Primary Drive Drive sprocket taper fit?

[billirwinnz]

I have overhauled the top end of my A twin to fix smoking and leaking. I'm re-assembling the primary drive but the fit of the drive sprocket doesn't feel right to me. The washer that sits under the sprocket holds the sprocket just off the taper. I can tighten the nut to get it to grip and it must have been gripping OK before I took the motor apart but it doesn't feel right to me. I would have expected the sprocket to just grip when pushed on by hand against the washer rather than spin as it does now. It's not the original washer. If I make a new one so that the sprocket just grips when pushed on by hand will that give the correct interference fit? We are talking only a few thou so it won't worry the chain alignment.

Bill

 

[vibrac]

I had taper problems with a Douglas flywheel it was sorted with timesaver paste its application made the surface's a perfect match when the paste was removed far more applicable than a grinding paste

 

[greg brillus]

Bill doesn't the sprocket sit against a washer (slinger) that presses the outer ball bearing race against a large diameter double spring washer (Thackery washer) this pre loads the bearings to keep the inner races loaded and turning with the shaft. From memory this was how it works on the singles, as the outer bearing is not a tight fit in the steel bearing housing.......The actual location of the crank, sideways is from the small ball race on the timing side......Cheers.

 

[oexing]

Bill, when having a taper assembly you cannot have a washer in there to press up other components. I´d take out that washer and bolt things up at same torque you can do later. Then check the gap from sprocket to inner race or whatever comes first. So then you will get the size of the washer and machine one a bit shorter by say 0,2 mm forn to be safe. A wave washer may be allright as well for loading the gear shaft for zero side play. I cannot tell, not familiar to your bike.

Vic

 

[Gene Nehring]

Bill,

Are you attending the NZ rally in Cambridge? Looking forward to meeting you.

Best,

Gene.

 

[billirwinnz]

Bill,

Are you attending the NZ rally in Cambridge? Looking forward to meeting you.

Best,

Gene.

Yes. I'm planning to take my Prince. See you there .

Bill

Bill, when having a taper assembly you cannot have a washer in there to press up other components. I´d take out that washer and bolt things up at same torque you can do later. Then check the gap from sprocket to inner race or whatever comes first. So then you will get the size of the washer and machine one a bit shorter by say 0,2 mm forn to be safe. A wave washer may be allright as well for loading the gear shaft for zero side play. I cannot tell, not familiar to your bike.

Vic

Hi Vic

The washer is shown in the parts book so it must be part of the designed spacing. The diameter is smaller than the two surfaces it fits between which makes me think it's not the original one.

I've been thinking about the setup and I believe what has happened is that the internal spring has forced the bearing outwards reducing the clearance. I'll experiment today by tightening the nut with a piece of tube in place of the sprocket so that I can see what is going on.

Bill

 

[billirwinnz]

I had taper problems with a Douglas flywheel it was sorted with timesaver paste its application made the surface's a perfect match when the paste was removed far more applicable than a grinding paste

I use a trick taught to me by an old motorcycle mechanic years ago. Blackboard chalk. In this case the tapers are perfect. I now think the problem is that the spring-loaded bearing has moved outwards since I removed the sprocket.

 

[Simon Dinsdale]

Bill, it’s a few years since I put my A together but I seem to remember the spring / Thackeray washer between the drive side bearings is stronger than you would assume and so you cannot just push the tapered sprocket fully on by hand. When you tighten the nut on the sprocket the last bit you can feel it tightening against the spring and so compressing it a bit.

 

[billirwinnz]

Hi Simon

I’ve just tested by doing up the nut with a sleeve in place of the sprocket. Sure enough the bearing retreated into its housing. Problem solved.

On my TTR the setup was nothing like what is shown in the parts book so I just went with a conventional setup which seems to have worked ok.

Cheers Bill

 

[greg brillus]

My understanding of this set up is that it moves the slinger washer just inboard enough that it just misses the outer bearing shield/cover......this minimizes oil loss into the primary chain-case area from the engine crankcase.......not dissimilar to how the beveled slinger works behind the generator sprocket on a post war twin, close to but not touching the inner face of the ET 164.