Diode Boards & Grounding Wires
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diodebds&grdgwires.htm-18
Diode board testing for faults, as well as repairing the faulty Wehrle manufactured ones (with non-bent over large diode leads) is covered in depth in the June 1999 issue of AIRMAIL, an article by BMW Guru Oak Okleshen. That is a really good article. Many airhead owners will want to obtain or at least read this article. I am not going to repeat all of that article HERE, just make note that the early Wehrle manufactured boards have a problem with solder joints and non-folded over wires on the 6 power diodes, and a board modification may well be needed, especially if you have a R100 engine, which develops more heat.
1. Diodes can be tested for forward resistance
on your ohmmeter (should be fairly low, and just about equal on your meter, but
the actual reading could be 8 to 120 ohms perhaps, depending on the meter...this is not an absolute)
on X1 range (if it has adjustments for range). An ohmmeter
has a small internal battery that turns on the
diode (some expensive ohmmeters do not turn on diodes) in the so-called forward mode of the diode,
when the leads are properly connected. The reverse mode
of the diode should indicate a very high resistance and can be tested for this
by reversing the ohmmeter leads to the diode and raising the full scale setting
on the ohmmeter (if it has one), as the reading should be in the millions. All
diode board diodes can be tested in this manner. In fact, most any
diode can be tested this way. This test can
be VERY confusing if anything is connected to that diode. It does,
however, work fine on the already connected Airhead diode board, with some minor
reservations. Better is with the board removed.
A better test
FOR THE SIX LARGE DIODES IN THE DIODE BOARD (I like BOTH ohmmeter AND the
following test to be
done), is a test that passes appreciable A.C. current through the diode.
If you stay under one ampere or thereabouts, this test is safe for the small
diodes too. Obtain a 12 or 14 volt lamp...a taillight or turn signal lamp
is fine, and a 6 to 12 volt transformer. A suitable transformer is Radio
Shack #273-1352 or 273-1511. An old bell ringing transformer might be just fine.
So might be modifying leads for an old desktop high intensity lamp unit...maybe
with its lamp!
You can purchase a socket with wires attached for the
lamp if using a transformer. Connect the lamp in SERIES with the
transformer, leaving two wires for testing. When the wires are touched together, the lamp will light up brightly. When the wires are
touched momentarily to a diode, the lamp will NOT BE LIT if the diode is
faultily open, FULLY lit with a shorted bad diode, and considerably dimmed on a good diode. Getting a nice set of test prods from Radio
Shack and making a nice little tester out of all this is a NICE idea.
This type of test is called a dynamic test. It is the best test for your
diode board parts.
2. BMW used rubber diode board mounts on MANY models. From about 1979 to about
1993, with some exceptions.
[Airheads that ALREADY SHOULD HAVE solid
metal diode board mounts (check your bike, no matter the model) are: /5 models;
/6 models; 1978-1987 R65 and R80 models]
I believe BMW thought that installing rubber mounts would
cure the problems they were having with the boards, which turned out to NOT be vibration.
The problem was improperly formed and soldered leads on the Wehrle manufactured boards,
with the solder joints failing especially on fairing equipped models, from their extra heat.
The rubber mounts caused the need for extra grounding wires from the top (grounded side) row of
diodes; AND, the mounts did not transmit diode board heat well to the
timing chest casting, nor did the grounding method work as good as solid mounts
types did. The rubber mounts deteriorated, and if the diode board mechanically disconnected from
the bad mounts sparks could fly, with resultant burned or otherwise damaged boards. The answer
to ALL the rubber mounts problems are to replace them with solid metal aftermarket mounts, which
have additional grounding benefits as well as lasting forever and removing more heat from the diode board heat sink areas. Metal mounts are available from both Thunderchild
and Motorrad Elektrik. Those mounts are FAR nicer than making ones of
stacks of washers!!
http://www.thunderchild-design.com
All mounts, rubber or the above, are a PIA to install...some tricks to it, for the difficult starter motor side of the mounts, such as gluing nuts to your fingers to ease the assembly, but the modification is VERY worthwhile. Once you install metal mounts, you will NOT have to remove them for replacement, again. Installing the mounts is very easy if you are also doing a timing chest/chain type of job. In any event, it IS worthwhile, and highly recommended!!!
If
you are too cheap to purchase metal diode board mounts from either of the two
above companies, then you may want to make them on your LATHE yourself.
Please do NOT use stacked washers! Make from 0.5" round
stock. You can use aluminum or brass. The "middle part" is
to be 0.5" diameter, 0.58" (approximately) wide; and, each end MIGHT
(read on...) have a threaded portion sticking out from that 0.5" round
piece. You could use a threaded piece of rod at each end, and thread the
inside of the round piece, or, just make the entire piece on the lathe from one
piece of aluminum or brass, and thread the ends. If you
use threaded rod, or a cut-off screw thread, use Loctite RED on the ends going
INto the round piece. Another way of making these would be to use an
allen screw in from the starter compartment area, and not have that particular
end of the mount have a stud...only the other end...or, actually, you could have
no studs (threaded material) at either end....just make the 0.5 x 0.58 piece,
drill and tap it through, and use allen screws at both ends. DO use
Loctite RED at the rear, the starter cavity screw. If you decide to
make these, you may also be interested in the stud or screw you use.
