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850 clutch shims & alignment

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850 clutch shims & alignment

Posted by mike_steer at July 02. 2017

1. Just looking to re install the clutch now on my 850 rebuild.  During the 'dry run' I see at the back of the clutch sprocket shims need to be in place.  On the strip down I tied mine together.  I have 3 shims with a total value of .114 (2 x .032 and 1 x .050). The spacer (06 0747) is extra to this so haven't confused it with the shims

I see in the parts book and on the Andover web site two shims are evident, both .036.  (AR As Required) So where has my third one come from. Is .114 excessive?

2. Again with the dry run I used the book method of aligning the clutch and engine sprocket with a straight edge.  I have to say its very very ambiguous as to its accuracy.  With either 2 or 3 shims on the shaft behind the clutch sprocket it was impossible to detect any difference with the straight edge sprocket to sprocket although there must be. Surely there must be a more accurate method to ensure some accuracy?

 

your thoughts

Re: 850 clutch shims & alignment

Posted by robert_tuck at July 03. 2017

Hi Mike ,whatever you do ,make sure the back of the clutch and shimms/spacer do not load the end of the sleeve gear from the box, this will ruin you light gearchange.

Re: 850 clutch shims & alignment

Posted by john_holmes at July 03. 2017

The factory supplied 36 and 48 thou shims.

114 thou is not excessive, long distance and a lot of joints of dubious accuracy between the 2 shafts.

The crank probably had 20 to 30 thou of endfloat if its still as it left the factory, as that's nearly one small shim a more accurate method is not required.

If it was working before then stick with your 114/110 stack.

Compared to other contemporary Unit engines the Commando chain is long and will cope better with small misalignments.

Re: 850 clutch shims & alignment

Posted by mike_steer at July 03. 2017

Previously robert_tuck wrote:

Hi Mike ,whatever you do ,make sure the back of the clutch and shimms/spacer do not load the end of the sleeve gear from the box, this will ruin you light gearchange.

Rob thanks.  How do I ensure this does not happen?

 

regards

Re: 850 clutch shims & alignment

Posted by mike_steer at July 03. 2017

Previously john_holmes wrote:

The factory supplied 36 and 48 thou shims.

114 thou is not excessive, long distance and a lot of joints of dubious accuracy between the 2 shafts.

The crank probably had 20 to 30 thou of endfloat if its still as it left the factory, as that's nearly one small shim a more accurate method is not required.

If it was working before then stick with your 114/110 stack.

Compared to other contemporary Unit engines the Commando chain is long and will cope better with small misalignments.

John thanks for the info.  The bike did indeed have 30 thou end float on the crank which I have now shimmed down to about 12 thou.

Re: 850 clutch shims & alignment

Posted by robert_tuck at July 03. 2017

If it was working well don't add any more, some engineers blue should show if there is contact.( a bit of the wife's lippy is nearly as good).

Re: 850 clutch shims & alignment

Posted by mike_steer at July 04. 2017

Previously mike_steer wrote:

Previously robert_tuck wrote:

Hi Mike ,whatever you do ,make sure the back of the clutch and shimms/spacer do not load the end of the sleeve gear from the box, this will ruin you light gearchange.

Rob thanks.  How do I ensure this does not happen?

 

regards

Rob have I missed something here.  With the circlip in place surley its impossible for the back of the clutch shims/spacer to load the sleeve gear?

Re: 850 clutch shims & alignment

Posted by david_evans at July 04. 2017

Unless you leave the nut off the RH end of the gearbox mainshaft (unlikely) then the circlip will keep the circlip spacer and shims well clear of the sleeve gear. With the crankshaft sprocket nipped up and gentle pressure applied to the clutch drum towards the gearbox, a straight edge along the edge of both sprockets will reveal if there is an error that needs dealing with. I recall that a 12 inch rule is not quite long enough to get a good idea.

Re: 850 clutch shims & alignment

Posted by mike_steer at July 05. 2017

Previously david_evans wrote:

Unless you leave the nut off the RH end of the gearbox mainshaft (unlikely) then the circlip will keep the circlip spacer and shims well clear of the sleeve gear. With the crankshaft sprocket nipped up and gentle pressure applied to the clutch drum towards the gearbox, a straight edge along the edge of both sprockets will reveal if there is an error that needs dealing with. I recall that a 12 inch rule is not quite long enough to get a good idea.

Thanks David. Your mention of the mainshaft nut got me thinking, and on inspection yes I did leave it off.  Have just looked through the workshop manual and cannot see any mention of it at all.  Yet looking through pics I took of the strip down it is most definately there.  Is it just a tighten down nut or is there a torque for it?

Digressing slightly the gearbox sprocket nut is an 1 1/4, is this an

1 1/4 Whitworth do you know?

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