• Welcome to the forum website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Online Forum Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this forum website.

    If you have previously registered to use this forum website, you should log in now. CLICK HERE.

    If you have never registered to use this forum website before, please CLICK HERE.

Comet Blowing Out Blue Smoke after running slowly

Matty

Well Known and Active Forum Website User
VOC Member
My Comet had a new piston (VOC Low expansion Type) and liner about 3 years 9,000 miles ago. It had had the cylinder oiling hole drilled, though some people said afterwards this is not required.

It always seemed to have piston slap when cold, which I did not expect, but had allegedly been bored to the correct tighter clearances and seemed OK when I checked it. It is quiet when hot.

The exhaust valve guide was changed at the same time and the inlet looked fine so was left.

It runs fine but blows out quite a lot of blue smoke after running slowly but is clean when running on main roads, motorways etc.

The cylinder oil hole was drilled at an angle just below the lowest point reached by the scraper ring. Could this be in some way a cause of the oil use - which only seems to be about 500 miles per pint, but raises comments on the slow VMCC runs!!

Is it safe for me as an experiment to blank off the feed to the cylinder oil hole by sealing the feed to it from the timing cover to see if this cures the blue smoke problem please.

Matty
 

timetraveller

Well Known and Active Forum Website User
VOC Member
It's safe to blank it off but it might not be working anyway. You write that you drilled at an angle. There is a significant height difference between the feed at the rear of the liner in the crankcase and the height of the scraper ring. Normally a slot is milled into the rear of the liner. An angled drilling is not likely to have done it. Did you check the clearance of the piston skirt in the liner with a feeler guage at several places? Clearance should be about 3 to 3.5 thou. If not then you might have put a new piston into a worn or oversized liner.
 

Matty

Well Known and Active Forum Website User
VOC Member
Thanks timetraveller.
The new standard liner was bored by a Vincent specialist to fit the new low expansion piston and I think I checked the clearances at the time. The drilling from the "slot" has to be angled down by the way in order to get the oil hole to come below the lowest position of the scraper ring ( see page 65 of F.J.Griffin's Instruction Sheets).

Will try blanking the oil feed and if this doesn't fix the problem will pull the engine apart in Winter.


Matty
 

mercurycrest

Well Known and Active Forum Website User
VOC Member
I agree with everything Timetraveller says, but, add that you should check the intake valve guide. it sounds like you might benefit from a new guide with a seal.
Cheers, John
 

nkt267

Well Known and Active Forum Website User
VOC Member
Does it blow smoke at tickover or when revving at a standstill..If it does then disconnect the oil return to the tank at the head pipe union and divert the hose into a can.If the smoke clears very shortly after this then it will be the guides at fault.Don't run it for too long like this though.John
 

david bowen

Well Known and Active Forum Website User
Non-VOC Member
put metering steel wire in the ET100 rocker feed bolt one of the engine guy can tell you the thickness of the wire I think .032 but check and go for a run and see if this helps
 

Matty

Well Known and Active Forum Website User
VOC Member
Thanks all I will try out your ideas above before taking the head and barrel off.
It only seems to blow out the smoke after ticking over for a while or after slow running.
When/if I remove the head it should be pretty obvious from oil on the back of the inlet valve if the guide is the problem - in which case I will fit a guide with a seal and perhaps a new valve as well.

Matty
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello Matty, My Comet smoked bad, Thought I had blown it, Put 40 grade oil in it and made it a lot better, If it was IN valve or piston I would have thought it would show on plug, If the plug is clean it might be EX guide and may be fixed by wire like David says, Good Luck Bill.
 

Tug Wilson

Well Known and Active Forum Website User
Non-VOC Member
Hi all, thought hole measured approx 32 thou? I believe max of 20thou was fitted originally but you could try 25? In the "books" if it's guides then the smoke starts after initial running not immediately on start up. My Comet actually does this but I am waiting for winter to strip and check. (Won't be long!)
 

deejay499

Well Known and Active Forum Website User
VOC Member
I guess it is not sumping, but a lot of oil in the sump will make it smoke for a while. Take the drain plug out and see how much comes out.
 
Warning! This thread is more than 11yrs ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Top