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Discussion Starter · #1 ·
Last summer I discovered that the splines on my 2007 Scrambler's sprocket shaft had significantly worn down. Eventually, they'll completely shear off, and the sprocket will spin freely on the shaft. The only real fix is to completely disassemble the engine and replace the shaft. I'm currently deciding between attempting to fix it myself, spending about $2500 to have a garage do it, or selling the bike at a significant loss.

Has anyone else done a full teardown of this engine? I've removed the covers on both sides (replacing clutch springs and crank sensors) and the cylinder covers (valve shims) but I've never tackled a repair this big. Are there any special tools it will require that I'm not likely to have? Are there other parts that are likely to need replacing that I won't have considered beforehand (not counting the obvious like dust seals and gaskets)? I've read through the shop manual about this procedure several times, and it doesn't seem impossible or even particularly difficult, just time consuming, but I'm wary - if I screw it up, it'll make the other two options much more difficult.

Thanks for any input!
 

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How many miles on your motor? There may well be more items worn which would increase the cost once you got into it. Maybe a low mileage motor from a breaker would be the way to go, swapping a motor is easier than rebuilding one and they seem to cost less than $2500.
 
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Discussion Starter · #3 ·
About 25k miles. The upper portion, at least, is definitely in good shape, having recently been looked over when I had it dyno'd. I'm the only owner, so I'm not concerned that anyone mistreated it in the past and it had a bad break-in or anything.

Used engines don't seem to go for that much less than a garage would charge to rebuild, and I'd rather have the assurance of knowing my engine's history than pay nearly as much for an unknown quantity.
 

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Respectfully, What you describe is HIGHLY unlikely. Do you have play in the gear? Do You have picture?

When I rebuilt the transmission at 103,000 because of a worn out 5th gear. With my "discount" ...FIVE years ago ...two gears, bearings, clips, seals etc was over $1500 in parts. $2500 would be a gift. The labor isnt difficult just time consuming. You will need a press. It took three weeks for parts to show up....about a weeks labor working at my leisure in between customers at the shop. The engine cases do have to be split. The head, jug and crank do not require removal.....I used an Automotive Engine stand mounted to the Head and Upper Motor Bolts. Flipped the engine upside down and split the cases.
 

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Discussion Starter · #5 ·
Respectfully, What you describe is HIGHLY unlikely. Do you have play in the gear? Do You have picture?
The link in the first post is to a thread where I asked about this and includes pictures.There's no question of what's going on, it's visibly obvious and I can rotate the sprocket several millimeters when it's on the shaft.

Near as I can tell, everything else about the engine is just fine. What I'm hoping, but understand isn't likely, is I can just put the existing components on a new shaft. There are lots of transmission assemblies on Ebay for less than $100, it would be cheaper to buy several and use the best bits from each than to buy a brand new transmission shaft.

The estimates were from a Triumph dealership and another local shop where I'd had my bike dyno'd, both of which I'd sent pictures of the issue to but never actually brought the bike in. The dealer wanted a bit more, the independent shop a bit less.
 

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Bear in mind I am not overly familiar with these transmissions. However, are you absolutely certain it is the spline on the shaft that is worn? On several engines of other brands, I have seen this happen and everytime the sprocket spline is worn. Typically, the sprocket is regarded as a sacrificial spline and the shaft spline is made a lot harder. Purposely to try to prevent the shaft spline from wearing. Myself, I find it very unusual that a gearbox output shaft spline is worn beyond use. Hope that helps.
 

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Discussion Starter · #7 ·
However, are you absolutely certain it is the spline on the shaft that is worn?
One hundred percent certain. The link in my first post has more pictures with the sprocket on, here's the shaft with no sprocket on.
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I used stainless steel sprockets instead of aluminum - turns out they were harder than the shaft splines. It's possible I also failed to sufficiently tighten the sprocket nut, exacterbating the issue.
 

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One hundred percent certain. The link in my first post has more pictures with the sprocket on, here's the shaft with no sprocket on.
View attachment 774511
I used stainless steel sprockets instead of aluminum - turns out they were harder than the shaft splines. It's possible I also failed to sufficiently tighten the sprocket nut, exacterbating the issue.
Fair enough. Good luck with it.
 

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I'm only throwing this out there because I saw it done by a friend. He has a Suzuki DR650. Rides the absolute hell out of it. The splines wore on the CS sprocket shaft exactly as you said. Rather it was due to a loose sprocket, thumper pounding that did the wear, I don't know.
Ok - here is what he did when it got so bad the sprocket was about to or did start slipping on the shaft.
I know -I know - it sounds crazy. He got a brand new front CS sprocket and then had a guy weld it right onto the CS shaft. Yep, right on to the countershaft. Weldor hit it fast and had a cooling towel on the backside while doing as quick a weld as possible. He has over 30k+ more miles since that was done and still going... Figured he would ride it until it was truly dead, and he will.
Just an option - crazy as hell but an option. By no means am I suggesting, recommending, or would consider it myself but there it is. I don't know if I would have believed it but It works because I have seen it work. Always a funny story -at least to me anyway.
 

