Further musings on Enfield crankcase breathing *updated*

[Triton Thrasher]

[CHR15]

have you got any photos of the head + valves when they're coked up?

that may give a clue as to how and where the oil is being burnt.
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Turbocharged drag thing / project death weapon / GK73A
Ste: I'm not entirely sure how you'd go about verbally abusing someone with a potato but I'm sure it's possible.

[stinkwheel]

Now with added science!

I'm finding some of the numbers I'm getting here fairly mind boggling.

So:

Description
Late model Royal Enfield 350 bullet engines breathe an inordinate amount.

It has already been established that by repositioning the crankcase breather from the oil tank to its original design location on the crankcase, an as-yet unquantified vacuum exists inside the oil tank/crankcase.

It is possible to allow the oil tank to ventilate itself. It is uncertain what effect this will have on the quantity of gas being expelled fron the breather system.

Hypothesis
Venting the oil tank to atmosphere while retaining a direct crankcase breather could effectively turn the engine into a compressor.

Equipment
A 2007 350 bullet with a retro-fitted crankcase breather utilising a non-return ball valve, standard oil tank breather stub in oil tank and blanked-off timing chest return stub.

A bucket of water

A 750ml wine bottle

A length of silicone tubing.

A Royal Enfield duckbill breather hose.

A stopwatch (nokia).

Method

By filling the bottle with water , covering the neck and inverting it in a bucket of water, it is possible to insert a rubber hose into the bottle without disturbing the water. Any pressurised gas passed through the hose will displace the water.

The volume of the bottle is already established. By timing how long it takes to displace all the water, a rough gas flow rate can be calculated.

The engine was set to a fast idle speed of approximately 1,200prm then the end of the crankcase breather hose connected to the measuring apparatus.

Results

With the crankcase breather modification blocked off and a standard duckbill breather on the oil tank stub, the gas flow rate was 1.8 litres per minute.

With the crankcase breather modification active and the oil tank vent blocked, the gas flow rate was 1.7 litres per minute.

With the crankcase breather modification active and the oil tank free to ventilate to atmosphere, the gas flow rate was 10.0 litres per minute.

Conclusion
The gas flow rate breathed by the engine is not significantly affected by having relocated the crankcase breather to the oil tank.

By allowing the crankcase to breathe directly, a significant vacuum must occurr in the oil tank. By ventilating the oil tank, the engine breathes at a rate nearly an order of magnitude higher.

Discussion

To put these figures in perspective. A 350cc single cylinder engine will be displacing 420 litres of gas per minute both above and below the piston when rotated at 1,200rpm.

It is considered desirable to have a slight vacuum in the crankcase. This helps to avoid oil being forced up past the piston rings. If too high, it will cause resistance to the piston rising on the compression and exhaust strokes.

It is not considered desirable to have a vacuum in an oil tank, this can provide resistance to oil egress into the high pressure part of the lubrication system.

It would appear that ventilating the oil tank while allowing one-way breathing from the crankcase results in a massive increase in the rate of gas being breathed out. Suggesting some sort of through-flow effect not unlike a compressor. The effect of running an engine under load in this state remains to be seen and will be the subject of further experimentation.

What the effects of the differing breather locations at higher engine speeds has not been established.

Also video of the above experiment:

https://youtu.be/ET0Rv4fh-Yc

TL;DR Piss off, you wouldn't have got this far down the thread if you didn't have a reasonable attention span.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[stinkwheel]

[CHR15]

what does the valve chest side of the head look like?

from what you wrote, my understanding is that the oil is scavenged from the crankcase and fed into the head, before dropping back down into the oil tank? (what a lovely simple way of lubricating the head and deaerating the oil!)


with the engine in the frame, is there the possibility of oil pooling around the guides to the point where it reaches the level of the stem seals?
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Turbocharged drag thing / project death weapon / GK73A
Ste: I'm not entirely sure how you'd go about verbally abusing someone with a potato but I'm sure it's possible.

[stinkwheel]

[CHR15]

i would suggest taking it for a run, at a point where you dont have to use it for a while afterwards.

park it up on the sidestand and remove the carb, spin the engine to tdc on compression and leave it overnight. have a look if theres any oil coming down the stem or pooled on the head in the morning.
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Turbocharged drag thing / project death weapon / GK73A
Ste: I'm not entirely sure how you'd go about verbally abusing someone with a potato but I'm sure it's possible.

[Triton Thrasher]

10W/40 is so thin that it will burn in an old Brit bike, even if the engine has no real faults
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Rrrrrrrrrrrrrrrrrr

[stinkwheel]

[mysterious_rider]

[stinkwheel]

[Triton Thrasher]

Some cheap oils lose their multigrade qualities (and other qualities) quite quickly.
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Rrrrrrrrrrrrrrrrrr

[Northern Monkey]

[stinkwheel]

Holy thread resurrection batman!

I just stripped the crankcases on this engine ready for swapping the main bearings after a catastrophic valve failure.

https://lh3.googleusercontent.com/gg0WSrR8JOM7gJeZMbG4eSrhN62BzRyC9L71UZcT-UZyCTNrlEGPT-RChKX5LjPezS7EsqmZhKqSTYTUr7ytyBm2qZDohEkFGnENawdzWrWFSaFg5OaoTbINyfb44QTvoBDAj1tdWg=w931-h698-no

Can you spot it???


The crank seal is in backwards. I have owned this bike for 10 years. It had 300 miles on the clock when I bought it. The previous owner was in his 80's and I'm pretty certain he hadn't drained the timing chest and removed the timing pinnion befroe I got it. I'm absolutely certain I haven't. So it came from the factory like that!

Bugger me!
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[BusterGonads]

Enjoyed this thread and like your approach to testing to find the fault. What a bummer all this trouble and strife was caused at the factory. I'm drawn to these old chuggers, but not sure I could stand the level of quality control problems they have. I was looking recently into the Enfield Himalayan but was put of when looking at facebook groups and seeing tales of new owners of six month old bikes having problems with chafed wires near the headstock causing electrical faults on bikes with a few hundred miles on them.

I love the archaic nature of these engines, but probably not the foibles.

Glad you found the cause and hope the re-build proves reliable.

[MCN]

I'm almost certain I told you about the seal in my post on this thread in 1987. 🤣
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[BusterGonads]

[Northern Monkey]

[BusterGonads]

[ajb235]

[MCN]

My BSA C12 was a pig to start. Iridium plug helped that but it was very under powered and got mad hot on short 3-4 mile runs on the flat.
I found that the ignition was only 180 degrees centigrade out.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.