Comet Blowing Out Blue Smoke after running slowly

[Matty]

Thanks - no I don't think it is sumping because the blue smoke only happens when the engine is hot and particularly after slow running, long tick-over or opening up after going down hill on light throttle. Sometimes there is no smoke even under these conditions. The bike is used most days and I have never had a sumping problem with it and it does not really use a lot of oil.

However have blanked off the feed to the cylinder but have only run for about 40 miles or so.

Bike has not siezed when driven quite hard, and smoke seems less, but need more time to prove if the cylinder oiling was a contribution.

Matty

 

[Howard]

Hi Matty

A bit of lateral thinking - is your breather working properly? Bit of a long shot, but it's easy to check and fix before getting involved in engine strips.

H

 

[Matty]

Thanks Howard - have checked and the breather is "puffing" as required. There is no smoke from the breather however which might suggest that there is not "blowby" between piston and cylinder.

It still smokes, much the same with the cylinder oil feed blocked, so I have now restricted the feed to the inlet rocker by inserting a metering wire of 0.030" diameter (which does not seem to be a very tight fit) into the modified screw used for the special clamp I have to secure the rocker aluminium bush into the head tunnel.
The metering hole should be 0.032, but I think mine is a fraction bigger, so with any luck some oil - and probably enough in the short term for a test - should get through to the rocker.

Will have a drive around Sunday to check for smoke and will keep an eye on the inlet rocker assembly to make sure no harm is being done.

Matty

 

[Matty]

Did about 85 miles and smoke seems much less with a restriction in the oil feed, so it is probably the inlet valve guide worn.
I gather there is a guide available with a seal built in - is this just a straight swop for the standard one please?

Also how critical is the oil feed to the rocker/valve area - there still seems to be plenty of oil in the area even with my much restricted feed.

Matty

 

[roy the mechanic]

Whilst oil is useful to the top-end, it's more important to the cam+followers. if the inlet feed is restricted, premature follower wear is to be expected according to Neville Higgins writing in mph in the '70's.

 

[Matty]

Thanks Roy - I had seen the Neville Higgins comment so had only restricted the flow and on removing the cap over the rocker, there was still oil in the rocker area. Presumably in operation oil will normally run down the push-rod onto the cam follower and then overflow onto the cam.

The "tappet" clearance still seems to be unchanged so I guess no damage has been done.

Have now put the original 25thou meter wire back.

Matty

 

[clevtrev]

Presumably in operation oil will normally run down the push-rod onto the cam follower and then overflow onto the cam.



Matty

Only when the engine stops. If you want to see what really happens, fit some see through windows, and see nothing but oil.