Oil Blowing out of crankcase breather - Model 50

I suspect that all is well. The non-return valve probably doesn't work that well (mine never did) and the reason that the oil tank has not filled up is that you lost some through the breather. I should just top up the oil tank, check things over (make sure there are no unexpected rattles/oil leaks and that the oil return is spitting into the tank like they do) and go for a ride. Then you'll feel better.

Hi Mike - My 1950 ES2 wet sumps all the time . I do not want to fit an oil tap for fear of the consequences of neglecting to turn it on - it only takes one time . I would caution against starting the bike with the crankcase full of oil as you run the risk of damage to the cases or bending the connecting rod - I drain the crankcase at the plug and pour the oil back in the tank befor starting if I have not run it for a while .

I have a tap fitted to my 1952 ES2 (fitted by the previous owner) and have decided to keep it. It only needs to be turned off when the bike is left for a few days or more - not for brief coffee stops or even overnight when touring.

A roller bearing engine like the ES2 will run quite happily for some time with no oil feed - remember they're derived from "splash" lubricated models - but of course this is not recommended! The first indication would be the piston tightening up.

I'm interested in Richard's reply. I often start my ES2 when the oil tank is close to empty and, apart from once when it smoked a bit, I have had no problems. If the bike will turn over easily using the decompressor, how can damage to the crankcases or conrod happen? I admit I am not an engine guru but I have quite a few years in the motor trade under my belt and am a bit puzzled.

Hydraulic issues can happen if liquid gets above the piston but below seems a bit far fetched. Please feel free to shoot me down, Richard.

Previously christopher_shepperd wrote:

I'm interested in Richard's reply. I often start my ES2 when the oil tank is close to empty and, apart from once when it smoked a bit, I have had no problems. If the bike will turn over easily using the decompressor, how can damage to the crankcases or conrod happen? I admit I am not an engine guru but I have quite a few years in the motor trade under my belt and am a bit puzzled.

Hydraulic issues can happen if liquid gets above the piston but below seems a bit far fetched. Please feel free to shoot me down, Richard.

Hi Christopher - no shooting down here - only discourse as part of learning ( I'm still learning I hope !)

My ES 2 engine only has a small vent for the crankcase above the drive side main bearing -1/4" inch or so IIRC - 50 wt oil can only pass through this hole at a given rate . The piston compresses the air between it and the crankcase on it's downward travel. The higher the the oil level ( incompressible )in the crankcase the less air there is to compress . As the air compresses it acts upon the oil trying to displace it. As stated above , the oil can only escape through this small hole at a given rate - once that rate is exceeded something has to give. As I am sure you are aware the smoking you experienced was the result of the oil getting past the rings and burning - well seated rings with the minimum of end gap provide more resistance to this bypass and therefore put more of a strain on the cases. Remember that even the newest of these crank cases are over 50 year old sandcast aluminum - not the toughest stuff around.

I agree with you that regardless of the amount of oil in the case rod or crankcase damage is unlikely when turning the engine over with the kickstart - it's when the engine lights up that damage can occur as the dynamics of these forces increase exponentially . Also remember that the valve lifter only lessens the forces acting against the piston on its upward travel.

I also agree that rod damage is far more likely from hydraulic issues above the piston but it stands to reason that a higher loading is imparted on the rod when the crank is fighting the resistance of a crankcase full of 50 wt. oil - the reason we employ dry sumps in our engines is to negate the horsepower robbing effect of this resistance .

I am cautious by nature ( except for the motorcycle riding bit ! ) and after investing four years and far too much money restoring my ES2 it makes sense to me to simply drain the crankcase when needed - the plug hole is helicoiled and the entire process takes less than 5 minutes - small investment of time .

I am certainly open to rebutle on this - interesting subject to contemplate .

Cheers - Richard

Like you Chris Im no engine guru but from a common sense viewpoint if the crankcase is - say - half full of oil then the air displaced by the descending piston has only half the space to be compressed into. This will have a couple of effects. 1) the pressure under the piston will double; 2) The air/oil will find somewhere else to get out so oil seals can pop, oil can spew out of the vent and air will be forced up the push rod tubes into the rocker box cover increasing the pressure up there with possibly more leaks.

Furthermore, apart from the drag on the big end of the business passing through the oil there will be the added drag of the piston pulling a partial vacuum as it rises having displaced 250cc of compressed air and trying to replace with 500cc.

I've run out of ack-ack shells! Not having "go's' just trying to think it through.

George

Thanks chaps. You have argued the point well and I accept your arguments. When I go for a ride, I don't usually want to faf around draining oil and putting it back into the tank so I will continue to live dangerously. After all, the crankcase must have a considerable volume and would not be filled up, even by the contents of the oil tank. When my bike smoked on starting up, it only lasted a few seconds and it was a very still day so the smoke hung in the air for a while. It was after we had the snow this year and she had not been started for a few weeks.

Previously christopher_shepperd wrote:

Thanks chaps. You have argued the point well and I accept your arguments. When I go for a ride, I don't usually want to faf around draining oil and putting it back into the tank so I will continue to live dangerously. After all, the crankcase must have a considerable volume and would not be filled up, even by the contents of the oil tank. When my bike smoked on starting up, it only lasted a few seconds and it was a very still day so the smoke hung in the air for a while. It was after we had the snow this year and she had not been started for a few weeks.

Attaboy Christopher ! I know some ladies like a dangerous man so you may have to fight off their attentions as well !

Just to give a contrary view, if the breather is blocked by oil then the pressure will only increase if the piston started at tdc, if was at btdc then the pressure would reduce as it rises and then normalise as it returns!

Good point Dan. But if it starts at say BDC and on my assumption that the crankcase is half full of oil, then it will try to pull in 500cc of air. via the vent and through the oil. As it descends, if there is less than 500cc of available space above the oil then the excess of air will push the oil out as described above. This will happen each time until there's at least 500cc air space below the piston. I think!

Previously George Phillips wrote:

Good point Dan. But if it starts at say BDC and on my assumption that the crankcase is half full of oil, then it will try to pull in 500cc of air. via the vent and through the oil. As it descends, if there is less than 500cc of available space above the oil then the excess of air will push the oil out as described above. This will happen each time until there's at least 500cc air space below the piston. I think!

Yes I agree and I think thatâs correct! But if it sucks air in it will surely be able to blow it out?. It would be interesting to know if the oil has bubbles in it when itâs pushed out of the breather. Mine rarely wet sumps so I canât tell!

Dan