Fitting a Bob Newby belt drive

Fast Eddie

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Sounds like yours are a bit slacker than mine, but not by much. But mines hardly a 100bhp hot rod either!

It definitely hurts when these posh uprades let you down like that !
 

t ingermanson

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Sounds like yours are a bit slacker than mine, but not by much. But mines hardly a 100bhp hot rod either!

It definitely hurts when these posh uprades let you down like that !
They are a lot of money, but not much more than a stock new clutch, if you're starting with nothing as I was. Once I got the gearbox to stop spewing its contents onto the back of the clutch through the high gear bush, it's really been fine, short of that one wrecked pulley.

I had started with a Conical hub, but traded it out for a modified GS550 hub for the cush, hoping that the lack of cush was causing the pulley to wallow on the spline, and perhaps a loose nut being a symptom not a cause. Apparently, no such luck.

I'm about to purchase another BNR belt for a Dominator project. Some people never learn...
 
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The Suzuki hub was a good move. I fitted one to my 920 a few years ago, & apart from being a little on the heavy side it's far better than the comedy cush drive that Norton fitted.
 
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I ran a T140 Hayward belt drive wet for over a decade (albeit not many miles, a few thousand) with no problem. When I rebuilt the bottom end I converted to a dry setup with breather from front engine mount and primary 3 holes sealed with patent plate rivets etc. The expensive "krankvent" Reed would clog with oil so I removed it (since found out that repositioning further away is probably the answer). Tony Hayward reckoned no primary ventilation necessary after a looong discussion (as per every TH discussion!).

The old belt was showing some tooth wear but no misalignment issues.
The new "improved" red belt lasted a few hundred miles and shredded badly. An almost exact same outcome was/is visible on Sump publishing Web site and their T140 TH belt experience.
I went back to a primary chain and can't tell the difference tbh.
My take is the new belt tension was too tight, though don't recall any difference with the old one?
Other root causes are plausible including overheating but can't imagine significant cooling from previous wet setup?
Not anti belt, next project on the commando is a RGM set up, but that has a leaky primary, weighs 40 lb more (so I'd like to lose some of it) and critically for me, adjustable belt tension.
Just my 2p worth?
 

acadian

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Got my belt drive installed, will have to wait until the new season to test it, but the tension does seem a bit on the tight side. Slotted a spare stator cover plate for ventilation.

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I thought I would drop just a couple of comments here. I used a Newby primary and clutch in my 750 AHRMA race bike (mid 60s hp, above 50 ft/lbs from 5000-7000) for many seasons with almost no problems.

I had several differences from a street bike— I used a Nourish crank, I welded up the vent holes and put the vent on the timing cover over the end of the exhaust cam— I always considered the breather In the timing hole a bad idea and when I went to the pork chop Nourish crank it pumped oil out of it quite efficiently. I solved both transmission and clutch key and taper problems by getting a splined high spec steel mainshaft from Nourish (splined like a Norton, not tapered and keyed), and a matching Norton splined hub for the Triumph clutch from Newby. I used an ARD ignition timed off the intake cam, later used dead loss Boyer ditto, and then switched to a PVL based crank triggered ignition so I never had a standard Lucas alternator fitted. To make that far outboard PVL rotor fit I machined a close fitting spacer exactly the same diameter as the end of the crank and a close fit on the I.d. of the grade 8 bolt I mounted it with to give it something precise and steady to bear on.

I was always cautioned that cooling air venting was important to belt life so I spaced the primary cover out 1/4 inch on spacer washers I cut out a quarter inch sheet and lengthened the case screws. I also left off the timing adjustment cover and the window behind the clutch. That helped the air circulation significantly but probably not the best for the street.

I cut off flush the abutment for the primary adjuster.

I originally used 40 mm belts but changed to 30 mm when I installed a PVL based ignition, Bob warning me the narrower belt might be a problem for racing but it worked acceptably. I always carried spares to the races but only changed a few. I think in 15 seasons I changed belts maybe 4 times at the track, and maybe a couple other times, and the clutch plates and springs once. Very reliable. I like a LOT of spring tension so I had the studs sticking out 2 turns. I consider this essential to avoiding clutch slipping, heat, and failing belts and clutch plates, but it could be very uncomfortable for the street.

I always tried to set up the pressure plate to less than .003 or closer runout using a dial gauge. That allowed it to engage without resistance and go from the one board to green flag with no creeping.


I went from endless problems and parts changes every race, with stock design parts, to zero problems with the Newby stuff.

Just be aware, the loose unsealed clutch bearing will run itself dry and bears some attention/greasing every once in a great while.
 

acadian

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The timing plug breather does throw oil, yes, but I've run this set up before. I've got some stainless mesh wadding stuffed into the vent tube just above the threaded plug. This prevents some of the oil from getting pushed up the tube, and the breather itself (XS reed valve) is vented to an outlet tapped into the oil tank rather than atmosphere to catch and recycle the remainder
 

Fast Eddie

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I use the timing plug hole as a breather on my ‘68 T120, it feeds into a reed valve and then ‘up n over‘ the rear mudguard. I get a couple of drips out of the vent pipe after a good run, but other than that it seems to work very well.

