Skip to main content
000000 000003 000006 000009 000012 000015 000018 000021 000024 000027 000030 000033 000036 000039 000042 000045 000048 000051 000054 000057 000060 000063 000066 000069 000072 000075 000078 000081 000084 000087 000090 000093 000096 000099 000102 000105 000108 000111 000114 000117 000120 000123 000126 000129 000132 000135 000138 000141 000144 000147 000150 000153 000156 000159 000162 000165 000168 000171 000174 000177 000180 000183 000186 000189 000192 000195 000198 000201 000204 000207 000210 000213 000216 000219 000222 000225 000228 000231 000234 000237 000240 000243 000246 000249 000252 000255 000258 000261 000264 000267 000270 000273 000276 000279 000282 000285 000288 000291 000294 000297 000300 000303 000306 000309 000312 000318 000321 000324 000327 000330 000333 000336 000339 000342 000345 000348 000351 000354 000357 000360 000363 000366 000369 000372 000375 000378 000381 000384 000387 000390 000393 000396 000399 000402 000405 000408 000411 000414 000417 000420 000423 000426 000429 000432 000435 000438 000441 000444 000447 000450 000453 000456 000459 000462 000465 000468 000471 000474 000477 000480 000483 000486 000489 000492 000495 000498 000501 000504 000507 000510 000513 000516 000519 000522 000525 000528 000531 000534 000537 000540 000543 000546 000549 000552 000555 000558 000561 000564 000567 000570 000573 000576 000579 000582 000585 000588 000591 000594 000597 000600 000603 000606 000609 000612 000615 000618 000621 000624 000627 000630 000633 000636 000639 000642 000645 000648 000651 000654 000657 000660 000663 000666 000669 000672 000675 000678 000681 000684 000687 000690 000693 000696 000699 000702 000705 000708 000711 000714 000717 000720 000723 000726 000729 000732 000735 000738 000741 000744 000747 000750 000753 000756 000759 000762 000765 000768 000771 000774 000777 000780 000783 000786 000789 000792 000795 000798 000801 000804 000807 000810 000813 000816 000819 000822 000825 000828 000831 000834 000837 000840 000843 000846 000849 000852 000855 000858 000861 000864 000867 000870 000873 000876 000879 000882
English French German Italian Spanish

Navigator oil problem


So after last Saturday´s ride which ended in an oily mess around the bottom of the bike I followed Nick´s advice to check the oil level. Oil tank was almost empty. I did not shut my anti wetsumping valve and this is what came out the crank case:

Oil sump


As mentioned this was since Saturday! 5 Days. What could be wrong? Oil pump totally worn out or did I mix up the hoses from and to the engine?

I looked into the chainguard where the vent hose from the oil tank ends:

vent hose


It looked clean so the oil must come from somewhere else.

The chain looks messy so maybe the gearbox seal?


This is the rearside of my oil tank:

back of oil tank


I guess I mixed up the hoses from the (early) breather and the oil mist hose running  towards the chainguard. The bigger one is the breather hose in my case and the smaller one is the mist hose.

So I guess the oil is routed directly into the crankcase? That´s why it was full of oil?

The breather hose should be on the left and the mist hose on the right. according to this diagram found in the online Lightweight compendium:

oil diagram




Hi Ulrich, I can't see how mixing the breather and mist pipes up could cause the wet sumping although it could cause excessive lubrication of the chain - I've made that mistake in the past and it had that effect.   All my Lightweights have wet sumped to a greater or lesser extent but no where near as much as that and not that quickly.   Did you recondition the oil pump or replace it with a new one when you rebuilt the engine?   Excessive oil pump wear will allow oil to drain back down into the sump like that.   Checking or replacing the oil pump is a reasonably straight forward job but does require taking the timing side cover off which inevitably means retiming the engine I'm afraid!   If I am doing that job I always remove, check and clean the oil pressure relief valve and it's gauze filter and replace the crank shaft oil seal and the one behind the points (making sure they are the right way round!).   The other cause of leaking round the drive sprocket is the oil seals behind the gearbox sprocket and clutch - a check of the gearbox and primary chain case oil levels will give you a clue to whether that is happening.   Another less obvious one is a leaking crankshaft oil seal on the primary side - that allows engine oil and piston blow by to leak into the primary chain case pressurising it and forcing oil past the oil seal behind the clutch with the effect you have seen.   When I first got my Navigator I had oil leaking from round the gearbox sprocket and I had to replace all three of those seals to cure it.   Sorry that all seems negative and extra work but since I replaced all those seals my engine has stayed remarkably oil tight - it can be done!   I hope that helps, good luck and keep at it, the Navigator is a great little bike once you have got it settled down!   Nick      


You´re right Nicholas. Wetsumping is not caused by mixing up the hoses. I did recondition the oil pump.I have a spare one in my boxes somewhere. I will have a look at this also. I also renewed all the seal inside the engine. Maybe they leak now because of the pressure caused by the oil in the engine?

oil pump

Maybe there is something blocked inside the oil circulation so that the oil is not transported back into the oil tank properly. I did check and topped up the oil before I went for that ride on Saturday.

