Yamaha TRX850 Enthusiasts Forum

So this evening I thought I'd go and adjust the chain and while I was down there I noticed one of the rubber chain followers was missing (dunno if you have them on a trx) and then I thought I may as well inspect the front sprocket while I was down there - and it was lucky I did...

The front sprocket retaining nut was completely off, having been rubbing on the plastic outer casing for some time. Its thread was completely stripped and the inner tab washer was detroyed totally.

God I hate bodgers! Clearly the last time this was worked on they re-used the tab washer and bolt without thinking of the possibility of it coming undone.

Boy am I lucky...the consequenses of this guys stupidity could have landed me in big trouble had it locked up on me whilst riding back to London from the sellers owners house in Newcastle on Saturday.

Never again will I buy a bike this far away and ride back (sling it in a van from now on) as there's just no way you can be sure everything is 100% safe until you've really started stripping it down and checked it all closely.

Looking at its design and knowing how slapdash people are, I suspect this is quite a common problem. Am I right?

It's been reported on the Mk1 TDM, but I haven't noticed many comments on it here...

Sp!ke wrote:Looking at its design and knowing how slapdash people are, I suspect this is quite a common problem. Am I right?

Is there anything about the design that makes it more open to problems with dodgy workmanship, do you think?

Are there other designs that are better?

Well other bikes I have owned had a more robust tab washer that bolts separately to the output shaft using two separate loctighted bolts. A design that means you can re-use the components repeatedly.

This design requires the replacement of the tab washer and locknut each time so I think it is inherantly unsafe as many people would overlook this and try and reuse the parts with rather dangerous consequences.

More likely improper torque and not having the lock washer seated in the splines... Yamaha has used this for years and if done properly, it doesn't come loose. Yes, replace the washer if it's been used more than a few times. It's not expensive.

Yeah I nicked the one off my spare motor to get me mobile again.

I can imagine removing the bolt would be a pain in the butt without a proper impact driver.

Sp!ke wrote:Yeah I nicked the one off my spare motor to get me mobile again.

I can imagine removing the bolt would be a pain in the butt without a proper impact driver.

s'also worth repalcing the nut too sometimes as the thread from it can shear off when yer torking the fecker up !!!! the output shaft is a tough hardened steel and the threads on it are tuff but the nut is alot weaker and of lesser kwality in my humble onion. i have heard of several instances of this ending up in very costly repairs and or the output shaft being lunched and peeps having to weld front sprockets in situ

I can imagine removing the bolt would be a pain in the butt without a proper impact driver.

I've done this recently, I didn't use an impact driver - use a 1/2" square drive breaker bar instead and a six sided impact socket, it's a lot stronger. My technique was to tighten the nut further slightly first to 'crack' the tension on the thread, then undo it. I still had the old chain on and used a piece of 3" square timber between the swinging arm top and one of the spokes of the rear wheel, and engage first gear to prevent the wheel turning. That way you haven't got to bounce on the rear brake pedal to stop the wheel turning.

I also bought a new lock washer and nut as follows:

NUT, SPROCKET (3LD), part number 90179-18667 at £5.39

WASHER, LOCK, part number 90215-2129000 at £1.91

Earywig

Yup, that'll work too. And btw, it wouldn't be a bad idea to always keep a spare lock washer handy in case you need to pull the sprocket during a cleaning (lots of gunk builds up in there). TZ250 spares kits came with a bag full of the silly things.

earywig wrote:
I've done this recently, I didn't use an impact driver - use a 1/2" square drive breaker bar instead and a six sided impact socket, it's a lot stronger. My technique was to tighten the nut further slightly first to 'crack' the tension on the thread, then undo it. I still had the old chain on and used a piece of 3" square timber between the swinging arm top and one of the spokes of the rear wheel, and engage first gear to prevent the wheel turning. That way you haven't got to bounce on the rear brake pedal to stop the wheel turning.

That would work I suppose but remember I had to undo this bolt on a loose engine so I didnt have the luxury of being able to brace it anywhere to stop it turning.

The 12v Clarke Impact driver is a godsend for things like this. Cheap as chips and it works a charm. I recommend putting it on your chrismas list - seriously.



http://www.machinemart.co.uk/product.asp?p=060810610

I'm not sure what all the fuss is about. Its only about 80Nm tight. A breaker bar will get it off no bother with your foot on the back brake.
I suppose for £1.50 you may as well use a new lock washer, however, if you reuse the original and just bend it in a new location there should be no worries.

I never had any problems either.

I am in the process of doing this now. Dumb question before I start. Is the drive sprocket nut LH or RH thread?

I can only say hmmmmm!
Bodging was obviously carried out by a bodger unqualified in bodging rudimentaries.
As has already been said,the soft lock washer should have been bent over one of the nut flats in a different position than that which had already been used,SIMPLES(I love that wee mongoose)
And the two 6mm bolted plate type of sprocket fixing(Honda,Booo Hissss)isn`t all that either,I`ve known bikes have to have the output shaft replaced because the groove in it has worn and the sprocket can oscillate off centre like a dick in a top hat!
PROPERLY tightened sprocket nuts,small lick of copperslip(or graphite grease)on the threads and a good secure seating of a tab washer has never let me down in forty years of biking.
The grease just aids disassembly when the time comes for a sprocket change.

Rural Rat wrote:I am in the process of doing this now. Dumb question before I start. Is the drive sprocket nut LH or RH thread?

Regular RH thread.