seized front sprocket.

Sooty09

Sooty09

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Last year I changed my chain but the front sprocket was so tight I stripped the thread on my three leg puller. I was so worried about damaging the shaft or bending the teeth on the sprocket I left it alone and hoped I was covered by the chain recall. Now at 24000 its time to have another go.
Im hoping to find somebody with a hydraulic puller. I don't mind covering the sprocket in hot rags and puring boiling water on it, but I'm not keen on heating it up with a flame.
Has anybody overcome this problem?
 
Sooty -

TBH I can't see how this could go wrong - it should be really simple, especially with the area being quite greasy ...

I'm not being patronising but can you describe what you did to try and release the sprocket? Stripping threads on a three leg puller takes some doing and IMHO the sprocket should have given up its struggle long before that!

Regarding heat - personally I wouldn't have a problem using a blowtorch of some sort, so long as you have some kind of control over the flame and it's not too wild (I'm thinking a roofing blowtorch here lol) you should be ok - just be sure to remove any plastic covers first. The heatgun is a good idea but I think it will have a much greater area of heating, a torch with a nice 'cone' flame gives much more intense heating to a smaller area .... more expansion and thermal shock tends to help break the bond.

Cheers

G
 
Greggers - Only BMW can make such a simple procedure so difficult. I've changed dozens of sprockets on my dirt bike without even needing an extractor.
My sprocket removal & refitting is as follows.

1) Remove the plastic guard.
2) Apply the back brake and unscrew the sprocket retaining bolt (Normal thread)
3) Split the chain and remove from bike. Cut a section of old chain and wrap it round the old sprocket, this gives a better landing for the sprocket puller to grip.
4) Fit a threaded protector into the output shaft centre, I have a bit of bar I machined up, it screws in to the sprocket retainer so any thrust is onto the shaft end not the thread. A countersunk dimple on the end of the bar helps centralise the puller. ( Yes the splines of the sprocket are free to pass over this bar)
5) Fit three legged puller and extract the old sprocket.

I have changed two sprockets, a GS650, and a friends GS800. Both were a very tight fit on the shaft and needed a lot of pull on the extractor. To refit my wifes F650 sprocket we boiled it in cooking oil for 5 minutes, it still needed a bit of a knock to slide on the splines. The F800 needed boiling only, there was no chance of it fitting cold.
There was no sign of rust on either bikes sprockets or shafts. The tolerance is just completely wrong, It should be a loose sliding fit not a press fit.
 
Had a few & had to heat sprocket up with oxy/acete & a large 3 legged puller
 
Could this be the cause of all the failures that have occurred?
Most bikes have a floating front sprocket that is held by a retaining plate, allowing some movement.
 
Its off at last, I have spayed penetrating oil at the splines every few days for the last few weeks and tried a new set of three legged pullers. No good , it was still stuck. I dare not use direct heat in this area, its surrounded with generator cables and wires to the gear indicator, not to mention a plastic fuel tank next to your head.
I had a moment of inspiration and dug out the steam wallpaper stripper, it has a nozzle to fire a fine jet of steam. I wrapped damp rags behind the sprocket and packed round the cables etc. After about 10 minutes plying the jet round the sprocket it was very hot to touch. I refitted the puller and by putting a long bar between 2 legs to prevent it rotating and using a very big spanner managed to start its extraction, once on the move it became much easier.
The splines were very clean and with a good coating of copper slip the new sprocket pushed on cold, just needing a small tap with a mallet to get it started.
 
The splines were very clean and with a good coating of copper slip...
Click to expand...

Jesus thats the last stuff to put on a spline application :eek::eek:.
What you need is a grease thats suitable for a spline application like Optimoly MP3 paste.
Copperslip will cause fretting of the splines on the shaft.
 
"Jesus thats the last stuff to put on a spline application ." (Skywalker)


Although the sprocket is held on with a spline it is very tight and is not going to slide like as a spline in a drive shaft. There is 0 movement and Im willing to risk a bit of fretting for easy removal in the future.
Copaslip is advertised as a high temperature, high pressure anti seize compound for threads and hubs.
I have searched the Internet and can find advise to use Molybdenum grease to resist fretting, but nothing to say copper will aggravate the problem.
There is frequent reference to applying a lubricant that will not dry out and will prevent oxidisation at the fret points which cause most of the problems, copper slip seems to fit this requirement.
Several sites recommend fitting an adhesive to prevent any fretting, Im wondering if BMW apply this on assembly and thats why it was so difficult to extract my old sprocket.

Thanks for the warning Skywalker, Iv enjoyed researching this and would now have used MP3 paste if I had any, but my conclusion is any lubricant which will not dry out and will leave a coating is better than nothing.
 
Front Sprocket change

I swapped my 16 tooth frontie yesterday for a 17 to ease the vibes on motorway speeds.

Never had a sprocket pop off so easy. Undid the nut, got the slack in the chain by moving the rear wheel forwards, slipped it off rear sprocket, then off the front, then pulled the sprocket off by hand, fitted new one with the help of a hide mallet with one gentle tap.


I can't see why everyone else has been having such trouble. :augie





And yes the vibes have gone as it's lowered the rpm 500 at cruising speeds in top gear. Well worth the outlay of £15
 
Just my five eggs ...

Moly's probably the one to use, but copaslip will be ok too - the fretting thing isn't such a worry as the sprocket is held tight by the retaining nut.

Using copaslip in dissimilar metals is going to cause a problem though, for example a steel bolt in an alloy casing - the copper in the grease can exacerbate the galvanic reaction between the two metals producing aluminium oxide which can build to sufficient volumes to completely seize the stub/bolt beyond extraction - DAMHIKT!

G
 
Five eggs more - I know where your coming from Greggers but folk used to put copperslip on the rear wheel splines on old boxer twins & they were supposedly tight etc.
 
Encountered the seized front sprocket myself today :(

Was planning on fitting the 17 teeth sprocket on the 800 (lower revs on long motorway stretches) but when I loosened the bolt, I found the sprocket to be as good as welded on. No way in getting it to move since I don't have a sprocket puller at home.

Guessing I'll be paying a visit to the dealer for this, the chain is probably at the end of its life span so may very well change that to.

Grtz, Philip!
 
Just put a 17 tooth sprocket on this morning and mine was also seized, luckily i had a slide hammer and off it came straight away, well almost straight away.

Made sure I put plenty of copper slip on when it went back on with loctite on the bolt to ensure that it doesn't come off again so easily.

if any one needs there's changing and there local, your more than welcome to pop in and Im sure we can manage it.

Now time to out and see what the 17 T sprocket is like.

Regards

Mark
 
Phluppe said:
Encountered the seized front sprocket myself today :(

Was planning on fitting the 17 teeth sprocket on the 800 (lower revs on long motorway stretches) but when I loosened the bolt, I found the sprocket to be as good as welded on. No way in getting it to move since I don't have a sprocket puller at home.

Guessing I'll be paying a visit to the dealer for this, the chain is probably at the end of its life span so may very well change that to.

Grtz, Philip!
Click to expand...

Have you tried heating it? A blowtorch from B&Q is cheaper than an hours labour at the dealer...
 
Nope, haven't got a blowtorch. Might go down to the shop and look how much a puller and/or blowtorch is gonna set me back. If it's to much, I might go down to the deales anyway, I'm guesing the chain is at the end anyway.

About the chain, you guys all using the BMW chain, or is there a better brand on the market?

Grtz, Philip!
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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