Fitting a Bob Newby belt drive

I‘ve got a Bob Newby belt and clutch kit I’ll be fitting to the T140.

Whilst it’s not rocket science, the ’instructions’ are frankly a bit of a joke. Has anyone who’s done this got any hints and tips to share please ?

Fast Eddie said:

I‘ve got a Bob Newby belt and clutch kit I’ll be fitting to the T140.

Whilst it’s not rocket science, the ’instructions’ are frankly a bit of a joke. Has anyone who’s done this got any hints and tips to share please ?

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Ring Bob, which I have done about another aspect. Very helpful.

Instructions? I got no instructions! But if you ping him he does respond and you can get spares from him as well.
Have two of his belt clutches and I found it impossible to adjust the belt free play to what most say is correct. In other words
the belt will rub on the alternator tower castings. Yes, I "relieved" them but until I took a lot of the free play out it would eat the belt. Having a TTI box there is likely less worry about too much load on the shaft and bearings or that is what I tell myself.
As for the belt mine is low miles yet, 8K, but I think Kenny at NYC NW uses a stronger one and I think he posted this on this list
some time back. If not at some point Ill see if I can dig out my extra belt and get the numbers off it.
One other thing: the back of the basket tends to get eaten by the gearbox shaft and Kenny made me a hardened washer to
fit in between. This was for the Norton and the TTI.

Nigel,

I have a couple of Newby belt drives & a friend has another on his Norstar which I maintain. What are you having problems with?

No problems yet, I’m just getting into it now. The questions have are (remembering it’s for a T140):

Clutch ‘space’: The ‘instructions’ say to leave off the gearbox sprocket Access plate behind the clutch for ventilation purposes and to allow space for the clutch. I don’t want to do this, it’s a road bike and doing this would allow all sorts of grime and shite in there. I’ve mocked up the pulley and there seems to be ample space behind it so am thinking to leave it in place. Am I missing something?

Ventilation: what are your thoughts on the need for this on a road bike? I can punch some holes in the cover, but kinda prefer the stock look if possible.

Alternator mounting: I read on t’internet (I know, stupid mistake) and some folk are reporting all manner of problems with alternator stud length, crank nut too short, rotor out so far there’s hardly any crank register for it to mount on, etc, etc. I’d like to hear from some sensible folk if I’m likely to end up pulling my hair out here?

I will talk to Bob, but I value real world experience from sensible people highly...

My Newby drives are on a Matchless twin & a Royal Enfield single so no help there. On the other hand I did a long time ago fit a Hemings Commando type belt set up to my 750 Tiger. It took a lot of re machining & farting about to make it fit in the space. The biggest problem & the reason I sent it back for a refund was enging breathing. Micks solution was a union screwed into the timing plug hole at the back of the crankcase which was shit. Since then I have found out about reed valves so may have another go at it in the future.
One problem you might encounter is the belt being a little to tight or a little to slack as there is no adjustment as on a pre unit set up. Another thing I had to do was grind the inside of the primary cover to clear the alternator which had to be spaced out further. I think Tricor make spacers to help with this problem. Might be worth checking their website.

Thanks Martin.

I use the timing hole for a breather on my T120 and it works fine, but I do use a reed valve, I’d have happily done the same on the T140, But it doesn’t have the timing hole! I have to block off the 3 small holes in the primary and fit an oil seal, and I’m planning to weld a breather pipe to the timing cover and route the hose to the reed valve then airbox, as I have it currently.

I know it’s a faff, but keeping the oil out is my primary objective. I ran Hayward belts with modified versions of Triumph clutches and all sorts, right up to a 900cc 8 valve and they worked perfectly... but they were all dry.

Hi Eddie
As you know I ran Bob's belt drive on my first race bike 8 valve T120. Bob changed the belt it whistled to a different one. He explained how much difference there was between centre's on Triumphs & tension. I also ran a breather from the tdc it pumped oil. Big breather of the timing cover inner chaincase sealed. I have run one on a Triton, pre unit alternator. Twenty years.
Bob is a great person to ask advice from. Probably seem it all.

Ok, progress has been made on the Newby fitment...

After a lot of checking and looking, I left out the 0.040” crank to sprocket spacer and 0.010” shim that was in there. I kept the sprocket access plate in place but removed the gasket to save a knats cock of thickness. I painted the inside of the clutch area mat black so I’ll easily be able to see if there’s any rubbing in future.

Some might find it useful to know that Triumph timing cover badge knock in rivets are perfect for blocking the 3 oil return / breather holes.

I struggled with stator clearance to the outer cover. Until I realised the pattern stator (unknown make) was somewhat thicker than the new pattern ‘Lucas‘ I’d got in stock.

I did the same with the rotor / stator gap as I did on the Commando last time, I took 0.040” off of the diameter of the rotor, opened out the stator mounting holes a tad, ensured the 3 mounting studs were straight, wrapped a cut out piece of milk carton around the rotor and tightened the stator up. So I have a generous .020” air gap all around.

But the new stator had really stiff wires poking out, and fouled the cover, so that required some removal of potting material and re routing.

