Help with blowing smoke

Hey guys I could use a little guidance. 1972 Commando engine rebuild. Runs great at idle with no smoke but as soon as I accelerate the bike blows a large cloud of gray smoke out of the right side only. Oil also drips from pipe/muffler junction. The smoke persists while the bike is at high RPMS. Disappears once back to idle

The rebuild included:
new pistons/rings overbore .40
New valve guides.
reground valve seats.
skim surfaces flat.
New gaskets and seals.
This is not my first engine rebuild, but I am a specialist

The oil level is correct. I emptied the sump and added the required oil. Bike has cnw reed valve. Carbs and timing seem right on. Bike start on one kick and holds idle.

There is no obvious oil leaking from the engine. When I look under the tappet covers it is very oily in there. Could it be over oiled?

I am set to pull the head in the morning. Carbs are off, head stay is off, just have to loosen the bolts. Any suggestions are welcome. I am puzzled why I get so much smoke on one side only on acceleration.
Thanks Gary

Plug oil fouled?
Did you pull the header pipe to look for oil escaping around the guide?
Valve seal in place?

Scott

Hey Scott... you back yet?
Anyways what does "plug oil fouled" mean?
I can pull the header tomorrow to check the guide. There were only valve seals on the intake valves... doi need them on the exhaust valves too?

My Atlas was puking oil out the header pipe, and leaking at the pipe-muffler joint . Comnoz found one exhaust valve guide was leaking oil under the guide seat. The fix required over boring the guide hole in the head and installing an oversized guide.

Pour some oil into the rocker box ..... it should drain away quickly without puddling on the rocker box floor. If not, investigate return path blockage. Do Scott's suggestion to pull header pipe and look for source of oil. Try more oil in rocker box while looking into port.

The Atlas does not use stem seals on the exhaust valves and does not seem to miss them.

Slick

Just a few weeks more...

I was referring to the spark plug on that cylinder being oily.

No exhaust side seals.

how do I check the oil drainage through the head?

Pull the rocker box cover on the right side, pour in a quarter cup of oil. It should drain away quickly. You will have to judge if it seems sluggish. There should not be a standing puddle. While you are at it, pour a quarter cup in the intake rocker box as a check on its return passage. The intake and exhaust return paths are separate.

My guess is your problem is the same as mine was .... leakage around the valve guide, as opposed to leakage thru the guide bore (along the valve stem). Leakage thru the bore will show up as an oily plug, as Scott is having you check for. Leakage thru the guide bore goes into the cylinder and is burned, but will not show up as raw oil leaking out the muffler joint.

Keep reporting what you find.

Slick

so if I pull the pipe I should be able to see the oil leaking around the guide by looking into the exhaust port, right?

It will be wet appearing around the guide and chamber walls. Depending on how much soot build up you have, it can be obvious.

Another possibility with an oily plug are that your piston ring gaps lined up and are allowing oil to pass.

Like Slick said, I bet you have a leak around the guide.

Scott

When the guides were replaced did they heat the head up to make the guide go in easier or were they put in cold, if the guides went in with force could have caused a crack which would or could have caused your problem, this happen to my head way back in the 80s when a so called head expert put my new guides in and other work on the head, I had oil coming out my exhaust flanges on both side and the head had to be repaired, the cracks were right where the guides were, it was easy to see the cracks one on each side, the head had to be welded then reground and ported, but I got someone else to do the repair and the other person paid for the repair found out he never worked on British bike heads before.
I am still running that head and orginal valves today and the person who did the repair was spot on, so look for cracks where your guides are fitted.

Ashley

Note that, as has been discussed, too much oil in the rocker boxes can exceed the drainage capability to the point that the valve guides/seals will be submerged in oil and overwhelm the capability of the seal to stop it from entering the combustion chamber.

This can be caused by some sealant used when reinstalling the head/barrels inadvertently blocking the tiny drain from the cylinder head through the barrel and into the crankcase. It can also be caused by having the rocker arm spindles oriented 180 degrees out, causing oil to be dumped into the boxes faster than it can be drained.

RE that and FWIW, when I bought my Commando in '06 from a very well known US dealer of vintage Brittbikes. He assured me the bike was in perfect condition. Among a long list of serious (as in safety-related) items I had to fix, the engine smoked rather badly. Turned out the spindles had been installed backwards. Reinstalling them correctly eliminated the smoking.

Further FWIW - the oil drain hole through the barrels from the head is very small - surprisingly so IMO. If you pour cold oil into the intake rocker box, it will not drain as rapidly as you might expect (or hope).

