Intermittent drive??

[The Other PaulG]

I'm throwing this one out there in the hope that this is familiar to the assembled wisdom...

Bike - 1992 R100GS P-D
60,000 miles

Last week I was trying to bump start the bike (see battery thread...) when I lost 'drive'.

At rest and without the engine running, the bike went through the gears perfectly but when in a gear, acted like it was in neutral - the rear wheel would spin freely and the kickstarter turned the engine over (still didn't bloody well start, though...).

During the bump starting, it was all pretty gentle and certainly nothing made any noise to suggest I'd stripped splines or similar.

Tonight with the new electric boot it started but again, when in gear it just acted like it was in neutral. Whilst stationery (little choice at this point) I went right up the box into 5th, at which point it suddenly regained drive. Back down to 1st, it set off perfectly and now goes through all the gears and rides perfectly normally.

Could it be that during repeated attempts to kick-start and bump-start it, I somehow put it into a state where it had a box full of neutrals and it'll never happen again.... or am I sitting on a serious gearbox issue and shouldn't go more than a mile from home without an RAC card??

Any thoughts or experience gratefully received!

Paul G

 

[Smug]

Clutch somehow stuck in the disengaged mode?

 

[Voyager]

Clutch somehow stuck in the disengaged mode?

The kickstart wouldn't have turned the motor if that was the case.

Interesting one this.

If the kickstart turns the motor then the input shaft and clutch are OK.

If there is no drive, no nasty noises and the drive suddenly comes back I can only think that the output flange has come loose on the output shaft.

The flange is on a taper, there are no splines or keys in there so it could just slip.

Being on a taper it may have suddenly caught and given you drive again.

The flange is torqued to 163 lbs/ft and usually needs a special tool to get it to release, maybe the last person to put it together has been a bit too gentle with it .

Drop the swing arm and undo the propshaft, that will give access to the nut that locks the flange to the gearbox shaft. Ideally you will need a locking tool and a large torque wrench to check it out.

I can't think of any other possible causes. If the box is changing normally you won't have a load of neutrals in there.

Let us know how you get on with it

Bob.

 

[(RIP) Proff]

As Him above says,
If the outputshaft ain't done up ever so, ever so, [happy now?] tight
Bumping them can shock the flange loose against the direction of outputshaft thread, just hope you ain't friction welded the flange to the taper now..

 

[The Other PaulG]

Thanks Voyager, Proff, that sounds like excellent advice.

I'll get in there, have a ferret around and report back.

PG

 

[Steptoe]

A loose flange........

Do you know how many years i've waited to post that comment.

 

[nick.ct]

As Him above says,
If the outputshaft ain't done up ever so, ever so, [happy now?] tight
Bumping them can shock the flange loose against the direction of outputshaft thread, just hope you ain't friction welded the flange to the taper now..

Exactly what happened to mine.............. Take the flange off and hope you haven't damaged the gearbox output shaft

 

[The Other PaulG]

A loose flange........

Do you know how many years i've waited to post that comment.

What would you recommend I use to lube the loose flange?

 

[(RIP) Tunneruk]

How about a bit of this .....












Well, seeing as we're talking about flange and all that ........

 

[The Other PaulG]

OK, gaiter and 12-sided bolts removed, swing arm and wheel detached and ready to be removed, I'm going in tonight and expect that the first job will be to manufacture a tool to hold the flange with (steady, chaps...) - wish me luck.

When re-fitting the 12-sided bolts, Haynes make a lot of fuss about using the right tool because use of a normal torque wrench or spanner will spell disaster... really??

Please, what's the collective opinion on re-tightening those bolts? I bet I don't really need the special tool???

PG

PS, how good is the original BM toolkit??!! I had forgotten that bikes could come with a genuinely decent quality set of tools.

 

[Kenny]

Just really feckin' tight is about right. They are stretch bolts.

 

[Beemerboff]

They are tough little bolts, so as tight as you can get them with the longest 10mm combination you have will be OK.

Or you could put one of the old bolts with a nut on it in the vice and do a bit experimenting with a torque wrench and the chosen spanner to get a feel for the required torque.


And remember all torque values are clean / dry unless stated otherwise.

 

[(RIP) Tunneruk]

Just really feckin' tight is about right. They are stretch bolts.

This would suggest that they need to be replaced and not refitted?

