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Topic-icon '76 R75/6: Points don't open

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1 week 4 days ago - 1 week 4 days ago #6868 by Dschroeder
'76 R75/6: Points don't open was created by Dschroeder
I just received my grandfather's '76 r75/6 because I was tasked with getting it running again. I am new to air cooled bikes and motorcycle repair in general. I've been working on it the last couple days and finally got the starter motor to run. The starter relay doesn't work so I powered the starter motor with a jump from the battery. I wanted to see if the spark plugs would make a spark, but they didn't. The ignition coils seem to be getting power, but I discovered the points never open even when the crank is turning. Could this be why the plugs aren't sparking? If so, how do I get the points to open?
Last edit: 1 week 4 days ago by Wobbly. Reason: Mods altered title

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1 week 4 days ago - 1 week 4 days ago #6870 by Wobbly
Replied by Wobbly on topic '76 R75/6: Points don't open
Welcome Aboard !

Wow, you inherited a classic if there ever was one !

Yes, it is quite common for the points to stick open on bikes that have been sitting. It is also common for there to be unseen corrosion on the surface of the contacts after long storage that stops all electrical flow. The fix is VERY easy. Disconnect the battery, then remove the front cover. Remove the 10mm hex nut and the auto advance will slide straight off, and give better access to the points. Wiggle the points arm until it moves freely. Clean both contact faces with a doubled-over piece of fine emery. Oil the auto advance with motor oil and make sure it moves freely, and put it all back together.

With the spark plugs laying on the cyl heads and connected to the plug wires, you should have spark on both sides as you kick the bike over with the battery re-connected.

There's going to be 100 tiny tasks like this to do before you can ride, but it's going to be VERY rewarding when you finish. I highly suggest hauling the bike to a local Tech Day near you. (Maybe even 2 or 3 Tech Days !) That's the fastest way to learn your way around a very unique engine and motorcycle, and get the really in-depth technical help you may need.

There's more info... HERE.

And ask lots of "stupid" sounding questions because buying lots of unnecessary BMW parts will cost you a fortune. You can't ask anything that we haven't asked ourselves. So these questions only sound silly to you.

All the best.

Don't hide 'em, Ride 'em !!
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Last edit: 1 week 4 days ago by Wobbly.

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1 week 4 days ago - 1 week 4 days ago #6872 by Dschroeder
Replied by Dschroeder on topic '76 R75/6: Points don't open
Thank you very much for your response. I took your advice and cleaned the contact faces. The points move easily if pulled back, but always spring back to the closed position. Still when the bike is turned over or if the crank is turned they never move from the closed position and there is no spark.

Edit: Please correct me if I'm wrong, but it seems like the shaft that the advance unit is attached to is not perfectly round, and there are bumps on it that push the point out. Could the reason why the point doesnt open be that it is not making contact with this shaft?
Last edit: 1 week 4 days ago by Dschroeder.

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1 week 4 days ago #6874 by 8166
Replied by 8166 on topic '76 R75/6: Points don't open
Sounds like the rubbing block is worn to the point that the cam won't open the points. You can try adjusting the points to correct that, but the procedure to do so is involved and has been covered here and in other forums in the past.

8166 Scot Marburger, This email address is being protected from spambots. You need JavaScript enabled to view it.
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1 week 4 days ago #6875 by Dschroeder
Replied by Dschroeder on topic '76 R75/6: Points don't open
Yep, that was the issue, I adjusted them and thy work great. Thank you

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1 week 3 days ago - 1 week 3 days ago #6882 by Wobbly
Replied by Wobbly on topic '76 R75/6: Points don't open
Hey, that's great news. Some suggestions...

• The correct points gap is set when the points are riding on the highest part of the ignition cam lobe. There is a specific gap distance that must be used.

• Typically, a dab of high temp grease is added to the ignition cam face to keep the phenolic cam follower from wearing down as fast.

• Sometimes the ignition cam surface may become covered in rust. That will act like sandpaper on the phelonic follower, so it has to be removed. Simply wrap the ignition cam in fine emery and rotate the auto advance unit back and forth. Polish it to a high luster. Pitting of the cam face is inconsequential... the pits only hold more grease. The grease mentioned above will stop any new rust.

• Anytime you adjust the points gap (as you have just done) you have also changed the ignition timing. It may be close, or there could have been considerable change. No one can tell you. If you restored the proper "points gap" it's probably good enough for your garage tuning purposes, BUT the timing must be very accurately set before venturing out onto the roads. And until the timing is accurately set, you won't be able to accurately "tune the carbs". Or stated in the reverse, you should fully expect to re-do all the carb adjustments after setting the ignition timing.

Hope this helps.

Don't hide 'em, Ride 'em !!
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Last edit: 1 week 3 days ago by Wobbly.

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