layshaft end float when box in frame?

[mikeb]

I’ve pulled the outer cover off my super rocket’s (swing arm STD) gearbox to replace the kickstart and gear shift bushes (oil leaks). The box is still in the frame, clutch and primary attached. The box shifts fairly well tho can resist or clunk a little when changing in to 2nd gear from either direction, especially when cold.

Now I notice there’s about 50 thou end float in the layshaft. My understanding is end float is set by various thicknesses of the thrust washer (67-3203) between first gear and whatever is next inboard (3rd gear?). And the layshaft outer bush has some movement in it.

Questions:

• is there anything else that sets layshaft endfloat? (other than the gasket thickness).
• I assume I can pull off the inner cover, then first gear, and remedy that spacer? All without taking the box out of the frame….. yes???
• are all such thrust washers 67-3203 the same thickness?

I’d also do that bush, but as you have guessed, I don’t want to take the box out at this stage so don’t plan to do a thorough job. Summer is coming and I have other plans... 

thanks

[Swarfcut]

  Yes, all can be done with the box in the frame.

    With the inner cover removed the first gear cog simply slides off, revealing the thrust washer. The inner cover can be removed complete with mainshaft, for example where the primary drive and clutch are not fitted, otherwise it's just the kickstart ratchet assembly  that needs to come off, allowing the mainshaft to remain in place.

  The top hat rim of the layshaft bush in the inner cover is subject to wear, so a replacement bush may effect a cure. Hooligans trick is to heat the cover, push out the bush and put a packing washer under the rim, moving the bush towards the clutch side. Oil hole needs enlarging as the oilway will be obstructed slightly. A custom bush can be made with a thicker rim.

 The original thrust washer is hardened, but there is no reason you can't make a replacement if facilities are available. They may have come in several thicknesses back in the day, but as far as I know only one is listed. Inner chamfer faces clutch side, to clear radiused change of diameter on the layshaft. You're also correct about gasket thickness being a factor.

 Richard Clamp is the man who knows, contact details in Suppliers section of the Forum.


 Swarfy.

[mikeb]

Thanks Swarfy, super helpful. Im off to find the hammers and have a go...

[JulianS]

The 67 6203 thrust washers are all the same nominal thickness, though  there is some variation in thickness in the ones I have.

The "T" boxes use a spacer/thrust washer 42 3079 (0.113 - 0.115 inch) between the first gear and the inner cover. There were alternatives 42 3212 (0.120 - 0.122 inch) and 42 3213 (0.127 - 0.129 inch). These washers were also used in the A65 box on the layshaft at the clutch end.

Maybe consider removing the bush flange and using one of these? There is a slight difference in the diameter of the thrust flange on the first gear pinion use on the "T" box and the bushed box.

Cautionary tale - I use an STD T box on my A10 and some years ago, after a strip and reassembly I found engagement of first gear to clunk significantly whilst the other gears work as fine as usual. I used the bike for about 4 weeks to and from work then finally got fed up with the clunk and stripped it out to find that I had left out the thrust washer between first and the inner cover. The pinion had milled the inner cover - see photo - but no other apparent damage. Reassembly with the washer in place removed the clunk. The gears were still fine as usual.

So in my case the lack of the thrust washer only effected first gear selection.

[mikeb]

Thanks Julian - that's great info.
tho that pic is a bit alarming - interesting way to remove some metal!

[JulianS]

The oil was like silver paint when I drained it. I was speachless when I saw what I had done!!!

[mikeb]

i know that feeling Julian. when i spun the timing-side bush the oil was my first clue - black gold!

[Jules]

I have this issue too and found Swarfy's comment " The top hat rim of the layshaft bush in the inner cover is subject to wear, so a replacement bush may effect a cure. Hooligans trick is to heat the cover, push out the bush and put a packing washer under the rim, moving the bush towards the clutch side. Oil hole needs enlarging as the oilway will be obstructed slightly. A custom bush can be made with a thicker rim." interesting....
the placement of a shim at that end of the layshaft would do the same (hooligan's) job Swarfy without touching the blind bush, is that an effective solution though or does it upset gear alignments somehow? the same question applies to increasing the thrust washer thickness, in each case the location of the gear on the shaft is moved, is its location critical??

[Swarfcut]

  The position of the lay gears on the layshaft is governed with reference to the fixed pinion on the blind bush end. This is positioned by the circlip. This results in the face of the pinion being slightly proud of the shaft itself, and this face runs on the top hat of a fixed blind bush, or the thrust washer in the case of a needle roller box. So that end of the box stays the same. But in essence the aim is to reduce layshaft endfloat, and this is down to the thickness of the hardened thrust washer and the amount of wear on the inner cover bush face. Moving the bush towards the blind bush is just one way of doing it.

 If you are thinking of putting a washer at the blind bush end, it's easier to move the pinion down the shaft slightly towards the blind bush. In theory this is fine, and easy when building up a box. A lot of work for an assembled box, hence the cheapskate hooligan's trick. Adding a washer looks at first sight to be the solution, but this moves the whole layshaft towards the kicker end, and may give more problems than it solves.

  Keeping to the standard or reduced thickness of the hardened thrust washer reduces the risk of slipping out of gear, too thick and the depth of engagement for the second gear dogs may be reduced to a critical level, especially with worn or damaged first gear slots.

 Swarfy.