 

[Voyager]

Please, what's the collective opinion on re-tightening those bolts? I bet I don't really need the special tool???

I refit the swing arm and attach the rear brake rod/cable.

Use a 12-sided ring spanner on the (new) stretch bolts.

Stand on the back brake pedal and stand on the ring spanner .

Rotate rear wheel to line up the opposite stretch bolt and repeat.

Do the other pair.

Re-fit gaiter.

Job done.

I'm about 13 stone - I've never broken a stretch bolt, but neither have they ever come loose ,

Bob.

 

[The Other PaulG]

Thanks guys, I'd never have had the nerve to tighten them that much without those comments.

Just imagining stripping one of the internal threads at the gearbox end makes me feel slightly nauseous...

 

[Rob Farmer]

Just imagining stripping one of the internal threads at the gearbox end makes me feel slightly nauseous...

It would only strip a thread in the flange. A new one of those is £47 + vat so not the end of the world. Your more likely to pull the thread off the small bolt than the flange.

For all their mechanical simplicity the airhead gearboxes are nice things to work on. The biggest killer of them is people using the wrong oils or running them dry.

 

[Beemerboff]

http://jeep.yager.net/docs/trans-to...f Sealed-Clean Bearings for Transmissions.pdf

Using 1RS sealed bearings instead of the proper NSK ":Sealed - Clean" TM bearings doesnt help either.

 

[The Other PaulG]

And the winner is........

.....Voyager!

Thanks everyone for their input.

I got to the big nut that holds the flange onto the shaft, as recommended, and indeed it seemed to have been left too slack.

It tightened almost another half turn, so the theory that this might have been the culprit seems to be born out.

I test rode it for about 30 miles today, doing some hard acceleration and also deceleration using the gears to see whether anything would let go but it all held nicely.

Unlike the airhead gurus, my mechanicing is at roughly Haynes three spanner level, if you know what I mean, so here are a few extra bits in case you're also not up to the five spanner rating yet

Overall, it's not a hard job.

1) I removed the wheel and drive shaft/paralever arm all in one - next time I'd remove the wheel from the paralever arm first to make it easier.

2) If you then lean your wheel/shaft against the wall, when you return to it there may be a large puddle of oil under it! Oil runs out of the gearbox end of the paralever arm if it's laid so that part's lowest (and if you have the problem in 3).

3) That oil in the paralever arm may have come from the gearbox (pretty sure mine did). A clue may be that the flange had oil on it. Check that the screw which secures the earth strap and speedo drive is not blocked (it has a narrow hole right down the middle - mine was blocked so I'm hoping the problem will disappear). There's much written elsewhere on this site about that screw and some stories end with goosed gearboxes, so be careful!

4) Making a tool to hold the flange while you tighten the nut is essential but easy with a piece of Homebase flat steel bar, a drill and a power file.

5) When tightening the big nut, it suddenly went slack - CR@P - !!! It felt like it had stripped, but then I realised it was just nipping up on the tapered shaft, and so this is in fact just what you'd expect.

6) Getting the front boot back on was a bitch, it helped when I (again) disconnected the earth strap. Engage the boot at the rear first then run your fingers to the front in order to seat it. On the 20th attempt...

I hope this helps.

Thanks again to all those who offered their wisdom - it would have taken me a lifetime to track this down otherwise.

Paul G

 

[Voyager]

3) That oil in the paralever arm may have come from the gearbox. Check that the screw which secures the earth strap and speedo drive is not blocked (it has a narrow hole right down the middle.

5) When tightening the big nut, it suddenly went slack - CR@P - !!! It felt like it had stripped, but then I realised it was just nipping up on the tapered shaft, and so this is in fact just what you'd expect.

Thank-you . . Thank-you. (but I just beat Proff to the post ) .


III). Hmmmm there shouldn't be oil in the shaft. There is usually a 'V-shaped' vent hole in the gearbox casing just above the output shaft oil seal. That has to be sealed on a Paralever. Strangely, I can't see the vent in your picture .

V). The output flange nut has a shake-proof washer under it - its a heavy spring steel washer with a bit of a dish/twist to it. It was probably that flattening out that produced the momentary slack.

Glad to hear that you got it sorted

Bob.

 

[Beemerboff]

No response to my stirring on the sealed bearings then?