seeley Norton with Triumph Gearbox

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Hi to all
I am in the stage of planning to build a Seeley with a modified Commando 750 cc motor. I want a 5 speed transmission and i am considering pairing it with a Triumph 4 speed gearbox fitted with a later 5 speed internals which is a popular and not very difficult modification for Triumphs. What does anybody think about that?
 
If you already have all of the parts required, then its a cheap way of getting a 5 speed box.

The pre unit Triumph gearbox shell is not massively strong however, this is why Dave Nourish made a stronger one. If your motor is very hot, and especially if you're going to race it, you might want to consider this.

If you don't have the parts and are going to have to buy them, then I wouldn't even consider it, better to put the money towards a 5 speed box designed for the purpose (Hemmings or TTI).
 
Well the bike is not going to be raced, will be a fast street and for some track days bike. I believe also that even if you buy the parts the difference in cost between this and the ones you mention is substantial.
 
Well, yes there is a cost difference, but my point was that a blown up gearbox is a waste of money, no matter how cheap!

But... if it’s for street use, and it’s a 750, I think the Triumph box will be fine.

You’ll have to decide which clutch and gearbox mainshaft to use though.

Tony Hayward (uk parts supplier) sells a 5 speed Triumph gearbox mainshaft that has Norton splines instead of the Triumph taper. Might be worth calling him (but beware, all calls to Tony are long ones).
 
I have a reinforced pre-unit gearbox, but not sure if it's the model you want (there are several varieties)

Of the ones that I have, two have the clutch lever that pivots between the filler/inspection cap and the kicker shaft (cable abutment on the inner cover), the other one has the lever that pivots above the inspection "window" (no cable abutment, also accommodates the SlickShift lever)

The one in the middle is the one that is reinforced (welded plates above and below to the mounting tunnels)-

seeley Norton with Triumph Gearbox


$300 (take your pick), or all three for $750
 
I don't believe a Triumph box will cop what the standard Norton box will cop. Triumphs don't usually have such massive torque. However the ratios in the 5 speed Triumph box are pretty good. The mainshaft in the standard Norton box gets bent and becomes destructive, the Triumph one would probably be worse. The mainshaft in the TTI box is about 6mm thicker. There are lot's of Triumph 5 speeders being used in Australian historic racing, but virtually none of them are exposed to the level of torque a Commando engine delivers. Personally I would not do it, even on a road bike. The TTI box costs $5000, but a blown-up 5-speed Triumph box would probably lose $3000 for it's owner. The gearbox is more important than any other performance modification. 5 speed close ratio gives a lot more acceleration if you race-change up through the gears. Even if you use a totally unmodified motor, a good gear-box can make your bike competitive in many road races.
 
With the 5-speed Triumph box, Phil Pick made two pairs of gears which close-up 2nd and 3rd towards 4th gear. And Eddie has told me that Tony Hayward probably has them these days. But going down that path is probably false economy.
 
I have a reinforced pre-unit gearbox, but not sure if it's the model you want (there are several varieties)

Of the ones that I have, two have the clutch lever that pivots between the filler/inspection cap and the kicker shaft (cable abutment on the inner cover), the other one has the lever that pivots above the inspection "window" (no cable abutment, also accommodates the SlickShift lever)

The one in the middle is the one that is reinforced (welded plates above and below to the mounting tunnels)-

seeley Norton with Triumph Gearbox


$300 (take your pick), or all three for $750
Thank you for the great info and offer, i ll think about it and let you know, i am not ready for that yet.
 
Well, yes there is a cost difference, but my point was that a blown up gearbox is a waste of money, no matter how cheap!

But... if it’s for street use, and it’s a 750, I think the Triumph box will be fine.

You’ll have to decide which clutch and gearbox mainshaft to use though.

Tony Hayward (uk parts supplier) sells a 5 speed Triumph gearbox mainshaft that has Norton splines instead of the Triumph taper. Might be worth calling him (but beware, all calls to Tony are long ones).

Thank you for the info, i ll take it into consideration. The plan is to use a dry clutch belt primary drive , i don t have the specifics yet.
 
