Cush Drive Crankshaft Pulley

Tintin said:

SteveA said:

Does anyone use a Cush Drive in their engine pulley with a belt drive.

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The closest think I'm aware of to a cush drive together with a primary belt drive is the engine sprocket of a 1981(?) HD Sturgis. I think it retained the compensation mechanism of the original primary chain setup.


Tim

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80 - 82.
There is no "compensator" on front belt drive models.
However, the factory primary belt drives did utilise "rubber dampers".
However again.......... adjustment was by moving the trans, and not an easy task, nor a particularly accurate one, as far as tension settings go.
So......... well know is that loose belts break;they need to be under constant tension to avoid "snatch".
So the damping rubbers may likely be seen more as a shock absorber for belt protection, as opposed to a system primarily concerned with "pulse" control.
Back to Norton.....
Does looking at the HD belt tell us that Norton belts need a "cush" drive with a primary belt?
Not necessarily, and certainly not definitively.

Hi

Steves cush drive is based on a Triumph disc rear wheel. Nice system just like the P&M Rob North triple. Its a tight fit.
I copped out when my 750 did in the Dick Hunt Seeley disc rear wheel. I used stainless allen heads & they fractured. (thanks for your advice back then) They were replaced with good spec standard 'black' allen keys. Two meetings & again the sprocket was loose. All the heads were still lock wired together but the sprocket holes had ovalled & the threads in the hub are 'loose/sloppy'. A cush drive is the only answer, fitted somewhere in the drive chain.
I fitted a Honda drum rear wheel. Cheap available & already in the garage!!
I am having the Dick Hunt hub repaired as it has BSF threads with larger studs in a coarser pitch that will be fixed in the hub permanently. & then have sholdered nuts made to hold the sprocket & clear the bearing housing. Funny I never had these problems until the bike was given "the berries"
Steves website is well worth a look, just to lust after the products.

Chris

LogVil said:

Does looking at the HD belt tell us that Norton belts need a "cush" drive with a primary belt?
Not necessarily, and certainly not definitively.

Click to expand...

Well, looking at the remains of the mainshaft I pulled out of my Atlas and the pitting on all first and second gear pairs of the four gearboxes I tore apart lately tells me the system will benefit from a cush drive (and an additional outrigger bearing on the sleeve gear).


Tim

LogVil said:

Tintin said:

SteveA said:

Does anyone use a Cush Drive in their engine pulley with a belt drive.

Click to expand...

The closest think I'm aware of to a cush drive together with a primary belt drive is the engine sprocket of a 1981(?) HD Sturgis. I think it retained the compensation mechanism of the original primary chain setup.


Tim

Click to expand...

Does looking at the HD belt tell us that Norton belts need a "cush" drive with a primary belt?
Not necessarily, and certainly not definitively.

Click to expand...

I have looked a picture of the Sturgis item and from that it is not clear where the 'rubber' might be?, if anyone has better explanantion of how it works or what it does. But in any case we may be wandering of track.

The intention is not to give the belt an easier life, but to provide some shock absorption in the whole transmission run from crank to rear hub, and hopefully to also transfer fewer shocks to an ageing frame that I want to use in a race bike. In truth I would have though that the belt was the part that needed this shock absorbtion least of all the transmission parts, surely it is also the cheapest and can be replaced every few race meetings if desired. A cush drive pulley design does exist and Norman White will make me one. At a one off price.

The rear wheel cush hub works as far as I know, even the less than perfect Commando one. Older bikes used a spring based shock absorber on their single row primary chain, so perhaps I am just trying to use and older solution, modern bikes use cush hubs, so that it seems is all most of us think of to address the problem.

Steve Maney uses his rear wheel cush drives with a Seeley like setup and Triumph 4 bolt hub, and it is a reasonably popular solution and probably more effective using modern rubbers. But for my Rickman wheel and swing arm combination it requires a lot of modification, like a new rear wheel particularly considering that the rear wheel I have is the original Rickman type, complete with a new rim and 10" disc and a full set of sprockets.

I would also like to retain the original look, and the belt pulley will be hidden, a cush drive won't.

If you want to see some innovation in belt drives and reducing loads on components look at the link to the German '905' on the crankshaft thread, there is a third roller bearing out there innside the pulley that takes crank twisting loads!

Steve,

I guess you are intending to use the Commando clutch? But alternatively have you considered adapting a Triumph T140 triplex clutch to the gear mainshaft? The only reason I see as recommending is that the T140 clutch centre has a built in 3 segment shock absorber and the whole primary is also available in belt drive. On a bombed up '73 Bonnie I fitted Barnett race plates and springs and a SRM BSA A65 alloy pressure plate with a radial needle roller pressure pad. The push rod was cut in 2 sections and a single ball bearing fitted in-between. A very light and super tough clutch.

