Ideas needed: I have a 1960 reg Norton Jubilee, mileages 37,000. It has been rebuilt from the bottom up, new bores ,pistons, bearings, original pump, then done 79 miles. An anti wet slumping pump has been fitted, it works ok on feed to pump but return to tank is weak. Pump stripped and is ok. Lapped on body to engine face and end plate to remove v light wear. Spindle sound , no float. Much smoke. Stripped , rings ok - no obvious blow by. Blew all return through to tank. Rings good, breather seems clear from tank back to engine but smoke increases with running. Plugs foul/stop Return :- 1) is it sufficiently primed ? if not how do you suggest priming it? Via rocker feed tube from T piece at tank base or? How to spot faulty crankcase breather?valve guides not hugely worn but excess rocker feed?? All suggestions welcome . Lastly is there a diagram and description of oil flow around the unit?
Obvious stuff first .... flow back from the engine will always be a bit “ spurty” as the return works harder than the feed. Also have you checked the feed to the head? - is all the oil going there rather than back to the tank?
Finally when you say you have fitted an anti wet sumping pump, is it different from the standard jubilee pump?
If too much, it can flood the rockers and the vacuum of the inlets is easily able to suck it down the guides giving a slow but steady increase in smoke levels. You can try blanking off the oil supply to the top end (if still a rubber tube, squash it shut with some mole grips) and see if the smoking diminishes. Don't do this for more than a few minutes else the cam followers may begin to run dry- not ideal on a lightweight. If the smoke does reduce, it suggests that there is too much oil going to the head. The Jubilee had a restricted oil tank fitting to push more oil up top, but with wear and tear it might mean you need less restriction?
Anti wet sumping valve fitted
My Jubilee crankcase breather had been blocked with what looked like car body filler by a previous owner. I did not know the breather existed and the filler was the same colour as dirty aluminium casting so not easily seen. I had rebuilt the engine with new seals and I could not understand why the primary chain case was filling with oil at an alarming rate. Someone on this forum suggested a build up of pressure in the crankcase was pushing engine oil past the crank seal and that I should check that the crankcase breather was not blocked. When I found out where it is supposed to be of course it was blocked!!
I drilled out the hole (at the top of the rear of the crank case behind the inner primary cover) and inserted an 8mm copper tube to lead away from the engine and attached a rubber pipe to take any oil away in the direction of the rear chain. I check periodically that the breather is clear by blowing back down the rubber pipe and expect meet little or no resistance. Since this fix the primary chain case no longer fills with engine oil.
- Think excess oil to head is certainly a possibility so thanks for that
Another thing that can catch you out is oil left in the silencer from when it was burning excess oil before the rebuild. The best cure is a long run to get the exhaust really hot. When the smoke stops, problem solved.
There is an oil flow diagram in the excellent Light Twins compendium, page 71 of the on-line document. Look under the 'Technical ',tab, 'Light Twins' and load the on-line document. Lots of good stuff in there.