Should I change the main bearing oil seal?

Flatspot · Sep 4, 2022

A year ago I left my mk2a parked up while we went away on holiday for 10 weeks. On our return it had wet-sumped and oil had bled past the main bearing oil seal into the chaincase. The oil seal was original and 47 years old. Unfortunately I hadn’t changed it when I fitted a CNW electric start and belt drive etc. Thankfully the oil leaked out of the air slots on the inner chaincase and never reached the belt.

I stripped it all down, cleaned up the slight mess, and fitted a new seal. Note to self don‘t let it wet sump again. This was last November/December time.

All was well up until Feb. 6th this year when I had my heart attack. On my escape from hospital I wasn’t able to do very much for a while, I wasn’t permitted to drive a car, let alone ride a bike, and of course it was brrrr cold. So it stayed in the garage.

Knowing I was having open heart surgery in May I needed to get out for a ride, just in case I didn’t get the opportunity again. So I took out the T160 and Commando and emptied both of engine oil and suitably labelled the bike and keys “no oil”.

Then about 6/7 weeks ago I needed to get out and about on the bike as summer was nice and warm, and I was now feeling up to it again. So I filled the Commando and went riding. I went on several rides, not long but enough to know I’d still gone somewhere.

Then I left it for a few weeks and went to go out the other night. I checked the oil level and saw it was empty. It’s wet sumped once more. Ohbuggerit!

Rather than drain the sump by the sump bolt I decided to simply turn it over by the starter motor to get the oil back into the tank. It worked a treat and the tank was quickly refilled. Lots of oil came up the breather as well. Perhaps I should have stopped? But it cleared and all seemed well.

I turned on the fuel, started it up and it was all fine, oil was returning correctly, there was no smoking or anything to make it appear that I’d done something wrong. I went for a ride and all was well. Barring a couple of drips of oil from the n/s front. I wiped it up and went out the next night and again all appears to be OK.

Now I’m about to go away once more for a couple of months and so I have once more drained the engine oil, and I saw a couple of drops of oil at the front of the chaincase. That’s not good as it’s supposed to be dry!

I removed the casing and a half teaspoon of oil came out, obviously past the crank oil seal. Apart from that it was totally dry inside.

Now to the question, of what to do? Has my decision to spin up the motor when full of oil pressurised a little past an otherwise perfect seal damaged it enough to require replacing? Or is it going to be OK and don’t do something stupid like that ever again? The motor has done a genuine 11,500 miles and I’ve been responsible for the last 1500 of them with no ill effects

cliffa · Sep 4, 2022

Do you have the Comstock / NYC sump plug breather fitted? If not I can highly recommend it, as it will return wet sumped oil to the tank very quickly. If you don’t it’s possible the seal did pass some oil when cranking with a full sump, but it may not leak under normal operating condition.

Nortoniggy · Sep 4, 2022

Oil can get past the set screws that hold the inner primary chaincase to the crankcase so good idea to try and be sure it is the seal before changing it. Particularly as you have recently changed it. You can use sealant on the screws.

MichaelB · Sep 4, 2022

If you do go and change the seal, I probably would, add this oring the crankshaft.
Simple, yet brilliant.......

Cheap & easy solution for wet sumping problem

Here's what I think is the easiest, cheapest solution for the wet sumping problem which can blow your PTO mainseal by inverting the lip when firing up with too much oil in the sump (causing too much pressure against the main oil seal). A simple 1/16" cross section oring of 1-1/16" ID fits best...

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Lineslinger · Sep 4, 2022

I had the same idea as you did when I installed the CNW electric starter.

If I just turned the engine over a few time via the starter motor but pull the plug leads so it can't fire, it should pump the oil that has leaked down into the sump back to the tank.

But, before doing so I ran the idea by Matt.
His reply was quite clear. Drain it using the sump plug. The seal can be damaged aka ruptured by the pressure buildup of pumping the oil out to the sump and back to the tank via starter motor.

If you have already installed the CNW E start pulling the components and installing a new seal is not that big of a deal. You really already know how to do it.
And, are you ever going to be comfortable riding wondering if you are getting oil blowby via faulty seal into your primary case and oiling up the drive belt?

I am a real neatnik when it comes to engines/mechanicals. No leaking allowed. Even a couple of spots of any fluid on the garage floor get me all bent out of shape..

Flatspot · Sep 4, 2022

cliffa said:
Do you have the Comstock / NYC sump plug breather fitted? If not I can highly recommend it, as it will return wet sumped oil to the tank very quickly. If you don’t it’s possible the seal did pass some oil when cranking with a full sump, but it may not leak under normal operating condition.

No, but I have the AN sump plug with the removable drain that I should have used! There won’t be a next time.

cliffa · Sep 4, 2022

Flatspot said:
No, but I have the AN sump plug with the removable drain that I should have used! There won’t be a next time.