Mick

is this feasable?
I remember someone making adaptors to fit the Triumph clutch to the Norton mainshaft, these were used for pre Commando.
assuming that there is room under the clutch cover for a T140 clutch, why cant the duplex T140 clutch be used, the duplex chain could be run on two rows of the Norton triple engine sprocket.

madass140 said:

why cant the duplex T140 clutch be used, the duplex chain could be run on two rows of the Norton triple engine sprocket.

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T140 is a standard triplex - that's why its a good options for the Commando.

Mick

ok, good, not sure if the Triumph clutch will have clearance in the outer cover, but it sure would be a good option,

Here's a pic of the Norman White cush crank pulley fitted to the bike. I've removed the outer flange to show the innards. Norman hand cuts the rubbers from what I do not know but they are fairly squidgy ( I know, not very technical). I've only had to replace them a couple of times over about 22 years. They stand up to the power well but you do need to keep solvents such as brake cleaner away from them. I've also had to replace the outer pulley at least once, on the first one the anodizing wasn't done right and the teeth eventually wore. Subsequent replacement hasn't been a problem.
This one uses a 40mm wide belt,I also have another one I have on a street Commando which is 30mm wide.

I'm not sure I'd recommend adapting a T140 clutch to a Norton, I've only heard of it being done the other way round, ie people making splined mainshafts for Triumph 5 speeds to fit Commando diaphram clutches. I never had much luck making the Triumph clutch work nicely on my street TR7V but it was a long time ago (30 years) and I was probably only able to get hold of pattern replacement parts at the time.

SeeleyWeslake said:

Here's a pic of the Norman White cush crank pulley fitted to the bike....

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Thanks alot for this!


Tim

Absolutely fantastic.....thanks so much....it is not a myth...it exists...and it makes sense....brilliant....

Couple of questions,

1 which clutch is that?....but belt profile being the real issue...
2 how many teath?.......I am looking at 40 and your looks to be 38 or 40, but difficult to count...

Now to get one made at a price I can afford.....of course batch is better than one off I reckon...

SeeleyWeslake said:

I've also had to replace the outer pulley at least once, on the first one the anodizing wasn't done right and the teeth eventually wore. Subsequent replacement hasn't been a problem.
This one uses a 40mm wide belt,I also have another one I have on a street Commando which is 30mm wide.

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More thoughts.

Not going to ask for a pic of the Commando one 8) , but:

3 Is the Weslake crank taper the same as the Commando?

4 When you say you have replaced the outer pulley, is that all one piece?

5 Did Norman replace it for you?, or did you use the original one as a pattern and get it done local to you?

Thanks

I had a though about the rubber.....in the UK you can buy a suspension unit for a small trailer, I have had them on bike trailers. The suspension is called 'indespension' uses no dampers. The 'springs' are lengths of round rubber....probably quite 'squidgy' :wink: anyway, teh way it works is you take a box section, say 2" square tube, this will b erigidly mounted to the trailer chassis....and you then inset a smaller box section that just has clearance to rotate inside the larger box section. You insert the lengths of round rubber into the 4 voids between the two box sections. The wheel axles is mounted onto a short, say 6" box section welded at 90 degrees to the inner box. Force applied to the axle attempts to rotate the inner box section against the resistence of the rubber, which is self damping unlike steel. I suppose the lengths of rubber material are readily available in round section, possible also square section which may be more suitable in this application?

Steve

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I have 2 questions about this picture:

What is that wheel in the middle for?

Isn't there a problem with running the belt that tight? Everything that I have read on belts has said to run them loose because they shrink when hot.

bwolfie said:

Click to expand...

I have 2 questions about this picture:

What is that wheel in the middle for?

Isn't there a problem with running the belt that tight? Everything that I have read on belts has said to run them loose because they shrink when hot.

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The 'wheel' is referred to in the text of the posting, it is the outer part of the pulley and uses those three bolt holes in the plate and pulley inner section to retain it, and it then retains the belt....often called the 'keeper plate' depending on design it is needed on all belt drives to keep the belt on....

I know it is not clear that the hole in teh centre of teh plate goes over that nut on the crank, but I reckon it does and it is just and accident of the photograph that you can see a nut in teh centre of it. I am also curious to know if that crank shaft end nut has some form of one way valve in it to relieve crankcase pressure....I have seen that done before (G50 flapper valve)...

I think we should assume 'SeeleyWeslake' has some knowledge of belts if he has been running this pulley for 22 years....

I agree it looks tight, and that too tight is bad, but for one, its 40mm wide so probably does not sag much on either run regardless of tension, and two I understood as a rule of thumb that you should be able to grasp the centre of the top run and rotate something like 90 degrees,, unless you set tension methodically using sound frequency!....I'll go for the twisting thing...I have enough problems tuning a guitar...

If it is too slack you risk jumping teeth...perhaps not catastrophic like it was on my Land Rover cam belt back in December, but still not good....

The clutch is a Hemmings Commando with dry Barnett plates, hence belt/teeth are Gates HTD
Belt is a Gates Polygrip 976-8m, made in Germany and supplied by Bob Newby. Bob can supply belts like these in 1 tooth length increments which can be useful at times.
Pulley has 36 teeth which gives a primary ratio of 1.89, close enough to 1.78 for me.