Well, opening the timing side again and check the pump, seals etc.

In reply to by ulrich_hoffmann


Hi Ulrich

 Before taking things apart I would measure the scale of the problem. I  Would drain the sump, fill the oil tank to normal and measure the wet sumping per day for  a week. This is good information that lightweight owners might want compare to their own bikes for comparison. This would identify what is is average and what is excessive and how it compares with the wet sumping that occurs after fitting a new oil pump. I have found this useful for managing wet sumping on my own bike. For me wet sumping is not too big a problem in the summer if I use the bike a lot. Depending how long I store the bike I drain off the sump before using, it`s a pain but it is manageable problem.



Graham, your comment came too late!

I opened up the timing side today and this is what I found:

Pint of oil

About a pint of oil came out when I lifted the cover.

I removed the oil pump and I spotted something !

no oil pump

Have you seen it?

Here is a better picture:

blocked oil hole


The return hole for the oil pump is blocked by a blob of silicon sealant!


Here it is:

The Blob!


Ran out of time to test the bike and had to buy some oil. Stay tuned!



Another thing to look at is the sump plate & gaskets at the bottom of the engine, and that the oil return hole is not closed or blocked by gasket cement/silicon. Its a common mistake that is easy to make. Oil comes down to the engine - but cannot get back - except via the breather.

The oil, after use, drops to the bottom of the engine onto the sump plate via a strainer, then towards the timing side, where a pipe sucks it up to the pump - which pumps it back to the tank & rocker box.

There may be an article about this very subject in a Roadholder shortly....

The picture below shows such an instance of a blockage.

Blocked Oil Return


I see you found the problem! It was the same as I suggested .... but the blockage had moved!

You still need to check that all is OK in the area of the sump plate.

I use paper gaskets if possible held in place with goo  to one side. I nip the components lightly together and leave to cure. I then remove the components and trim up. This enables the gakets to be re-used and allows the flexibility in the junction to adapt to imperfect mating surfaces when finally nipped tight.



Yesterdays and todays self isolation task was putting together the timing side, re-torqueing the head,

filling up oil and make a test ride.

I was surprised how much I could tourque down the heads! Some nuts really felt very loose!

After that I adjusted the valve clearances.

One bolt was too loose:

oil bolt

Luckily I had a spare one at hand!

I used two paper gaskets and sealant for the rocker covers and filled up the oil.

2 continental litres. The oil level was 2" below the filling hole as Nick suggested. I swapped the two vent hoses and started the engine. Some anxious seconds later the oil was flowing back in the tank.

After some rides around the block there was still an oil leak from the left hand rocker oil bolt and from the bottom of the gearbox cover. I carefully tightened the according screws .

Will take the bike for another ride tomorrow.



Well done Ulrich, having the time to fettle the Navigator is a positive of the lock down!   It always surprises me how much you need to torque down head nuts after the initial running in period which proves why it is so important and worth all the work to expose them.   The healthy oil return sounds very promising and something I obsessively check, the dreaded silicone sealant blockage is always worth having at the back of your mind.  Lets hope that has cured your oil leak problem and you can now enjoy a successful running in period.  Keep us posted!    Nick  


Beware of too much pressure when torqueing down the head nuts.

The book states 15 foot/pounds (15ft/lb). DO NOT EXCEED THIS!

Google tells me the Metric Equivalent is 20.34 Nm - (I hope that is correct).

Remember to do all 6 on each head in the proper sequence, to avoid distorting the heads.

Head Tightening sequence


Wise words Andy, I so wish I had owned a torque wrench back in the 70s and 80s, it would have saved me so much wasted effort, hard won cash and heart break!  


A good friend of mine taught me to use wellseal applied with a paint brush on one half of the case - does not matter which, apply gasket then wet exposed surface with grease or oil, then wellseal the mating face with paint brush. Oil helps the gasket come away when disassembling. The advantage with wellseal is it will not block oilways, as seen from above pictures it takes a very small amount of goo to cause a real pain. Seems a bit old school but very satisfying and seems to me it cant go wrong. I have also come across an article the suggests use of silk thread and wellseal. I used that for my crankcases - dry so far. Though I have leaks else where ;-)


Regardless of what it tells you on the tube silicon sealant has no place in the rebuilding of engines. Invariably people use vastly to much sealant, with silicon this is a recipe for disaster and can lead to a blown up motor ,which I've seen . Silicon is for bathrooms.                 Far better is Wellseal, like a thin varnish, petrol proof and non hardening, applied sparingly with a small artists brush it works, I've  never used anything else.


Norton Owners Club Website by White-Hot Design

Privacy Policy