Crankcase pressure

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I was doing some winter tidying on my 73 roadster and found quite a bit of engine oil in my primary case. This was a bit disconcerting as I'm running a belt drive. Further investigation showed the oil to be coming from between the crank shaft and "oil seal." Also, I use a catch bottle for the crankcase breather hose (no original air filter) and that bottle was pretty full of oil. I'm suspecting excessive pressure in the crankcase is blowing oil out anywhere it can go. Anything other than the pressure relief valve to check?

Thanks,
Chris
 

Anonymous

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Chris,

Excess oil in your "catch" bottle could mean an overfilled oil tank. Another possibilty is that you have worn/damaged piston rings, which would permit combustion gas in the crankcase. The excess crankcase pressure would tend to force oil past seals and vents. Lastly, don't forget about the P1V1/P2V2 problem as a result of excessive wet sumping.

Regards,

Jason
 
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Jason said:
Chris,
don't forget about the P1V1/P2V2 problem.....

Regards,

Jason

Hi Jason ...this seems to be just what is being discussed in the "Sumpin" forum.....too much oil in the sump. But what is this P1V1 problem thing? Maybe I'm not up on the latest jargon....as to oil in the catch bottle, isn't that just a bottle that takes the place of the hose that routes the excess oil back into the oil tank on the 72 and later? If there is too much oil in the sump it will naturally fill the bottle, if the oil pump has let enough oil get down into the sump...could be made worse by bad rings, but even with good rings, the back and forth blowing and sucking (No double meaning there , boys!) of the air from the sump by the pistons moving up and down, will force any oil in the sump down or up a breather tube anyway, just depends how much oil was in the sump, as to whether the bottle would fill up, I'd say. Seems like the main problem would be the oil in the sump, and how it got there....I'd say Chris needs to change out the seal, maybe, get the oil pump looked at and see if the oil is too thin too....and amybe route this hose bottle mess into the oil tank where it can do no evil, like dumping a puddle under the rear wheel , like once happened to me, many moons ago......anyway....he ought to do something...and read the other foum too...it is the same subject....Best! Piperboy
 
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ah...to clarify.....the catch bottle is for the oil tank overflow pipe/breather. The crankcase breather is plumbed into the oil tank (which I mistated). So yes the overflow would indicate overfilling (the result of all the oil heading down to the sump) as we're all familiar with. As for the oil coming into the primary...the crank oil seal is of different make than my spare or other engine's seal, so I'll try replacing that. Still, I know I read somewhere(maybe in the tech manual) about a way to insure correct crankcase pressure. Will play with pressure valve too.

Thanks guys,
Chris
 

Anonymous

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Chris Barrett said:
Will play with pressure valve too.

Thanks guys,
Chris

what pressure valve...am I missing something or are you mistaken that the pressure valve on the oil pressure system would have something to do with it??? Think not, and there isn't a valve in the breather system, or???
 

ILLF8ED

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pressure valve

Several of us are using a PCV or brake one way air valve inline with the crankcase breather tube between the engine and oil tank. This is to prevent expended crankcase pressure being sucked back into the engine thereby creating a negetive pressure on the piston up stoke. This is suppose to help keep the engine more oil tight such as oil blowing through the crankshaft seal into the primary.

I've replaced this seal twice in the last year due to too much oil pressure in the crankcase from wet sumping. I'm more religious now about draining the crank if it's been sitting for a week or more. I lapped the pump body recently, but it hasn't stopped the sumping.
 
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Breathers and wet sumping

Greetings,
What we have here is two overlapping problems.
First the engine breather system:
As the pistons rise and fall, 750cc of air must go in and out of the engine case. Of course, this really only happens at kick-over speed. After starting there isn't time for all the air to get out or all the air to get back in. So you end up with a pulsating + to - in-case air pressure. Early Commandos had timed breathers on the end of the cam, later bikes had breathers on the back of the case, and later still bikes included the timing case. With healthy rings and under normal operating conditions, not too many problems. Some, myself included have tried to improve the system using some sort of PCV valve and/or the addition of other vent holes in the engine (such as the inlet rocker cover).
The problem comes when the oil in the tank seeps into the crankcase while your bike has been sitting. The variables are for the most part, worn/loose oil pump parts, and time. I suppose you could include oil viscosity too. If you run your bike daily you'll never have a problem. If you run weekly wet sumping may be occurring, but, you will probably never know it. Let your bike sit a month+, you could be starting your bike with the lower end completely full of oil.
If you kick it over slowly, you'll push the excess oil out whatever breather setup you have (and maybe on to the ground, air filter, or catch bottle depending on your routing). If your a 250lb gorrilla and jump on the kicker you could possibly blow out the left crank seal and dump oil into your primary case.
During the coming season I plan to start parking my bike on the center stand and pull the crank drain, then using a measuring cup I see if I can determine the rate of oil leak-by (for my bike).

justa thought,
G.B.
 

Anonymous

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wetsumping etc

Fit one of my antidrain valves to your Commando or Atlas and the wetsumping is over - forever! See: www.britishclassicbikes.de

To cure the leaky seal on primary side: fit a metric double lipped seal. The crank is metric anyway (30mm) but the case needs to be machined.
Fit a oneway valve (reed or ball) in the engine breather. Drilling of heads inlet cover will not help - how can it when the only way for crankcase pressure to get up there is the oilbore in the back of the right cylinderbore (which is more or less filled with the oil draining down from inlet valves) or up through the cam followers chamfer (which is more or less filled with the oil draining down from the exhaust valves).
If a valve of some kind is fitted to the crankcase and everything else is in good order inside - no leaky problems should occure. For better seal of rings try Total Seal - much better than the british crap.

