E: Engine Oil Consumption: 100 Miles Per Pint…

[lee_812d]

That is the usage for my Series C Comet over the last 1200 miles.
Only engine mods since the 60s (when the bike was last run) is steel idlers, locking feed bolts and changed some oil lines. Changed the oil and filter and made sure oil flowed from quill to sump etc, but no strip down and deep clean. I'm using Castrol GP50.

The exhaust is extremely oily with black oil and just recently started to smoke a lot.
About 100ml (4oz) of oil per 100 miles migrates to primary case
I have tried with and without metering wires, they are currently in. A lot of oil in the rocker tunnels, more in the exhaust side .
It currently has oil restriction disk on cylinder feed.
In the 60s the oil return was modified to T off to go both direct to tank and off to the exhaust then inlet feed. I've tried with this and the original Vincent layout.
Spark plug looks on the dirtier side of ok but not covered in oil or soot (NGK BP6ES currently)
125psi compression, ~10% leak down from the rings as far as I can tell (piston at bottom)
I used some Seafoam about 200 miles ago and this increased the compression from ~110psi but it's probably since then it's started smoking. Smokes a lot once hot and at idle - it didn't smoke much at all 1200 miles ago (exhaust system was clean and new).
Checked breather timing, can't see oil dripping from there. There are a few minor weeps here and there but nothing to cause much loss. Most seems to be in the exhaust and then primary.
Other than that, it seems to run great, idles nice and does 70-75mph on the flat, 80 down an incline.

Would I be justified stripping the engine to look inside?
What do all these symptoms suggest is wrong, one thing or everything?

Lee

 

[timetraveller]

Suspect the piston rings. It's been sat for sixty years.

 

[Bill Thomas]

Morning Lee , What oil do you use ?,
I like single grade oil 30 in the winter 40 in the summer ,
I have a lovely old Comet which runs fine and goes well,
But has smoked for a long while, To good to strip out,
I am too Old and Don't want to spend a lot,
So I use 50 !!,
I used to race it some times, So the engine is Race spec',
ie lots of piston clearance.
Cheers Bill.

 

[vibrac]

Justified!
Of course! strip the poor thing put it out of its misery

 

[Bill Thomas]

If it ain't broke -----------.

 

[lee_812d]

I use GP50. I siphon what's in the primary case out or will end up on the garage floor anyway. It's a bit wasteful.
Bill, how much oil does yours use?
I've seen some pictures on here of really oiled plugs - I can't believe mine are clean with this amount of oil being burnt. Unless it's going via the exhaust guide straight out of the exhaust.

"if it ain't broke" and "if it idles as well as that, can't be much wrong with it" are my dad's phrases!

I'm sure it's justified - even for curiosity. And I'm quite young, only in my 50s.

 

[Bill Thomas]

Hello Lee, Probably the same as yours 100 mile to the pint,
But I don't go far,
My plug gets a little oily, So I might change it every year.

Maybe you have a breathing problem ?,
The standard one is rubbish to me,
But others like it,
To me a breather pipe should go UP , As high as poss' , And be BIG ,
As an old racer I use a 3/4" breather pipe going into a car seperator,
Off the front tappet adjuster cap, The "D" had a cap with a big hole for a pipe to go on it,
It's just a plastic thing with offset holes and a gause inside,
I was a car mechanic and they used them on old Hillmans,

Trouble is I have seen blokes take a bike apart and be 3 to 10 years before it's running again !,
I don't have that time !, Or money !, I am only 75 ! ,
It's never just one thing, These bikes have been around the block a few times !!.
Good Luck, Bill.

 

[ClassicBiker]

A couple of years back my Shadow started smoking very badly all of a sudden. I had decent compression and a leak down test on both cylinders didn't indicate much loss. So after warming up the bike and smoking out all the mosquitos in the yard, I temporarily bypassed the oil return to the valves and sent it straight back to the oil tank. The smoking stopped after a minute or so. When I replaced the oil feed to the valve gear the smoking started again. That told me where I needed to look, at the heads. I removed the exhaust and carbs and shone a bright light up each port to see what I could see. I never bothered with the looking up the front carb, as it is on the left side of the bike and the other three are on the right, soon as I looked up the rear exhaust port I found the problem. The lower exhaust guide was no where to be found. I then pulled the rocker assembly out and saw what remained of the retainer ring, but not the top of the lower valve guide. I had removed the exhaust and silencer as a unit. So I separated the pipes from the silencer and up ended the silencer and out fell what remained of the lower valve guide.
Taking the oil feed to the rockers out of the equation for a few minutes won't hurt anything and it will tell you whether your problem is the result of excessively worn, or in my case missing, guides or if the problem lies else where.
Steven

 

[lee_812d]

I remember reading this exhaust guide thread and it does worry me a little as the bad smoking has only just started plus there is a sound from the bike I can't really explain - like a thin piece of metal vibrating that the fuel tank amplifies as if something is loose. These bikes make so many noises it's hard to tell. I have a video of the bike from not too long ago and there is no sign of smoke so it is something new or has got to the point of being noticeable.
A short while ago when I had the "T piece" oil return I did warm it up and then disconnect the feed to the rockers. I used gaffer tape to stop the oil flow - as soon as I kicked started it the gaffer tape blew off and half a pint of oil got dumped on the garage floor! So the pump works well, in fact I've had to put a deflector in the oil tank to stop the oil coming out of the cap vent hole. Anyway, I blocked the pipe better and then only ran it like that for a very short time, probably not even a minute as I was worried about lubrication but as I said earlier there is plenty of oil up there so I doubt I ran it long enough to clear as it made little difference. I think I'll give this another go, plus take the exhaust off and have a look for any "obvious" damage.
I think as the bike has been sat for 60 years and wasn't in the best state it is probably guides and rings (speculating here). The fact it had a diverted oil return indicates a guide wear issue.

 

[lee_812d]

Maybe a breather issue? I have checked this area out, I've widened the slot slightly and checked the timing by blowing in the breather - it is timed in the standard way. I haven't checked with a catch tank but after running the bike and parking it at most a drip will come out overnight. There is nothing significant under the bike in the garage just a few drips. These appear to come from the front (maybe magneto / timing chest screws need some sealant, and around the gearbox shaft from the primary). Not enough to bother with a drip tray.
The crankcase pressure is most likely the cause of the oil migration to the primary case.