Sliding dog

[Seamus murphy]

If you have the layshaft with the sliding dog spring and bearings assembled and you slide the gears on snd you push the sliding dog to the 1st gear position should the top of the sliding dog pertrude passed the end of the 1st gear mine does slightly. What lm botherd about in the packer pushing the sliding dog down causing problems with ball bearing not being located in corect postion for 1st gear selection. I hope that made sence

[rossclark]

I'd say not. I think that if the dog protrudes from the stack then it's possible that it will jam the shim against the endplate. Needs investigating. Is the stack higher than the layshaft?

[Warkton Tornado No.1]

Post by Seamus murphy » Wed Jan 04, 2017 11:33 am

If you have the layshaft with the sliding dog spring and bearings assembled and you slide the gears on snd you push the sliding dog to the 1st gear position should the top of the sliding dog pertrude passed the end of the 1st gear mine does slightly. What lm botherd about in the packer pushing the sliding dog down causing problems with ball bearing not being located in corect postion for 1st gear selection. I hope that made sence

I've witnessed this before & it was due to using Indian cursors, which are machined slightly out of position.

I think this has been covered before in detail, so it may be worth a search through the Forum.

[Seamus murphy]

I took the layshaft to scoot show at newark today to cut a long story short ive bought a new casa layshaft to go with tutto stratos sliding dog everything now works perfectly the gears sit just above the shoulder of the new layshaft and the sliding dog sit perfectly. so ultimately it was a worn out layshaft.thanks for your replys.

[Adam_Winstone]

Interestingly enough, I have just experienced the same testing a sliding dog and layshaft that came out of an import engine (everything inside said engine looked as you would expect of a factory motor, Innocenti) and the locating feet of the sliding dog did end up quite far beyond the end face of the layshaft when move by hand to select 1st. This confused me to the point that I then went to look at another pair that I have on the shelf and that is exactly the same.

The appears to be no major wear to the end of the layshaft and when assembled and shimmed, the motor still seems to select and stay in all 4 gears (by hand so not under load) so I'm guessing that many are like this I've not noticed this before, nor questioned it as I tend to assemble by finding neutral and leaving it in that position during a build. It does seem a little odd to me though.

Any feedback from others?

Adam

[Warkton Tornado No.1]

Post by Adam_Winstone » Sun Jan 08, 2017 11:15 am

Interestingly enough, I have just experienced the same testing a sliding dog and layshaft that came out of an import engine (everything inside said engine looked as you would expect of a factory motor, Innocenti) and the locating feet of the sliding dog did end up quite far beyond the end face of the layshaft when move by hand to select 1st. This confused me to the point that I then went to look at another pair that I have on the shelf and that is exactly the same.

The appears to be no major wear to the end of the layshaft and when assembled and shimmed, the motor still seems to select and stay in all 4 gears (by hand so not under load) so I'm guessing that many are like this I've not noticed this before, nor questioned it as I tend to assemble by finding neutral and leaving it in that position during a build. It does seem a little odd to me though.

Any feedback from others?

Adam

Adam, I think you are a Design Engineer, aren't you? Perhaps you might agree with my reasoning....


Actually, having thought about this a bit more, all the cursor protrusion amounts to is a slight amount of pre-load on to the gear shim.

It’s a reasonable assumption that it would have been a deliberate intention.

To have the selector balls not providing pre-load (in first) would have been not so easy to control from a machining aspect, requiring tighter tolerancing.

Wear would not have been significant as it could only occur in first gear in which case there are six flat lobes running against the shim in addition to the gear, so the shim is probably rotating with the assembly.

Essentially, the gear shim acts not only as a spacer, but a simple, plain thrust bearing face running in the oil bath.

What does spring to mind is the fact that many aftermarket shims will probably not conform to OEM (Original Equipment Manufacturer) standards of material & hardness....

[Adam_Winstone]

Hi WT1... no, a Civil Engineer.

All good food for thought as I too have been pondering the design.

Preload is a good idea as to why this may have been done and the impact on shim movement is also an issue that I've been trying to get my head around. Indeed, it then makes me question the relationship of shimming in neutral thru 4th in relationship to preload in 1st. I've not come up with any great conclusion yet but the grey matter is busy.

Cheers,

Adam

[HxPaul]

Sticky's book says when a gearbox is rebuilt there should be between 0.003 and 0.011ins clearance between the shim and the endplate,if you rebuild it to have 0.003ins clearance,then if the sliding dog protuded any further than that above first gear it would push the shim into the back of the endplate.

