Oil not returning to tank

Sounds like the pump conical seal is missing for a start.May be other issues,but replace that and try again.

Hi Oliver,

Providing your engine has the large sump plug, remove the sump plug and check for 'debris' blocking the filter in the sump plug. The oils return journey starts here. Also worth checking if any 'sealant' has made its way into the drilling going up to the pump.

Before stripping down, can I suggest that with the oil back in the tank, you try removing the oil pipe that goes from the engine to the oil filter at the filter end.  With a tray under the bike, briefly run the engine and see if any oil comes from it. foam and intermittent spurts are ok. If oil gets there, then refit that hose and remove the other  one from the filter. Does oil still flow? If not then the issue is with the filter.

If you get as far as removing the timing cover to check the seal (this shouldn't stop oil returning, just not feeding the crank), then I would remove the oil pump and blow through the galleries behind with an airline to ensure that they aren't blocked.

If you are feeling really keen, do a search on here for 'oil pump servicing'. Straightforward to do, and may give you a clue as to where the problem lies. Prime the pump prior to refitting with oil (immerse in oil and rotate drive cog a couple of turns) will also help.

Regards,

George

Did you use the correct tool that screws onto the end of the cam shaft and guides the points oil seal smoothly onto the cam shaft end when you refitted the timing cover, if not it will leak. Rev counter leak at the engine can be cured by changing the whole drive to a Mk3 version, buy it from Andover Norton and ask if it will fit a 750 engine, mine was an 850 MK1. 

Good luck I'm sure you can sort it.

You didn’t mention physically checking if oil is returning to oil tank with engine running. That would be the first thing to do as it’s the easiest job. Remove seat , remove oil tank cap with attached dipstick and watch for oil returning from return pipe entering tank near top of tank.

Hi Oliver,

Regarding the filter,  the housing should have arrows for in and out on it. If the pipes are fitted the wrong way to the housing, then if there is a non-return or anti drain valve in the filter (rubber seal inside filter between small holes and element, visible through the small holes - some filters have them, some don't) it will do a very good job of restricting the flow. The flow direction through the filter should be through the small holes, returning via the centre threaded boss. 

Do hope your issue is something simple.

Regards,

George.

I've just looked at the AN site and it appears that their improved housing with oil seal is the only version offered for all relevant models. Looking at the page for 1972 models all that is offered is:

TACHO DRIVE HOUSING WITH OIL SEAL (06.1090)(06.5200)

part-no: 06.7254

£19.95 + VAT

https://andover-norton.co.uk/en/shop-details/16977/tacho-drive-housing-with-oil-seal-06-1090-06-5200-

Likewise, the old plain drive gear is now replaced by the items also shown on the Mk III page:

TACHOMETER DRIVE GEAR with Groove for O Ring (06.1089)

part-no: 06.5201

and

REV COUNTER DRIVE GEAR, SCROLLED (06.5201)

part-no: 06.1089/S

Both are a heady £39.95 + VAT. It's not clear to me (but perhaps a Mk III owner will explain) whether both of these are compatible with the housing 06.7254.

I assume that the new housing is compatible with the old-type plain gear that relies on a push-on O-ring. 

Can't help you on that side call AN they will give you the answer you need. I tried the double oil seal fix which did not work very well, mine being an 850 the replacement housing was the proper fix.

Oliver when I changed the oil on mine, filled with oil and started the bike with the oil filler cap off, the oil took a long frightening time to return, to the point where I nearly stopped the engine to check.

.. a long time to fill the filter hence the delay.

... is normal as the return side of the pump has double the capacity of the feed. So it sucks up all the oil from the crankcase then continues to pump whatever it finds in there which as you've seen is bubbly oil.

Glad things seem to be sorted out now. One thing to remember is not to leave the bike for several weeks, look in the oil tank and see it's low then top it up. Most Nortons wet sump to some extent or another so the oil will have migrated to the crankcase.

… an extent which may surprise and alarm the innocent.

A few days ago I measured the amount of oil that came out of the crankcase after my bike had been standing for exactly seven days — 500 cc !

They do seem to vary wildly however, from those like yours to those which can be left for months.

The majority of oil in the sump in the first 24 hours comes from the timing cover, so this will distort any levels taken after the first 24 hours, the amount collected over the 2nd and 3rd day / week is what is actually passing. 

With the Combat engine known for failure, I know of two occasions when the debris has blocked the return oilway to the pump. One owner even checked with a pipe cleaner and though because the it stopped from both directions it must be clear, but he was hitting just blockage at the change in direction. Always prove oil ways with oil, not wire. 

The lipped oil seal in the modified tacho housing will work on a MK3, but what some owners do on the MK3 is not fit the O ring on the tacho shaft, then try and fit the shaft through the housing turning the lipped seal inside out. Fit the O ring as normal and with both parts in your hand put them together carefully while you can see it go through the seal ensuring it does not turn the seal inside out and then drop both parts together into place. 

All 72's suffer from the sump filter not being present, it was not a Combat specific feature.