Fitting a Bob Newby belt drive

This looks like a good piece. I like the seal bearing and I like the cush. If the slots and ears don't wear as most do then you have a winner.
 
Question: received the belt kit, but I'm wondering if I keep the 7 plate conversion I am currently running (all the plates are in fine shape), or stick with the standard plate set up that was delivered with the kit? The surface area of the friction plates in the conversion kit is, obviously, much less per plate than the standard set up, and slightly heavier than the standard set up in total. As I am going to run the primary dry, I'm wondering if the standard set up will be a better choice.
 
With more plates and those modern narrower friction areas out near the circumference, you will need less spring pressure to make it grip.
 
Triton Thrasher said:
With more plates and those modern narrower friction areas out near the circumference, you will need less spring pressure to make it grip.
Click to expand...

Thanks, already running T120 springs, just wondering if similar grip can be expected running dry with lighter springs and standard plate set up.

One last question, the parts manual shows the primary crank seal with spring side towards primary (which is counter to what I would expect), I assume this has to do with the seal surface running up against the shoulder of the sprocket, does this suitably resist the crank pressure blowing out the seal?

Thanks for the tips!
 
The thinner plates work by increasing the mean effective diameter of the friction area. They also seem to be sourced from reputable manufacturers. I would use the 7 plate kit if I were you. As already mentioned, it should allow lower spring pressures.
BUT, whichever you use, check the plain plates carefully for flatness. I am now fairly certain that this was the root cause of my clutch issues.
The seal goes with spring to the crank side if running dry. LAB explained once why BSA and Triumph fitted them ‘backwards’ and I forget the ‘logic’. But you should fit it with the spring to the crankcase.
 
Last edited:
Did you remove the chain tensioner abutment? The one pressed into the timing chest that the slipper slides onto?

I'm thinking it may not be necessary as the belt will be tensioned on the underside when running, and it looks like I've got about .125 clearance
 
I did not remove it for the Newby fitment on the T140. But I did remove it on my T120 (as the T120 chaincase is not sealed from the crank case, and has an oil suitable belt, I removed this thinking it would allow oil to always drain into the crankcase rather than ‘well’ in the chaincase).
 
thanks, answers my other questions as to whether it's a through hole
 
Anyone have any tips on keeping the pulley/rotor nut tight on a Newby (or other belt w/ alternator) system?

It's come loose on me twice, the first time wrecking the spline on the pulley. I've tried the Norton serrated washer, the Triumph tab washer. Both with blue Locktite, both came loose. The stud is red Locktited into the crank, and it's the nut that comes loose. There's about 1/2" thread engagement on the nut. Always clean and dry threads (other than the remains of the Locktite) when it comes loose.

Oh yea, forgot to mention: torqued as tight as I can with an impact driver, with the wheel locked. I know not perfect, but I'm not taking the engine apart to lock the crank.
 
Last edited:
I think the Norton serrated washer is too big? Triumph ditched the tab washer for their own serrated washer later on, maybe try one of these?

It does need to be pretty tight. Have you got any idea how tight your impact wrench is tightening it?

The workshop manual says 50ft/lbs for this nut. Personally I think that feels way too low. I go for 75-80ft/lbs. With that and the proper serrated washer I don’t have them come loose.

I knew a very good Triumph mechanic who used to put a very small (and therefore breakable) spot of tig weld on them. That worked too!

Perhaps the nut is tightening against the shoulder rather than the rotor? Clutching a straws here!

If the treads are good, the washer is correct and the torque is correct, it shouldn’t be an issue. Unless something is out of true and shaking it apart?
 
Ive got a belleville washer under there, as well as under the clutch but, blue tread locker, 50 ft/lbs.

Eddie may be on to something as far as something not being snug, are you sure the rotor doesn't have any slop on the shaft?
 
Fast Eddie said:
I think the Norton serrated washer is too big? Triumph ditched the tab washer for their own serrated washer later on, maybe try one of these?

It does need to be pretty tight. Have you got any idea how tight your impact wrench is tightening it?

The workshop manual says 50ft/lbs for this nut. Personally I think that feels way too low. I go for 75-80ft/lbs. With that and the proper serrated washer I don’t have them come loose.

I knew a very good Triumph mechanic who used to put a very small (and therefore breakable) spot of tig weld on them. That worked too!

Perhaps the nut is tightening against the shoulder rather than the rotor? Clutching a straws here!

If the treads are good, the washer is correct and the torque is correct, it shouldn’t be an issue. Unless something is out of true and shaking it apart?
Click to expand...

The Norton washer is the right size. It's the same Lucas rotor for Triumph and Norton, no? I'll check into the later Triumph one nonetheless. The nut is one I machined after being underwhelmed by the lack of insertion into the rotor. It's not too long. I checked that too.

I was concerned that the rotor was bottoming out on the inside radius on the pulley, but the supplied spacer is keeping it off the pulley. Double checked.

Not sure how tight the driver is going, but I think I'll try the old rope-down-the-spark-plug-hole trick to lock things up a bit better than I can with the rear brake. I'll be able to use the torque wrench then.

Maybe I ended up with a gearbox your buddy worked on. Welded shut at the sprocket nut and the kickstart shaft. That's a level of confidence I just don't have!

acadian said:
Ive got a belleville washer under there, as well as under the clutch but, blue tread locker, 50 ft/lbs.

Eddie may be on to something as far as something not being snug, are you sure the rotor doesn't have any slop on the shaft?
Click to expand...

No slop on the crank and the rotor fits really tight. Maybe even a bit tighter than I'd like after having to take it all apart a couple times. A Belleville washer is a good idea!

