Chain scaping.. bad shocks?

Posts: 238

Installed a 39t rear sprocket (stock 32t) on my Talon 150 a while ago, and discovered it's rubbing really hard against the bottom of my engine when the rear lands hard off a bump. So bad, that the bottom of the engine casing is rubbed out about a 1/8", and my new chain is slowly eroding. I can't avoid bumps and rocks... and I need this larger sprocket for hills. Could this be just really poor stock shocks? I have the rear shocks set at their stiffest... which helped, but didn't fix the problem. If I pull down on the rack, it pushes the engine right down on the sprocket far too easily. Any suggestions on what can be done aside from replacing? Any remedies?

Posts: 648

[quote="MikeK"]Installed a 39t rear sprocket (stock 32t) on my Talon 150 a while ago, and discovered it's rubbing really hard against the bottom of my engine

we did the exact sprocket change in a carter 150 with no issues except to grind a small amount off a unused bolt tab that was cast into the bottom of the case. The sprocket/axle and the motor both are stationary mounted into and onto the swing arm frame assembly. there shouldn't be any movement between the two. inspect the motor mounts? a bushing may be worn, allowing the motor to drop or shift. verify all your mounting bolts and chain tensoner are tight without play. your chain may be too loose. slack in the chain can cause it to whip up against the case. the clearance is close with the 39 tooth sprocket

Posts: 411

Maybe you could add a couple links to your chain to separate the sprockets a little more every link separates the sprockets 5 16ths apart. Don't know if that would help its just a thought.

Posts: 1163

Posts: 2583

On our Y'Dogs we have to grind off the same unused bolt hole. Haven't had any problems with rubbing though, unless the chain tensioner loosens up.

Posts: 1093

[quote="ckau"]

Posts: 238

My 150 is like the one you mention Spool... the engine pivots on the swingarm when the suspension is compressed. And when I went to check on the other suggestions, they were right, and it helped but didn't solve the issue.

I had 2 bolts on the rear support bar connecting those pivot points that were so loose I could move the nuts by hand, and it looks like the bushings are wasted, grease was everywhere and the dust shield on it was pushed out. So all that is tightened, (bushings still to be replaced) and the engine doesn't pivot quite as far as it did... but over a large bump it will likely still cause a few issues. I'll have to find a longer chain tensioner to add a few links to the chain I think, but that's a great suggestion. I was thinking of fabbing some sort of "stop" on the frame so the engine is forced to stop before it hits my chain when the suspension compresses. But me thinks that would have caused a real 'jolt' when landing off a jump... probably not the best for the weaker weld points on the frame. So I'll try a longer chain first. Thanks again for the help folks. I'll update when I get a new tensioner to see how that works.

Posts: 238

OK.. I had it backwards. In order to fit a longer chain, I'd need a SHORTER chain tensioner. I can't adjust mine anymore. The reason, is because I already had to adjust it as far as it would go to fit the extra 3 links I needed for the new 39t sprocket. So now, I have just enough threads to tighten the current chain, and that's it. The tensioner is bottomed out. So I'm out of room. Even if my chain stretches more then 1/8"... I'm in trouble. Anyone ever heard of a 37t single row sprocket? I think this 39t is about 1/2" too big. Wouldn't be a problem if the engine didn't pivot with the suspension.

I LOVE the torque this 39t gives me in the mountains... but if it destroys my engine casing, it's kind of a moot point. I might have to take off the tensioner, cut it down by an inch, re-drill the bolt holes and try that. Only other options I see are to weld a "stop" on the frame somewhere, or go back to 32t. Sad

Posts: 238

Here's how the engine pivots when the suspension is compressed, and where it's hitting the engine casing. Should I be able to pull down on the back rack this easily? Shocks are set to stiffest. And how big a risk is there of grinding right through the casing?

If I find a way to lift the engine a bit since I've already bottomed out the tensioner, there's some sort of unused mount on the top of the engine that will have to be shaved off to avoid hitting the crossbar... anyone predict me needing this in the future?

Posts: 2583

Tractor Supply has a 36T Sprocket...

http://www.tractorsupply.com/webapp/wcs/stores/servlet/ProductDisplay_105 51_10001_114236_-1______?rFlag=true&cFlag=1

You may have to drill some new holes in order for it to attach correctly but it should work.