5 speed mainshaft problems

Tigernut · Aug 1, 2022

I've found that the taper on the new Harris gearbox's mainshaft is wrong. I could detect some 'rock' when offering up the clutch hub (with drum & centre & rollers) when fitting the primary drive. It wasn't much, but seemed wrong. I reasoned that with a brand new Harris gearbox, it must be OK so went ahead and tightened the clutch nut (80 ft/lb). Next day (yesterday) the doubts got the better of me so I undid the clutch nut to see if the hub had seated firmly. It hadn't - the hub came off the taper without any effort at all - if I'd used it like this, it would have been relying completely on nut torque and the Woodruff key, which would not have lasted long.

I have other gearboxes including one with another brand new Harris mainshaft. I checked this. I offered up a new clutch hub and found, just like the other one, that it would rock. I pushed it onto the taper as hard as possible by hand and it doesn't bite. I tried the same new hub on a couple of good used (genuine) mainshafts and with just a bit of hand pressure, it locks tight enough to need firm thumb pressure to release it - just as you'd hope.

So, the Harris mainshafts have inaccurately ground tapers. Has anyone else used these mainshafts? Has anyone else come across, or heard about, this issue?

Tigernut · Aug 3, 2022

It doesn't look as if anyone's interested in this but just in case, here's an update:-
Mark at LFH has sent me another new shaft, from the most recent batch (they've only just had a new batch made since the last batch of 250, made in 2019).

The new one arrived yesterday and the taper is a lot better, but still not perfect. I had to lap a hub onto the taper until it would 'bite' when all cleaned up. No chance of doing this with the other LFH shafts - the taper is so fr out on them you'd be lapping away for a week and end up too far down the shaft by the time you'd got a good fit.

John Healey has published that he wouldn't trust these repro gearboxes in a tuned bike, though doesn't elaborate as the exactly what the defects are (are they down to manufacturing errors? Materials? Treatments? Quality of finishing - it would be nice to know.

So, with the new LFH shaft, I was able to lap a hub (also new) onto it so that it would 'bite' as I'd hope. Mark is going to send me another new mainshaft to exchange for the other defective one I've got.

Definitely 5 Star customer service. Maybe not quite 5 Star quality control?

Fast Eddie · Aug 3, 2022

Disappointing. LFH are supposed to be the good guys !

Tigernut · Aug 4, 2022

Fast Eddie said:
Disappointing. LFH are supposed to be the good guys !

Well I can't fault the level of customer service, which goes a long way beyond the norm. I didn't buy either the complete gearbox, or the individual mainshaft direct from LFH so they could quite reasonably have told me to take it up with the retailers. I only phoned LFH in the first place to ask a question, but Mark immediately said he'd send me replacements, which arrived the next day. The gearboxes and gearbox parts are made by outside contractors (I couldn't get a firm answer as to where in the world they're located but it was hinted that they're made in Italy). They are supposed to be made to Triumph drawings and within Triumph tolerances, but there's no way these tapers can be within tolerance. Hopefully, not too many of these shafts are out there, or there'll be quite a few people blaming themselves for not torquing up sufficiently when their clutches come off.

Fast Eddie · Aug 4, 2022

Sadly, given the large batch nature of industry, there are no doubt hundreds of these shafts now all over the world sat on shelves. Some will sit there for years before causing grief to unsuspecting buyers !

baz · Aug 4, 2022

Tigernut said:
Well I can't fault the level of customer service, which goes a long way beyond the norm. I didn't buy either the complete gearbox, or the individual mainshaft direct from LFH so they could quite reasonably have told me to take it up with the retailers. I only phoned LFH in the first place to ask a question, but Mark immediately said he'd send me replacements, which arrived the next day. The gearboxes and gearbox parts are made by outside contractors (I couldn't get a firm answer as to where in the world they're located but it was hinted that they're made in Italy). They are supposed to be made to Triumph drawings and within Triumph tolerances, but there's no way these tapers can be within tolerance. Hopefully, not too many of these shafts are out there, or there'll be quite a few people blaming themselves for not torquing up sufficiently when their clutches come off.

I'd always lightly lap in any new taper if they haven't been run together before
But yours sounds well beyond what I would call an engineering tolerance

Al's#5 · Aug 5, 2022

Tigernut said:
I've found that the taper on the new Harris gearbox's mainshaft is wrong. I could detect some 'rock' when offering up the clutch hub (with drum & centre & rollers) when fitting the primary drive. It wasn't much, but seemed wrong. I reasoned that with a brand new Harris gearbox, it must be OK so went ahead and tightened the clutch nut (80 ft/lb). Next day (yesterday) the doubts got the better of me so I undid the clutch nut to see if the hub had seated firmly. It hadn't - the hub came off the taper without any effort at all - if I'd used it like this, it would have been relying completely on nut torque and the Woodruff key, which would not have lasted long.

I have other gearboxes including one with another brand new Harris mainshaft. I checked this. I offered up a new clutch hub and found, just like the other one, that it would rock. I pushed it onto the taper as hard as possible by hand and it doesn't bite. I tried the same new hub on a couple of good used (genuine) mainshafts and with just a bit of hand pressure, it locks tight enough to need firm thumb pressure to release it - just as you'd hope.

So, the Harris mainshafts have inaccurately ground tapers. Has anyone else used these mainshafts? Has anyone else come across, or heard about, this issue?

Without a sketch or pic this is a stab in the dark and maybe a daft question; Is the hub bottoming out before positioning correctly?

Tigernut · Aug 6, 2022

Al's#5 said:
Without a sketch or pic this is a stab in the dark and maybe a daft question; Is the hub bottoming out before positioning correctly?

I'd say yes, it is. I tried lapping the worst shaft (the one that came with the complete new gearbox). I applied a very small amount of fine compound in lines down the full length of the shaft's taper. After a little lapping I cleaned up and had a look. There had been no contact from roughly halfway down from the major diameter.

Al's#5 · Aug 7, 2022

Tigernut said:
I'd say yes, it is. I tried lapping the worst shaft (the one that came with the complete new gearbox). I applied a very small amount of fine compound in lines down the full length of the shaft's taper. After a little lapping I cleaned up and had a look. There had been no contact from roughly halfway down from the major diameter.

I get your drift but I was thinking of a shoulder maybe on the shaft or in the hub. Lot of years since I meddled with the like but something stirred the old grey matter.

Tigernut · Aug 8, 2022

Al's#5 said:
I get your drift but I was thinking of a shoulder maybe on the shaft or in the hub. Lot of years since I meddled with the like but something stirred the old grey matter.

No, there is no shoulder to bottom out onto. The shaft taper blends into the parallel section and the hub taper is continuous all the way through.