The threaded stud, if you make or buy all-thread for its use, is 5 mm.
***The two completely separate grounding wires assemblies are
another story...hence the rest of this article.
HISTORY:
In September of 1988, BMW Service-Information bulletin 12-012-88 (2323) came out, and covered complaints of:
a) diode board connections having solder melting
b) low battery charging rate
c) GEN lamp would glow around half intensity
That bulletin covered all boxer models FROM 1981, that had the electrostatic dip black coating on the timing chain case cover where
that fits against the engine. BMW said that increased resistance at the diode board grounding points, due to corrosion, ground wire
connection deterioration; and, the exacerbating effect of the insulation by the paint at the diode board mounting points on the timing chain
case, ETC. were the causes. Their fix was to remove the diode board and scrape away the paint from all 4 mounts on the timing cover.
Rubber mounted boards were to have the existing ground wires replaced if they looked corroded or overheated, and those ground
wires were to be SOLDERED at their lugs. They also recommended cleaning the paint from
the cover around bolt heads for the ground terminals, etc. I have seen many models after 1981 without that
coating! STILL, the bulletin does apply...as far as it went.
In October 1993, another BMWNA S-I came out, this time it was 12-019-93 (2611). This bulletin was supposedly to cover all boxer
models from 1980, EXCEPT R1100 models (obviously, there were no R1100 models to say no to, for the prior bulletin).
THIS DATE OF MODELS 'FROM 1980' IS WRONG!....BMW made no mention of the 1979 model, which had the same setup, but the BOSCH board was
used (the Bosch boards did NOT have the bent lead problems...see earlier). NOTICE however, that it makes NO difference about the
boards HERE. The bulletin SHOULD have said 1979 onwards...and, the bulletin also
forgot that BMW changed back the type of mounts in 1992 (I think it was 1992,
some may have been later).
3. Well...that may be confusing, but OK, as another bulletin supersedes
that one. But, you will still need THIS bulletin information...
so...here is the information for this October 1993 bulletin:
COMPLAINTS: diode board grounding wires getting hot, stiff, solder melting, melted insulation, and alternator output falls below 13.2
volts.
CAUSE: increased resistance at the diode ground points due to corrosion of the ground wires and bolts.
REMEDY: install ADDITIONAL ground wire 12-31-1-468-013. That 'wire' is really
a three wire arrangement, one end of each connecting to a common lug. That means this harness that has 4 lugs total. This
entire assembly was to be installed such as to tie the diode board, timing case cover, and the engine housing, all together, electrically.
The second page of this bulletin listed the above wire, a hex bolt 07-11-9-913-015 (an error, it really should be
07-11-9-914-148); an
allen bolt 07-11-9-901-023 (should be 07-11-9-919-792); two washers 07-11-9-931-029; and finally, a 'cap'
46-62-1-453-668.
There was a sketch. I will describe where the connections are made, per BMW:
Facing the timing chest, the upper left and upper right diode board mounts were each a connection point for this 'wire assembly', and
these wire connections were made onto the mounts. NOTE!! This is in ADDITION to the already existing grounding wires at the top
mounts!..in the same position. Since there are now TWO lugs at each
mount....this spaces the upper part of the diode board outward a tiny
amount, the two washers in the kit were to be installed on the lower diode mounts.
SEE later note herein about those washers!!! The hex bolt in the kit is used at the threaded area
located directly below the large hole behind the diode board. The final connection is directly to the right of THAT...and the allen bolt
in the kit is used there. This point is through the sort-of large elliptical hole in the timing chest...and this point where this last lug attaches
is actually the engine case, the TRUE ground. Thus, everything is tied together
and grounded to everything else. It is important to note that it is this last connection through that elliptical hole to
the threads already available, that makes the REAL grounding of the diode board to the
engine itself.
NOTE: It is not a bad idea to use
some grounding wires even if you have solid mounts. In a few instances the
outer timing chest does not, because of painted joint surfaces, ground to the
engine really well. This is not something a simple ohmmeter will
show up.
4. In November of 1993, BMW came out with a REVISED S-I bulletin 12-019-93 (2611).
NOTE that it has the same bulletin number(s).
BMW carried forward the same 1979/1980 error, however. NOW, BMW is adding some additional 'causes'. Hot weather driving,
city riding, low battery voltage, full fairings...yeah, riiight!! BMW now corrected the parts numbering errors...and made some
additional errors! and, no, they never corrected the corrected revised version!
Well, here is the skinny, simplified:
The info on the wire harness and connections are correct as I outlined them
above. BUT, the -792 allen bolt now comes with a captive waverly washer, and, frankly, that M6
'cap' is not really needed...never really was anyway. You will want to GET a waverly washer for the -148 hex bolt,
however.
