A forum for owners of Yamaha TTR250 trail and enduro bikes!

I took the XT660R out for a run with the new 520 chain & sprockets and it ran ok from the start at 60mph (& a bit quicker a few days later). Proving it was the sprocket profile that was different causing the problem - maybe it was an older sprocket profile.

On my TTR250 I fitted new sprockets & 520 chain but it didn't settle in, the chain had harmonic vibration against the chain roller very badly. I tried different ways of solving it but non worked (including jacking the back up a bit to give more clearance, until I measured the thickness of the sprockets and I found a difference - the front sprocket was +0.010" thicker than the rear sprocket (in fact all the other sprockets I have from the XTR front & rear plus the TTR rear were the same even the one with a different profile XTR sprocket, all the new front TTR sprockets were 0.010" thicker.

I ground down the surface thickness down with and angle grinder & flap wheel until I had the thickness down to the same as the others, fitted it back on the bike and gave it a run = harmonic chain vibration gone.

I had this problem before, thinking it was an older chain on new sprockets, I fitted the nearly new 13T sprocket to my son's TTR and it ran ok so the chain may be slightly different.

I like your taste in bikes Petenz - I have the first two, sold my Bultaco years ago.

Yep it's a 'talon' sprocket stamped as a 520 sprocket as the other 'talon' sprockets but 10 thou to thick compared to all the other 520 sprockets I have, I'm going to contact the company as I can't be the only guy with chain chatter when running a Renthal chain.

Morning Brian, you don't expect to measure up components - never done it before. Working on the theory that all 520 chain sprockets must be the same thickness, I have had quite a shock when I measured all of them up, I only have an imperial Micrometer.

Yamaha TTR 250; Unused Talon 15T front 0.2385"   rear 52T 0.228". Original Yamaha sprockets (measured on un- worn part) F 0.0233" R 0.226".

520 sprockets on my XT660R;     JT (wrong profile) F 0.231" German ESJOT F 13T/14T 0.228" /0.228" (well that's the Germans for you)  JT R 0.238". Sunstar R now fitted 0.222".

I will take of the front sprocket cover to measure the F 15T Sunstar fitted with a new chain & Sunstar rear, as I ran the bike up the road then opened up to 70 with no chain chatter at all. As any claim the chain sprockets need 'running in' was not the case, plus with both components being very hard steel - they can't 'run in' as would soft bearings etc.

Since I surface ground 0.010" off the Talon 14T F sprocket all chain chatter has gone, I did a horse trial yesterday and the chain only wiped up to touch the chain roller on very rough ground (I haven't grown up yet). Before the chain was running against the roller constantly.

I had fitted a Talon 13T on my TTR with the old chain and it chattered at say 40-50mph but I didn't suspect it was sprocket thickness, I thought it was running a new sprocket on a slightly worn chain causing the harmonic chain noise.

I suspect Talon have worked to a thicker sprocket, it can't be an error with tooling their machines as they will be x10 times more accurate then my old Micrometer.

Have a good BBQ later on today 

Interesting post, for info the sprockets line up ok (& run perfect with the same 14T sprocket but with 0.010" ground off it). I also checked the gearbox o/p shaft, the rear sprocket for being concentric, plus different chain tensions. Raised the bike to give a bit more clearance with the chain roller but nothing worked until I thinned down the F sprocket. As the Renthal chain is rated as 'off road spec' it would be reasonable to expect it to run ok with off road bike sprockets.

As I put down earlier the new 520 sprocket and chain fitted to the XT660R  ran perfect at 80 but the TTR250 with a new 520 chain & new sprockets chattered at 40?

When checking by fitting a sprocket against a chain, that's a static check - running at speed is a dynamic test introducing harmonics. If the sprocket is stamped 520 then it must be the correct thickness for 520 chain as listed on one site is 6.5mm, if stamped 525 = a different spec that would give it as 7.94mm. Also there are about 4 different chains of the same pitch 520,525, and the old 3/8" (I'm now sure the JT sprocket on my XT660R that caused the bad vibration was an classic spec but the same pitch.

At the same time I fitted a nearly new 13T sprocket to my son's TTR, not sure what chain but it ran ok.

Like most I have never had a problem with chains & sprockets before. Although I have heard of industrial problems with some US chain where all the measurements had to be checked before using because of similar problems.

I'm not out for new freebee sprockets but just to inform others in case they have the same problem, plus I like solving engineering problems.

-- Edited by matador on Sunday 14th of July 2013 09:55:16 AM