Smokey Navigator

1) Is the smoke white or blue?

If white - the oil is getting into the exhaust after compbustion (suspect valve guide?)

If blue - its being burned in the combustion chamber (valves, guides or rings)

2) Compare both spark plugs - if one is sooty, means its either running rich, or burning oil.

3) Do a compression test - ideally both sides read the same, but your smokey side may be lower? If so, put a teaspoon of oil down the plughole & test the compression again.

If the reading is noticeably higher - then the rings may be suspect/broken - or a rebore is due.

If the reading did not change much, then the oil may be coming down the inlet valve guide. These bikes did not have seals on the inlet valves, but sometimes a knife edge was used to limit excessive oil down the guide.

Another guide is: when does it smoke? If it's at the bottom of a hill, when you open the throttle again - thats usually a sign of piston ring issues - as oil is being sucked up.

And - on a recently built engine its always possible that a piston ring got broken on assemly - easily done - or its been fitted upside down. One ring is usually a scraper ring, and as its name suggests, it scrapes oil off the bore. If fitted upside down - it pumps oil up instead. They are usually marked 'Top' to ensure they are fitted the right wasy round - but again, accidents do happen.

Good Luck!

Good parts for these bikes are getting hard to source . Be wary of condemming parts to the scrap bin unless you are sure they can't be used. 

Hi Nick,

About 3 weeks ago there was a thread Late Navigator Head Gasket. Read this through and there is some good advice about securing the heads. It seems that good threads, progressive tightening, sequence of tightening, and the maximum torque are all important.

Andy suggests you use the 'good cylinder' to compare with the smokey cylinder. If they are the same or very similar the problem may be worn valve guides. If a little oil raises the compression reading, it may be rings stuck in grooves, or ring/bore problem. If oil in bore does not raise compression, suspect valve seats or a valve tappet has no clearance and valve is not closing. Very hard to state a figure for a compression test. I suppose an 8:1 compression suggests 120 psi. theoretical maximum. Someone might have an idea.

If you contact your nearest branch secretary they might point you to someone nearby with lightweight manuals and experience.

Peter 

Good compression test readings - hard to give definitive answer, but:

1) To begin with, you should feel that there are compressions, but don't be alarmed if they do not feel verey powerful.

2) Most important - the reading should be the same both sides. Mine gives about 80psi on first kick - but you may get readings higher or lower

3) If one side (or both) are lower than you might expect, put a teaspoon of oil into the cylinder & try the test again. Remember, its the 1st kick reading you need. If one or other (or both) cylinders now show a much improved reading, then gases are escaping past your piston/rings. Inevitably, the more worn the engine, the greater the wet/dry difference will be.

Torque settings:

Big ends & cylinder heads are both the same - 15Ft/lbs. Although that may not sound much, do not be tempted to go higher - you run the possibility of distorting the cylinder heads. When tightening the heads, always use the tightening sequence in the manual. (I will post it later when home)

Hope that helps