What could have jammed my drive shaft?!

[Guest]

I must start with saying, I guess I should be lucky to be able to write this post.
If the failure of the driveshaft would have happened 200 meters earlier, in a left curve, while being in the right hand lane with lots of traffic before and after me, I probably would have been dead or seriously injured!

Last friday, I was going to work as usual. I had an open lorry with dirt/gravel on it, and I had dust blowing in my face. I thought I should take over, but decided to wait until I had cleared the curve.
Said and done.. after the curve, I went out to the left hand lane, went from 90 to 120 km/h to make a quick take over and get back into the right hand lane again. When I am along side the lorry, something happens. The rear wheel starts bouncing off the road for a few seconds, until it starts to slide. I don't really have time to think, I just held on and thought I must try to follow with the skids, not break with the front breaks and just keep the damn motorcycle up straight.

Fortunately, I manage to do so and are stopping just at the raid that are separating the traffic from each other.
I put the bike on the sidestand and quickly jump off to set myself in safety between the separating rails in case a car is coming and not able to change lanes or something.

Just so glad nothing happened more than a bike with a completely jammed driveshaft.
Rear wheel is completely locked and I can not shift down. Trying to shift from 5 to 4 is impossible, it never enters the 4:th gear completely, and the rear wheel is locked no matter what I do.
When I came to a stop, I also noticed fluids pouring out from the engine, around the drive shaft area.

So the question is, before I open the engine.. what could have happened? Any ideas?

[AMK]

http://www.thegsresources.com/_forum/showthread.php?248833-Secondary-gears-wanted

This may be what happened. Just a few posts below yours.

Also, glad to hear you made it through.

[noratx]

Hmm.. will be interesting to see if you are right when I start disassemble the bike.
How could this happen though? I mean, there were oil there, since the bike ****ed itself after it stopped, and the fluids came from the shaft, so it shouldn't have failed due to lack of lubrication.
(And on a sidenote, why the heck did it dump the oil when I finally came to a stop).

I just have all these 1000 questions whirring around in my head and I can't come up with an answer myself, so hoping for some early wisdom from others (ofcourse, I will be wiser when I hopen the engine and have a look, but still want to ask.. hope nobody minds..)

[AMK]

If it is the drive gears it may have taken out the rear seal (best case) or it could have cracked the tranny case (worst case).
The gears are easy to check without pulling the engine but if its in the tranny...well... I hate to think about that.

[Charlie G]

hope nobody minds..)

Your questions and repair add to the collective knowledge here. Please continue posting until it is fixed.

[phydeauxmutt]

Just a few posts below yours.

It might have been, at the time you posted.

A few minutes (or hours) later, it's nowhere in sight.

[storm 64]

I also have a 1982 850g with close to 50,000 miles on it. I would be interested in knowing what to listen for or know what broke. I've been following Redman's post. It seems his problem was more gradual. Keep us posted Noratx.

[noratx]

Sorry I didn't say anything until now.
I have not yet gone through opening up the engine, I have only just taken the whole bike apart and left it on shelves, but from that, I can atleast say that there are nothing wrong from the mounting of the drive shaft all the way down to the rear wheel, so it's internal in the engine.

I will open it up either tomorrow or next weekend, and will take pictures.

There never were any sounds.
Right before it happened, I noticed a little drag, as if there was something wrong with fuel delivery, so I didn't think more of it than what I normally do during those occations.
Less throttle for a few seconds and then back up again.
2 minutes later, this happened.

Will be very interesting to see what happened and also to see which way to go to restore one of the bikes.
Should I replace the secondary gear in the now spare parts engine and just swap engines from my other bike..
Or should I dig out the crank shaft from the spare parts engine and replace the crank shaft (that I suspect to be broken) in the other engine.

When I first bought this bike, it was for the spare parts, but I noticed how well and smooth the engine was running and thought to have this bike as the new one and the other one for spare parts.
After this accident, I don't feel confident to use this bike though, so I'd rather use it for the parts.

[Redman]

Nor,

Are you saying you have dissasembled the bike?

Some of the guys that have responded above (Mr Alan AMK in particular) I know to have lots of expereince with this secondary gears. I have expereince with one incident.

You can access the driven bevel gear (that drives the drive shaft) by looseing the crankcase bolts there by the back end, taking out the 4 bolts on the housing (#18) on the back of engine, and then pulling out that assembly. I have done that and I am not anything of a gear-head-mechanic.
And I understand that Can do the same for the drive bevel gear (driven by the transmission) by doing about the same with the housing (#6) on the side of the engine.