The MAIN reason I am having all this chit chat here is that if you see something that looks strange in your timing chest outer area, you will
know why...and if you see no wires and you have rubber mounts, you will know of the modification.
Frankly, I HIGHLY advise folks to install METAL mounts if you do not have them. I also advise
extra grounding of the two top diode mount screws,
to the INNER WALL, that being the ENGINE wall. As described, in the elliptical
hole.
NOTE 1: There MAY be an existing M6 x 15 hex bolt with a waverly washer at the position of the TRUE ground mentioned
previously, so why not use it!
NOTE 2: I have seen some very minor differences between some stock bikes.... maybe an extra
washer found at a mount, that type of thing.
NOTE 3: If you have the solid aftermarket mounts, just about all in this mess of information is
moot...except for
the grounding wires, which MAY help. Moot?....well......if the diode board fitting and mounts are CLEAN of
paint, corrosion, etc., and the timing chest and engine are making good electrical contact (can be
assured by adding a couple of grounding wires),...then this automatically ties the diode board
grounding top area to the timing chest and engine case.
Hassles on removing and replacing the
diode boards:
The nuts used on both ends of the rubber mounts, or the forward end of cast-in-place mounts, or both ends of aftermarket metal mounts, require a 8 mm wrench. In order to do this job properly, you WILL...really WILL, want the following tools, UNLESS you are removing the inner timing chest casting:
A small
combination wrench (that means open wrench at one end, box wrench, preferably 12
point, at the other end) of 8 mm size. You will want to take an acetylene
torch and bend this wrench, then keep it. Because replacing rubber
mounts is common, for OTHER folks, and I am the helpful sort, I keep this tool
in my bike's tool tray.
SOME folks have used a small 1/4" drive 8 mm socket, and drive handle,
etc., some modify those, some use a 1/4" universal U-joint adapter in using
that socket and drive handle. Whatever YOU want.
DO keep a wrench of some sort in your on-bike tool tray, that would enable you
to R/R the diode board, if it ever failed. You don't really need any
special tool to be in that tray for replacing the mounts...after all, you ARE
using metal ones.
ONE
idea for a removal of the diode board tool, besides the 1/4" 8 mm socket,
perhaps ground thinner is as follows:
Obtain an 8 mm tubular socket wrench....really just a tube incorporating a small diameter socket at one end and a wooden or plastic handle, often generically called a SpinTite wrench. Grind the end so it has a fairly small, yet still strong enough, diameter, and it is nice to grind the tip end so no INternal taper is on the working 8 mm area. I also do NOT like like to have this hex end too deep....shallower makes for easier starting a outer diode board nut onto the threads. There are versions of these commercial wrenches that even have internal magnets.
Medium length hemostats: you may well want this for the installation of the solid mounts (or, replacing the rubber ones if you are that stupid). Some folks glue the washer, then the nut, to their fingers. Removing the starter motor area cover (gas tank first, please) is really needed. Removing the starter itself is not necessary, but cuss words help. NEVER remove the starter cover without disconnecting the battery first....otherwise it is possible to short the hot starter solenoid terminal to ground, and cause sparks, etc. Check the starter motor and solenoid nuts...they need to be tight.
When you are trying to install the nuts in the starter motor cavity area, they, and the waverly washers you should be using, tend to fall down into cavities. They do NOT fall into the engine interior, but may be out of sight. Thus, having a magnetic wand is a nice tool to have here.
For the METAL mounts, I recommend that you not only use the waverly washer on the INside area (starter motor side), but have a wee drop of Loctite Blue also there.
Regarding those 5.5 mm flat washers, number 07-11-9-931-029: I have seen ONLY black colored washers. These do NOT conduct electricity well at all. That was fine, as they were in the KIT for use at the LOWER, electrically hot from ground two mounts, and were to compensate for the thickness of the wire lugs of the grounding wires at the top mounts. The diode board fit OVER these lugs/washers/mounts. Under no circumstances use these washers at the top studs, on the underside of the board, nor by mistake as a washer behind the nut on the outer side of the board. You MAY not even want these washers on the lower studs as specified in the kit instructions. The reason is a bit subtle and not easy to notice. The diode boards are NOT made the same, although they look similar, and I mean Wehrle versus Bosch. LOOK at your diode board UNDERside, and if the distance from the aluminum heat sink to the rivet end is the same for the two heat sinks, then you need the washers at the lower studs, they would go on first, before the board. If the lower, insulated rivets measure slightly more height overall than the grounded rivets, then just don't use washers. You will need at least a vernier or something to measure the distance, as we are talking only a wee bit of difference. NOTE that none of this discussion has anything to do with the various locking washers used on the starter motor side nor outer, forward, nut side.
Revisions:
02/03/2003:
review, upload final version
02/04/2003: add note and
hyperlink regarding HINTS article re: diode boards.
04/04/2003: considerably edited for clarity
09/16/2003: additional clarity, many places
01/30/2009: more clarity...esp. item 2.
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