I am trying to gear down my' 76 model 183. The current sprockets are 11T front and 46T rear. I'd like to lay my hands on a 10T (or even better a 9T)  front from somewhere but they seem to be unobtainable. I could go larger on the rear but to get anything over a 4% reduction I wold have to get a custom sprocket made and increase the diameter which I don't really want to do.

 

A 10T front will give me just over 9%, a 10T/48T will give me almost 13%.

 

Any suggestions ?

I think the bike came with a 13 to start with. The 11t is the smallest ever made. Anything smaller would not work anyway. An 11t usually is good, so the rear will have to be the way to go.

Correct gearing for a 183 is 11/46. From the 199/198 series on wards the gearing was 11/39 which gives the same overall ratio as a result on an internal gearing change.

Cheers Greg

PS I also have never seen a smaller front sprocket than 11

You could contact Talon in Yeovil, England, Great Britain,  They make sprockets and may be able to make you one.

I've had a 10 tooth but there are no manufacturer's markings so no idea who made it,  but Talon don't do them off the shelf. They will make them to special order, and it's about £90 for the set up. With a 9 tooth the chain would probably foul the sprocket nut.

 

In Motion here in the UK will have up to 48 tooth I think for a 528 chain  -  edit - I meant 520

Edited November 12, 201510 yr by woody

hi,

I am fully aware this reply will attract criticism, anyway here goes.    my father and I run a number of Bultacos and i try to avoid the fairground ride rear sprocket syndrome, which unfortunately with my riding style (i dislike having to slip the clutch all the time) and section becoming tighter and tighter seems a necessity.

so I bought from in-motion a Talon 10T 520 chain size front sprocket for a mono-yam (TY250)  i then bored the middle to them same internal diameter as the Bultaco one, I can't remember but i think it was either 0.5mm or 1.0mm bigger on the inside.  i used a carbide tool and took my time.

I then made a thin spacer or washer as the Bultaco is thicker towards the centre and the yam one is same thickness I think all the way down, either way the sprocket needs to sit the same distance off from the case as the Bultaco one.

next is the bit requiring patience, you have to dremel the female spline of the yamaha sprocket so they are wider, basically make the male bit (the bit that locates in the gearbox shaft spline thinner.  it is important to make sure you take the material off the same edge of every spline.  i did mine so as the drive takes up the sprocket is good edge is where the contact is and if you like the back edge which does nothing is the one where the width of spline is reduced.

you also need to either loctite the nut on or make a reduced lock tab otherwise the chain fouls the lock tab

 

I got my idea from Woody's 10T sprocket that can't be identified and thought somebody must have thought it necessary!! plus I like a challenge   

 

sounds like alot of work, it isn't and it is much easier to see when you have both sprockets in front of you.

 

i ended up with 10T front 46T rear and 1st gear is excellent for just plodding on tight turns, or for tricky loose bits or on rocks and best of all I don't have to fiddle with the clutch!    

 

hope this helps,

 

I will prepare myself for everyone telling me how i have wasted my time and it is not necessary.

 

 

Also, read Odgie's reply to this post:

 

http://www.trialscentral.com/forums/topic/15599-final-drive-sprocket/

A couple of good suggestions there, thanks. I'll contact Talon and also take a look at the modified Yam idea... I'm up for a challenge too (and have access to a lathe !)

Spark eroder/EDM is the way to go if you want a perfect fit on the spline but not many of you will have access to 1 like I used to. I made some very trick parts for 1 of my bikes when I was still working as a toolmaker