I was completely ignorant of all this until a few months ago.
One thing I had to learn is what is what, and what is called what, and how it all fits together and how it comes apart.
Looking at the microfiche does not explain much of any of that.
I have hand marked in a few things that took me a while to understand about the diagram above.
A couple other things are:
- all the stuff on the upper part of the drawing is all one assembly, the driven assemnbly, comes out as one assembly, comes out the back of the engine case. The #15 is the flange you see on back of engine after remove the shaft drive.
- all the stuff on the lower part of the drawing, the drive assembly, comes out the side of the engine. Is driven by the transmission.

IT seems like you are saying the bike was intended to be a parts bike... and now it really is...
Anyway, what I am saying is that you can get access to the driven bevel gear assembly and the drive bevel gear assembly without having to split the engine/transmission case. The gear assemblies can be taken out of the back and the side of the engine.

If you find the bevel gears damaged and that is the cause of the lockup, a chunk of a gear jammed in there somewhere, ... then the drive shaft and final drive is probably still good. Next question would be if the the transmission still good, I would think so. The secondary bevel gears are in their own separate oil/case.

>> later note: My problem had more to do with the nut (#17) and the threaded shaft on the end of the driven bevel gear. So the photos I have will be more confusion for you, so maybe not so much a help to you.
Your problem seems to be more with the gears of the bevel gears.

.

[Redman]

Found some pictures (not mine) that better show the drive assembly and the driven assembly.

[noratx]

Thank you!

Pulling these out will be very interesting.
However, I would not feel secure just pulling them out and then put new ones in, without inspecting the rest of the engine for any debris that could possibly make some other damage in the future.

Something must have jammed the gears in the first place, and whatever that is, must still be there, risking another jam in the future.
Alteast, that's what I think and are afraid of.

Or am I wrong there?

[Redman]

..........
However, I would not feel secure just pulling them out and then put new ones in, without inspecting the rest of the engine for any debris that could possibly make some other damage in the future........

Some comments:
- THe secondary bevel gears are in thier own gear box section of the engine crankcase. I dont think that includes the transmission, but am not sure.


- When pull out the driven gear set out the back of engine, that provides this view.
(mine, no damage to bevel gear)

And would then also have view/access from other side when pull out the drive set from the side of the engine.
I would think could feel around in there to find and remove any chunks.

- I think what folks are suggesting is you have had the bevel gear fail (like that in 2nd posting), and chunk of gear is what is jammed inbetween the gears.


- Yes, the driven gear assembly and the driven gear assembly can be replaced with another set. And you might think then they would be a matched set if both came from the same bike.
BUt, I understand that there would be some shimming reguired. These shims are metal that look like gaskets on the microfische (#10, #21) (not seen in the photos I posted).
This shimming process is described in factory manaul (and Clymers manaul). Involves measuring stuff with dial indicators, treating with that blue die indicating stuff, removing and reinstalling with different shims (that I have no idea where would get size different shims). I avoided that, was way beyound my expereince. You will have to decide if you want to do that on an parts bike engine. I was unwilling / incapabile to do that on my otherwise good condition bike.

[noratx]

So then, it does sound, considering the shimming, that moving over the working crank shaft from the spare parts engine would be a better solution, since I don't have what is needed to make sure I got the correct size shims.
(I would not trust my chinese digital vernier caliper with such fine precision readings).

Question then is.. is it doable to split the crank case to have the crank shaft replaced, without having to pull the engine out of the frame on the other bike.
Not having to pull it out would save me A LOT of time and work!

I have been looking in the factory manual, so I know how to split the crank case. I just don't know if it is doable while still mounted in the frame.

The main reason for keeping the engine still mounted in the frame, is more to do with the fact that i have my bike at a shared garage, and no way to move the engine around myself.
If mounted in the frame, I can atleast push the bike back and forth between my lot in the garage, to the working area on my own without having to rely on friends having time to come by and help moving the engine around.
(I don't have an engine stand, nor and space to keep it at due to the layout of the garage).

[Steve]

Why do you want to pull the crank? Why not just replace the entire engine?

You will need to remove the engine from the frame to split the cases, anyway, so why not just replace the entire engine?

.

[noratx]

Steve: The reason was stated in my last post. Because of limited space and man power (I can't take the engine out on my own).
That is entirely the reason why I asked if it was possible to split the crank case while it was till mounted in the frame.
If it is as you say, not doable, I would have no other choice than to call in some friends and ask them to help me take the engine out.
Replacing the secondary gears does sound simpler, if it wasn't for what Redman said earlier regarding shimming etc.

As I understand it, replacing the gears could require shimming and dying to make sure there is a good fit, which then makes me wonder if it is doable for me without the tools required (the dye and dial gauges).
The dye, I guess, wouldn't be too hard to come by.. but trustworthy dial gauges are when you are have a limited budget.
I am not sure I would trust the chinese $30 junk I can buy here when it comes to such precision measurements.