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That picture looks really familiar --- John, - is that you sneaking a picture in on a Triumph site? 😲 😁

That is the result of a loose CS nut.
 

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I'm only throwing this out there because I saw it done by a friend. He has a Suzuki DR650. Rides the absolute hell out of it. The splines wore on the CS sprocket shaft exactly as you said. Rather it was due to a loose sprocket, thumper pounding that did the wear, I don't know.
Ok - here is what he did when it got so bad the sprocket was about to or did start slipping on the shaft.
I know -I know - it sounds crazy. He got a brand new front CS sprocket and then had a guy weld it right onto the CS shaft. Yep, right on to the countershaft. Weldor hit it fast and had a cooling towel on the backside while doing as quick a weld as possible. He has over 30k+ more miles since that was done and still going... Figured he would ride it until it was truly dead, and he will.
Just an option - crazy as hell but an option. By no means am I suggesting, recommending, or would consider it myself but there it is. I don't know if I would have believed it but It works because I have seen it work. Always a funny story -at least to me anyway.
I have seen this done before. It does work. I have done this on snapped shifter shafts on bikes that require splitting the cases. The problem is you WILL wear out the front sprocket eventually. Repairing this is going to be $$$$ to fix correctly
 
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Can confirm what @DUCKMAN says: engine out, flip it, remove bottom half of crankcase. Once you've opened her up you'll see how insanely simple these motors are. You'll need a shop manual (Haynes is fine), a few tools, a week, and a few cold beers. If you don't have a press any local mechanic will do it for you...

Tim

~'05 Thruxton~Sport Evolution 1100cc~FCR 39mm~813 cams~shim-under-bucket~+1.5mm valves~Ignitech CDI~m-Unit~Acewell CA85~F3 Frankenfork~Hagon Nitros~6-piston Pretech~520 chain~wide 17" rims~tubeless conversion~Michelin Road 5~
 

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I have seen this done before. It does work. I have done this on snapped shifter shafts on bikes that require splitting the cases. The problem is you WILL wear out the front sprocket eventually. Repairing this is going to be $$$$ to fix correctly
Totally agree. As an engineer and also a weldor - I know I could do it and know it would work [until the sprocket wears out] but I also get it. Do the mod, run it until its dead, dead, dead,,,,,,,, which as a mechanical engineer it goes against 90% of my logic, but if it works for you - go for it.
 

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One hundred percent certain. The link in my first post has more pictures with the sprocket on, here's the shaft with no sprocket on.
View attachment 774511
I used stainless steel sprockets instead of aluminum - turns out they were harder than the shaft splines. It's possible I also failed to sufficiently tighten the sprocket nut, exacterbating the issue.
Could you get two sprockets welded together so the second one takes the drive on the remaining good portion of the spline, wouldn't even need the full sprocket, just the central splined section.
The original shaft should last the life of the bike with the nut correctly tightened so even on that slightly narrower section of spline you may get another 3,5 or even 10 years out of it, and who knows if you'd still even have the bike by then.
If that spacer is removeable you could machine some off that and do the same on both sides of the sprocket?
 

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I posted in the "other parts that fit our bikes" sticky -- a '98-'17 R1 sprocket will fit our output shaft, but is slightly thicker: meaning that you'll be able to use the good part of the splines but not be able to use the lock washer....

Tim

~'05 Thruxton~Sport Evolution 1100cc~FCR 39mm~813 cams~shim-under-bucket~+1.5mm valves~Ignitech CDI~m-Unit~Acewell CA85~F3 Frankenfork~Hagon Nitros~6-piston Pretech~520 chain~wide 17" rims~tubeless conversion~Michelin Road 5~
 

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Those are a couple of clever ideas and worth investigating. Depends on the threads available on the shaft and whether the sprocket would still be in the proper location. Sure something to consider. Good thinking.
 

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I posted in the "other parts that fit our bikes" sticky -- a '98-'17 R1 sprocket will fit our output shaft, but is slightly thicker: meaning that you'll be able to use the good part of the splines but not be able to use the lock washer....

Tim

~'05 Thruxton~Sport Evolution 1100cc~FCR 39mm~813 cams~shim-under-bucket~+1.5mm valves~Ignitech CDI~m-Unit~Acewell CA85~F3 Frankenfork~Hagon Nitros~6-piston Pretech~520 chain~wide 17" rims~tubeless conversion~Michelin Road 5~
Thats sounds like it may provide a simple solution if the sprocket has enough good spline to retain and with some Loctite retaining technolgy you may find technology which retains as well as fills the worn section of spline to retain the sprocket without going to a full engine costly strip down.

Check the sprocket if it has enough of matching with the good spline retaining required and then contact Loctite technical support for the mose suitable retaining technology to suit to retain so the sprocket nut will not loosen as well as retain the sprocket on the spline.

I use to be employed with Henkel who own Loctite in Australia and they have many retaining technologies as well as thread lockers for these challenges......

All the very best of luck with your bike and project.
 
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