End float spacer for main gearbox shaft C15

[Barnsey]

Hi All,
 
   I am working out what size of spacer I need for the end float on the main gearbox shaft in my C15. 

According to Rupert Ratio the smallest size available is 0.093" (40-3020).

 I've worked out that I need 0.047", although I could factor in a gasket (0.016) and make this up to

 Oddly the existing spacer is 0.074", maybe a B washer was used instead of an A washer. 

  So..   What is the best way to deal with this?  File down the washer?  Add multiple gaskets?
Could I get a custom shim spacer made up?  Or just run without one at all? 

  I am wondering if this might just be the original cause of some of the issues I have had.   

[DAVE BRADY]

Hi,

I have just done this and because of the excessive end float that was there the splines were slightly worn so I needed quite a lot more and ended up with two shims.
As there is nothing holding the shaft to one side or the other they also seem to as thrust washers. Also the clutch is on the one end and it will move in and out by the amount of end float available so barely feelable is what I went for.
I would think that washer/spacers that can be filed may be a bit soft. I found some proper gearbox shims in my box of bits and spent many hours reducing it on emery paper laid on the base of a pillar drill to keep it as flat a possible. I did not use a gasket.

Dave.

[Barnsey]

Thanks Dave! 

 I am also wondering if I need to replace the 'B' spacer but Rupert doesn't seem to do this. Does anyone know how to seperate the gears on the mainshaft in order to get at the B spacer?  They are locked together but I am not seeing a circlip or anything like this. 

[Rupert]

If I found that a mainshaft thrust washer only .047 was needed, I'd be looking for the reason elsewhere! I've never found one to be needed less than the standard alternative thicknesses in the position (as you say, thinnest original option .093") and more often a thicker than standard washer is needed.
Replacing the B spacer isn't usually needed as it doesn't wear much, unless you are fitting a new gear or shaft, then the correct thickness spacer is needed.
First thing I'd check is that the mainshaft 1st gear is pushed fully home on its splines.

[Barnsey]

Thanks Rupert!
 
   ( Are you the Rupert of the book?) 

   I double checked. The shaft is properly seated. Around 0.140" back from the side of the gearbox. 

  The bronze bearing protrudes by about  0.090"  Could this be the issue? This bearing came, ready-fitted to the replacement side cover which I bought. The original cover was cracked and the first replacement cracked similarly. 

[Barnsey]

I slept on it this afternoon, and woke up with a thought in my head.   In order to get a good measurement, does the clutch nut need to be done up on the main GB shaft?   I have been taking measurements with the shaft in place but not fastened.  I mean, we are only talking tiny measurements, might it make a significant difference?

[Rupert]

Clutch doesn't need to be fitted. Best way to measure mainshaft endfloat is to fit it alone, fully fit the inner timing cover and put a dti on the end of the mainshaft.
The mainshaft should easily slide side to side, the distance it moves being measured by the dti.Thats the thickness of thrust washer it needs minus about 4 thou to ensure it doesn't bind.
Agreed, the thickness of the flange on the bush at the kickstart end of the mainshaft is the other factor affecting mainshaft endfloat. I'll measure an original one and get back to you.

[Rupert]

Original mainshaft bush flange thickness .090"

[Barnsey]

Near as dammit the same as mine at 0.093"

[Barnsey]

BTW If I do it the alternate way and refit the side cover and measure the float with a DTI,  Is this possible with the engine in the bike?  DTIs are magnetic but the engine is largely aluminium. 
If so I will order a DTI.

  I might just have to get my wife to wobble the shaft while I hold the DTI in place. 

  I only ask 'cos in the video I saw, the engine was out of the bike and on its side. 

[Barnsey]

Lacking a DTI I measured the end float using the butt end of my digital calipers, with the help of my dear wife.  Several attempts later the float looks to be around 0.070 to 0.072".  The spacer is 0.074".

As previously discussed it looks like I have a B spacer rather than the 0.090" A spacer which I should have.

 I am tempted to fit a gasket (around 0.013") and maybe order the next size down B spacer (0.070") to stop it from binding. But I am bothered that this is a bodge to fix a bodge. 

  I haven't found any issues elsewhere. 

  Is it possible that someone has fitted a non-correct part from another model and messed up the float?  Just a thought.

  As ever I would be grateful for any ideas. 
 

[Barnsey]

I repeated the experiment with the spacer in place.  As soon as I tightened up the machine screws on the end cover the shaft locked up.  SMOKING GUN

[Barnsey]

Fitting a paper gasket (rubbish quality and a bad fit!)  was enough to unbind the shaft and give a float of around 0.002 to 0.003".  I'll try another gasket. 

[Rupert]

BSAnever fitted a cover on the inner timing cover so I'd agree - fitting a bodge to solve a bodge.
Re the issue of the mainshaft spacer being thinner than expected, have you checked the sleeve gear is fully home in its bearing? If not the space for the mainshaft thrust washer will be reduced.

[scifi]

I would try to get a method of grinding the Spacing Shim to the correct thickness.   One method which springs to mind, would be to put a round peg into a Vice and use it to hold the Spacer.   Then lightly touch an angle grinder onto the Spacer and it should rotate around the peg, on top of the flat jaws of the Vice. The angle which the grinder touches the spacer will determine how fast it spins... Be prepared to have to find it if it flies off across the garage..!