Cheers
HRD
Triumph 750 sprinter (blown), Norton Commandos 750/850, Norton featherbed racers 750/750, 650SS,500 Scrambler special, HRd special etc, etc.....
 

Anonymous

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Re: pressure valve

illf8ed said:
This is to prevent expended crankcase pressure being sucked back into the engine thereby creating a negetive pressure on the piston up stoke.

Dumb question....this can't function. If you only let the air OUT of the crackcase and stop the air flow from the oil tank back into the cases, you will set up a hefty vacumn each time the piston goes up and how can this be good? A vacumn will just as fast cause a leak in a gasket, as a pressure towards the outside will...either way, the gaskets get a load on them, and something has to give sometime. With the breather system unrestricted, the air is free to go back and forth and the pressure is relieved by this allowance and the gaskets have really no, or at least a balanced load. Mine just pumps the excess oil up the breather tube, and within a half minute or so, all is free, the pressure goes back and forth and all is happy. All this valve thing, will cause something to go bad...some seal or gasket...sooner than it would if you left it alone. Fix the oil draining into the sump problem, and leave valves and other toys out of the system...I've blown one crank seal in thirty years, and only because I used too thin a oil.....Peace
 

Anonymous

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This responds to the following statement made by "guest:"

"Dumb question....this can't function. If you only let the air OUT of the crackcase and stop the air flow from the oil tank back into the cases, you will set up a hefty vacumn..."

The crankcase check valve that illf8ed mentioned actually allows some amount of air to be drawn into the crankcase. And partial filling the crankcase reduces the volume and thus the pressure of the air that must be expelled from the crankcase on the piston downstroke. A minor increase in horsepower is also realized as a result of the decreased pressure.

Jason
 
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This post has become very complicated, what with maths formulas, valves here & there etc etc. We love to complicate matters sometimes.

I have been suspecting the crankcase oil that has been getting into my primary was finding it's way through one or all three of the inner primary mounting holes.

In fact I am certain of it & will be trying "plumbers tape" on the threads of the 3 mounting bolts. I suspect that the threads are worn out inside the drive side crankcase from taking the inner primary off & on over the years. 3 new helicoils is really what is required.

Maybe you could be looking at that possibility :?:
 
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That was my first thought, having seen those 3 do that before. They were quite dry, however and the crank end was very oily with oil surrounding the seal. Also the source of the leak can be summed up with the following formula where:

Primary Mounting Bolt = X
Crankcase Seal = Y
and
Oil = Z

Y+3X=Z+3X
Y+(3x-3x)=Z+(3X-3X)
Therefore
Y=Z
So clearly the oil was coming from the crankcase seal.
I hope this clarifies all the confusion within this thread....

Sincerely,
Chris Barrett
 

Anonymous

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Even Ray Charles can see that Y = Z!

Be careful with that Teflon tape ("plumber's tape"). It's excellent stuff if used sparingly but any excess may drift into the oil stream and plug up small passages.

Jason
 
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362
Jason, I actually have some "mechanics tape" & have taken note of your good advice. I have yet to plug up any oil passages using it.

It is a bit bit like the mechanics silastic, used sensibly it fixes everything when used in conjunction with a simple maths formula & making sure your bike is on the sidestand of course :!:

Saw "Ray" a week or so back & enjoyed the movie.
 

Anonymous

Guest
Jason said:
The crankcase check valve that illf8ed mentioned actually allows some amount of air to be drawn into the crankcase. And partial filling the crankcase reduces the volume and thus the pressure of the air that must be expelled from the crankcase on the piston downstroke. A minor increase in horsepower is also realized as a result of the decreased pressure.

Jason

Could make sense.....those things have been on cars for awhile...but as mine spews a fair amount of oil up, at each start...and has for years, I think the PCV would just make a blockage for the extra oil and cause problems...better to leave it as is.....Peace! PS someday I have to figure out just what to do to fix this sumping thing...in a couple of years, I won't be able to get this thing kicked over anymore if I don't....
 

Anonymous

Guest
Plumber's tape

Forget the plumbers tape. Replace the bolts with studs of the correct length. You can get them at any hardware store. One may have to be shortened, I don't remember. Loctite or Prematex them in, and there will be no oil leakage and the primary case will be held much more rigidly.
 
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well i found water in the bottom of my oil tank when i drained it today, hundred little balls of it which is too much, in my opinion - according to
http://images.google.com/imgres?imgurl= ... lAej-9jqAQ
yikes- hope that link works - its an oldbrit schematic of the Mk 3 oil and breathing pipes- ive got it plumbed according to the schematic but the line going from the front of the tank to the K&N is too little ,i believe, not pulling enough H2O out of the tank as it goes into the oil tank from the timing box - i was initially thinking about not sending the wet air from the timing chest to give it a chance to pollute the oil with water, but not sure now - but i think if i send a bigger pipe to the air filter itll scavenge "fog" from the oil tank better (mikuni 34 MM)(i plumbed a pipe into the K&N)-
 
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