Have I got the right sprocket..??

[Mr Gazza]

Just had the back wheel out ready for some new rubber, and I thought it would be a good time to see if the new chain and sprockets would fit, that I bought for my '98 M900 years ago.

The current bike is a 2000 M900Sie. No problem with the chain length or rear sprocket (Although the old sprocket is 38T and the new one is 39T. Gearing down a tiny bit will not hurt.)

The question I have is to do with the front sprocket, The one fitted to the Sie has a boss of equal hieght on each side, and and so the sprocket is central between the bosses.

The one I bought for the '98 M900 is flat one side and has a boss one side, twice the hieght of the ones on the Sie sprocket, so the offset will be different.

1) I don't know if the one I found on the Sie is correct (The chain is a couple of links short so I'm not taking anything for granted.)

2) I do know that the one I bought is correct for a '98 M900, but I don't know if it will be right for the Sie, or which way round it should go.

Logic tells me that the retaining plate should go to the boss side, as the boss and plate are the same shape. However this would place the sprocket further inboard than before, and the chain already runs very close to the tyre.

Does any one know if there is a different part No. for '98 and 2000 sprockets?

Strangly there seems to be very little wear on both the sprockets but the chain is in quite poor shape, almost as if someone put an old chain on new sprockets..?? Maybe because the chain is only 96 links instead of 98. it was run too tight when new?

Cheers

Gazza

[turbod]

I had a similar problem when i wanted to fit a 14 tooth front sprocket to my 2000 900SIE

I found that the sprocket has a boss on both sides ,i tried people like B&C express ,Talon ,etc but could not find a sprocket any size with a boss on both sides.

I ended up keeping the original front sprocket & getting a bigger rear sprocket

For some reason ducati fitted a sprocket with a boss on both sides for the 2000/2001 900sie ,all other models have one boss on one side only.

So the sprocket you have is right for a '98 M900 but not for a 2000 m900sie.

[Mr Gazza]

Thank you very much Turbod.

You have confirmed what I have deduced from trawling some other forums. It seems that this has come up before. and the 00-02 ie's are different.

However getting back to your 14T sprocket. I discovered that you can in fact easily adapt a "std" sprocket with a one sided boss, by milling down the single boss to the same hieght as the that of the special ie sprocket. Or space the plain side to the hieght of the ie boss.

I read that the "engine" side boss is 4mm high and the outer is 3mm, but never trust the wicked web!!

There don't look to be ought wrong with the original on mine so I might just risk it with the new chain, at least till I get a new one...Probably won't be able to get my '98 one milled down for any less than the price of a new sprocket..

Cheers

Gazza

[utopia]

I'm making assumptions here but, if there is space behind the std sprocket to allow the extra width of the bigger boss to clear the crankcases, then I would have thought that the washer trick should work.
You'd probably have trouble milling (or turning ) the boss down though, as I assume that the whole thing, not just the teeth, will be hardened and tempered in some way. It may need grinding.
But if you have room to leave the thicker boss there on the inboard side, I can't see it making any difference.
I could perhaps turn you a suitable washer if you do decide to go that route ..though a front sprocket is reasonably cheap anyway, so it may not be worth the bother.
I'd be inclined to accurately check your chain alignment once the bike is up on its wheels, and the wheels are nicely lined up, as in the relatively unlikely event that the chain is out of line, the washer could be made the right thickness to align things perfectly using your old sprocket.
Thus the "incorrect" sprocket may be the better choice in the long run.
But like I said, I'm making a few assumptions here.

[Mr Gazza]

As always Utopia your assumptions are pretty much on the money.

So I am nodding as I read your post:chuckle:

Yes there is plenty of room inboard of the sprocket, and I would favour the spacer option with the plain side of the sprocket outwards, for the reason that it would leave it wider and thus have more bearing on the splines, and hopefully not wear the shaft so much as if the sprocket were to be ground down narrower.

For spacers, I thought that a couple of retaining plates with the lugs removed would be ideal as they have the internal teeth that fit the splines. As yet I have not investigated the thickness of those though, nor have I looked to see if I might need longer screws to reach past the spacers....Could be an interesting mod for ie owners who want to play with the gearing or who can't find the correct ie sprocket...Will keep you posted.

BTW thanks for the offer of turning up a spacer..

Cheers

Gazza

[gary tompkins]

The 900ie was the only model that used this sprocket offset. This is the reason I run a stock front 15T sprocket with aftermarket rear to set gearing. Chain and sprocket suppliers don't stock the correct offset front cog so you are stuffed, unless you get a custom one machined. Just milling the boss down on a standard 900 sprocket won't work, because the front face will sit too far back from the retaining plate.

I would stick with the standard 15T front and use something like a 40 or 41T at the rear

[Mr Gazza]

Well after spending some time comparing both sprockets and doing a lot of measuring, I decided to bite the bullet and make a spacer for the single bossed sprocket.

Some careful measuring with a steel rule under my stand mounted and illuminated magnifying glass revealed that both bosses on the ie sprocket are 5.5mm from the face of the teeth...That's allowing for a little wear on one side.

The retaining plate is 2mm thick, so the closest I could get would be 6mm by stacking 3 of them on the shaft.
That seemed a bit untidy to me, plus they would need easing to clear the retaining bolts when they were rotated out of the slot onto the splines, and I do not have 3 spare plates anyway.
I do however have a nice piece of 5mm ally (a 1976 T140V number plate) which I can work with woodworking tools...So worth a shot for a prototype even if 5.5mm would be ideal.

I cut a disc with a 50mm hole saw then bored out the centre with a 25mm flat bit...not what they teach you in metalwork class, but okay if you go carefully with a powerful cordless drill and sharp tools. two peripheral holes for the bolts finish the machining, then just a tidy up and de-burr is all that's needed.

My only slight concern was that I was now robbing the 15mm screws of 5mm of their reach, so I used thread lock on them untill I can get some 20mm or longer bolts...That said, the retaining plate is under very little load and just stops the sprocket floating up and down the shaft.

With the wheel alignment and chain tension correct to the swinging arm marks, everything squints up perfectly with my joiners eye (bionic laser..:mand:)

A short test run proved no problems whatsoever....just need to adjust the new chain again to account for it settling a bit.

It is so easy to change out that I think I will draw up a spacer the same shape as the plate with no splines and get some milled to 5.5mm thick from 6mm ally on the ol' CNC router.

With two 20mm screws it would be a kit that would enable the stock 900 Ducati sprocket (15T, 14T whatever.) to be used on the ie models....any one up for it??