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oil leak

Coxy

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Australia Mate !
Gday Mates
Greetings and salutations

Im seeking some help and aspirations about a problem on my recently finished K1 750 the gold one !

So the engine breather hose comes from the cylinder head cover down to a low part of the frame out to atmosphere [no other connection]
During a ride on Sunday I noticed the oil light flash
so on further inspection I saw a lot of oil all over the rear wheel and lower frame and was coming from the said tube/hose and the tank was pretty much empty
Freak out was my first reaction !!!
To be honest Im unsure where the hose should be run to and if that much oil should be coming from the hose so high on the engine anyway. the position of this hose is unknown to me as the manual I have is useless.Q.Is the engine under pressure due to a broken ring ect
The rebuild on the donk cost a packet yeh ?

so any thoughts please
Ya mate form down under
Coxy

PS Ive just finished a 1980 GS1000 not sure if you want suzuki pictures in here
 
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Was the engine rebuilt or is it the way you got it? No issue with the breather location, it is fine like that and is not the source of your issue. About the only thing that i can think of at the moment is you either have extreme pressure in the crank not letting the oil drain back down from the head or the drain backs in the head are blocked from sludge or debris. How much oil is in the crank case? There should be maybe a quart at the most...if it has several quarts then your scavange pump is working and not pumping the oil back to the tank. The oil pumps in the 750 are bad for getting air locked if you put them in the engine dry without priming them in a bucket of oil, or if they have been sitting empty for many years and the oil drains out of the pump. The scavenge pump pumps more volume then the pressure pump which will help to keep the crankcase pressure down, but if it is air locked it wont pump oil out of the engine and lead to no oil in the tank and pressure in crankcase. Just some thoughts and things to look into.
 
Gday Mate
Thanks Dirt Digger

How do I know how much oil would be in the engine as I have continually topped up the tank?
Just to up date that the engine is fully reconditioned by a bloke who does only cb750 engines
Would the air lock have remained after several months?
Is there a way to test out the theory
Can the pump be primed in position

I seem to be asking a lot of questions [sorry] but Id rather get it right rather than break something else
ITS a great bike and is going into its first bike show in a week or so

Thanks again for your input great advise seems to be right on the money
There is a lot of oil coming form some where
I have even run the breather hose up over the frame but that has not stopped the oil coming out
The mechanic said that some breather outlets have a type of re-stricter built in to the rocker cover [what about that ]

Coxy AU
 
No there is not supposed to be any type of restricter in the rocker cover, they are free flowing....you dont want to restrict the airflow, this is the only crank vent on the 750. This is a vent you should never get liquid oil out of this line, slight blowby gas is the only thing you should ever see.

There should never be more then 1/2 quart of oil in the crankcase, these are a dry sump engine...if you have a lot more then you have an issue.

You need to drain the crankcase and see how much you have in there. With the oil tank full and the engine running can you see oil circulating in the tank? Does the level stay about the same or does it empty the tank? Pull a intake side valve adjuster cap...is the valve cover full of oil when running for a while? It should never be full only oil splashing around.

I have bleed the oil pumps in the bike. I pull the oil return line off...not the supply line, and point it down into a container and start it up. Shut off as soon as you get oil squirting out then reconnect the line. It works most of the time.
 
No there is not supposed to be any type of restricter in the rocker cover, they are free flowing....you dont want to restrict the airflow, this is the only crank vent on the 750. This is a vent you should never get liquid oil out of this line, slight blowby gas is the only thing you should ever see.

There should never be more then 1/2 quart of oil in the crankcase, these are a dry sump engine...if you have a lot more then you have an issue.

You need to drain the crankcase and see how much you have in there. With the oil tank full and the engine running can you see oil circulating in the tank? Does the level stay about the same or does it empty the tank? Pull a intake side valve adjuster cap...is the valve cover full of oil when running for a while? It should never be full only oil splashing around.

I have bleed the oil pumps in the bike. I pull the oil return line off...not the supply line, and point it down into a container and start it up. Shut off as soon as you get oil squirting out then reconnect the line. It works most of the time.

Hi dirtdigger

Ok seems straight forward great advise
So there is only 1 [one] oil pump within the engine
looking at the manual diagram if there is only one pump then it must have some sort of restriction issue and looks as though it is serviceable from below
but ill try a few of those check measures first

Cheers Mate
 
Hi dirt digger

Seems straight forward great advise thanks
So I understand that there is only 1 [one ] oil pump in the engine
Looking at the manual diagram there are restrictions and valves within and is serviceable from below
But first I will do those a few tests
To measure the total amount of oil in the sump would the tank need to be drained first yeh ?
I dont feel its impossible to have too much information so I like to be well informed rather than a "trial and error method "

Thanks so much
Your old mate
Coxy
 
There are two pumps in one unit. The scavange pump that pumps the oil out of the sump into the oil tank...and also oils the transmission and the high pressure oil pump that lubes the engine itself. Yes you can pull the pump out with it in frame just remove the oil pan.