[mikeb]

Bit of an additional mystery to solve... I did Swarfy’s ‘cheapskate hooligan’ trick and got the layshaft endfloat down to 5 thou. On reassembly and road test, I pretty much couldn’t find second from either direction.

Then I noticed the layshaft trust washer (67-3203) and kickstart rachet washer (67-3161) had been swapped by a PO. So I put them where they should be, removed the ‘hooligan’ washer under the bush and endfloat now about 20 thou. Tried it - hard to find second shifting down but at least it is there.

So I put it back to how it was with parts in the 'wrong' place – the thinner 67-3161 on the layshaft and thicker 67-3203 behind the kickstart ratchet. Layshaft endfloat back to 50 thou-ish. Slightly better but I’m still struggling to change down gears. It requires a slow second push/graunch to select. For round town its basically unrideable.

So, parts are back to how they were and the box won't change down! The only other thing I did was change the outer bearing (original was noisy), slightly bevelled the inner face of the washer (67-3161 that is now on the layshaft between first and third), and did the outer cover bushes on the kickstart and gearshift (as this job was about keeping oil in the box). BTW the new gaskets were identical thickness to the old - 19 thou - and the gear change quadrant appears to engage fine with dots aligned.

Any thoughts on this? All I can think of is the mainshaft has moved a little and the dogs aren’t engaging. But if the mainshaft is located against the outer bearing (24-4217) by the kickstart ratchet then how? I did fit a standard bearing – RLS6. Is it supposed to be a c3 or something exotic? is there a torque setting for the kickstart pinion nut? i'm tempted to push the mainshaft inboard with an extra washer outside of first gear - at least as an experiment - is this a terrible idea?

Thanks for any ideas you may have.

[Swarfcut]

 If the box won't change down this is more a symptom of a bind of some sort in the selector mechanism, a mal-adjusted camplate plunger is number one suspect, followed by a problem with the selector forks, camplate, selector rod. These latter are more likely on a box built up from unrelated parts.

 I've had bowed rods and a camplate that was too thick, both resulting in a load on the selector arms making the camplate bind. This was a real conundrum and took some finding as changes up the box were fine, foot pressure overcoming resistance, but coming down the box I found the camplate needed a bit of extra assistance to turn, this is provided by the plunger. So worth looking here first.

 The mainshaft washer is fitted outboard of the ball race, so the thickness is only critical if it results in major mis-alignment between kickstart quadrant and the kickstart ratchet pinion. The mainshaft position is fixed in relation to the inner cover, fixed pinion abuts the bearing. so time to investigate the depth of engagement of the layshaft second gear cog with the big first gear. Here the thickness of that thrust washer is critical as mentioned in earlier post.

 Move the mainshaft and another can opens up, primary chain alignment.....

 Swarfy.

[mikeb]

ok so despite taking dissasesmbly photos and attempting to be careful the problem was i installed the selector quadrant one tooth out - the dots not aligning, as per the other curent thread by jhg1958. gah! at least I'm not alone. alway, problem solved, slight clunk on some changes but that will have to wait for a proper strip down to examine the dogs.

along the way i got interested in how the box works and made the attached pic, which makes sense to me at least, and may help others like me who are new to the dark art of gearboxes. if there is a better illustration elsewhere or any errors please let me know and i'll remove or edit this.

thanks for all the help Swarfy, Julian and Jules- i would have been lost with out it.

cheers

[Swarfcut]

 Slight error with the captions. Second and third gear diagram titles are transposed. But otherwise  makes sense for those folks who are amazed by how it does it. The box is always quietest in Top Gear, this is when there is no load on the Layshaft bearings. In every intermediate gear the diagram shows the layshaft  blind bush to be carrying load, this load is most concentrated in Third Gear, so the typical "They all do that, Sir" third gear moan from a worn bush or scored layshaft. Wear to the layshaft fixed pinion teeth has also been mentioned on the Forum as the source of this annoying noise. In first gear the layshaft is being driven from the kickstart end, but moving up the box puts  successively more sideways thrust on the layshaft  blind bush, hence the higher load in Third Gear.

  Designation of the gears A,B,C, etc will help those lost souls struggling to understand Haynes, Page 70 in my well thumbed 1973 edition. All good stuff.

 Pub quiz fact....The total number of teeth on each pair of gears is the same, 43 in the case of this design of gearbox. As for faults and malfunctions, yes we all have sleepless night puzzling the cause, but as in this case, correct assembly with the right parts solved the conundrum, and as noted, the dots don't always work.

 Good to know it is back together and working, and for folks fearful of gearbox internals, this design is one of the simplest ever, earlier BSA efforts are truly on the scale of  Charles Babbage's Difference Engine in their complexity. Springs, Pawl and Ratchets, Pivots, Pins and Rivets. These are the boxes to fear, early Plunger Pre-War B Models being typical.

 Swarfy.

[JulianS]

Mike has it right.

When the box is off the bike you can see the movement and position of the pinions as the selectors move.

First gear -  the layshft F gear slides to engage in the layshaft H gear, the big one.

Second - the layshaft D gear slides to engage on the layshaft B gear.

Third - the mainshaft E gear  slides to engage on the mainshaft G gear, the small one. When these pinions wear the box become suscepitble to sliding out of third gear particularly when under load.

Top - mainshaft C gear slides to engage in the mainshaft A gear, the sleeve gear.