New Member Question and Intro 1975 R90/6

Just an update for folks. I found that even after replacing the throttle cables the throttle still refused to return on its own. I once again disassembled the handle and this time slid the handgrip off the handlebar. Underneath was 30+ years of congealed grease/oil which I cleaned off with some Goo Gone. Squirted on a dab of oil, reassembled and I have a working throttle!

Now the down side. I ended up pulling the tank to make it easier to replace the cables and remove the completely frozen master cylinder and must have knocked something loose because now I have no spark whatsoever. Looks like I'm pulling the tank again to find out what i did.

Two steps forward, one step back. Just like normal . . .

How about some advice on the master cylinder from you, o learned ones? Just chuck it and buy a new one, or try rebuilding it? It's really stuck, I'm not sure I'll even be able to pull the piston rod out. Worth the effort or not?

Larry

Oh, I almost forgot. A special thanks to Chip who is sending me a replacement center stand. He's my new hero! Much appreciated, I do love communities like this that jump right in to help out fellow members.

Reminds me of last summer when my wife and I were returning from a trip in the MG. We both heard an odd knock coming from the left rear of the car, but it didn't repeat so I took the car to the gas station after dropping the better half off at home to see if I could get it to make the noise again. Got all the way to the station and most of the way home when the noise came back with a vengeance. Made it to the house but couldn't get up the really slight incline in the driveway, fortunately a neighbor walking by helped push it into the garage.

Found out that one of the axle bearings had disintegrated and threw ball bearings into the differential gears. Exploded it like a pumpkin. I posted on an MGA forum for a replacement on Saturday, got a call on Sunday from a fellow MGA'er in California who put one in the mail to me on Monday. By Thursday I had a perfectly good used replacement rear end (just the pumpkin, fortunately) and by the next Saturday was back on the road.

Larry -

As for the lack of spark, one thing I'd check is that the small black jumper wire is still in place that connects the two coils. Without that, no spark. On the down side, there's power at the coil terminals so if you touched the tank to the power side, it could have fried something. But look for the small black wire first.

RE: the master cylinder...I like keeping original equipment. There is a process to convert to a handlebar master cylinder...there seem to be positive benefits there. But I like the feel and performance of my under-tank master cylinder. I'd use various penetrants like AeroKroil or the best yet is a 50-50 mix of ATF and acetone. Soak things and see if you can free it up. You may find it's beyond saving, but there are companies that can resleeve the bore.

When I recently rebuilt my master cylinder, I followed Brook's blog on this...was very helpful:

https://brook.reams.me/bmw-motorcyc...nd-restore-front-disk-brakes-master-cylinder/

Thanks Kurt. I do have a can of Kroil (bloody expensive stuff I might add) that I'll squirt it with every day or two. I also like original stuff but I'm wanting the bike to eventually look like it just rolled off the showroom floor so that does mean at least SOME new parts. In this case the brake fluid reservoir as it's quite yellowed. It seems intact for now though so I'll likely hold off on that.

I want to ride the bike for a bit as-is for that 'survivor' look before I tear it all down and start repairing/replacing/repainting.

I was looking at the coils when I had the tank off and maybe even jiggled the wire you're talking about. Sounds like I might not have a good connection any longer so time to clean some contacts.

Larry

Things just go from bad to worse. Last night I pulled the tank off to investigate why I no longer have any spark at the plugs. I did open the points manually with the key on and got a spark there, so the problem seems to be at the coils.

I pulled each coil individually and thoroughly cleaned all contacts on the coils, then reinstalled them making sure I put all the connections back where they came from. I also check the black cross-over wire for continuity and found it good. Both coils show exactly 1.5 ohm across the negative and positive terminals, so it all seems fine there.

Next, I swapped the plug wires across and checked for spark on the left cylinder with the plug laying on the cylinder head to make sure it wasn't a bad plug wire. Still nothing. I put the plug wires back to their original locations and checked the right plug for spark (plug out and laying on the cylinder), no spark there either so it's not the plugs.

Then I pulled the starter relay after making a diagram and carefully labeling each wire. I shined up the relay contacts and scraped out the individual plug wires as best I could with a small screwdriver and reassembled and that's where it all fell apart. Now I get nothing at all when I press the starter button. The headlight and turn signals still work, but nada from the starter.

I have the wiring diagram from the Haynes manual and am looking through it to try to track down the problem but any suggestions on what to check next would be greatly appreciated.

Regards,
Larry

You may have knocked a wire loose or your points maybe the issue. I would check them to see if you have the correct gap.
As far as your M/C, 14mm come up on e-bay frequently, but if you want to just rebuild it, it may need to be sleeved. I have used a Mark Frappier to do M/C, he sleeves them in stainless, 800-528-5235, cost is about $100.00, great work, items sleeved, honed and returned in about a week.

If you are getting a spark when you manually open the points then I would recheck the point gap. The spark the manually tells me that all wiring through the coils and points is in working order.

Thanks for the tip on the MC rebuild Gerard, that price sounds a heck of a lot better than the $350-$400 for a new one.

There is a good chance that my fix on the camshaft nose didn't hold, I'll check the points gap when I get home tonight. I'd love it if that was the issue on the no spark. I do still have to figure out why it's not cranking now after I cleaned the contacts, probably didn't get one of the connections on well enough.

Larry

How's your battery? Put your digital voltmeter across the battery terminals and measure voltage before hitting the starter button and while hitting the starter button. Report back the voltages. If the voltage drops well below 10v, the battery is bad.