In case you aren’t familiar….

Reed Breather Kit

The Norton twin cylinder engine creates a serious amount of pressure in the crankcase as the motor spins. Over the years the factory attempted several methods to reduce this pressure – from a timed breather off the end of the cam on earlier motors, to a crude straight pipe from the timing chest on

nycnorton.com

No crawling around on the floor and oil leaks a thing of the past.

I have no affiliation, but consider this to be one of the best upgrades available.

Bonzo · Sep 4, 2022

cliffa said:
In case you aren’t familiar….

Reed Breather Kit

The Norton twin cylinder engine creates a serious amount of pressure in the crankcase as the motor spins. Over the years the factory attempted several methods to reduce this pressure – from a timed breather off the end of the cam on earlier motors, to a crude straight pipe from the timing chest on

nycnorton.com

No crawling around on the floor and oil leaks a thing of the past.

I have no affiliation, but consider this to be one of the best upgrades available.

Order now in time for Christmas

Tornado · Sep 4, 2022

I agree with confirming leak is not at the inner primary attachment bolts. I have had an original 47 yrs old seal split from the outer ring, due to starting with a wet sump situation. I have heard the seal ring can also be forced out of the casing and some suggest using locktite or epoxy to better secure it in the bore.

If OP is only getting a half teaspoon of oil after bike was sitting (weeks/months) then hardly worth worrying much (unless this is considered significant for belt drives?).

gortnipper · Sep 5, 2022

Flatspot said:
A year ago I left my mk2a parked up while we went away on holiday for 10 weeks. On our return it had wet-sumped and oil had bled past the main bearing oil seal into the chaincase. The oil seal was original and 47 years old. Unfortunately I hadn’t changed it when I fitted a CNW electric start and belt drive etc. Thankfully the oil leaked out of the air slots on the inner chaincase and never reached the belt.

I stripped it all down, cleaned up the slight mess, and fitted a new seal. Note to self don‘t let it wet sump again. This was last November/December time.

All was well up until Feb. 6th this year when I had my heart attack. On my escape from hospital I wasn’t able to do very much for a while, I wasn’t permitted to drive a car, let alone ride a bike, and of course it was brrrr cold. So it stayed in the garage.

Knowing I was having open heart surgery in May I needed to get out for a ride, just in case I didn’t get the opportunity again. So I took out the T160 and Commando and emptied both of engine oil and suitably labelled the bike and keys “no oil”.

Then about 6/7 weeks ago I needed to get out and about on the bike as summer was nice and warm, and I was now feeling up to it again. So I filled the Commando and went riding. I went on several rides, not long but enough to know I’d still gone somewhere.

Then I left it for a few weeks and went to go out the other night. I checked the oil level and saw it was empty. It’s wet sumped once more. Ohbuggerit!

Rather than drain the sump by the sump bolt I decided to simply turn it over by the starter motor to get the oil back into the tank. It worked a treat and the tank was quickly refilled. Lots of oil came up the breather as well. Perhaps I should have stopped? But it cleared and all seemed well.

I turned on the fuel, started it up and it was all fine, oil was returning correctly, there was no smoking or anything to make it appear that I’d done something wrong. I went for a ride and all was well. Barring a couple of drips of oil from the n/s front. I wiped it up and went out the next night and again all appears to be OK.

Now I’m about to go away once more for a couple of months and so I have once more drained the engine oil, and I saw a couple of drops of oil at the front of the chaincase. That’s not good as it’s supposed to be dry!

I removed the casing and a half teaspoon of oil came out, obviously past the crank oil seal. Apart from that it was totally dry inside.

Now to the question, of what to do? Has my decision to spin up the motor when full of oil pressurised a little past an otherwise perfect seal damaged it enough to require replacing? Or is it going to be OK and don’t do something stupid like that ever again? The motor has done a genuine 11,500 miles and I’ve been responsible for the last 1500 of them with no ill effects

I had the same thing happen, and I thought it was the crank seal as well. I had not installed the new one with the CNW kit as I had a Maney seal in that was only a few years old and it looked good when I installed it.

When I pulled the belt drive off and it still looked good and I did not see an oil leak up high or inside - it was outside the chain case only. I checked the chain case mounting bolts, and sure enough I could get about 1/6 turn on each one of them, so I pulled them off and re-installed with black RTV and did not get a weep again.

Should I change the main bearing oil seal?

Flatspot

cliffa

Nortoniggy

MichaelB

"Sons of Arthritus"

Cheap & easy solution for wet sumping problem

Lineslinger

Flatspot

cliffa

Reed Breather Kit

Bonzo

Reed Breather Kit

Tornado

gortnipper

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