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Diode Board mounts

RPGR90s

RPGR90s

Member
I'm replacing the timing chain cover on my 1974 R90s. The used one I picked up doesn't allow the rubber diode board mounts to be installed to hold the board.
Instead, the mounting points are raised, tapped threads, and part of the casting.

My original timing chain cover is from a very early R90s (build date 10/73), and I don't anticipate any issues as the diode board would just be mounted on the raised areas with bolts, without the rubber mounts.

Of course, with the rubber mounts, there are two ground straps that I think I can omit also. (the ground straps run from the two top diode board bolts to the timing cover).

I just wanted to check the experts here for any gotcha's.

Thanks,

RPGR90s
 
The solid mount is a huge improvement. Lots of rubber mounts get converted to solid. I would still use the grounding straps because the electrical grounding of the cam chain cover can be affected by the gaskets between it and the engine block plus paint and corrosion on the bolts that mount it to the block. Easiest and best (I think) to give it a positive electrical bond.
 
Timing Chain Cover

beemerphile said:
The solid mount is a huge improvement. I still use the grounding straps because the electrical grounding of the cam chain cover can be affected by the gaskets between it and the engine block plus paint and corrosion on the bolts that mount it to the block. Easiest and best (I think) to give it a positive electrical bond.

Does the newer timing chain cover still have the mechanical tachometer drive or are you converting to electronic?
Click to expand...

It still has the mechanical tach drive. Thanks for the clarification on the ground straps. I'll continue to use them on the new cover.

Guess I'll be selling the billet aluminum diode board mounts I had been using.

Thanks,

RPGR90s
 
I'm not sure I understand...you're going back to rubber mounts? Those have proved to be the wrong approach. Solid mounts, one seller is Motorrad Elektrik, along with the ground strap, is the best solution for better grounding along with heat transfer out of the diode board.
 
Rubber mounts

20774 said:
I'm not sure I understand...you're going back to rubber mounts? Those have proved to be the wrong approach. Solid mounts, one seller is Motorrad Elektrik, along with the ground strap, is the best solution for better grounding along with heat transfer out of the diode board.
Click to expand...

You're misunderstanding.

The original timing cover had rubber mounts that I upgraded to aluminum billet some years ago.

The new (still used) timing cover doesn't use any kind of mounts for the diode board. The board fastens directly to the cover.

Ironically, both the old and new covers have the same part number stamped on them, FWIW.

BMW must have changed the casting early on in the /6 run, negating the use of rubber mounting the diode board.

Or maybe I have it backwards. Maybe the /5 bikes didn't use rubber mounts, and I purchased a used, but older timing cover than the one that was built with the bike.
 
I guess pictures would help. I'm not understanding how an OEM timing cover wouldn't have mounting features for the diode board. You say the board fastens directly to the cover...how? Are there machined threaded mounts or something? Update...I went to Snowbum's website and now read the following:

http://bmwmotorcycletech.info/diodebds&grdgwires.htm

BMW used rubber diode board mounts on many models, from ~1979 to ~1993, with exceptions. Airheads that came with solid casting metal diode board mounts from the factory are: /5 models; /6 models; 1978-1987 R65 & R80 models.
Click to expand...

So that's something new for me. My Sept 1977 produced 1978 model had rubber mounts which I have since changed out to solid mounts.

As Snowbum further mentions, the rubber mounts were used to cure a problem that they believed was due to vibration but was really due to poor electrical work and high heat. So, it stands to reason that metal mounts should be used whenever someone is in this situation. If the rubber mounts deteriorate enough, the board can become loose, falling forward/backward and causing lots of electrical problems.
 
BMW used rubber diode board mounts on many models, from ~1979 to ~1993, with exceptions. Airheads that came with solid casting metal diode board mounts from the factory are: /5 models; /6 models; 1978-1987 R65 & R80 models.
Click to expand...

Which is another way of saying BMW only ever fitted rubber diode board mounts to R100 engines ... which is the case.
 
20774 said:
I guess pictures would help. I'm not understanding how an OEM timing cover wouldn't have mounting features for the diode board. You say the board fastens directly to the cover...how? Are there machined threaded mounts or something? Update...I went to Snowbum's website and now read the following:

http://bmwmotorcycletech.info/diodebds&grdgwires.htm



So that's something new for me. My Sept 1977 produced 1978 model had rubber mounts which I have since changed out to solid mounts.