Conversely, I fitted a breather to the timing cover on my T140, a very common place, and that pumped a lot of oil out. Taking the hose up high, reducing the diameter and putting some mesh inside the hose seems to have got it working fine now.
 
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The timing plug is lined up with the flywheel. Subjected to street type use and rpm, and with a stock crank with full circle flywheel, the timing plug will work ok, because the full circle flywheel doesn't throw a lot of oil at reasonable rpm. On the other hand, as I said, I used this in a race bike, and I had the pork chop Nourish crank, which acted like an efficient paddle wheel to pump oil out the timing plug vent. Not only that, the bike was shifted, every shift, every few seconds, above 7000 rpm, and that timing plug vent setup simply won't work for that kind of use. Mine always filled a one quart catch bottle in 5 minutes so I had to move the vent elsewhere.

As to the breather on the timing cover, I used the 90 degree breather fitting from the primary side, welded onto the timing cover and pointed up, with the vent hole at the very end of the exhaust cam. There is a picture up above of a breather welded on directly in line with the outer circumference of the cam gear. There is a fair amount of oil following the gear set around in the timing cover. At high rpm and high temps, the cam gear will sling oil directly off it, and that may be why it would not work for you. I put mine directly over the end of the exhaust cam pointed up, with the vent at the center of the cam gear, where it would not sling oil, not at the circumference, and it worked fine, with a 3/4 inch vent line routed like yours, up and over to a catch bottle behind the left shock. I ran mine open, because several racers I knew who put reed valves in said they constricted the flow too much and led to problems. But again, race use is quite different than street use, and for instance I now use a one way valve on my Norton street bike and it works just fine. I also tried putting a long spring up the vent line to discourage oil flow, but it didn't seem to make much difference. It did seem to like about 8 inches of vertical in the line, before the line angled over to the left side of the bike, to discourage oil in the catch bottle.
 

Fast Eddie

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Thanks, that all makes sense. I like to think I ride my bikes ‘spiritedly’ but 7,000 is the exception rather than the norm!

I’m a fan of using the triangle shaped forward engine mounting on unit Triumph as a breather chamber and outlet. But that requires a stripped engine, so will have to wait until I have a good enough excuse to do that!
 

acadian

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Question, did you encounter spacing issues with the primary cover fitment?

Reason I ask, my stock front sprocket was shimmed out from the TS bearing. When I measure up the belt pulley alignment with the clutch, If I omit the shims the belt runs precariously close to the inner edge of the clutch and subsequently the inside of the chain case.

Keeping the shims resolves that issue, but now the whole assembly (rotor, stator etc.) must also be shimmed out, which is preventing the cover from seating properly. I fabbed up some alloy spacers to sit between the cover and the case, this creates a 1/8" gap which I thought would work for ventilation.

There's also a concern with proper contact between the pulley and oil seal lip with everything shimmed out as is, reading up on some posts by Healey suggests this is one of the reasons for the oil seal being installed spring towards the primary.
 

Fast Eddie

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How close is close?

To reduce stress on the mainshaft and exaggerated tilting of the basket with the clutch operated, you actually want the belt to run as close to that inner edge of the pulley as possible.

So when you say it’s close to the crank case, how close? Can you use a smaller shim stack / spacer to get ‘just enough’ clearance?

It was indeed a bit of a juggling act to check everything on mine, I ended up using the front pulley with zero shims. This gave a perfect belt position. The pulley is wider though, and spacing the rotor and stator out accordingly did cause a slight fouling of the outer cover. Two thick gaskets cured that. Doing more would cause yet more work with the left hand gearchange !
 

acadian

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How close is close?

To reduce stress on the mainshaft and exaggerated tilting of the basket with the clutch operated, you actually want the belt to run as close to that inner edge of the pulley as possible.

So when you say it’s close to the crank case, how close? Can you use a smaller shim stack / spacer to get ‘just enough’ clearance?

It was indeed a bit of a juggling act to check everything on mine, I ended up using the front pulley with zero shims. This gave a perfect belt position. The pulley is wider though, and spacing the rotor and stator out accordingly did cause a slight fouling of the outer cover. Two thick gaskets cured that. Doing more would cause yet more work with the left hand gearchange !

Without the shims the belt rides right on the inner edge of the clutch basket, with the shims it sits in by about .120, which pretty much accounts for the cover fouling. I'll stick with the .125 spacers I machined to sit the cover off the case, more worried about the oil seal engaging enough with the front pulley, as the chamfer on the end is more pronounced than on a stock chain pulley
 
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