Front Sprocket Issue

[Pfrhodes1]

Hey All,

Trying to see what I can do as an alternate to splitting the motor apart to resolve the final drive axle issue where the bolt holding the sprocket in place has come off and the sprocket coming off and staying on the grooves has now ground the grooves off. Someone mentioned using a compression clip and washer. Any thoughts on a solution?

[pefrey]

Compression clip and washer will never do it. I don't think you have any choice but to split the cases or source a new engine. Is this a bike you just bought?

You could try welding the front sprocket to the output shaft but that's the ghetto method.

[thatkid]

Why you gotta hate on the ghetto method?

[willandrip]

Had the splines on the shaft been that tight on the sprocket as to be an interference fit; I would have tried the external circlip solution .

As they are far from that and the sprocket is able to rock on the shaft; I think it will fail in a short time.

On the welding method; It is an economical way to save an engine.
Use a new sprocket of the best quality you can source.

It is far from ideal; but will work for the life of the sprocket, just inspect it fairly regularly.
It is preferred to weld a suitable nut/heavy spacer to the shaft to retain the sprocket rather than weld the sprocket directly to the shaft.

[buzzawak]

Just a thought but wouldn't you melt the seal on the shaft and end up with a permanent oil leak?

[willandrip]

Mig welding produces very little heat compared to other methods.
The shaft would take a considerable amount of heat over a long period before it transferred it to the seal.

What needs to be considered is the cost of parts and labour to replace the shaft versus the alternatives.
Unless the bike is of very low mileage; I would consider a further two sprocket changes (providing good quality components are used and a cleaning/lubrication regime followed) would exceed the life of the engine and probably the machine itself.

Is it worth spending £200 on a gasket set (£120 pattern + £80 OEM head/base) plus the price of a shaft/lockwasher/nut on what is a £250 engine ?

How many 50,000 mile FZR 600's do you see ? (longevity)

It is a cheap and effective fix for what would otherwise condemn an engine/motorcycle to spares status.

Many owners are heartbroken/furious when they find a new acquisition has a welded up front sprocket.
They get over it, once the reality of the cost of shaft replacement is thoroughly investigated.

It may be possible for a experienced engineer who has the inclination to rig up tooling in order to reduce the shaft dia. and rethread with a smaller dia. nut.
It would not be a financially viable exercise to perform commercially.
More of a task for an enthusiastic acquaintance with a machine shop.

I solved mine with a new up rated nut and dressing of the remaining threads by hand.
I was lucky/unlucky; the PO fitted the incorrect sprocket and the threads were not too badly damaged.





I would not have hesitated to re-weld the new sprocket back on if necessary.

Use the very best O/X ring 530 chain sprocket combination you can source so as not to have to repeatedly re-weld a new sprocket on.

[pefrey]

Why you gotta hate on the ghetto method?

LOL not hatin', just statin'. There's good ghetto and bad ghetto. Good ghetto gets the job done safely and effectively, but is not the textbook method. Bad ghetto only gives the appearance of getting the job done.

I'm still interested in learning how the front sprocket came loose and proceeded to spin and grind off the splines on the countershaft.

[willandrip]

The original, and SOME replacement sprockets never seem to cause this problem.

Often a replacement sprocket is of the incorrect width (narrower) than stock.
JT are noted for this on SOME models (the TDM 850 is particularly vunerable)
The Renthal often requires a second lock washer on the spline before the sprocket is slid on. This is very pronounced on some FZR 400 models.
The above cases are usually caused because a range of Kawasaki models utilise the same spline pattern and tooth numbers/chain pitch as the Yamaha.
However the Kawasaki sprocket is very slightly slimmer than the Yamaha.
The pattern sprocket manufacturer does not make two "fractionally" different sprockets but supplies the one that fits both makes for economy.(the slimmer Kawasaki pattern unit)
Some pattern units spline pattern is a very poor fit.
All the above then allows the sprocket to float across the splines which in turn dislodges or wears the inner splines on the lockwasher resulting in it no longer being engaged with the splines on the shaft. The sprocket retaining nut is then only held by the tightening torque. Eventually the inevitable occurs.

The problem is also exacerbated by;

Incorrect chain adjustment.(places undue strain on sprocket causing it to rock on the shaft splines)

Re-use of a worn out lock washer. (How many replace this at each sprocket change ?) I reuse mine; but totally re-flatten it on an anvil and utilise a different portion to fold over.I also keep a brand new item in stock on the shelf if required.

Not fitting a lock washer at all.

Refitting an overtorqued nut with damaged threads.

Removing and replacing a nut with a hammer/chisel where no correct sized tool is available.

Incorrect torqueing of retaining nut. (Too tight destroys the lockwasher inner splines; insufficient allows the nut to slacken slightly until the sprocket movement dislodges the lockwasher splines)

Owners never inspecting the gearbox sprocket fitment from one set of chain/sprockets installation until the next are considered required.

The original nut was designed in 1968/9 for the 250cc YDS5.
It was intended to secure a sprocket to which probably 25 horsepower was to be applied from a two stroke in relatively soft
power transfer application.
To still be in production and to contend with the massive increase in horsepower and how applied just shows how well engineered Yamaha motorcycles are.
Eventually even the designers recognised this and an uprated nut was produced (first for YZF R6)
It is still the same dia and thread ;only slightly wider to help retain it on the shaft via torque as well as the lockwasher.
It is an easy and cheap upgrade and should be utilised if the original is looking anywhere near worn.

Finally; once the sprocket has left the splines and is sat rotating on the shaft splines, the rider very rarely notices immediately.
He usually revs the living daylights out of the engine a few times whilst in gear causing the sprocket to further destroy the fine threads on the shaft before coasting to a halt.

All in all; incorrect poorly fitting parts being badly installed and not inspected at intervals causes the majority of these failures.
Design flaws may account for less that 5% IMHO.

[pefrey]

Incorrect installation / maintenance. Got it.