Found engine oil in primary, suspected leaky main seal.

Found engine oil in primary, suspected leaky main seal. The engine has been rebuilt a couple of years ago with a new seal. I pressurized the crankcase with low pressure air and found no leaks around the seal. I would think I would see air bubbles at the leak with soapy water. Why wouldn't that test work? Actually turned the engine over a little, the pistons must have been down.

Static test.

Dynamic is far different.

Have you been starting bike with a wet sump situation? I blew the main seal in two pieces doing that. First sign of problem was d10 or 15 min down road, rear tire oil coated as primary filled up and spat oil out the gearbox shaft opening.
A better test for your seal. Start bike with primary off and see if any oil starts to trickle down from crankshaft area. Better yet. Let bike sit a few days or weeks then do the above, as that will show wet sump pressurization if any.

The dreaded engine oil in the primary trick the oil could leak from a blown main seal or from the bolts that hold the inner primary case to the crank case, on the pre 75 the lower of the 3 bolts can leak engine oil up the threads of the bolts, I been caught out with that one but just use sealant on the threads will stop that and replace the main seal at the same time, I use a little JB weld on the outside edge of that seal when installing so it don't blow out, haven't had a problem since and that was over 20 years ago, easy fix but the need to pull the primary chain, ALT/Rota and sprocket to get to fix it.

Ashley

Just a guess about your test - When I rebuilt my N15's roadholders I put in too much fork oil and it seeped up and over the new seals. I fixed the oil level and the forks don't leak. So in a static state the oil would seep, but wouldn't leak under pressure in my fork's case. Perhaps a similarity there.

Not specific to your question but I just replaced my seal due to oil in primary causing a slipping clutch. The seal was fairly new, maybe 1K miles after rebuild, but on inspection I saw the bottom was not flush. There was seepage of oil with the bike on the side stand and oil in the sump. I know I put that seal in correctly, and think the cause was one time I started it with a sump full of oil and dislodged it. I learned to drain the oil out before starting as it was a big cloud of smoke. I had no previous Norton experience and learned fast. Bike has a new seal (prolly could have tapped old one in...) , clutch plates and refreshed oil pump and all is good.. for a while anyway.

concours said:

Static test.

Dynamic is far different.

Click to expand...

Static test did work.
pressurized the case, couldn't get any soap bubbles. I couldn't figure out why. Thought maybe the case was full of oil , but could not push the oil out by the air pressure. I was right, most of the oil was in the case, after I drained it I got bubbles around the outside of the seal. Took the timing cover off, and found the MK3 anti sump plunger stuck open.