Burman Clutch Centre

 Over the last few days I've assembled the primary drive and the clutch, tightening the mainshaft nut in the process.

I've installed the clutch spring studs with Loctite 271, the red thread locker. That won't come loose; originals were peened in place, but it's not 1950.

Fitting the plates revealed some rocking. I pulled them all out again, and found that three of the four plain plates were distorted by up to 2 mm, and discoloured from heat.

Geoff will send some new ones tomorrow.

SQ4 gearbox rebuild

 Now we know what we have to do, we can get started with the rebuild helped by these lovely new bushes from Geoff at AOMCC Gearbox Spares

First job is to remove the two Welch plugs over the layshaft and camshaft; I drill a hole in these and lever them out:

With some heat in the casting, you can drift the layshaft and camshaft bushes out from the drive side:

The sleeve gear bushes come out with a bit of tube; the new ones go in with a large flat drift. They go in quite easily with a hammer (you don't hit the bush directly), but it's times like this that I wish I had a press.

The new drive side bushes can be pulled in with suitable studs and washers:

You need to be careful with the layshaft bush. It's easy to get it misaligned, and there is an anti rotation pin designed to keep the grease groove at the top. At the factory this was drilled and fitted from the drive side, but with a replacement bush you must align the slot in the bush when you put it in.

All this work culminated in 0.13 mm end float (5 thou) on the layshaft. That's better than the 9 thou I had earlier, and I have the proper gasket fitted now.

What's not so good is the 0.37 mm I have on the camshaft. That's about 15 thou and will have to be sorted with shims.

I've also decided to discard these two nuts and make some new ones. The threads are poor and the nuts would be better twice that thickness.

We'll fix the camshaft end float with this 0.3 mm shim. It's a commercially available 26 mm ID shim that I've opened out to fit:

This shim fits inside the inner cover. Unfortunately, I found out later that this is a 0.5 mm shim in a wrongly-labelled bag - testing revealed a selector shaft that was firmly clamped in place.

Here's the selector shaft assembled and greased ready to go in.

A trial fit, with shakeproof washers under the BSW nuts (to prevent them coming loose) revealed the shim problem. I went through two bags of shims with a micrometer and found that all the shims in the 0.5 mm bag were 0.3 mm and all the ones in the 0.3 mm bag were 0.5 mm...

Easily found and fixed, fortunately. It pays to measure and test at every step. 

With that fixed and the selector shaft showing about 0.05 - 0.07 mm (2 thou or so) end float we can set up to measure the mainshaft and sleeve gear end floats.

The mainshaft endfloat still measures 0.88 mm or 35 thou: not surprising, since we haven't changed anything.

The sleeve gear shows 1.11 mm when in top gear:

A call to AOMCC gearbox guru Geoff suggested I make a spacer to reduce that to 0.11 mm, 4 thou, to maximise spline engagement. Geoff provided a useful spacer to make that from:

This is the spacer that sits under the gearbox sprocket, inside the oil seal. It parts off quite easily on the mini-lathe, once you remember that you don't want the lathe in high gear!

The spacer fits neatly on the inside of the main sleeve gear bearing, pushing the sleeve gear splines into further engagement with the mainshaft sliding gear splines.

To deal with the excess mainshaft end float, I have machined a 0.5 mm recess into the mating side of the nut. This will restrict mainshaft travel a little more and should bring the end float down to somewhere near 0.38 mm, or about 1/64".

Reassembling the gearbox reveals sleeve gear movement at 0.8 mm; I must have measured that wrongly as I thought I had 1.11 mm and added a 0.75 mm spacer. Mainshaft end float is now 0.6 mm, down from 0.88 mm and around 25 thou. This is 1/40", within Ariel's stipulated range of 1/64" - 1/32".

All good news; however, since tightening the inner case nuts for what I thought was the last time, I've realised that the camshaft is too tight. It turns, but that 2 thou end float has clearly been taken up by gasket compression - I may relieve the bush a little or I may fit shims to 0.2 mm (8 thou) rather than the 0.3 mm currently fitted (12 thou) which should give me what I need.

As it turned out, smoothing the surface of the camshaft bush was all that was required to return to normal operation, so I tightened up the end cover. The last step was to fit the two Welch plugs, which have to be done before the sprocket goes on for the last time. It would have paid to ensure the bores for these were clean before the bushes went in, as enthusiastic staking at the factory had left a lot of material in the layshaft bush bore which had to be scraped out with a twist drill ground flat, like an end mill.

Next job is to close up the other end of the gearbox, but I can't do that without the clutch in place as I can't hold the mainshaft to do the nut up on my own.

