If you go back to post #120, you will understand why I have a “saved search” on ebay for a wide ratio gearbox cluster. Since then I have acquired a couple of parts books for the Triumph Twins, one from 1959 and one from 1964, to help try to understand the various little quirks that these engines have. I now know that the gearbox cluster in my engine, and the one referred to in post #120, are the standard ratio from the earlier models.
Just before the Manx the saved search came up trumps, a set of wide ratio gears that actually matched the number of teeth in the parts book.
I put in a bid of what I thought they were worth and crossed my fingers, as the auction ended whilst I was on the ferry to the Isle of man. Happily, I won, and at a fair price.
Whilst competing in the Manx, I spotted that one of the other Twins there had the spark plugs in a different location. This attracted my attention, as I keep catching the left hand plug cap with my knee and knocking it loose. Not enough to stop the engine, and I can quickly push it back on, but one wet day this is likely to hurt! I asked further about this modification and it turns out the owner had had a fall where the sparkplug had snapped and stuck into the side of his knee. Hmm.
Once back home I contacted Bill who had rebuilt the engine last year, to see if a) he had heard of this mod, and b) if he could do it? He had heard of it, and knew what it entailed, so we arranged for him to collect the head from me a week later. In the meantime, mindful of problems other people have had with different gears I set about measuring shafts and clearances on the gear clusters. All seemed ok, except the layshaft had a smaller end diameter than mine. I rang Bill to ask about sleeving this to fit while he was doing the head. He explained to me that the later models had a needle roller bearing where mine has a bush, but why didn’t I just swap the “fixed” gears off the new layshaft onto mine? Because I didn’t know you could do that. But I do now.
Spot the difference. Not the clearest of pictures I know.
Pulling the gearbox apart is becoming very easy now. Before I started though, I made a chart of how many crank revolutions were needed to turn the rear wheel once in each gear, with the set up I have been using for the last couple of years.
With the gear selector side all bolted up, we can turn our attention to the clutch side.
New seal should keep the gearbox oil in.
New 14 tooth gearbox sprocket.
New seal in the sprocket cover should keep the engine oil in.
The clutch hub is keyed onto the shaft, then you have to painstakingly refit all 20 rollers for the clutch basket to spin on.
Then the clutch centre and torque up the nut and lock tab it on.
Top tip for refitting duplex chains with a split link. Pull the ends together first with a cable tie.
When I came to fit the clutch plates, and then the pushrod, there was a head scratching moment. The clutch wouldn’t disengage. It was almost as though the pushrod was too short?
For the moment I ignored this problem and set to counting crank revolutions with the new ratios.
As I had been led to believe, 4th gear was almost identical, but the spread of gears was much wider, leading to an exceptionally low 1st gear. This meant I could change to a smaller rear wheel sprocket to get back to the 1st gear I was used to, but now with a higher 4th gear and the subsequent rise in road speed.
New sprocket is 44t, old is 54t. Something of a difference!
Now to look at that clutch problem before refitting the head.
Mark