 
You’re quite right there, the Norton and Triumph washers do have the same nominal internal diameter. But...

The Norton nut is of a bigger hexagon. If you look at the pic below you can see that the Norton washer just doesn’t have much material inside of the outer diameter, the tangs are quite feeble, this is not a problem with the Norton nut, but if memory serves me correctly, the Triumph nut isn’t big enough to sit securely on the outer diameter of the washer. IMHO this leave the nut potentially inadequately supported, especially given the high torque and high stress that nut is subjected to, well that was my conclusion when I was going to use one, and decided not to.

The Triumph washer is thicker material, the tangs basically fill the available space, it fully supports the Triumph nut. With the tangs being thick and sharp, they bite very securely. Bevel washers are good, but in this particular application I can’t see them being any better than the Triumph washer IMHO.

Rope down the plug hole is a good idea and will allow you to really confirm the torque. I find that disc brake bikes work well re the brake brake / in gear method but not drum brakes.

If you’ve got the timing cover off, a soft (brass, copper, alloy) bar can be inserted through the breathing hole to lock against the crank cheek.

Pic: Norton washer on the left, Triumph washer on the right:
851FE5A5-2A53-46B3-82FE-83D1A348CA57.jpeg
 
Last edited:
Buy yourself a Bellville washer & use a torque wrench. If it still comes undone there is a problem you haven't spotted.
 
t ingermanson said:
The Norton washer is the right size. It's the same Lucas rotor for Triumph and Norton, no? I'll check into the later Triumph one nonetheless. The nut is one I machined after being underwhelmed by the lack of insertion into the rotor. It's not too long. I checked that too.

I was concerned that the rotor was bottoming out on the inside radius on the pulley, but the supplied spacer is keeping it off the pulley. Double checked.

Not sure how tight the driver is going, but I think I'll try the old rope-down-the-spark-plug-hole trick to lock things up a bit better than I can with the rear brake. I'll be able to use the torque wrench then.

Maybe I ended up with a gearbox your buddy worked on. Welded shut at the sprocket nut and the kickstart shaft. That's a level of confidence I just don't have!



No slop on the crank and the rotor fits really tight. Maybe even a bit tighter than I'd like after having to take it all apart a couple times. A Belleville washer is a good idea!
Click to expand...


With the rope in there, I got another quarter turn and another 25 ft/lbs on there. up to 75 ft/lbs now.

Fingers crossed. Thanks.
Fast Eddie said:
You’re quite right there, the Norton and Triumph washers do have the same nominal internal diameter. But...

The Norton nut is of a bigger hexagon. If you look at the pic below you can see that the Norton washer just doesn’t have much material inside of the outer diameter, the tangs are quite feeble, this is not a problem with the Norton nut, but if memory serves me correctly, the Triumph nut isn’t big enough to sit securely on the outer diameter of the washer. IMHO this leave the nut potentially inadequately supported, especially given the high torque and high stress that nut is subjected to, well that was my conclusion when I was going to use one, and decided not to.

The Triumph washer is thicker material, the tangs basically fill the available space, it fully supports the Triumph nut. With the tangs being thick and sharp, they bite very securely. Bevel washers are good, but in this particular application I can’t see them being any better than the Triumph washer IMHO.

Rope down the plug hole is a good idea and will allow you to really confirm the torque. I find that disc brake bikes work well re the brake brake / in gear method but not drum brakes.

If you’ve got the timing cover off, a soft (brass, copper, alloy) bar can be inserted through the breathing hole to lock against the crank cheek.

Pic: Norton washer on the left, Triumph washer on the right:
View attachment 20481
Click to expand...
Well, looks like I bought a "Norton" washer, but received a Triumph one. The one I've got is the one on the right. Perhaps someone at my supplier agrees with you.


The nut I made started as 1" hex bar stock and there's good coverage of the tangs under the head.

Is there a longer CEI 7/16" stud out there I should consider replacing my crank's stud with?

The torque wrench indicated 75 ft/lbs (the highest torque value for my wrench) with the rope-in-the-chamber trick, 25 ft/lbs more than I could get with the wheel locked, with no cush getting in the way.

I'll ride it around without the primary cover off (damn sweptback pipes!!) and check occasionally before I button the primary back up.

Thanks again.
 
Well, with 75ft/lbs, as Matchless says above, if you get trouble now there’s sumthin else wrong somewhere.

If you’re running a Newby clutch I’d be interested to know how far you have the screws wound in and how it holds up to slip.

Ref longer studs being available, I’ve no idea on that one.
 
Fast Eddie said:
Well, with 75ft/lbs, as Matchless says above, if you get trouble now there’s sumthin else wrong somewhere.

If you’re running a Newby clutch I’d be interested to know how far you have the screws wound in and how it holds up to slip.

Ref longer studs being available, I’ve no idea on that one.
Click to expand...
I'm running a T120 pre unit, not a T140. It's hopped up a bit with hotter cams and bigger carbs and pipes, but it's still a 650.

I adjusted the pressure plate with a dial gauge, but the nuts are averaged just to the point where the studs are protruding into the flat. They may be able to be loosened up a turn or so, but I once had to take my bike apart (damn sweptback pipes!!) at a gas station once, after I couldn't kick it due to slip. Not sure why it changed so much once hot, but taking my pipes off and dismantling my primary case in a parking lot was not awesome, and I could do without that again. Trying to stave off the reputation of unreliable brit bikes, even if we all know it's true.
 
You must log in or register to reply here.
Back
Top