I wound the clutch springs in a bit further than the ‘starting point’ suggested by Bob (clutch slip is what started this whole exercise after all) and it feels really nice with the hydraulic clutch.

I gotta sort the breather outlet on the timing cover next though before I can test it out (previous engine breathing was through the primary case).

Can you ventilate it by having gaps in the gasket between outer and inner covers?

Triton Thrasher said:

Can you ventilate it by having gaps in the gasket between outer and inner covers?

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Yes that’s an option. Although, with it being left hand gear-change, the cover holds the crossover shaft in place, so I gotta check that doesn‘t cause any issues.

Bob told me he didnt vent his road bike. I haven't vented either of mine.

Onder said:

Bob told me he didnt vent his road bike. I haven't vented either of mine.

Click to expand...

That’s good info thanks. I was kinda leaning that way, you‘ve just helped me over the edge !

I think clean is more important than cool. After having years of oil escaping from the crank side into the primary, I used a speedi sleeve and now a thousand miles later it is bone dry. Huzzah. However, Id keep a regular eye on the interior as the clutch does
exhale material and dust will collect inside.

Fast Eddie said:

Ok, progress has been made on the Newby fitment...

After a lot of checking and looking, I left out the 0.040” crank to sprocket spacer and 0.010” shim that was in there. I kept the sprocket access plate in place but removed the gasket to save a knats cock of thickness. I painted the inside of the clutch area mat black so I’ll easily be able to see if there’s any rubbing in future.

Some might find it useful to know that Triumph timing cover badge knock in rivets are perfect for blocking the 3 oil return / breather holes.

I struggled with stator clearance to the outer cover. Until I realised the pattern stator (unknown make) was somewhat thicker than the new pattern ‘Lucas‘ I’d got in stock.

I did the same with the rotor / stator gap as I did on the Commando last time, I took 0.040” off of the diameter of the rotor, opened out the stator mounting holes a tad, ensured the 3 mounting studs were straight, wrapped a cut out piece of milk carton around the rotor and tightened the stator up. So I have a generous .020” air gap all around.

But the new stator had really stiff wires poking out, and fouled the cover, so that required some removal of potting material and re routing.

I wound the clutch springs in a bit further than the ‘starting point’ suggested by Bob (clutch slip is what started this whole exercise after all) and it feels really nice with the hydraulic clutch.

I gotta sort the breather outlet on the timing cover next though before I can test it out (previous engine breathing was through the primary case).

View attachment 19277

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This setup looks really great ,I can remember long battles with my t140 clutch
Either slipping or dragging or both
I can remember going into my local triumph dealer (excel motors in Enfield) buying new plates, clutch baskets and clutch hubs
When the t140 was still being made at meriden and every time they used to say "we are sorry about this son, one day triumph will adapt the commando clutch to fit"
Happy memories of Joe excel and his son running that shop

FE: what is your final clutch nuts adjustment? . I found when running them at about that
amount of preload (per your photo) I could get clutch slip when pushed. But higher nut pressure gives higher lever pressure and after two hours last ride my wrist was not happy. Lots of shifting up on the moor.

I can stick the vernier down the nut to the stud, they are all at 1.8mm.

The lever is stiffer than I was hoping for at this, even with the hydraulic clutch actuator, I’ll be rather miffed it it slips to be frank !

Credit to Bobs machining, measuring the nuts as described to ensure they’re all equal gives perfect pressure plate run out.

What's your rationale for goin to the belt? I've considered, but already have an alloy 7 pate drum kit in there, and she doesn't leak. I can send you some machined primary plugs for venting, I have a set I made on my shelf that have never been used

Very kind sir, thank you, I’ll PM you.

Rational? I like belts, they’re lighter, cleaner, have less power loss and smoother running etc. No single reason is big enough really, but I just prefer them. I’d had this kit on the shelf for some time too so the cost of purchase wasn’t part of the decision.

But the primary motivation this time was the slipping clutch. I had a new 7 plate conversion in there, and the springs wound in to the point it would be almost unrideable as standard, but I could do so because I’ve got a hydraulic clutch actuator fitted. Pressure plate was set up cock on.

So when it started slipping (which it only did after I did the top end and tightened up the squish) I was really pissed off and just thought “f*** it” !!

Truth is, I’m now pretty sure it was slipping due to poor quality and not flat pattern plain plates, almost certainly Wassell items.

All kinda ironic in a way cos whilst I know folk complain about Triumph clutches, I always found them to be OK provided genuine parts were used. Even in my 8 valve TSS which got thrashed mercilessly, the clutch was never an issue.

Ok, I got my timing cover sorted, despite a brief consideration of breathing from the rocker boxes, I decided it seems best to breath closer to the source of pressure, so went with the old favourite big pipe on the timing cover method !

Cos Ive now got a dry clutch I took great delight in treating the old girl to a new paper frame filter and a fill up of Royal Purple HPS 20W50 (not suitable for wet clutches).

The reed valve breather farts like a builder when kicking it over. Hopefully it’ll quieten down when it’s got some oil in it. It better do otherwise my two daughters will wet themselves laughing every time they hear it