the knobs without breaking them. The knobs turn easily enough and there is no leaking, so I figure I’ll just leave them until they do start leaking or show some other kind of issue. I replaced the fuel lines, put in some filter covers over the intake tubes, cleaned the petcocks connectors (they were pretty rusty/grimy), reassembled it all and installed the tank. A bit of fuel inside, and the bike fired up. I took my nephew on a short ride (not trusting the tires at this point for any substantial distance), and then shut it down. Oh, I also changed the plugs, which looked very fouled.

That was all last week. Today is changing the fluids. One bit at a time. Hopefully in a month or so it will be road-worthy. I feel like there is still a lot of work to do on it ... especially after watching boxer2valve.com’s R90/6 barn find video ... but I’ll get it bit by bit.

Thanks for your help, Wobbly, and everyone else.

• You never talked much about what you found under the tank. I had advised you wash the electrics to remove all the spilled and leaked DOT4 brake fluid. The Number 1 offender when any brake fluid has been leaking is the Starter Relay. All system power passes through the Starter Relay on your bike, and the relay AND its contacts MUST be in pristine condition. Most of the OEM relays are shot by this time in 2020 since they are 40 years old. I highly advise replacement. Not sure you can afford it, but HERE'S ONE for under $6.50 !!

• The unplugging and re-connection of several terminals says to me you have electrical connector corrosion caused by 40 years of riding in the rain and bike washing. Once the corrosion starts it doesn't magically stop. It WILL return. All you need to do now is decide whether to fix it at home, or on the side of the road. The fix at home is easy. Order the smallest vial of No-Ox-Id and add a very small amount (about 1/2 drop) to each electrical connector, relay, light bulb, etc, etc you ever disconnect. HERE. This compound ends the corrosion, promotes connectivity, and keeps corrosion from returning.

This is a good job for Junior. Set him in front of the head lamp shell (lens removed) and have him unplug every connector one at a time, treat the connector, and then plug it back in. Don't forget the battery cables (both ends), the harness connector near the tool tray, the voltage regulator plug, and all the relays... plus all the connectors under the fuel tank, horn terminals.... well, you get the picture.

All the best.

- Concerning the tank underside, I think I had an auto-correct-induced typo in my last post. The white paint on the tank is flaking (not flaming) off near the petcocks and revealing the original paint underneath ... at least that’s what it looks like. The original paint, from the records I have, was “dull brown,” and really, what looks to be revealed under the flaking paint is just the original paint. It’s brownish-red and glossy, (rather than rough) and it looks more like another coat of paint. When it was a bit dirty, it did look rough, like rust, and that might have been what Ron at Bavarian was seeing. I don’t know much about repainting a tank ... do you typically remove the original paint first?

- I must have missed where you suggested cleaning the connections, above, but it is a good suggestion. I ordered the electric grease and will put it on.

- As far as the starter relay goes - I ordered the $6.50 part you suggested ... is it a standard-type relay? Do you mean that I don’t necessarily need the $30 one from MAX or some other supplier?

- Should I replace the voltage regulator also since it’s up in the same sort of location as the starter relay?

- My the beeper linked to my buzzer relay is not beeping like it should when the turn signal is on and the clutch is let out ... which is actually less annoying for me, but is a bit concerning, since I haven’t done anything to it other than clean and reconnect the relay. MAX shows this as a discontinued part ... which isn’t surprising, since my understanding is that it was only included for a couple of years. If it fails, I guess I just remove it somehow ...?

- Question on driveshaft and rear bevel drive oil ... I replaced these, but just eye-balled the amount I put back in. Is it essential to measure the amount that goes in there? I haven’t driven on it yet since I replaced it, and have no problem draining and replacing it again in both spots, but I don’t have a syringe yet to measure it out.

Again, thanks for your help.

- As far as the starter relay goes - I ordered the $6.50 part you suggested ... is it a standard-type relay? Do you mean that I don’t necessarily need the $30 one from MAX or some other supplier?

The only thing "standard" is the size and format. There must be 30-odd relays with that general form factor. Is it equivalent ? YES. If you have questions, each one has a schematic on the side of the unit. Compare the schematics before plugging it in.

- Should I replace the voltage regulator also since it’s up in the same sort of location as the starter relay?

You should replace the voltage regulator because 1) your OEM VR is mechnical and is slap worn out after 40 years, and 2) because the PC680 is an AGM that desires a higher charge voltage than the OEM wet cell battery. Motorrad Elektrik sells an all-electronic VR specifically for AGMs.

- My the beeper linked to my buzzer relay is not beeping like it should when the turn signal is on and the clutch is let out ... which is actually less annoying for me, but is a bit concerning, since I haven’t done anything to it other than clean and reconnect the relay. MAX shows this as a discontinued part ... which isn’t surprising, since my understanding is that it was only included for a couple of years. If it fails, I guess I just remove it somehow ...?

I'll bet you $5 it starts working again with the application of No-Ox-Id.

- Question on driveshaft and rear bevel drive oil ... I replaced these, but just eye-balled the amount I put back in. Is it essential to measure the amount that goes in there? I haven’t driven on it yet since I replaced it, and have no problem draining and replacing it again in both spots, but I don’t have a syringe yet to measure it out.

• You can "eye-ball" the volume in the final drive, because there you can see the liquid level. 240cc fills to the bottom of the threaded hole, which is the correct (and critical) oil level.

• You cannot "eye-ball" the oil level in the drive shaft because you cannot see the level due to the presence of the shaft itself. You got to be kidding me. Get yourself to the Baby Section in any big store and spend 69 cents on a plastic baby bottle graduated in CC's. Use this for the forks, drive shaft, and final drive oils. It's a life time tool. I've been using the same baby bottle since 1971 and it's not nearly worn out.