You can measure for 12v across the coils. 12v comes into the left coil terminal...put your digital meter with one connected to ground and one on the left terminal...you should read 12v. Then do the same thing with the output terminal on the right coil. Should be 12v. If not, you have a supply problem. If you do, then, as pointed out, the points are not working properly.

Hi Kurt,

Just a note, I do have two issues which may or not be related. Initially, I stopped getting spark to the plugs after having it starting up reliable for a month. While attempting to resolve that I made it worse and the starter motor now refuses to even think about turning over. Flat out nothing from pressing the starter button.

The battery is brand new and has been kept on a battery tender. All starting on the bike is with a green (fully charged) light on the tender.

I'll do the voltage test on the coils in the next day or two. I can say that I'm not getting any clicks at all from the starter relay when I press the starter button, so it appears that my cleaning of the terminals may not have gone well. Either that or the starter button had decided to take early retirement on me (after all, the bike is only 44 years old).

Thanks,
Larry

I wouldn't rely on the lights on the battery tender. Put your voltmeter across the battery terminals and read the voltage when you hit the starter button. If it shows around 12v when hitting the starter, then the problem is probably the starter relay since it is not latching. If it shows something like 8-9v, then the battery is probably bad.

Consider lighter throttle return springs on the carbs

Now that you have the throttle working properly, consider installing lighter throttle return springs on the carbs. These are the external springs visible on the engine side of the carb's body.

The stock springs are stiff, meaning you will be fighting them on long trips (the throttle 'lock' screw can help, but is a sub-optimal solution, IMO). The results is stiff neck muscles.

I installed a pair of EZ Pull springs on my 1975 R90/6 years ago and have never looked back.

Left Bing carb #: 64/32/11; right 64/32/12.

You want the Type 908 for your machine.

Needle nose pliers can help with the job.

Hi Folks,

Being in the middle of preparations for my wife's 60th birthday party this weekend has kept me from any serious time with the R90/6. I was able to replace the headlight bulb so I now have a low beam AND a high beam. One more step toward a ride-able bike.

Looking over the wiring diagrams I cannot for the life of me figure out what this wire is. There doesn't seem to be anything left over going to the back of the bike and it has been there since I got the bike so it doesn't seem to be critical to the bike running and starting. Any suggestions on what this might go to?

Note - the white paper is just to highlight the wire as a black wire against a black frame is difficult to pick out.

Does the other end of the wire disappear into the wiring harness or has it been added later and it just following the wire run? Any chance to see where the other end is?

Since it has the length to end where the coils are, almost seems that's the region where it might go. For the stock coil setup, a green/black wire comes into one coil connector (typically the left one), then there's a small black wire jumper over the other right coil, then a black wire coming off the outside connector on the right coil which goes to the capacitor under the front engine cover. Do you have all those?

Black wire

I've known about that wire since the 70s and still don't know where it goes and what the function is. Don't worry about it.

It could be the wire that eventually attached to the coil for the electronic tach in 1978. Prior to that happening, BMW began to make a compatible harness for that eventual change and put those harnesses on earlier models. All functions still worked but a few connection points went unused. '75 models seem a bit early but you never know.

Just as you say, it disappears into the wiring harness. The other three wires (green/black, black jumper and black to capacitor) are all there.

Good to know it has puzzled others and I can safely ignore it.

Thanks all!

20774 said:

Does the other end of the wire disappear into the wiring harness or has it been added later and it just following the wire run? Any chance to see where the other end is?

Since it has the length to end where the coils are, almost seems that's the region where it might go. For the stock coil setup, a green/black wire comes into one coil connector (typically the left one), then there's a small black wire jumper over the other right coil, then a black wire coming off the outside connector on the right coil which goes to the capacitor under the front engine cover. Do you have all those?

Click to expand...

Got to spend a few minutes in the garage today and measured the voltage at the battery. Nominal voltage was around 12.4V with absolutely no change when I hit the starter button.

I skipped the check of the coils in favor of trying an idea I saw on another post of shorting the positive terminal to the solenoid wire. Did a happy dance when the bike fired right up and ran well!

So apparently, the starter, points and coils are fine and I get to track down whatever else is causing the starter switch to not work.
I'm leaning toward Kurt's diagnosis of a bad starter relay since that seems to be where the issue started. Any thoughts on the $10 relay from Motorrad Elektrik? It looks identical to the stock one which I'm seeing anywhere from $37 to $75. I'll readily throw a sawbuck at the problem - if that's not the issue, no big loss and I have a spare on hand.

Or should I play it safe and order an OEM or OEM replacement relay?

Thanks,
Larry

Motorrad Electric

Get the part from Motorrad Electrik! This is the way to go! When I had my independent airhead shop I did a lot of business with Rick.
A case in point involved an alternator rotor from him that only lasted one day. In the course of our followup conversation, Rick asked me what my hourly rate was. So the next day I got the replacement part with a check for an hour of labor!
This man is my hero.

Bruce, thanks for the recommendation for Rick at Motorrad Elektrik. I spoke with him and ordered several items that I know I'll need.

Next question for you more experienced Airhead tinkerers. I would like to keep the bike as stock as possible, including the rear shocks. I understand OEM shocks are no longer available but have an opportunity to buy a pair of like new shocks that were taken off a 1979 R65 shortly after purchase.

The seller claims that they will fit most 750, 900 and 1000cc bikes, true or not?

The shocks do not have the covers like the ones on my R90/6, can I transfer them to these shocks?

Thanks all,
Larry

I don't think the R65 shocks will work.

1) Different part numbers for R90/6 and R65 per RealOEM

2) Ikon's website has a different shock part number for the two bikes.

Ikon does have an offering 7610-1298 with /6 shock covers for $500.