GS850G crankshaft or secondary gear replacement

[noratx]

Hi!

During this summer, I noticed that my bike was giving som noise.
Considering the noise it makes and after having asked some friends (and also here), I am sure it is crankshaft bearings that has been fried (possibly after running too warm).
When I hit 3000 rpm, it sounds like a jackhammer.

I have since then found another bike, with an engine that sounds really great.
That bike, however, nearly killed me though, so it will never be on the streets again with me as a rider.
It has been taken apart for spare parts.
The rear wheel jammed in high speed and after disassembly of the bike, the drive shaft are spinning on it's own when turning the wheel, so my only conclusion so far is that the secondary gear has been damaged.
(There is another thread about that somewhere in the forum. I have promised pictures, and will update it as soon as I open the engine).

Now, to the big question...
Depending on the damage on the spare parts engine, I will either pull the crankshaft from the spare parts engine and replace the (most likely) damaged one on the first bike.
OR, I will pick out the secondary gear from the first bike and replace it in the spare parts engine and just swap the engines.
I will decide which way to go next weekend when I open the spare parts engine and can see what damages there are.

However, if I decide to just swap the crankshaft, is it possible to split the crank case and do the swap with the engine still mounted in the bike?
If possible, I'd prefer to keep it as simple as possible and unless I decide to swap the engines, keep the engine mounted in the frame of the first bike.

I hope I make any sense at all.

 

[Nessism]

Maybe this?...http://members.dslextreme.com/users/storagecliff/images/bevel_gear_shaft_repair_zooks.pdf

 

[noratx]

Seems promising, unfortunately it is not "as simple" as just the bolt that have snapped off. The joint is sitting tight where it should, so I am quite sure it's the gears that has failed.
I am considering to just swap the engines and fix the secondary drive/driven gears, I am just afraid of the shimming procedure which may require tools I don't have. :/

 

[Nessism]

Just realized you have an 850. That broken threaded stud is for the 650.

Crank failure on the 850 is extremely rare. Starter clutch maybe?

 

[noratx]

Well, the crank failure is not as much a failure as fried bearings.
The engine is knocking BADLY, sounds like a jackhammer, so my guess is that there are bad bearings due to overheated engine.

It started after I felt I had to chase after an idiot in a car, who was in such a hurry that he, while having his 5 year old daughter in the passenger seat, snuck between me and the road separator. I could feel the side of his car gracing my knee so I decided to chase after him and teach him a valuable lesson. (Asking him if he REALLY was in such a hurry that he thought it to be a good idea risking my health and life while risking his 5 year old be a witness of a possibly tragic accident with her father being the cause of injury or death. Damn he looked scared when he realized.. I am quite sure he won't do it again... at least not with his daughter in the passenger seat).

Anyway, chasing after him got into high speed and revs, with an overheated engine as a result.
In hindsight, I wish I didn't chase after him.. would probably have saved me quite a lot of work (if only I had noticed the low oil level. Draining the engine left me with just about 1.8 liters of oil instead of ~3. Interesting though that the oil level lamp never lit up).

So, the switching of crank shaft was because I suspect (and are quite sure of) that it's the bearings that are the cause of knockings.
Ofcouse, I won't know until I open the engine..

So question remains.. which would be simpler and requires less special tools.
Swapping the crank or the secondary gears?

 

[Nessism]

You can't fry crank bearings with a high speed chase. The bearings don't need much oil at all so that's unlikely to be the problem. Only thing that kills the bearings are metal debris getting into the balls.

 

[noratx]

Then is the question, what could be giving these knockings if it isn't the crank bearings?

 

[Charlie G]

Then is the question, what could be giving these knockings if it isn't the crank bearings?

Grinding gears/shaft? Timing? Crank, doubt it......

 

[noratx]

Ok. So not the crank then.
Set the noise problems aside and focusing on changing the secondary gears.

Switching the secondary gears from one engine to another, would that require me to have proper gauge dials considering that the secondary gears and everything is intact on the bike with the noises?

I am just trying to establish the most proper way of getting one of the engines to work.

The engine with the damaged secondary gears is performing wonderful, it sounds great, but its the problemnof secondary gears.

The other engine has very loud knocking sounds and does really sound like a jackhammer.

 

[Charlie G]

Ok.
Switching the secondary gears from one engine to another, would that require me to have proper gauge dials considering that the secondary gears and everything is intact on the bike with the noises?

I would suspect that if you took a set of gears, shimmed and matched to each other, and used them to replace damaged ones, you would most likely not have to re-adjust.

 

[noratx]

Thanks Charlie.
It's the "most likely" I don't like too much though.
In hindsight of what happened that day when the gears jammed, it's a scenario I would most definitely not have to go through again.
I was lucky not to come off the bike and live to tell the tale.
It could have happened 300 meters earlier when I was in a turn.. that would probably have had me seriously injured or dead.
I wish I did have the necessary dial gauges to make sure all is good after switching..

You are hopefully right though...
Since I anyway have to take the other engine out of the frame, I might as well just try switch the gears and see if it works the way it should.
I do really hope it does...