Is my bike now dead?

[shchuka]

Ok, sad story...

I was on my way to work a couple of days ago.  As I was slowing down to a traffic light, I downshifted into first gear - something clanked and knocked around the gearbox and the bike wouldn't go any further.  As I released the clutch, the bike wouldn't move, although the engine would pick up the revs.

Got the bike onto the side walk and onto the centre stand.  When I put it into a gear, the read wheel spins a bit, but not fast.  If I open the throttle, it doesn't spin faster.

I had to call RAC - something like AAA in the States. The guy that came over check it and said that it's probably a problem with the clutch.  He towed the bike back to my home. Didn't have time to do anything about it yesterday, but today took the cover off - and what do I see?  The front sprocket's inner opening is a perfect circle - no threads to grip the gearbox shaft.  Ok, took the sprocket off - and, apparently, the gearbox shaft, where the sprocket normally sits, is almost perfectly smooth - I mean, there are virtually no threads for the sprocket to grip.  Basically, the gearbox shaft is gone.

I had a mechanic have a quick look at it - and he says I shouldn't bother repairing it, considering the age and the mileage.  Basically, to get it fixed properly, the engine would have to come off, fully cleaned from any grease, etc., gearbox separated, opened, taken apart, the shaft replaced - then everything put together and the engine put back onto the bike.  Considering I only paid about £700 for the bike, this sounds like an excessible expensive thing.

Anything else I can do - cheaper (and I mean, a lot cheaper) to put it back on the road?

[elader]

In the US, labor is $100 an hour. I can't imagine it'll be less than $500 to take apart an engine and put it back together again.

[aaront1988]

You had a look on Ebay for a complete engine? Think I saw one for about £70 when I was having snoop yesterday.

[shchuka]

I've thought about new engine.  My bike is 97 GS500E - would the engine have to be exact year/model or what else would match?  I'd guess it's about a 3 hours job to take an engine out and put a new one it - how wrong am I?

[The Buddha]

89-00 motors are identical.
01+ ones are close enough.
3-4 hours is a good estimate for a engine pull and replace, I wont count on getting all the things back on at that stage, look for another hour or 2 of fine tuning ... carbs, pipe, air filter etc etc ...
Cool.
buddha.

[steitsma]

not sure if it would work but could he weld the sproket to the shaft?

[shchuka]

I don't think that's a good idea, as when the chain is replaced, the sprockets are normally replaced along with it.

[kman]

do you have to pull the engine to get into the gearbox?  could you get a new shaft and do it yourself?  that sounds like the cheapest to me if you can put in the time. 

[gsJack]

I had a 97 GS that I put 80k miles on and after I got my 02 GS my son took it for a commuter and ran it up to 88k miles and then replaced the engine with a low milage used one mostly because oil consumption had become too high at freeway commuting speeds.  I first changed the front sprocket on that 97 GS at 37k miles when I put the third chain on it, the original front sprocket went 2 chains.  My chain/sprocket log:

http://img.photobucket.com/albums/v443/jcp8832/GS500_brakes_chains.jpg

Also note I ran the same front sprocket from 37k to 67k miles on my current 02 GS thru the life of 2 chains.  In both cases a Suzuki oem sprocket was used.  I now have 81k miles on the 02 GS and expect it to go 100k miles.  I never changed a rear sprocket on any of the 5 chain driven bikes I've had putting 80-100k miles on a couple of them.

When I read your first post in this thread I thought why not just weld a good quality sprocket on the shaft and use the bike another 30-40k miles and then change the engine if the bike is still usable, you have 45k miles or so on it now.  Like steitsma suggested above it's a fix I would consider myself if you can find a good welder to get it on square and concentric enough.  Could cause a lot of vibration otherwise.

[burning1]

Usually there is some freeplay in the front sprocket, otherwise that sounds like a good idea - there isn't much to lose since the countershaft is buggered anyway. Worst that could happen is premature chain failure.

[lilwoody]

Either weld or cut a keyway into the shaft if possiable. But both would be a bit hinky. A new/used motor shouldn't cost more than 500 bucks and some sweat equity. That's the route I'd go.

[black and silver twin]

if your gonna weld it (thats prolly what ide do) use a new sproket so it lasts longer.

[shchuka]

Thanks, guys!  I guess I don't have anything to loose by trying to weld it.
I need to find a local welder now who'd come over to do the job.

[shchuka]

Ok, so the welding is done - and the bike is back on the road! Thanks everyone!

I did get a new front sprocket - and, interestingly, it's quite a bit thicker than the old one (about twice the thickness).  If I were to just replace is as normal, I wouldn't be able to fit it, as there was no length of the gear shaft left to fix it in place.  But welded onto the shaft - works a treat.  100 miles so far, including some motorway at about 90 mph - no problem.

Thanks for the suggestion!

[ivany]

Question I have is, how the hell did this happen in the first place?

[DoD#i]

Question I have is, how the hell did this happen in the first place?

Well, it sounds kinda like somone put on a 89-93? (I forget when the change ocurred) sprocket, which has no extra thickness at the splines as the 94?-up sprockets do. They are bad enough on a bike designed for them (I have a '90) and would be worse from slopping around on a bike that did not keep them properly in place (if designed for the thicker boss, which also reduces the force per spline area - presumably why that change to a thicker splined section was made)

...or, if there's really no room on the shaft to properly clip the thicker base sprocket( correct for a '97) the engine might have a lot more miles than the bike (ie, it might be a high-mileage '89-93 engine).

In any case, one of the major contributors to wearing the splines out/off is not keeping the spline joint greased - if you have a rust pattern that looks like this, you have a developing problem, and should replace your sprocket and heavily grease the splines when you do. Fortunately mine wore more on the sprocket than on the shaft, but the shaft is definitely worn. When it gets too bad, I'll probably try brazing on a new sprocket as being slightly more possible to do again than welding one on. My bike has over 100,000 miles.



That light-colored rusty pattern towards the middle is indicative of "fretting" - it's basically rusted dust - the spline area itself is highly polished, but that's from bumping back and forth and wearing off bits of metal every time you go from power on to coasting/braking. A new sprocket has flat parts between the splines - this sprocket was worn until the flats were gone, and just had sharp points. I'd only pet a few hundred miles on the bike when I got to looking at the sprocket and chain seriously, so it's mostly an inherited problem.