Breather pipe flow

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brxpb

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What would be a normal quantity of oil to come from the breather, it was flowing good and proper when I started the bike which I presume was some wet sumped oil, but I still can't really take the oil tank cap off after a while due to oil spraying and spurting out of the breather outlet in the tank. It has an xs reed breather fitted joined onto the rear crankcase breather housing, oil return pipe has trickle type flow but steady. I was going to tape a clear cap over the oil tank neck to see how it settles, what would be judged normal viewing. Any advice greatly received.

Paul.

P.s. it's a 72 750 combat, rear crankcase breather block.
 
"oil return pipe has trickle type flow but steady" worries me. Scavenge oil should be a strong steady stream. The oil coming from the breather, after any wet sump oil is purged, should be more of a mist than " oil spraying and spurting".

I suggest pulling the timing cover and checking the scavenge galleries.

Slick
 
That sounds normal for a Combat engine that has wet sumped. The oil is forced through the breather on your Combat engine to the oil tank until cleared. Other engines rely on the oil pump to do that job and the main seal can get blown out by the pistons slamming against oil. The same breather on your Combat engine allows the oil build-up at high revs at the rear of the engine a pathway out of the engine. My Combat engine was recently modified to move the oil pump pick-up to the rear of the engine but the rear breather (attached to a oneway valve) remains where it is as insurance. Note: oil returned by the normal breather circuit on your Combat engine to the oil tank is unfiltered.
Ta.
 
texasSlick said:
"oil return pipe has trickle type flow but steady" worries me. Scavenge oil should be a strong steady stream. The oil coming from the breather, after any wet sump oil is purged, should be more of a mist than " oil spraying and spurting".

I suggest pulling the timing cover and checking the scavenge galleries.

Slick
Click to expand...

Is the scavenge capacity of the pump greater or less than the feed capacity?
 
Oil retun to the oil tank should be a steady flow when running, as for the breather hose should be more air than anything, I run my breather to a clear catch bottle between the engine cradle (1ltr bottle) without a top so the bottle can breath, I also run the XS reed valve, after about 12 months of riding the catch bottle will only have a very small amount of oil in it (less than 50ml), but if I let my bike wet sump, which I don't, it would fill the catch bottle, but if I don't ride much I turn my oil off so it don't wet sump, but I ride it regularly so don't have wetsumping issues.
If you can't have the oil tank filler cap off to check the flow because it blows out oil then maybe you have your oil tank over filled with oil, you should be able to take the filler cap off without any oil coming out of the cap, it shouldn't spray out of it.

Ashley
 
Scavange side is double the feed, the oil return should normally be air and oil once the sump is clear so it either spurts or is oilwil obvious air bubbles.
 
Hi brxpb.
Trying rubber banding layer(s) of cling wrap around the oil tank filler hole and look to determine if the breather inlet is whipping up the oil as it is returned by the pump or continues to spurt from the breather constantly. Does your breather hose have a vertical alignment instead of diagonally? A oneway valve with vertical hose from your Combat's breather means air is pumped into a standpipe full of oil and will splutter constantly.
Ta.
 
Check that the screen in the sump plug is clear. (if you have the large plug type)

Slic
 
texasSlick said:
Check that the screen in the sump plug is clear. (if you have the large plug type)

Slic
Click to expand...

Not applicable for this question as a Combat engine does not have that large sump plug. A partial blockage in the scavenge galleries is valid as excess oil would then be returned via the breather circuit.
Ta.
 
my 2 Combats would send a solid pencil thick jet of breather hose back to tank for 30 sec or so, so hard could not get much above intial cold start idle or blew out cap but after about a min only pump oil return which was much less and more a layer on tank with some bubbles than Combat 2ndary return breather, unless reved up then sprayed out cap but breath only air not even mists, on these 2 non reed valve systems. Just general Combat info w/o knowing if instant case is Combat spec cases with a low down dirty breather feature.
 
brxpb said:
I still can't really take the oil tank cap off after a while due to oil spraying and spurting out of the breather outlet in the tank.
Click to expand...

Is the oil separator "foam" (and discs) still fitted inside the breather body? Probably not I would guess as I think the presence of the separator foam may help to reduce the amount of oil that gets blown back to the tank through the breather-and could also have a damping effect on the airflow which would reduce the spurting?
 
as a long shot, my Atlas oil pressure relief valve stuck in the closed position which built up too much pressure and INVERTED the crank seal in the timing cover which then swamped the crankcase.
 
