The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Barry on July 18, 2012, 04:43:16 AM
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There has been some discussion on the Airheads list recently about the problem of pawl spring breakage in the gearbox. When this spring breaks and it has happened to a few unlucky people you are stuck in whatever gear happens to be selected and that could be neutral which would certainly be a problem but 1st or 5th would be very unpractical too. When the spring breaks a pawl arm falls down preventing the gear lever movement from being transmitted to the shift mechanism. A tool has now been devised to temporarily lift the pawl back up so you can operate the gear lever and change into 3rd which is considered to be the most practical gear in a get you home scenario.
Snowbum has now published this very useful information on his website.
http://bmwmotorcycletech.info/emergency-shifting-tool.htm
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Did snowbum just put a rod through his transmission oil filler plug or is that another part?
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The modified Al Vangura-designed tool in the photos is by Bob Sipp; as are the photos. Bob da Snowbum did not say he made on for himself. Bet he already has one.
The drilled-out filler plug and knurled knob are nice touches on the Sipp tool. I need another small project. ;)
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Thanks for that Barry!
You know, that got me thinking about the 'improved' version. ;)
It may be possible to engineer it to operate via the clutch cable for normal shifting.
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It may be possible to engineer it to operate via the clutch cable for normal shifting.
It's an interesting proposition. Would you have to take the gearbox end cover off to engineer it accurately ? I've never needed to open up an Airhead gearbox so I'm no expert but looking at the published pictures of the tool in use it occurred to me that if a a suitably positioned hole was machined in the gearbox end cover then a much simpler design of tool could be used and the hole wouldn't look too out of place if threaded to take a standard. level/filler plug.
On the other hand it might just be easier to do something about preventing the spring breaking. The other bit of info that surfaces in this pawl spring debate is why it breaks in the first place. There is a suggestion that the pawl boss which supports the spring may be slightly too large in diameter causing the spring to bind when it is under tension. As far as I can make out the springs is #7 and pawl #8 in this diagram.(http://)
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I think I'll just call a tow.
k_enn
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The one time that I had the shift spring brake I was down shifting into 3rd gear. Luckly i was just down the street from home. I had a buddy that his broke in 1st gear and rode home about 200 miles like that. This tool would be nice to have so you could at least get in 3rd gear to get you home. Your stops and start would not be to bad in 3rd.
I would use the tool to get in a better gear for any long distance travel and put the filler plug back in and not have this installed while moving.
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Big buzz about this "tool" on the Airlist.
After posting drawings and photos, Robert Fleischer, aka The Snowbum, said he will offer no further details nor commentary.
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I've never had one break, but ride enough that it's possible it'll happen at some point. I've heard that the early five speeds (74-5) had to large of a boss and the spring would bind. But our R65s are newer and out of that range.
I was thinking like this:
Use a bolt with a welded-on arm instead of a drilled oil fill plug. Drill a hole through the bolt and either mount a seal or a felt inside to keep the oil in.
Bend up the steel as shown inside the transmission. But once it passes through the bolt, bend at right angles.
Attach a spring to keep it disingaged.
Attach a cable from the bolt's arm to the rod, then to the clutch arm at the back of the transmission. Make it easy to attach, and then when the clutch is pulled in, it also releases the 'pall activator'.
That way you'd be able to shift normally.
That's an interesting idea to put a hole in the back cover. I even thought of running a cable or rod up through the top of the transmission. But it seems like the simplest solution is to do what I've just laid out. It would still be small enough to take up very little room, and could allow the bike to be ridden many thousands of miles normally until the right time to fix it properly, and would eliminate the need to slip the clutch through towns or run down the highway in third.
Even though I've fixed something like ten or twenty of these transmissions, I don't totally understand them. Thinking on this more, it seems the pall needs to be in contact with the pins all the time and has a spring because the shifter moves back and forth. It may be possible that a spring type mechanism is all that's needed on the outside of the transmission (with our rod solution) to provide constant tension on the pall arm. That would be a much easier solution!
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... It may be possible that a spring type mechanism is all that's needed on the outside of the transmission (with our rod solution) to provide constant tension on the pall arm. That would be a much easier solution!
That's how I read it.
I knew that Snowbum was only publishing the info and did not invent the tool. What surprised me is that the tool was developed 13 or 14 years ago and we only just heard about it !
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I get the impression that there is very little chance for the broken piece('s) that remain inside to cause further damage. Is it the fact that gravity and it being bathed in gear oil keeping it out of the way of damaging the rest of the moving parts? Maybe a stronger magnetic drain plug would be helpful here...
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That's a good point. I haven't seen a broken spring but hopefully it's the coiled part that breaks and both pieces stay put on the boss.
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Don't trust immunity in newer transmissions-it happened to me on an '83. Left me two up in Highlands with 4th and 5th. Careful planning for only downhill stops enabled me to get back to Atlanta.
There was an update to the shifting assembly which was supposed to help, but I do not remember the details.
Bob
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Any spring can break, so don't think the newer style is immune to this problem. When the spring breaks, I believe the bit that breaks off just falls to the bottom of the transmission, the rest stays where it is. No way for it to get tangled in the gears.
I've got a few transmissions in pieces around here, I think I'll look into this.
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as a very lucky fellow who has had this spring break 4 times on my '82 R65LS, I am all ears about "why" this happens. The dealer sure doesn't ......
mine has broken about every 20,000 miles ..... fortunately I was close to home each time. Most recently was just last August.
ACTUALLY, make that 5 breakages. The 3rd time it broke the dealer fixed it. The morning I picked it up, the mechanic himself rode the bike from the shop alley to the parking lot in front .... and the new spring broke right there before he hopped off.
