Fitting a Bob Newby belt drive

cliffa · Oct 30, 2020

Just a suggestion FE, but if you have to come out the top of the timing cover, why not use a 90º pre molded hose or spigot which will reduce it's aesthetic impact (fugly), and go straight across to the fart valve..

Triton Thrasher · Oct 30, 2020

I lead the hose straight up vertically, as high as is practicable, before putting any bends in it.

I also fit the reed valve close to the engine.

Fast Eddie · Oct 30, 2020

cliffa said:
Just a suggestion FE, but if you have to come out the top of the timing cover, why not use a 90º pre molded hose or spigot which will reduce it's aesthetic impact (fugly), and go straight across to the fart valve..

I am looking for such a hose... open to any ideas...

Although, the up and over idea is supposed to reduce oil egress.

cliffa · Oct 30, 2020

Fast Eddie said:
I am looking for such a hose... open to any ideas...

Although, the up and over idea is supposed to reduce oil egress.

Here's one example supplier on Ebay, but I get you point about oil. Can you still get the silver breather hose they used to fit on Triumphs? Maybe that would look better.

Roose Motorsport 90 Degree Elbow Coolant & Boost Silicone Hose Bends | eBay

Ideal for: Water, Air, Coolant / Antifreeze, Mild Oil Mist. Silicone 90 Degree Elbows. 150mm Leg lengths. hand craft and inspect every hose. We are adding to our range of vehicle hose kits constantly.

www.ebay.co.uk

Or use an inline valve like the Yamaha Cygnus version, and put it closer to the 90º elbow .

Valve Air Depression Yamaha 125 Cygnus MBK Flame X | eBay

Find many great new & used options and get the best deals for Valve Air Depression Yamaha 125 Cygnus MBK Flame X at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

Fast Eddie · Oct 30, 2020

Thanks but I’ve been through those thoughts Cliffa. I‘d be in grave danger of making a pigs ear in trying to make it neater with joints and hose clips galour!

This set up is only temporary. When I get around to doing the engine one day, I’ll drill through into the front mounting chamber and take a discreet breather from there (as I’ve done before).

baz · Oct 30, 2020

Fast Eddie said:
Thanks but I’ve been through those thoughts Cliffa. I‘d be in grave danger of making a pigs ear in trying to make it neater with joints and hose clips galour!

This set up is only temporary. When I get around to doing the engine one day, I’ll drill through into the front mounting chamber and take a discreet breather from there (as I’ve done before).

How well does using the the chamber work Eddie?
A mate of mine is doing this to his t140
I think he is going to drill multi holes from the crankcase to the chamber
Then a pipe from the top of the chamber
Cheers

Fast Eddie · Oct 30, 2020

Works well Baz.

Don‘t need too many holes IMHO. Two 3/8 ish high up for breathing and two 3/16 ish as low as possible and at an angle for oil drainage. Only one outlet is needed despite the fact that many fit two.

I ran this very successfully before. Now I’d add a reed valve high up under the tank to make it even better. I’m a big fan of reed valves these days !

acadian · Oct 30, 2020

There's also the option of using the timing plug hole behind the cylinders, throws a bit of oil, but this can be mitigated with some stainless mesh in the outlet hose

cliffa · Oct 30, 2020

One general observation. When you look at the pictures of your engine and take for example the cylinder head. The quality of the castings is far superior to the Norton of the same era. I'm beginning to want a Triumph. ( a bright yellow Tiger Trail)

cliffa · Oct 30, 2020

acadian said:
There's also the option of using the timing plug hole behind the cylinders, throws a bit of oil, but this can be mitigated with some stainless mesh in the outlet hose

I was wondering if that was still on the later Triumphs. That has to be the neatest solution surely?

Fast Eddie · Oct 31, 2020

cliffa said:
One general observation. When you look at the pictures of your engine and take for example the cylinder head. The quality of the castings is far superior to the Norton of the same era. I'm beginning to want a Triumph. ( a bright yellow Tiger Trail)

Hey, I want wanna them !