[Warkton Tornado No.1]

Oops! Sorry about the assumption as to your profession. You'll be used to real money then....

TBH, I looked @ the Parts Illustrations to get my own head around the function which took all of five minutes.

In all the years, I'd never really thought about it, but if my conclusions are correct, it does make sense.

No pre-load would probably tend to encourage jumping out of the gear that is subjected to most torque...

[Adam_Winstone]

"Oops! Sorry about the assumption as to your profession. You'll be used to real money then.... ", you must be thinking of a different sort of Civil Engineer!

HX... shimming is typically done in neutral (certainly by me) so any preload pushing the shim over would not reduce clearance as this would only happen in 1st gear.

Adam

[HxPaul]

Ah...I understand.

[Warkton Tornado No.1]

Shimming should be done in neutral as you say, Adam.

However, what I’ve been waffling on about is the fact that I now firmly believe that the cursor should protrude beyond first gear as the OEM Design intent & for very good reason.

[Adam_Winstone]

"However, what I’ve been waffling on about is the fact that I now firmly believe that the cursor should protrude beyond first gear as the OEM Design intent & for very good reason.", yep, I get that and can understand your reasoning.

Adam

[Adam_Winstone]

Guess what?

This same motor is being put through its stride and doesn't like to stay in 1st gear! Selector spring, gear mesh faces and cursor faces are all fine, which now makes me think that this may be a question of 'how much protrusion is too much?' The bike does select 1st but likes to slip back to neutral so I think that this is likely to be a strip down and revisit the issue

Adam

[Fast n Furious]

I recon the Lammy gearbox is a pretty good design except for the end-plate fixings.
This is the way I see it.
The loose layshaft gears must have preload on the shim. The shim thickness controls how much preload will apply.
Without preload toward the endplate, the gears would be free to load in the opposite direction knocking it out of gear.
The preloading force is associated with the action of torque acting between the finger ends of the cursor and the drive slots in the loose gear.
This force try's to crush the finger ends into the centre of the layshaft. This effect helps to force the loose gear set toward the shim.
If the finger ends of the cursor protrude past the end of the first gear by any more than 3 -11 thou, then the cursor will hit the shim and interfere with the ability of the loose first gear to preload correctly.
I remember back in the 70's working on a mates scoot with an Omega 5 speed box, which was always jumping out of gear because the loose gears weren't machined correctly so it couldn't preload properly.

[Adam_Winstone]

WOW! Don't you just love good advice?!

So, after noticing how far the sliding dog protruded beyond the end of the layshaft, when selecting first gear, I was sure that this would be the cause of my bike wanting to jump out of 1st gear, So sure of it that I went through my various VGC used items and found a pair that remained almost flush in 1st, stripped the engine, replaced it all (taking the opportunity to change my 47 rear sprocket for a 46 to give me slightly higher gearing as I was quickly in 4th and pulling it easily during my few test miles), and find that selection and ability to remain in 1st was unchanged

At this point I revisited a PM that I'd been sent, which questioned clutch cable interference against the inside of the headset casting, where the cable links through to the alloy lever housing. I'd discounted this as this new motor was replacing a fairly standard iron 175 that had never given me this issue, with none of the cables (or routing) having been changed, so couldn't imagine that a change of motor would impact on the cable routing and gear selection... how wrong I was! I guess that it only takes a slight difference of wishbone on selector shaft or of early type pinch-bolt gear selector top for this to change selection fractionally and for that to have an influence.

I also need to review the comment in Sticky's manual that talks about Dean at Rimini Lambretta Centre reworking this self same area of the headset to ease selection... perhaps even mentioning helping to stay in gear?

Anyway, this was indeed the issue and I could have saved myself a transmission strip down (then again, I'd probably have settled for the short gearing so I can convince myself that it was worthwhile ) and when I stripped the lever housing off to see the internal format, the headset had 2 nasty casting ridges (one top, one bottom) with the top one effectively trying to scissor the clutch cable when selecting 1st, and the pressure being enough to push it back into neutral with ease (a lot of strain).

So, a big THANK YOU to Captain Pugwash for the good advice, which I would never have considered as it had been fine with the previous 175 motor and same cables. Lesson learnt not to discount anything!!!

Adam

PS - My headset bottom is a Spanish short type, similar to chrome ring Italian.