The Nourish crank has a straight splined mainshaft and is I think the same as a T140. NW made the pully with a plain hole in the middle and then sent it to Dave Nourish to broach. Dave still had the broach from when he used to make his own triplex chain sprockets.
NW would obviously do a Norton taper himself.

The complete pulley is just 3 pieces, the inner hub, steel , the outer pulley, Al ,and the outer flange, steel. ( and the rubber bits)
NW made the replacements outers for me. He did need my old one to copy from though. I think there was a bit of fine adjustment to the tolerances and fits going on. I think he gets the outers as blanks with teeth already on them and then just machines the interiors.
I haven't had a local company make these for me ( yet) but I might if Norman gives up on them and retires

Bwolfie,
Well spotted on the belt tension. I just checked it tonight and it only has a 45deg twist which is less than what seems to be recommended on this site. In my defense it is a 40mm belt and is shorter than the typical Commando installation.
When I built the bike I calculated the center distance from the tech data and I think I got it pretty close. The engine plates are not slotted so there is no adjustment. I remember at the time thinking that it was a bit tighter than desired but decided to live with it and keep an eye on the gbox mainshaft bearings. So far I haven’t had any problems. I think Norman White told me he recommended between 45 –90 deg twist so I am at the low end of that.
The main reason belts get tight when hot is I believe due to the crankcase and engine plates expanding, as well as the clutch pulley itself. Perhaps someone on here has already done the sums?
The wheel in the middle of the pic is the pulley outer flange which I just parked on the cover stud to take the pic. The large hole in the middle allows it to go over the crank nut

Steve A
The crankshaft nut has indeed a flapper valve in it and connects to the crankcase via the hollow mainshaft. At one time I was paranoid about breathing so I fitted an extra breather off the cam cover plate. It runs into a PCV valve but having read all the stuff on this site I think a better solution is probably the XS650 reed valve ( but it would mean having a Yamaha part on the bike!)

As belt gets tighter by the power unit thermal expansion you are putting undo loads on the tranny main shaft and its weak wearing sleeve bushes. Check the twist hot and see. Shorter the belt run the more this occurs. Measure the pulley center distance when full hot, not cold.

A centered belt on trued pulleys does not need side plate to stay on but may if the shafts begin bowing from thermal expansion strain and drive torque.

But if run hard and getting away with it - this belt tension is obviously tolerable, so far. Too lose it can jump teeth of course.

Chris said:

Hi

Steves cush drive is based on a Triumph disc rear wheel. Nice system just like the P&M Rob North triple. Its a tight fit.
I copped out when my 750 did in the Dick Hunt Seeley disc rear wheel. I used stainless allen heads & they fractured. (thanks for your advice back then) They were replaced with good spec standard 'black' allen keys. Two meetings & again the sprocket was loose. All the heads were still lock wired together but the sprocket holes had ovalled & the threads in the hub are 'loose/sloppy'. A cush drive is the only answer, fitted somewhere in the drive chain.
I fitted a Honda drum rear wheel. Cheap available & already in the garage!!
I am having the Dick Hunt hub repaired as it has BSF threads with larger studs in a coarser pitch that will be fixed in the hub permanently. & then have sholdered nuts made to hold the sprocket & clear the bearing housing. Funny I never had these problems until the bike was given "the berries"
Steves website is well worth a look, just to lust after the products.

Chris

Click to expand...

I started running a Dick Hunt Seeley rear drum about 4 years ago in the race bike. I noticed that the sprocket bolts did seem to loosen off even though they were saftey wired. I assumed it was due to thermal expansion of the different parts, Al sprocket, steel sprocket carrier/lining and Mag hub. My sprockets also had a set of pins locating them as well as the bolts (5/16 BSF). I do have the Norman White cush drive on the crank so maybe mine didn't suffer quite the same destruction as yours for that reason.

SeeleyWeslake said:

It runs into a PCV valve but having read all the stuff on this site I think a better solution is probably the XS650 reed valve ( but it would mean having a Yamaha part on the bike!)

Click to expand...

It's not actually a Yamaha parts, just sold by a XS650 parts specialist. You're safe.

SeeleyWeslake said:

The clutch is a Hemmings Commando with dry Barnett plates, hence belt/teeth are Gates HTD
Belt is a Gates Polygrip 976-8m, ...

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You might be interested in this Gates belt/sprocket interchange guide. The pdf (link on the right) is more comprehensive.

I'm not aware of a "Polygrip" - Gates supplies "Poly chain" and "Power Grip" brands AFAIK but that might have something to do with local or older brands. The more modern profile is the Poly Chain GT2 and the corresponding sprockets are also used for the Poly Chain GT Carbon which is pretty interesting for a primary drive application as it reduces the necessary width quite substantially. Unfortunately "Poly Chain GT2"-profiles are not recommended (14mm pitch) or "incompatible" (8mm) for HTD profiles.


Tim