Fitting a Bob Newby belt drive

When I was at P&M a couple of years ago I was chatting with Dave about a TR7 motor he had built for a bloke. He used a Matchless type breather in the end of the crank. The drive side shaft is drilled to 1/4" dia & the valve fitted to the end & used to hold the alternator rotor on as per AMC twins. Dave reckoned that no oil came out. By coincidence, I have been working on my AJS CSR 650 today which is fitted with the very same setup, & the primary case oil did not appear to have been contaminated by any engine oil.
I did toy with the Manx style breather slot in the front chamber of my TR7 cases when I tried the Hemmings belt drive, but didn't want a breather pipe running up the front of the engine. With hindsight I should have done this.
 
Triton Thrasher said:
If the rocker box breather works, that’s interesting.

It’s an easy way to plumb a breather in.
Click to expand...

So TT... you didn’t sound too convinced about this rocker box breather idea if I may say so.

Well, in the interest of adding to the body of knowledge...

With breathers fitted to inlet and exhaust rocker boxes, and the timing cover breather blanked off, after a 50 mile fast ish road test, the main bearing seal passed oil into my dry primary, not a lot, but more than none.

With the timing cover breather fitted, tested on the same route, it does not, the primary remains bone dry.

So, I can absolutely confirm that NO, the rocker box breather idea does not work !
 
Fast Eddie said:
So TT... you didn’t sound too convinced about this rocker box breather idea if I may say so.

Well, in the interest of adding to the body of knowledge...

With breathers fitted to inlet and exhaust rocker boxes, and the timing cover breather blanked off, after a 50 mile fast ish road test, the main bearing seal passed oil into my dry primary, not a lot, but more than none.

With the timing cover breather fitted, tested on the same route, it does not, the primary remains bone dry.

So, I can absolutely confirm that NO, the rocker box breather idea does not work !
Click to expand...

I was under the impression that Triumph fitted the exhaust rocker box breather to mitigate pressure within that rocker box in particular, not for engine breathing purposes (which was still facilitated via the primary vent).
 
acadian said:
I was under the impression that Triumph fitted the exhaust rocker box breather to mitigate pressure within that rocker box in particular, not for engine breathing purposes (which was still facilitated via the primary vent).
Click to expand...

Not sure. As mine was originally connected to the frame I had assumed it was to allow the frame / oil tank to breath?

My thinking was that if I fitted another to the inlet, then took them both to the reed valve, the combined breathing capacity would be enough for engine breathing.

I was wrong !
 
Think I'm going to bite the bullet on a belt drive while waiting on new valve seats to be installed, any chance you know the dimensions of the drive side seal?
 
acadian said:
I was under the impression that Triumph fitted the exhaust rocker box breather to mitigate pressure within that rocker box in particular, not for engine breathing purposes (which was still facilitated via the primary vent).
Click to expand...
It looks more like a way to recirculate oil tank fumes.
 
acadian said:
Think I'm going to bite the bullet on a belt drive while waiting on new valve seats to be installed, any chance you know the dimensions of the drive side seal?
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Can’t help with the seal, mine is kinda buried !

Which belt drive kit are you going for? Are you going dry? If so, what are you going to do about breathing?

On my T120 I used a kit suitable for oil because the oil seal area is damaged making a seal impossible. I pulled out the tensioner blade locating peg leaving a very low point by which any oil in the chaincase can drain back to the sump. This way, some oil mist gets into the case but no real oil quantity, so the clutch seems to stay dry, which I wanted. The other reason for not wanting the belt to run in oil is that oil gets sandwiched between the belt and pulleys, effectively increasing the belt tension, and some attribute this to belt failures.

I didn‘t try this on the T140 but can’t see why it wouldn’t work. There were a few occasions whilst I’ve been pissing about with breather arrangements when I thought the above would have been a better route!

Or are you joining the fugly hose club...

Fitting a Bob Newby belt drive
 
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Fast Eddie said:
Can’t help with the seal, mine is kinda buried !

Which belt drive kit are you going for? Are you going dry? If so, what are you going to do about breathing?

On my T120 I used a kit suitable for oil because the oil seal area is damaged making a seal impossible. I pulled out the tensioner blade locating peg leaving a very low point by which any oil in the chaincase can drain back to the sump. This way, some oil mist gets into the case but no real oil quantity, so the clutch seems to stay dry, which I wanted. The other reason for not wanting the belt to run in oil is that oil gets sandwiched between the belt and pulleys, effectively increasing the belt tension, and some attribute this to belt failures.

I didn‘t try this on the T140 but can’t see why it wouldn’t work. There were a few occasions whilst I’ve been pissing about with breather arrangements when I thought the above would have been a better route!

Or are you joining the fugly hose club...

View attachment 20037
Click to expand...
Going with the Hayward belt kit, though it can be run wet my plan is to run dry. Last time I was in the primary (swapping to an alloy clutch basket) the seal area looked to be in good shape. I did manage to locate the seal dimensions: 36x54x6.5

I'll keep the exhaust rocker breather I have set up, and use the timing plug as well. So it will be the 'less fugly' hose club for me ;)

Fitting a Bob Newby belt drive
 
That should work well. Hayward kit is good stuff. I use that timing hole for the breather on my T120 and it works great.

The only thing to remember when running a Triumph clutch dry is to not sit with the clutch in and give the clutch rollers a hard time.
 
Fast Eddie said:
That should work well. Hayward kit is good stuff. I use that timing hole for the breather on my T120 and it works great.

The only thing to remember when running a Triumph clutch dry is to not sit with the clutch in and give the clutch rollers a hard time.
Click to expand...

That's one of the huge benefits with the BN kit you have, it uses a sealed bearing, no? I just can't justify the cost right now
 
acadian said:
That's one of the huge benefits with the BN kit you have, it uses a sealed bearing, no? I just can't justify the cost right now
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Yes it does. I still don’t sit with the clutch lever in though!

Provided all your clutch plates and centre are good, the Hayward kit is far more sensible economic choice.

I used to use a Hayward on a 906cc Nourish / Triumph racer with 84rwhp and never had an issue with it.
 
I’ve used a Hayward kit in a Pre-unit 650 for more than 50,000 miles. It’s in a primary chaincase that I don’t put oil into. Some oil does end up there, but not much. The clutch roller bearing is a non-issue.
 
Re the BNR clutch sealed bearing: what sealed bearing are you referring to? Mine has no sealed bearing...
 
You sure?

We‘re referring to the bearing twixt clutch centre and clutch outer drum, ie the bearing that comes into play when the clutch is disengaged.

Many refer to it as a sealed bearing, I’ve not stripped mine but looking on t’internet it doesn’t appear genuinely sealed, and folk do seem to recommend re packing with grease.

Fitting a Bob Newby belt drive
Fitting a Bob Newby belt drive
 
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Yes mine has a race of tiny balls. They are not sealed one must grease them if you are running a dry (belt) clutch.
I would love to have a sealed bearing there. Did Bob change to this?
 
Onder said:
Yes mine has a race of tiny balls. They are not sealed one must grease them if you are running a dry (belt) clutch.
I would love to have a sealed bearing there. Did Bob change to this?
Click to expand...
I think I edited my post as you were replying...
 

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