More next time.

SQ4 Gearbox Investigation

Starting the Square Four up mid winter is something I do at least once a week just to make sure it's all working, which it usually is - except when it isn't.

This week I was met with an unexpected noise, like gear-dogs clashing - it sounds like it does when you put it into first gear. Listen to the sound, especially obvious around 28 seconds:

The noise stops as you disengage the clutch (which is dragging badly) as the mainshaft slows to a stop. It's also not present if you run the bike in gear on the rear stand.

Casting to the forum & FB world for advice, I ended up having a chat with AOMCC gearbox guru Geoff - 30 minutes of good advice. To summarise:

• Poor Sleeve gear position leads to dropping out of top gear. It seems I might need an extra spacer to move the sleeve gear towards the mainshaft sliding gear
• Minimise Layshaft end float, centralise in new bushes
• Minimise Camshaft end float
• All the bits are available from AOMCC Gearbox Spares, no bushes need reaming 

Here's the gearbox drawing, for reference:

So on with the work; first job is to get the bike on the lift. This entailed fitting the centre stand springs to the FH, which is a story in itself. Having the half-built FH on the bench is quite a different experience to having the SQ4 up there - you realise how heavy it is, but the lift is quite happy and accommodates the rear stand quite well.

Yet again the bench proves it's worth, supplemented by the new lights overhead. I bought some strip lights to add to the interior light circuit, and when I put them up I moved the old interior lights, which used to face the benches, to face the bike on the lift. Then benches are taken care of by their own circuit, and now I have both sides of the bike illuminated.

Removing the outer cover reveals no issues with the selector or kickstart. I must remember that this box is missing it's kickstart rebound rubber if I recall correctly.

I set up the DTI on the lift deck. This isn't ideal, as it reveals the bike is swaying about a little on it's stand but the arrangement serves to reveal 1 mm end float on the mainshaft, 0.3 mm on the layshaft and 0.3 mm on the selector shaft. The limit specified in Waller for the mainshaft is 1/32", which is about 0.8 mm. There's nothing specified for the other two shafts.

You might recall some issues we were having with the clutch towards the end of last season - I wrote them up here in a post called Clutch Investigation. The end float in the mainshaft possibly contributed towards this problem.

We'll move to the other side now; the first discovery is no surprise - the clutch centre nut has backed off again, though the tab washer prevents it moving too far. The reason for this is the splines, which are very worn and won't take any load without moving a little:

This is a new AOMCC clutch centre. The splines are wider and have square shoulders:

With the clutch off, I was able to get a better quality mainshaft endfloat measurement of 0.88 mm (35 thou) with the DTI magnetic base mounted on the engine/gearbox plate

Moving the DTI to a steel plate clamped to the gearbox produced some better numbers for the layshaft and camshaft:

In summary, I have end floats as follows:

• 35 thou on the mainshaft, a bit over 1/32”. Ariel's stated limits are 1/64" - 1/32"
• 9 thou on the layshaft. Ariel only state a minimum for this end float.
• 9-10 thou on the selector. Ariel only state a minimum for this end float.

So, barring the sleeve gear, I have it all apart and can measure up. The parts washer is such  useful piece of equipment.

In no particular order, here are some pictures. Having stripped the gearbox I have discussed it with various experts on the AOMCC forum and Facebook pages, and twice with Geoff, the AOMCC gearbox spares specialist. These are the two selector pins - the wear is obvious, but not measurable. These are not going to be changed.

 

This is layshaft 2nd; dogs are good, teeth are good.

This is the layshaft sliding 'clutch' - dogs are good, splines are good.

This is mainshaft 3rd; dogs are good, teeth are good.

Selector forks are a little worn but show no sign of bending, burning or major damage. They are a good fit in the grooves on the sliding sleeves.

Two things in this picture - the sleeve gear, which I can't remove yet (big box spanner on the way) and the drive side layshaft bush. The shiny ring shows you where the layshaft output gear has passed it's end load.

The dimensional survey revealed the following: 

• 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 3rd 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 inner  journal 0.928” sleeve gear bush 0.941” 13 thou clearance
• Kickstart pawl bush length 0.81”
• Layshaft timing side bush 0.663” shaft journal 0.652”, 11 thou clearance
• For some reason I didn't record the dimensions of the layshaft drive side bush or the camshaft bush, but I guess I had already committed to changing them because of the end float. Well, that's the best excuse I have right now.

And another one from the experts - it looks like the timing side mainshaft nut is wrong, as it doesn't bear on the kickstart pawl at all.

So that's it! New layshaft, camshaft and sleeve gear bearings and a new kickstart rebound rubber.