Cheers,
Carl
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If I were you Carl, I'd be looking for a good replacement shifter mechanism. Either that, or get someone to take a close look at yours -- there's very definitely something wrong with yours and it needs to be corrected. These things don't break all that often - statistically speaking - and yours breaking that many times aint right.
That tech you mentioned that had it break riding it out of the shop - he should have gotten wise to this right then! I mean, he pulled the transmission to fix a broken spring, and the new one breaks before the customer can even ride it!
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Snowbum has some views on why the spring breaks :-
The last bit about post 81 transmissions gearboxes being immune doesn't seem to be bourne out by Bob W's experience.
WHY the breakage? TWO reasons primarily. The early spring rubs on itself during operation, wearing itself thinner. The spring may wind too tight on the boss,
causing excessive force on the spring. Possibly some faulty springs, possibly a few other things; we just do not know.
Pawl spring breakage fixes: One can turn down the boss it rides on by about .060". The boss needs to be
around 0.613" or below. If yours is about .630, then machine it down. Tom Cutter posted to the Airheads list that the original was 15.95-16.0 mm;
and the change should be to 15.55-15.6. I don't hold to such tolerances. Here is my take on the matter:
The post the spring is on has had its diameter changed in the 'shift kits'. You can certainly reduce the diameter of the stock type. The spring must
not bind-up in its operation. Certain of the so-called 'shift-kit' parts, Pawl 23-31-1-242-892; and Segment (offset link) 23-31-1-231-578,
supposedly will 'cure' broken pawl spring problems....but modifications work well. As noted in 6B, above: The OFFSET segment for pawl
spring clearance was one of BMW's changes. What has not been said hardly anyplace, except perhaps Anton Largiader's page, is that the Shift Kit,
incorporated by the factory since sometime late in 1981, will keep the pawl engaged, if the spring breaks.
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wirespokes,
I couldn't agree more ..... but have been unable to find a private person in SoCal with the knowledge of how to take all this apart.
-- which is to say, the only people who can do the take apart are the mechanics employed by the local BMW dealers, and they are "not" very interested in such a private project.
Cheers,
Carl
(edited to add "not")
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...and they are very interested in such a private project.
I'm sure you meant to say " they aren't very interested in such a private project."
I can understand that - 'just get the thing fixed, getcher money, and go home!"
I figure it's something like what Barry just quoted - the boss being too large in diameter, which stresses the spring under compression. No idea why or how that could have happened, but that's my first suspicion.
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wirespokes,
oops .... you are correct ..... I edited my above post to add "not"
Yep, I've looked around a bit for a local BMW enthusiast who can handle a transmission disassembly but haven't found one.
On The Other Hand: is it that tough for a shade-tree mechanic ?? I've been scared of it, because I heard many years ago that there are special tools necessary to get a transmission apart (and reassembled). And of course, "secret" knowledge about the inside pieces and parts, and how all that fits together .....
Cheers,
Carl
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Well, yeah - it does take special tools to remove the U-Joint flange, but that's all you'll need to get inside.
If it's shifting fine, then reshimming might not be necessary. However, sometimes the shims fall out of the bearing pockets and get mixed up when removing the cover. Then you're screwed, as the special tools will be needed to figure out which goes where.
The transmission is a puzzle in that some parts can't be extracted without first removing someting else. And the proper technique for working on them is important, otherwise expensive parts can be damaged; things like knowing how to heat the cover, how to reset the shafts, checking for play when it's back together...
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So, the smart play is to find someone local who knows what they are doing ...
AND of course, the obvious question is: why the heck does this pawl spring problem even exist ??
--- more of a rhetorical rant/chant as to why either the BMW engineers, or the much smarter community in general, hasn't figured it out ??
Cheers,
Carl
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Who knows, Carl? Nothing's perfect, that I've heard of. There's always some down-side to put up with. So you pick what does best for you, and has the least negatives - or at least the ones you can live with.
Some like to think the German engineers designed the most perfect equipment. And then they're upset when something breaks or doesn't work right. All things can break, just a fact of life.
But I agree - why not have it fail in a working mode rather than total failure?
It's kind of like the Motometer speedometers - there's a gear that tends to slip rendering the odometer inoperative. This lasted the whole run of airheads from 1970 to 1995. They never changed it! I've heard the same thing about VW and BMW car speedometers, except with them the gear is plastic. Never changed. Someone finally made metal replacements, but not Motometer (or VDO, don't recall which).
It doesn't help getting upset about it - it is what it is, so let's do what we can to resolve it. Springs do break, and sometimes there's something defective, something machined wrong, who knows? Maybe it got dropped on the assembly line and now there's a mis-alignment causing all the problems. Or something's binding. Now it's a puzzle and someone who's willing to take a good close look, and knows what he's looking at, needs to check it out.
In your position, I'd find another transmission, make sure it's in good shape and install it. Then have the original looked at and the trouble found. I would't want to ride a bike farther than I could push it home if I knew it had a ticking time bomb for a pall spring.
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I'm thinking that ol' 'Spokes is traveling along my thought trail. There just may be more wrong within that specific R65LS gearbox than bad pawl springs. Four breaks speaks volumes.
Reminds me of some of the death-knell Meriden Triumph factory fiascos brought on by their use of mix n' match, wash n' wear bits used to cob together sorta-complete bikes from the leftover stores of years gone by.
"The Japanese will never be a threat to the British motorcycle industry" - Edward Turner
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as always, the best advice is always found here !!
Cheers,
Carl