As Snowbum further mentions, the rubber mounts were used to cure a problem that they believed was due to vibration but was really due to poor electrical work and high heat. So, it stands to reason that metal mounts should be used whenever someone is in this situation. If the rubber mounts deteriorate enough, the board can become loose, falling forward/backward and causing lots of electrical problems.
Click to expand...

As you say, photos might help. In the first image, the arrows point to the solid diode board mounts I installed to replace the stock rubber pieces.

original_early_1974_R90s_diode_board_mounts.jpg

In this image of the cleaned replacement timing cover, note the solid posts for the diode board mounts, negating using rubber or solid mounts.

The stamped part numbers are the same on both parts.
The red square also highlights '74', which is also stamped on both timing covers.

replacement_timing_cover.jpg
 
Those original solid mounts look like something I bought years ago from Motorrad Elektrik.
 
Dedicated ground wire is what has been recommended over the years. Gee, now I'm gonna check mine. Haven't been in there for six years, and it's snowing like crazy. Thanx for asking.

Question: ain't it likely a solid mounted diode board may get hotter sitting on the engine, than insulated by rubber and likely have air from the front louvres passing over it? Just sayin. Two sense FWIW.
 
8ninety8 said:
Dedicated ground wire is what has been recommended over the years. Gee, now I'm gonna check mine. Haven't been in there for six years, and it's snowing like crazy. Thanx for asking.

Question: ain't it likely a solid mounted diode board may get hotter sitting on the engine, than insulated by rubber and likely have air from the front louvres passing over it? Just sayin. Two sense FWIW.
Click to expand...

They were rubber mounted on the R100's because it was thought that failure was due to vibration when it was really crappy solder joints. Solid mount conversions have been the preferred fix for years.
 
RPGR90s said:
...they're aluminum billet.
Click to expand...

I love that word. A billet is a chuck of something. Aluminum billet is just a chunk of aluminum bigger than the part you are going to make with it. You could have a billet of wood or nylon. Sometimes it is used to distinguish that the part is machined rather than cast. Almost any aluminum spacer you could buy would be aluminum billet. Count on paying double the cost if it is "aircraft grade" billet aluminum. Normally "aircraft grade" aluminum turns out to be 6061 T6, but there are lots of grades of aluminum used in aircraft. All of the common aluminum spacers that this company makes could be said to be made of "aircraft grade billet aluminum"...

http://aluminumspacers.com

Just having fun with words on a dreary day.
 
Billet Aluminum

beemerphile said:
I love that word. A billet is a chuck of something. Aluminum billet is just a chunk of aluminum bigger than the part you are going to make with it. You could have a billet of wood or nylon. Sometimes it is used to distinguish that the part is machined rather than cast. Almost any aluminum spacer you could buy would be aluminum billet. Count on paying double the cost if it is "aircraft grade" billet aluminum. Normally "aircraft grade" aluminum turns out to be 6061 T6, but there are lots of grades of aluminum used in aircraft. All of the common aluminum spacers that this company makes could be said to be made of "aircraft grade billet aluminum"...

http://aluminumspacers.com

Just having fun with words on a dreary day.
Click to expand...

Good points Lee, I confess to having equated "billet aluminum" to a higher grade, higher quality of metal. Maybe it is. Maybe it isn't, but it does sound kind of cool. :)
 
In my case

On my 84R80RT, I have the diode board mounting system like RPGR90S is showing in his picture. There is no need for rubber mounts or spacers of any kind on this timing chain/diode board combination. You just have to be careful to get the proper length Allen bolts for the four mounting points. Too long a bolt runs the risk of bottoming threads before the diode board is tight. Or, worse case, a broken bolt.

For what it is worth, is this the correct timing chain cover for this bike? I have no experience with swapping parts from newer bikes to older bikes.

My Motorrad Electik diode board I installed on my bike along with the higher output alternator did not need rubber grommets or spacers. I just had to find shorter mount bolts. The original bolts are M5X20-, I went with M5X10. This set the diode board properly.
I did use the two supplied ground wires, what the heck, it is a BMW. St.
 
RPGR90s said:
Good points Lee, I confess to having equated "billet aluminum" to a higher grade, higher quality of metal. Maybe it is. Maybe it isn't, but it does sound kind of cool. :)
Click to expand...

Marketing hype. I put it right up there with "synthetic brake fluid".
 
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