Oil leak at exhaust port?

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Motown1

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I tried to attach picture but no luck!! Anyway, engine just rebuilt by reputable British shop, it’s a 73 commando 750 rebuilt stock. After a run Saturday...not hard, i noticed a little oil on my left pipe “SS” pipes. I cleaned off thinking just typical oil leaks from things being new and setting in. I ran the bike Sunday and did not. Notice any oil on pipe at all? Ride again today and had to throttle up “rolling hills” to the house and looked down and saw oil on pipe again! Not much but there. Stop bike on driveway and the bottom of the pipe at the exhaust port is wet at the threads and the lock ring. There is no oil on top of threads q-tipped to check for oil and dry. I looked around the base of the head gasket and it looks dry except for a real tiny bubble from the gasket sealant? Lols like they used a copper gasket. The plugs are dry and no oil smoke from exhaust. Any ideas? Thanks.
 
Go to the easiest ones first, re- torque cylinder head , then remove exhaust rocker covers, check tappets and clean all of gasket away with brass rotary brush, then check covers for flatness before replacing with new gasket. Then run engine again.
 
Sh—-t, I should have told I did re-torque head...slight turn on #3 and 2. it was very minute.
 
Bernhard said:
Go to the easiest ones first, re- torque cylinder head , then remove exhaust rocker covers, check tappets and clean all of gasket away with brass rotary brush, then check covers for flatness before replacing with new gasket. Then run engine again.
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Bernhard, if the entire area above the threads is dry, how does the bottom of the threads and the ring become wet? Or is oil coming internally out exhaust Port?
 
Not unless you did some porting work and broke through the top to the rockers/oil.
And/or porous head.
 
There was recent thread on this same sort of leak location. Turned out to be a minute seep from the rocker spindle cover that couldn't be seen on head area around the cover plate, but accumulated down around exhaust collar. Can also be from rocker cover and or the lower cover stud. Best to use locktite or thread sealant on those studs into head to prevent oil seeping up past threads and out. Are you running a reed valve breather or silimar?
 
Usually these leaks can be traced to the rocker covers or oil feed lines to the head
It's easy to be deceived by this especially when the oil is new
Copper gaskets can take a while to settle
How much oil are we talking?
 
If you really can't find any source of an oil leak externally
Take the exhaust off and look in the port
But if your plugs are a good colour and no smoking then I doubt you'll find anything amiss
 
Talc powder blown on suspect areas can help revel culprit as seeping oil wets the white powder.
Does anyone ever use that fluorescent dye common in car repairs for leak detection? My go to work light has a violet/UV mode for this sort of work.
 
Factory breather? I’m new to this so excuse my ignorance. I will double check all gaskets and use some foot powder. Not much oil...just a little over cautious since I spent money I will follow up soon.
 
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Motown1 said:
Factory breather? I’m new to this so excuse my ignorance. I will double check all gaskets and use some foot powder. Not much oil...just a little over cautious since I spent money I will follow up soon.
Click to expand...
I believe the '73 750 uses similar breather pipe as the 850....just a hose off the timing chest to the oil tank. A lot of folks have incorporated a reed valve on that line to the oil tank to help provide some negative pressure in the crankcase & rocker chamber....helps eliminate a lot of pressure related leaks. Here's a thread on this: https://accessnorton.com/NortonCommando/xs-type-reed-valve.29838/
 
I would check the rocker spindle covers .. oil will blow forwards on to the port... counter intuitive I know
 
Was the head rebuilt or new guides put in, but first find where the oil is coming from if it is coming out of your exhaust ports then remove your exhaust pipes and look inside the ports for sign of oil leak or cracks near the guides, could also be oil dripping from your lower valve cover studs, if they leak the oil will look like its coming from your exhaust ports, anyway find out where the oil is coming from first, the problem with oil leaks it can travel before it drips, hopefully it be something that needs to be tightening up or a stud that needs to be sealed, fingers crossed its something simple.

Ashley
 
Plugs are good, no smoking from silencer(s) leads me to think the oil leak is external.

The suggestions for external oil leak detection are all good. I'd be careful with the foot powder which may have corrosive chemical components, may be therapeutic for athlete's foot at body temperature, but which may react quite differently when mixed with oil and exposed to high temps, a bit out of my knowledge of chemistry (which I did well in college---45 years ago), others may be able to add some depth on this.

I suggest that you clean the engine with something like Simple Green then go for a ride. When you get back to your mother ship wad up a Kleenex put on an heat resistant glove and dab the spindle cover, rocker oil feed banjo then around the rocker cover. The Kleenex will show any oil it picks up. If no results get a Q-tip and probe between the head and barrel. If no results then same drill on the right side.

Best.
 
If you find the oil is coming out of your exhaust ports then I be looking for cracks around the exhaust guides, this has happened to me after new guides were put in my head by a so called motorcycle head expert back in the 80s after 2 week of oil coming out of my exhaust ports he had to pay to fix his mistake but not fixed by him, not all are British bike experts, head had to be welded, ported and new guide put back in still running the same head today and still original valves.

Ashley
 
Bad news!!! Less than 100 miles and looks like a cracked guide or guide hole!!! Wet oil in exhaust track and you can see the green oil all around the guide!! Thanks all ...time to make a phone call
 
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