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Gearbox horrors

Submitted by john_pullen-appleby on Wed, 27/09/2017
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Light Twins

Hello All,

The Navigator gearbox is it seems the gift that keeps on giving. After all the malarky with the massive (3.5mm( end float for the kickstart ratchet I made a bearing bronze thrust washer that gave me just percievable endfloat with the nuts holding the inner gear plate done up--revolving but no real in and out movement.

Showering poor Andy S with messages in the process I went through not being able to get the oil seal behind the F/D procket to fit and assembled the gearbox. Moving the ratchet with a socket gave me 4 years one neutral--I had realised that the gears are one up and three down. My BSA C25 had been built like that--I put it together by the book and had hours of fun trying to pull away.

Anyway--I tried the outer cover on and--while trying to turn the sporocket (stiff double lipped oilseal) round can sometimes get all the gears but---

I noticed that the cases would not mate together. I put the square seal in (for the kickstart shaft) and made it worse.

It seems as if it is a by product of my shiming. The only possible solution I can think of is a thick gasket--about 2.5mm thick.

Any suggestions very welcome#

#Cheers

JPA

Submitted by patrick_mullen on Wed, 27/09/2017

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Hi John,

You are having problems. I'm not convinced that a thicker gasket is the answer. This could give trouble with gear selection. The question is why does the gear box outer cover not fit properly when presumably it did before.

As the only thing you altered was the layshaft bush and then added on the bronze thrust washer it seems most likely that this washer is too thick and needs reducing to allow the outer cover to fit. Or is the outer cover fouling on something else?

I have only ever tested for end play with the gearbox fully assembled and the outer cover fitted.

Patrick

Submitted by john_pullen-appleby on Wed, 27/09/2017

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Hello Patrick

I am inclined to agree. The cover is flat and is being held up by the kickstart shaft as fitting the square rubber seal holds it off the fqce even more.

All this time I have been trying the endfloast with the kickstart ratchet in the inner plate--I have never tried it with the outer cover on. Is this with the rubber seal in place incidently (and for that matter the spring under tension)? Both could inhibit movement

What I cannot see though is how checking the kickstart for end float can give any accurate indication as several things seem to be potentially pressing in it. It seems as 'end float' as I am using the term--IE the physical clearance between the face in the back of the gearbox (head of the bush--thrust washer in my case) and the bush in the kickstart shaft is not what is actually being measured.

To take out all excess play--the kickstart shaft must protrude further into the out cover.

It does sound a possibility mind as --3.5mm 0f endfloat does not just appear from nowhere.

I'll take it down and try again.

Cheers

JPA

Submitted by patrick_mullen on Thu, 28/09/2017

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I have always been lazy and never bothered inside the gearbox unless something was obviously not working - so I have only ever shimmed first gear if it was actually jumping out of gear. So any testing for 'end float' was done with the gearbox in full assembled working order including oil etc. i.e the American principle "if it's not broken don't fix it". So as far as is practical I believe very much in getting an engine/gearbox actually running first and then assessing what attention is actually needed. They were not high tech when new so they keep running even when well abused.

One surprising item about shimming is the fact that there is no layshaft shim listed in the 1959 spares listing - it appears later in the 1961/62 listing - so they probably didn't worry too much about end float when first introduced.

Patrick

Submitted by john_pullen-appleby on Thu, 12/10/2017

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Well, a solution has ben found. A previous owner had assembled the gearbox with the thrust washer that lives under the kickstart shaft (under the worm gear) and--I bought one and then did not know what to do with it. I shimmed it out there (it still had 40 thou or so to take up.

With all the shake being taken up in this fashion--the kickstart ratchet would not clear. I have a 10 thou shim in the normal position and the rest taken up by shims under the worm.

The ratchet works and the out cover mates to the one under it. I can change gear with a spanner on the ratchet and can after a fashion (rotating the sprocket and working the lever back and forth) get the gears with the cover temporarily on. I still need to replace the washer that (with the tin can affair) encloses the pawl spring-distances are tight in there--I made one that is evidently too thick as--with the fitted--the cases do not mate. The saga continues

JPA

Submitted by patrick_mullen on Sun, 15/10/2017

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I have the cover of a gearbox so without actually dismantling I reckon the inner washer is 1.6mm which probably translates to 1/16th.of an inch. Anyway it looks quite a thin washer but I can't guarantee that's 100 per cent accurate or original but should be close enough for practical purposes. The gearbox does work.

Submitted by john_pullen-appleby on Thu, 19/10/2017

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Previously patrick_mullen wrote:

I have the cover of a gearbox so without actually dismantling I reckon the inner washer is 1.6mm which probably translates to 1/16th.of an inch. Anyway it looks quite a thin washer but I can't guarantee that's 100 per cent accurate or original but should be close enough for practical purposes. The gearbox does work.

Thanks Patrick. I made one out of some heavy shim steel--probably30 thou of so and it all seems to work fine. I have not put the cover on permanently as I am waiting for a clutch cable and by the looks of things--it will be easier to fit the cable with the outer case off.

Primary drive next--I have put the inner cover on and tried the clutch on a while back. hopefully I shall get my re-line barrels back soon.

Cheers

JPA

Submitted by andy_sochanik on Fri, 27/10/2017

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Hi All,

Just a word of warning here.

There should be little or no discernable end float in the gearbox, when measured on the kickstarter shaft coming out of the gearbox - WHILE IT IS ASSEMBLED!

I stress that last bit, as recently messages got crossed in email exchanges with one correspondent - who was measuring end float whilst the box was dismantled. There was an outer wire circlip and it was that movement (to & from the circlip) that he was measuring. The circlip - if fitted - is largely redundant. I think it was put there to protect the soft aluminium of the inner cover against abrasion from the k/start spring.

It greatly enhances measuring this end float, if the engine is still in the bike (or in a solid fixing) and the k/start lever is in place.

 


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