Also, although the thinking back in the day was that exhaust valves didn't need seals, that is not the thinking today and exhaust seals are common on most engines. Oil can be sucked past the guide/valve stem into the exhaust stream by the venturi effect of the hot exhaust gasses rushing out of the cylinder head.

Same symptoms I had with my cracked head. Fine at idle but rev it up and smoke everywhere. I got a fullauto head installed now and the old head is still in my mechanic's shop. I dont remember where the actual crack was but it didnt appear repairable at the time.

Need to confirm if intake seals are properly set...they can pop off their recesses. I installed Kibblewhite Viton seals to replace the hardened originals when my right side started giving puffs of oil smoke on throttle blips. Completely cure it. Note I was able to do these replacements without pulling the head off following procedure found on another thread here.

So quick update: I had a few minutes so I checked a few things. Some more pieces to the puzzle:

Popped off exhaust. Right exhaust outlet oily. Left one dry.
Filled outlet rocker with oil and no oil leaked through or around valve guide.
Both inlets and valves were dry
Filled inlet rocker area with oil. Very slow to drain. After 1/2 hr its still got a well of oil on the bottom.
I turned the crank a few times in each of the steps.
Rocker spindles pointing the right way.
Plan to pull off head later today and check oil flow canals and if seals are still on inlets...
Open to other ideas?

Right exhaust port oily suggests leak around valve guide.
No oil leaking around guide, when viewed from exhaust port with header pipe removed, and rocker box filled suggests problem is heat related. Try running engine until hot, then checking for oil.
As MexicoMike says, the inlet drain hole is so small, it defies logic, but as a guess, I would say a quarter cup of oil should drain in 10 seconds. This is something to investigate ..... The hole drains from the head on the timing side, thru the barrels, into the timing chest, then turns 90 degrees into the sump. That 90 degree turn area can be easily obstructed.
The flats on the rocker spindles are turned outward on the Commando, inward on the Atlas/Dominators with the low pressure oil system.

Keep us posted.

Slick

Another update:
Right inlet valve seal in place and intact.
Oil canals all open in head
heated up the exhaust valve and still no leaking around right exhaust valve guide.

Am I right that the only way for uncombusted oil to blow into exhaust is if it leaks around the guide?
What is confusing is that there was no smoke at idle and a thick cloud on high rpms. Smoke went away as rpms dropped

Since it's happening at higher RPMs, could be related to increased oil flow - I'm thinking some kind of drainage problem in the head.

First: Raw oil dripping from header/muffler joint indicates oil leaking around valve guide or crack in head. This happened to me, and others above who described same symptom. It is very confusing that, except for your report of finding the right exhaust port oily, you cannot verify this situation.

Second: Smoke at high rpm, and your report that oil poured into intake rocker box was still puddling in the rocker box after 1/2 hour, indicates drainage problem. Such a problem can be expected to flood the intake rocker box at high rpm, and oil will be aspirated into the combustion chamber along the valve stem, seals not withstanding. This will produce lots of oil smoke.

Third: Are First and Second related? I can imagine that so much oil is being aspirated by the second condition, that it is not all burned, and some is left to produce the oily port and drip at the muffler. I can imagine this, but would not expect it.

Where do you go from here?

Try revving engine and holding at high rpm with intake rocker cover removed. If oil is being delivered to rocker box faster than it drains, you should see (perhaps with a mirror) oil filling the rocker box. At the level the oil tops the valve guide, smoke should appear. This test, if it goes as I describe, will prove either excessive oil delivery to the rockers, or insufficient drainage.

Your report that acelleration caused smoke is evidence of the second condition .... oil level will rise at rear of rocker box on acelleration.

Slick

PS: Are you sure rocker spindle flats are turned right way? Read again MexicoMike's post.

I have seen bikes blow smoke for some miles after a rebuild due to a buildup of oil soaked carbon in the muffler. This increases as the rpms go up but usually passes in less than 50 miles.

An excessively rich mixture will create gray smoke also as the extra fuel washes down the cylinder wall. Is your enrichener slide lifting?

You can certainly get a wet exhaust port from oil going past the rings also. If you don't find an oil drainback/ guide problem I would be checking for a ring problem.

qside said:

.. as soon as I accelerate the bike blows a large cloud of gray smoke out of the right side only. Oil also drips from pipe/muffler junction. The smoke persists while the bike is at high RPMS. Disappears once back to idle

Click to expand...

Warm engine up .
Block oil line to head with plain bolt (s) 5/16 BSF 22 tpi.
You can safely test ride for 5 - 10 min .
See if smoke disapears or not .
Go from there ..

Edit :
I see you already started taking things apart .
A good surgeon will do the diagnosis before operating .
Once the patient is sedated and cut open , you can no longer ask him where it hurts ..