Fast Eddie · Oct 31, 2020

acadian said:
There's also the option of using the timing plug hole behind the cylinders, throws a bit of oil, but this can be mitigated with some stainless mesh in the outlet hose

Sadly, this hole was moved on later bikes (to facilitate the e start I believe). Shame cos I use that very hole on my ‘68 and it works fine. I get no oil loss from it, think the reed valve prevents this.

Onder · Oct 31, 2020

Well first a FullAuto head negates the need to go Triumph and if the reed valve line empties into the oil tank then the hassles
of exhausting oil out that line are taken care of.

Fast Eddie · Nov 14, 2020

Hmmm...

The timing cover bodge dumps quite a lot of oil out of the breather. I had assumed that the reduced pumping as a result of the reed valve would have prevented this. If anything it seems to make it worse as it doesn’t allow the engine to suck anything back in.

Gonna try the rocker box breather outlet next.

I got some small diameter plastic pipe and inserted it through the frame vent right up high into the frame and sealed it in. Then routed a frame breather down and out of the way. My theory is that this will still allow the frame / tank to breath, but no oil slosh can make its way out.

That freed up the rocker box breather (which normally connects the frame to the rocker box).

It‘s all plumbed in ready to try, just waiting for it to stop raining ...

Triton Thrasher · Nov 15, 2020

Are you expecting the crankcase to breath through the four small drain holes in the tappet blocks?

Fast Eddie · Nov 15, 2020

Triton Thrasher said:
Are you expecting the crankcase to breath through the four small drain holes in the tappet blocks?

Yes. Or at least, that’s what I wanted to try. If you look at the size of the passages with a stock timed breather, it should be enough. IMHO, the problem with the timed breather was the timing. Whereas with a reed valve, it’s always ‘timed’ perfectly.

I’ve seen it done before, though I confess it’s not my preferred option, but with a reed valve it is surprising how little ‘flow’ there is compared to without.

Anyway, I did about 60 miles today and it does seem to work fine. There’s no oil exiting the breather hose, and gasses clearly are.

One day, I’ll strip the bottom end and use the front mount area as mentioned previously, but until then, if this works, it’ll do !

baz · Nov 15, 2020

When I ran my t140 with an open primary I only blocked off the 3 oil level holes in the crankcase
I never fitted a crankshaft oil seal,and no oil ever came out of the crankcase behind the the drive sprocket
I'm wondering if you just block the 3 holes and and just use the standard breather in the chain case would work?
Cheers

Fast Eddie · Nov 15, 2020

baz said:
When I ran my t140 with an open primary I only blocked off the 3 oil level holes in the crankcase
I never fitted a crankshaft oil seal,and no oil ever came out of the crankcase behind the the drive sprocket
I'm wondering if you just block the 3 holes and and just use the standard breather in the chain case would work?
Cheers

On my ‘68 T120 I fitted an oil proof type belt and clutch and did similar to what you suggest, I also removed the tensioner blade pin, which is very low in the case, so any oil that did make its way in would drain back. This seems to work well, but there is evidence of oil mist in the case. With the Bob Newby set up I think oil mist would be problematic for the belt and for the clutch.

Triton Thrasher · Nov 15, 2020

If the rocker box breather works, that’s interesting.

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

Fast Eddie · Nov 15, 2020

Triton Thrasher said:
If the rocker box breather works, that’s interesting.

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

Indeed!

I ain’t celebrating yet though, still an experiment in process...

There‘s some good info in this article, using the front mount casting is something I’ve done before (only relevant for unit construction of course), but pre reed valve, it would clearly work better with one me thinks.

Triumph Breather Diagrams

Several alternative methods for installing a crankcase breather on a vintage Triumph twin

www.vintagebikebuilder.com

Regarding those wee holes in the tappet blocks, look at this breather type Commando cam, can’t be any more breathability through this cam than there is through Triumph tappet blocks...

Fitting a Bob Newby belt drive

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