You do not have to drain the oil tank to drain the sump. There is a checkvalve in the pump that should keep the oil from draining out of the tank, but they do go bad and there is a guy that makes a rebuild kit for them.
 
You only can have pump wear problems if the engine has been running a while, any 'airlock' would have been an issue immediately. No restriction like said in the breather tube but there should be some baffling of some type to recover as much oil as possible before it hits the hose. The hose needs to go up a bit to do the same and then down but sounds like already that way. Past that you have scavenge side pump wear or the engine ring seal is dead to get too much oil or air pumping inside and then the oil pumps out of the breather due to too much flow of either one. The extra air leaking past the rings has to go somewhere.

Run a compression test, done correctly that should give some idea.
 
I have a 1972 CB750 that has developed an issue where I am losing oil out the oil tank breather.

All hoses have been removed and are clear to breathe through. All hoses are connected as per the workshop manual - i.e. crankcase breather correctly connected and clear, the small hose from the back of the oil tank to the rear of the gearbox correctly connected and clear, the oil tank breather correctly connected and clear. The engine is in good condition, and doing what a CB750 should - i.e. it runs sweet.

I have shoved a small LED light in the oil tank and had a good look around with a mirror on a stick, and all looks fine - vertical oil return pipe, oil / air separator, small-bore drain from the separator to the rear of the tank etc. Oil supply and return lines to / from the oil tank to the engine are good. When running, by lifting the oil tank filler cap and dip-stick, you can see the oil returning to the tank with some air bubbles - that is correct as the scavenge pump shifts about 125% of the volume of the pressure pump - so it will be shifting some air once the sump is empty.

I am almost out of ideas, and am now coming to the view that I may have used the wrong oil. I was using Castrol 15w50 'Active' 4T (suitable for four-stroke motor cycles with a wet clutch). The workshop manual says to use Castrol 10w40 GTX - but that is no longer manufactured. What I did (I think in hindsight as an error) was use a Castrol 10w40 'Power 1' 4T 10w40 - it is a semi-synthetic modern oil with detergent suitable for four-stroke motor cycles with a wet clutch - and I think it may be foaming. Is this possible and am I on the correct track to resolution?

The oil coming out of the oil tank breather is white and looks aerated.

H - E - L - P !

Any comments would be appreciated.

Best wishes, and stay safe,

Gary.
You only can have pump wear problems if the engine has been running a while, any 'airlock' would have been an issue immediately. No restriction like said in the breather tube but there should be some baffling of some type to recover as much oil as possible before it hits the hose. The hose needs to go up a bit to do the same and then down but sounds like already that way. Past that you have scavenge side pump wear or the engine ring seal is dead to get too much oil or air pumping inside and then the oil pumps out of the breather due to too much flow of either one. The extra air leaking past the rings has to go somewhere.

Run a compression test, done correctly that should give some idea.
 
I have a 1972 CB750 that has developed an issue where I am losing oil out the oil tank breather.

All hoses have been removed and are clear to breathe through. All hoses are connected as per the workshop manual - i.e. crankcase breather correctly connected and clear, the small hose from the back of the oil tank to the rear of the gearbox correctly connected and clear, the oil tank breather correctly connected and clear. The engine is in good condition, and doing what a CB750 should - i.e. it runs sweet.

I have shoved a small LED light in the oil tank and had a good look around with a mirror on a stick, and all looks fine - vertical oil return pipe, oil / air separator, small-bore drain from the separator to the rear of the tank etc. Oil supply and return lines to / from the oil tank to the engine are good. When running, by lifting the oil tank filler cap and dip-stick, you can see the oil returning to the tank with some air bubbles - that is correct as the scavenge pump shifts about 125% of the volume of the pressure pump - so it will be shifting some air once the sump is empty.

I am almost out of ideas, and am now coming to the view that I may have used the wrong oil. I was using Castrol 15w50 'Active' 4T (suitable for four-stroke motor cycles with a wet clutch). The workshop manual says to use Castrol 10w40 GTX - but that is no longer manufactured. What I did (I think in hindsight as an error) was use a Castrol 10w40 'Power 1' 4T 10w40 - it is a semi-synthetic modern oil with detergent suitable for four-stroke motor cycles with a wet clutch - and I think it may be foaming. Is this possible and am I on the correct track to resolution?

The oil coming out of the oil tank breather is white and looks aerated.

H - E - L - P !

Any comments would be appreciated.

Best wishes, and stay safe,

Gary.
Thanks for this. I don't think I have a compression ring problem (but a compression test will confirm one way or the other) as there is no fuming at all coming from the crankcase breather hose - that's the one that connects to the rocker cover. Any 'blow-by' from weak rings would (in my view) firstly exit the crank-case breather. I'll do a compression test and post the result. Thanks again for your reply and helpful comments. Gary.
 
When you remove the oil fill cap, do you hear and feel air pressure? Maybe the cap is not venting properly? Also, did you install the small oil orifices which limit the oil to the head?

These are shown in the parts diagram #6.
Partzilla Parts Diagram
 
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