I don't believe a Triumph box will cop what the standard Norton box will cop. Triumphs don't usually have such massive torque. However the ratios in the 5 speed Triumph box are pretty good. The mainshaft in the standard Norton box gets bent and becomes destructive, the Triumph one would probably be worse. The mainshaft in the TTI box is about 6mm thicker. There are lot's of Triumph 5 speeders being used in Australian historic racing, but virtually none of them are exposed to the level of torque a Commando engine delivers. Personally I would not do it, even on a road bike. The TTI box costs $5000, but a bloconsidering wn-up 5-speed Triumph box would probably lose $3000 for it's owner. The gearbox is more important than any other performance modification. 5 speed close ratio gives a lot more acceleration if you race-change up through the gears. Even if you use a totally unmodified motor, a good gear-box can make your bike competitive in many road races.
Thanks, I really don t think similar cc Triumphs and Commandos are sooo much different in torque although a mainshaft destruction is an issue... with the commandos.Anyway i am also considering as an option the quaife gearset in a commando or other reinforced box, i ll see what i ll do.
 
Buying the expensive gearbox is something I held off from doing when I was racing regularly. I regret that. Once you own it, you don't have to sell it with the bike, if you have still got the gearbox it replaced. I have a 6 speed TTI box in my Seeley, as well as a 4 speed close ratio box under my bench. If I ever sold the Seeley, the 6 speed TTI box would not go with it. That box has a multitude of uses. If you race old bikes, you need two things - the good front brake and the good gearbox. Personally, I hate drum brakes because I was always too miserable to buy a Fontana or an Oldani. There are some things you just cannot afford to cheap-skate on. The gearbox is another - if it destroys itself, it can create the biggest nastiest crash of all time.
 
Thanks, I really don t think similar cc Triumphs and Commandos are sooo much different in torque although a mainshaft destruction is an issue... with the commandos.Anyway i am also considering as an option the quaife gearset in a commando or other reinforced box, i ll see what i ll do.

I used to race a short stroke Triton and I have ridden others with normal 650cc motors - all methanol fuelled. The difference in torque of a 650 Triumph compared with an 850 Commando is stupendous. The overall gearing I use with my 850, is much higher on the same circuits. What surprised me was the 4 speed close ratio Norton box did not give up when during a clutch start, I revved the tits off the motor to about 7000 RPM and dropped the clutch.. In most races I used to be up with the lead bunch because I was too chicken to do that. In that race I was right up beside the leader when the fuel line popped off. With our local race circuit, I know how fast a bike has got to be. My Seeley 850 is on methanol and does not hang about.
 
Ok considering all these, still considering the Quaife gearset as a good and cost effective solution vs the TTI and i ve beed told is comparable if not better.
 
Bruce Verdon ( TTI ) provides an excellent service. If you live in New Zealand, whatever you do must be excellent or you do not survive. If you consider people such as Hugh Anderson, Rod Coleman and John Britten - they are or were, total fanatics - worse than Pommies in their level of commitment.
 
Concerning the worries about the Triumph 5-speed being strong enough, I think you are probably safe with a healthy street 750 Commando. A friend of mine (Rob Tuluie) raced a Commando in the '80s with a Triumph 5-speed with a mainshaft to take a Commando clutch, and never had a problem with it. I don't recall if he used the stock case, or modified it, or made his own. He was using a belt drive with higher primary ratio, which reduces the load on the transmission. He ran it mostly with a short stroke 750 engine, but also at least once with a 920 engine at Daytona. That seems like a pretty good reliability test to me.

This is a picture of the bike when he rode it to a local meet in Texas, still a race bike, but without the numbers, etc. No lights, no kick starter, totally illegal, but he managed it anyhow. It shows the right side of the transmission reasonably well, so someone might recognize what it is, or what it started out as.

seeley Norton with Triumph Gearbox


This is a picture of it in race trim at Daytona in 1990.

seeley Norton with Triumph Gearbox


The good old days, right?

Ken
 
Ken, that bike has modified unit construction outer gearbox covers (a good and common mod) but it’s not possible to tell what shell he’s using.

The Triumph cluster is plenty strong enough. Only lead booted riders seemed to struggle in my opinion.

It’s the case that can’t handle too much power and can split. In Triumphs defence, they were never designed to handle anything like the power and torque some folk expect them to handle though! As it was not deemed a super stressed component by Triumph, I would imagine there to be huge variation in thickness of castings and thus strength. 60+ years after being made, there’ll also be huge variation in fatigue and stress that’s built up.

Personally, I only ever saw Triumph cases split on big engines, Nourish and Puma etc. So I think it’s big torque that does it. And I doubt this would be a risk on a street 750.

Either way, as you say, that’s a good enough reliability test for someone building a street bike I’d say!

Interesting looking swinging arm on that bike BTW...
 
If I had a street Commando and a pre-unit 5 speed Triumph box, I would use the Triumph box. However I would not buy one for that purpose, it might be false economy. If you are going to ride the bike sensibly on public roads, you should not have a problem. If you start fanging the bike, a gearbox failure is usually a certain big crash, when everything locks-up..
 
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