Hope this helps.

Hi. I really don’t mean to be asking extremely (and possibly offensively) simple questions, but I’ve tried to make it clear before that I am really new to all of this. If my questions are unwelcome, please let me know, and I’ll seek elsewhere for help.

My question about the driveshaft oil was really just to ask how critical it is to have the exact amount of gear oil inside. (Again, I don’t know - this is the first time I’ve changed it.) I’ve seen and read different views on this, and was just asking your opinion.

Yes, “eye-ball” in its literal sense was not the correct phrase to choose for the driveshaft, since I can’t actually see the level of the oil in there.

What I take away from your statement is that it is, in fact, critical to put the correct amount of gear oil inside the driveshaft. I trust your judgement. I’ll drain it and refill it with the correct amount.

► It is critical only in the sense that failure to do so is going to cost you $400 to $500 to correct, and become one more road block to finally getting to ride this bike. The act of riding, possibly creating a great and very important time for you and your son. I know it was for me and my youngest.

Critical because the drive shaft U-joint and splines are splash lubricated. If the level isn't correct (possibly also due to a torn U-joint boot) then the drive shaft doesn't dip into the oil and sling it all around. If there's trouble, then swing arm assembly has to completely come off the bike and be sent to a shop with Airhead tools. The shaft is made into the housing and does not separate without tools. Then, when it returns you'll need to work through all sorts of SA bearing adjustments to center it all back up.

The final drive is another piece that cannot be set without a full shop. The ring and pinion gears are individually shimmed into place using dial indicators. Sure you could get a replacement FD housing assembly off Ebay, but even those range from $100 to $250, plus shipping. So even inserting a used FD housing is costly. Bottom line.. both reservoirs lubricate very costly items that you absolutely don't want to fail.

► Nothing was "offensive", I was simply in total shock that of all the times you had taken liquid medicines there was no awareness that the containers are graduated in CC's. Kitchen measuring cups too, for that matter. And we won't mention baby care products. Graduated containers are all around us and a great many are disposable plastic types that otherwise go into the recycling bin. Many a kingdom is lost for the want of a horse. The simple tools sometimes end up being the most useful and shouldn't be discounted.

I'm sensitive to the fact you have a lot of spinning plates in the air right now. Sorry if my comments caused you undo concern. It's all good.

I'm reviewing this (now) 5-page thread. You've never told us the year of your bike. It looks to be a '78 or '79 model, but a year would help.

Thanks.

Awesome. Thanks. That’s great info. I appreciate it.

No offense or difficulty on my end ... I completely see your point (and laugh about it now). The fact that I didn’t remember right off that cc=mL would probably also make you roll your eyes ... I have been dispensing plenty of mLs of cough and flu syrup over the past few months (to my daughter, actually - the boys in the photo are my nephews).

Again, I seriously appreciate all of your help and insight. There are so many different things to learn about how the bike works. It’s probably just really important to err on the side of precision with anything I do regarding it. Good lesson to learn.

Oh, and my bike is a 1978.

the amount of oil in the shaft is quite critical, but there is an odd reason. there is an oil seal between the final drive and the shaft. if the seal fails oil will pump from the final drive into the shaft leaving the final drive low and the shaft over filled. not good. The shaft oil level can be checked with a dipstick. Usedto be one in the toolkit...one of the tools had a line scribed on it for that purpose. But you can make your own from a piece of 1/" wide strap aluminum. Do your regular shaft oil drain, hot, overnight.Then fill carefully with with the correct quantity of oil. Helps to heat up the oil. Then plunge the aluminum strap in the fill hole, withdraw and scribe a line at the oil level. This is used in the future to check the level. I check the 90 wt levels any time I change engine oil although the 90wt oil changes are at a longer interval.

I have picked up a couple lab stands and clamps at yard sales and flea markets over the years. These are ideal to hold a long necked funnel with my measuring container in it over the fill hole for a half hour for all the oil to drain down. I use graduated cylinders for the fill work. Again, heat the oil. Stand the bottle in the sun or stand it in a pot of hot water.

I use Moly in my engine and gear oils. Liquimoly products. MoS2 Anti-Friction for gears in the 90 wt and the same in the engine treatment. But I go somewhat light with them. Moly is a plating lubricant and it takes very little. You will also want some HondaMoly 60 from the Honda Bike dealer for the transmission and rear end splines. I fatten it up with some powdered graphite to make spline butter.

When mounting petcocks use Great White sealant on the screen washers (thou shalt run the screens). This is a non- hardening sealant that is everything proof. use it on the threads as a sealant and lube and the screen washers. It makes a bit of a mess but just wipe up. Buy a tube, never a tub unless you are doing a bunch of pipe fitting in your house. Plumbing isle at hardware store. (Wobbly, The MSDS and product lit. on this stuff is impressive). No more varnish on the petcocks.

The petcocks should feel very smooth with clearly defined detents. Not-leaking is not good enough, bad things can be happening inside if they are not smooth. Rebuilding them is easy (and often free) but there are some tricks to know. Ask if you go into them.

ALL fluids should be of correct amounts. Too little, not good. Too much, not good. Everything in engineered that way. As Wobbly said, don't eyeball anything. Just go out and get a marked cc/mL funnel that has the tube connected to it. The tube will allow you to get in the fluid at odd angles. BMW fluid fill locations are all in odd spots (rear end, trans, forks, etc.) Also, as a tip, don't torque by "feel". get a torque wrench. You won't be happy if you snap any cast aluminum...