An oil pressure gauge as a diagnostic tool would be of assistance for this question.
Ta
 
L.A.B. said:
brxpb said:
I still can't really take the oil tank cap off after a while due to oil spraying and spurting out of the breather outlet in the tank.
Click to expand...

Is the oil separator "foam" (and discs) still fitted inside the breather body? Probably not I would guess as I think the presence of the separator foam may help to reduce the amount of oil that gets blown back to the tank through the breather-and could also have a damping effect on the airflow which would reduce the spurting?
Click to expand...

L.A.B. I seem to remember removing the innards of the breather before fitting the reed valve, are you suggesting to try them back in, was that the original intention of the foam, to damp the airflow?

Needing, yes my outlet pipe is coming straight up off the reed valve housing, if I understand correctlly you are talking of the effect of pouring liquid out of a bottle, glugging while it is held upside down, pouring nice when it's tilted?

It doesn't help that my breather outlet doesn't go into the neck side on but has been modded by p.o. and now faces upward in the neck looking straight in your face with lid off. I was given some strange looks in our chinese takeaway yesterday only to get home and find I looked like Fangio after 60 laps with a dodgy oil cooler. Moral being: don't stare down my breather outlet with the engine running. :roll:
 
brxpb said:
L.A.B. said:
brxpb said:
I still can't really take the oil tank cap off after a while due to oil spraying and spurting out of the breather outlet in the tank.
Click to expand...

Is the oil separator "foam" (and discs) still fitted inside the breather body? Probably not I would guess as I think the presence of the separator foam may help to reduce the amount of oil that gets blown back to the tank through the breather-and could also have a damping effect on the airflow which would reduce the spurting?
Click to expand...

L.A.B. I seem to remember removing the innards of the breather before fitting the reed valve, are you suggesting to try them back in, was that the original intention of the foam, to damp the airflow?
Click to expand...

The "separator" would seem to have been put there intentionally to reduce the amount of oil that would otherwise be "blown" back to the tank through the breather line? I can only suggest you refit the separator innards and see if it makes a difference?


The fact that the breather outlet has been modified so it blows oil out of the filler obviously isn't helping matters-so why not do something about that?
 
Problem identified i.e. "...It doesn't help that my breather outlet doesn't go into the neck side on but has been modded by p.o. and now faces upward in the neck looking straight in your face with lid off..."
Fix this.
Ta.
 
Naw wait for something else to be a show stopper like winter as now ya know oil gets back to tank in spades - just leave cap on if running to test its sealing til weeps indicate cap cork gasket time.
 
Bob Z. said:
So what is currently connected to the fill neck pipe stub on your bike?
Click to expand...

The fill neck doesn't have a pipe stub. The previous owner seems to have altered the hump on the top where the tank breather stub is and shortened the neck of the tank, the engine breather is half inch copper pipe which is braised to the inside of the neck about 1/2" to 1" down from the brim, then travels through the inside of the tank and pokes out of the forward facing sloped part of the tank, again braised with about 1" left as the stub. 1/2" i.d. hose then goes to my crankcase breather. I am the fourth owner and I knew the two previous owners, the last one heavily modified the bike, most mods I came to understand why he had done them, to make what was a very practical daily hack, but this one mod has always defeated me, I always assumed it was perhaps to accomodate a non standard seat pan, it came with a cut down seat but I imagine several years of r&d were done before he decided on this option. Also on topic the oil return pipe when it comes inside of the tank is about 3/8" o.d. with a blanked end and several 1/8" holes drilled in the outer wall, perhaps to help frothing? I don't know.
 
Tried the bike this afternoon , used a freezer food bag rubber banded around the neck, oil was gushing out the breather outlet at start up but settled to just a random cough or splutter but mostly air, then with the engine still running I pulled the return pipe off and put it into a glass bowl and flow was definitely consistent and better than yesterday. I think the bike must be wet sumping faster than I thought. What started me looking at this is that I recently changed oil and filter and after a run I checked the oil and the level was right down on the stick compared to usual. I sure I put 2.8l in but I'm not sure if normally I just fill it till it's right on the stick. Is 2.8l correct amount or should you put a bit more if you've changed the filter as well.(screw on type)
 
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