Oil leak

[alans]

Hi, I have a 1972 750, my current problem is an oil leak just under the left side exhaust. Fairly major leak, about a dessert spoon full after 5 minutes. Your thoughts please

 

[maylar]

what kind of oil?

primary cover seal?

gearbox main seal?

 

[eskasteve]

A couple of things over the years that have caused me oil leaks in the area that you describe. (assuming that the oil is on the cylinder barrel)
1) Pesky valve cover. Solved with a new one with a smear of hi temp brake caliper grease on both gasket faces.
2) Oil migrated forward from the left rocker box oil feed banjo bolt. Hylomar sealant applied to the bolt threads and new annealed sealing washers.
3) Rocker spindle plate gaskets. Old friend Hylomar to the rescue once again.
4) Rocker oil feed line leaking. New oil line (Duh)
5) Now the one that involved the most work, a leaky head gasket. Many different ways have been outlined in this forum for improving the sealing ability. I've always used an old sports car racing trick of giving the new fiber gasket three or four coats of hi-temp aluminum spray paint. I also hand paint a couple of extra coats around the pushrod holes. Retorque the head a couple of times in the next 1,000 miles or so. 50 years of Norton ownership has proven to me that this method works. I've even done the paint thing on properly annealed copper head gaskets with the same no leak results.

 

[lazyeye6]

While the source of oil leaks on a Commando can often be baffling, the location you indicate strongly suggests that the giant o ring
gasket for the primary cover is leaking. Does the primaryhave the amount of oil in it that it should? Take out the oil level screw
and see if oil comes out (over filled). You really need to take it off and see what's going on inside the primary. If none or little oil
dumps out on removal, that is the source of the leak. Does your bike wet sump? A sump full of oil is prone to leaking through the
inner chain case via the threads in the crankcase's lowest of the 3 mounting screws. It could be that the crankshaft seal is leaking
badly, requiring replacement (possibly due to excessive crankcase pressure due to starting the engine with a sump full of oil).
Clean up the entire engine and see if you can better pinpoint the location of the leak.

 

[alans]

hi all, thanks for your prompt replies. I should have been clearer on the source of the leak. It is coming from the left side exhaust outlet. I appears to me to be leaking from the head / barrel joint. Would a blown head gasket be the problem? and if so, how?. Thanks once again

 

[ashman]

It could be a blown head gasket or the head needs to be retorqued as they are prone to leak at the pushrod area, or in some case it could be the lower stud that holds your rocker cover and leaks down where the head gasket is, so first thing to do is clean the whole area and to make sure where the oil is leaking from, retorque the head be my first step after cleaning, if all good there then check the rocker cover studs if leaking there pull the studs out and put some sealer on the threads before refitting, I have been fooled by these studs before thinking my head gasket was blown, another thing you can try is after cleaning sprinkle some telcum power in the leak area and start it up the oils will leave a trail on the powder and will tell you where its leaking from, and sometime you have no say at all and need to replace the head gasket, not a hard job if you know what you are doing.
If you are in Brisbane area or close enough I could help you out.

Ashley

 

[Tornado]

Also, consider fitting a reed valve breather to eliminate pressure pulses within the casings as these contribute to oil being forced out many places like pushrod passages and rocker covers.

 

[laurentdom]

I had the same issue a while ago. The oil didn't come from a leak at the head gasket level (thks to Jim Schmidt's method with the copper wires), but from the rocker oil feed banjo, and dripping down so that it appeared as coming from the head gasket.
Solved by installing a new set of annealed copper washers and re-torquing the banjo.
Not very much time and effort involved in investigating that cause, so worth a try I think.

Laurent

 

[dennisht]

I had same location of oil leak as laurentom. Could have swore oil was coming from head but alas it was from the banjo oil head feed, rear one. I could not see the oil coming down account motor was just rebuilt and oil was still very clear so could not see source. Put new head gasket on among other things before I figured it out. Betcha you have the same source of oil leak. Let us know.

 

[alans]

Hi all, thanks for the considered input. Had another, much closer look yesterday and bugger me dead it was the rocker feed line. New line ordered and will be back on the road again soon.

 

[baz]

Hi all, thanks for the considered input. Had another, much closer look yesterday and bugger me dead it was the rocker feed line. New line ordered and will be back on the road again soon.

Glad you found it