Amelia Squariel: SQ4 Gearbox Investigation

Beginning the Sq. 4 up mid winter is one thing I do at the least as soon as per week simply to verify it is all working, which it often is – besides when it is not.

This week I used to be met with an surprising noise, like gear-dogs clashing – it sounds prefer it does whenever you put it into first gear. Hearken to the sound, particularly apparent round 28 seconds:

The noise stops as you disengage the clutch (which is dragging badly) because the mainshaft slows to a cease. It is also not current for those who run the bike in gear on the rear stand.

Casting to the discussion board & FB world for recommendation, I ended up having a chat with AOMCC gearbox guru Geoff – half-hour of excellent recommendation. To summarise:

  • Poor Sleeve gear place results in dropping out of high gear. It appears I’d want an additional spacer to maneuver the sleeve gear in the direction of the mainshaft sliding gear
  • Minimise Layshaft finish float, centralise in new bushes
  • Minimise Camshaft finish float
  • All of the bits can be found from AOMCC Gearbox Spares, no bushes want reaming 

Here is the gearbox drawing, for reference:

So on with the work; first job is to get the bike on the elevate. This entailed becoming the swinging arm springs to the FH, which is a narrative in itself. Having the half-built FH on the bench is kind of a special expertise to having the SQ4 up there – you realise how heavy it’s, however the elevate is kind of glad and accommodates the rear stand fairly properly.

But once more the bench proves it is value, supplemented by the brand new lights overhead. I purchased some strip lights so as to add to the inside mild circuit, and once I put them up I moved the outdated inside lights, which used to face the benches, to face the bike on the elevate. Then benches are taken care of by their very own circuit, and now I’ve either side of the bike illuminated.

Eradicating the outer cowl reveals no points with the selector or kickstart. I have to do not forget that this field is lacking it is kickstart rebound rubber if I recall appropriately.

I arrange the DTI on the elevate deck. This is not preferrred, because it reveals the bike is swaying about a bit on it is stand however the association serves to disclose 1 mm finish float on the mainshaft, 0.3 mm on the layshaft and 0.3 mm on the selector shaft. The restrict laid out in Waller for the mainshaft is 1/32″, which is about 0.8 mm. There’s nothing specified for the opposite two shafts.

You would possibly recall some points we had been having with the clutch in the direction of the top of final season – I wrote them up right here in a submit known as Clutch Investigation. The top float within the mainshaft probably contributed in the direction of this drawback.

We’ll transfer to the opposite aspect now; the primary discovery isn’t any shock – the clutch centre nut has backed off once more, although the tab washer prevents it shifting too far. The rationale for that is the splines, that are very worn and will not take any load with out shifting a bit:

This can be a new AOMCC clutch centre. The splines are wider and have sq. shoulders:

With the clutch off, I used to be capable of get a greater high quality mainshaft endfloat measurement of 0.88 mm (35 thou) with the DTI magnetic base mounted on the engine/gearbox plate

Transferring the DTI to a metal plate clamped to the gearbox produced some higher numbers for the layshaft and camshaft:

In abstract, I’ve finish floats as follows:

  • 35 thou on the
    mainshaft, a bit over 1/32”. Ariel’s acknowledged limits are 1/64″ – 1/32″
  • 9 thou on the layshaft. Ariel solely state a minimal for this finish float.
  • 9-10 thou on the
    selector. Ariel solely state a minimal for this finish float.

So, barring the sleeve gear, I’ve all of it aside and might measure up. The components washer is such  helpful piece of kit.

In no specific order, listed here are some footage. Having stripped the gearbox I’ve mentioned it with numerous specialists on the AOMCC discussion board and Fb pages, and twice with Geoff, the AOMCC gearbox spares specialist. These are the 2 selector pins – the damage is apparent, however not measurable. These usually are not going to be modified.


That is layshaft 2nd; canine are good, enamel are good.

That is the layshaft sliding ‘clutch’ – canine are good, splines are good.

That is mainshaft third; canine are good, enamel are good.

Selector forks are a bit worn however present no signal of bending, burning or main harm. They’re match within the grooves on the sliding sleeves.

Two issues on this image – the sleeve gear, which I am unable to take away but (massive field spanner on the way in which) and the drive aspect layshaft bush. The shiny ring exhibits you the place the layshaft output gear has handed it is finish load.

The dimensional survey revealed the next: 

  • Layshaft 2nd gear bush 1.061” gear 1.065” 4 thou clearance
  • Layshaft 1st gear bush 1.062” gear 1.0653” 3.3 thou clearance
  • Mainshaft third shaft journal 0.786” gear 0.788” 2 thou clearance
  • Sleeve gear bearings: 
    • Mainshaft outer journal 0.931” sleeve gear bush 0.940” 9 thou clearance
    • Mainshaft interior  journal 0.928” sleeve gear bush 0.941” 13 thou clearance
  • Kickstart pawl bush size 0.81”
  • Layshaft timing aspect bush 0.663” shaft journal 0.652”, 11 thou clearance
  • For some cause I did not document the size of the layshaft drive aspect bush or the camshaft bush, however I suppose I had already dedicated to altering them due to the top float. Effectively, that is one of the best excuse I’ve proper now.

And one other one from the specialists – it seems to be just like the timing aspect mainshaft nut is unsuitable, because it would not bear on the kickstart pawl in any respect.

In order that’s it! New layshaft, camshaft and sleeve gear bearings and a brand new kickstart rebound rubber.