Breather tube sizing - MK1

[camstevens]

Hi All
I'm taking the opportunity to fit a better/larger timing case breather to my MK1. I will seek to use as big a tube diameter as I can get away with as I have a Morgo fitted (as I saw in someone's photo, I will also bring the breather tube over the top of the oil pump, tipping down).
My question: is a 10mm OD copper tube of sufficient capacity for a tube length of that distance? The next size up is 15mm, but I haven't checked as to whether that would fit. I do know from bitter experience that a 7mm OD tube over that length doesn't cut the mustard.

Cheers
Cam

[allan.walker]

Hello Cam,
I've no experience of using a larger i.d. breather on a Square Four, but I do wonder that, if you are losing too much oil through the existing one, have you considered routing the pipe from the back of the timing case upwards rather than downwards? A flexible hose can then be led to the back of the bike.

My thinking is that a vertical rise from the breather would allow condensed oil vapour to drain back down into the engine. I haven't tried this on a Square Four, but an upward-routed breather hose is standard on my Commando. Any thoughts?

Allan.

[nevhunter]

A lot of that condensate is WATER and grim blow by products. You don't want any of that sort of thing in your motor. With a Commando you have two quite large pistons going up and down together causing Pulses. The Sq 4 doesn't have that situation. Nev

[allan.walker]

Fair point, Nev.
I'll get me coat......

[Roger Gwynn]

A larger breather is pretty essential on a SQ4 with a Morgo pump unless you never intend to unleash the power of the beast for more than 1/4 mile. I fitted a 15mm tube some years ago and don't remember the details but I do remember it wasn't easy and adds yet more stuff that gets in the way when you want to do anything to the engine.

[camstevens]

Hi Roger
As far as I can tell, using appropriate fittings would allow 15mm tubing. I would be best to drill/tap the entry point to 3/8 BSP.
And yes, it's incredible what effect the Morgo has when steaming along! As big a tube as feasibly possible

Cam

[daveleek]

This is a print screen from an old post, the modification has been a success even though going from 15mm to the original smaller sized fitting through the case as I was reluctant to enlarge the hole

[nevhunter]

Having a larger dia breather is no problem but surely BLOWBY is what we are talking about with the breather volume/flow. There are no pulses in the Sq4 due the four cylinders. The water is also related to blowby and the fact that for each liter of hydrocarbon fuel burned you get more than a liter of water produced.. IF the motor is hot enough that will be as steam which has also to pass through the breather. IF the motor never gets very hot that water will stay in the oil and corrode your motor's innards and form sludge. Nev

[simon.holyfield]

A larger breather is pretty essential on a SQ4 with a Morgo pump unless you never intend to unleash the power of the beast for more than 1/4 mile. I fitted a 15mm tube some years ago and don't remember the details but I do remember it wasn't easy and adds yet more stuff that gets in the way when you want to do anything to the engine.

Am I missing something? My Mk1 has had a Morgo since I built it 11 years ago and I've never seen much from the breather.

Should I be thrashing it more??!

[Gui.dorey]

Hi Cam,
I don’t remember the size of the tubing I installed, but it was just large enough to fit snugly into the breather hole inside the timing case. I ‘m sure you’ll find a picture in one of my threads.

BUT…. If a lot of oil, and not just condensate, is coming out of the breather, then I believe there is too much oil coming into the timing case. The cause should be investigated, and the problem is surely not because one has a Morgo pump like I also have. I spent a lot of time trying to solve this on my MkI and the mod with the pipe didn’t cure it. On mine the problem was the plain bearing with too large of a tolerance, which spewed large amounts of oil into the timing case and sump. You probably read what happened in the end.

You can try the following to check the state of the tear bearing. I did this and it’s fine. Start and run the engine with the timing cover off. Check how much oil is coming out through the main bearing. Film it and we can compare videos. Mine was a steady stream, which we now know is not good. If it’s not much then at least you know your plain bearing is still good to go. You can do the same at the front by taking the inspection cap off.

Cheers
Gui