Blowing Smoke

Hi
I am having a bit of a problem with blowing smoke and oil out of my 1972 Combat.
First off I had completed around 1100 miles after top end rebuild, new +0.080" overbore pistons and rings, new valves, guides, exhaust valve stem seals, valve springs ect.
Everything was running well until on a club run on a hot day 43 C while overtaking a Toyota at around 70 mph the engine cut out.
Could not restart so put the bike on the back up trailer and at the next stop, pulled the plugs RH side very oily as in dripping off the plug, wiped the plug dry, gave the bike a kick and started and ran OK, except for lots of smoke, left it on the trailer.
When back home I lifted the head, barrels and all looked OK, so gave it a quick hone, fitted a new set of rings, checked the head over it all looked OK, button back up then took it for a bed in run, now oil out both exhaust pipes and wet plugs again.
Removed head and barrel again, all still looked good, filled ports with kerosene, no leakage into head or through the valve guides, decided I must have stuffed up the honing job so this time I used a new Flexihone, double checked the rings fitted correct way up, gap still OK ect. all looked correct.
Double checked the rocker oil drain ports are clear all good, refitted head and barrel checking all the way, checked oil return to tank looked good.
Went for a bedding in run this afternoon, all looked good and felt good, for about 4 miles and then back to smoking again, did another 8 miles and noticed that no smoke (not that I could see in mirrors) if just cruising, lots and lots of smoke on hard acceleration, no smoke on overrun.
Been through lots of previous threads but have checked most of the suggestions, any advice greatly appreciated, Oh piston look like new still except for all the oil.
Best Regards
Burgs

Hi Burgs, there is a recommended modification to the oil pickup system in the 1972 models,
to better collect and return the oil to the tank. Has it been done to your bike do you know ?

Another member here recently noted that the flats on the shafts for the rocker gear in the head were facing the wrong direction,
and caused significant over-oiling in the head - and smoking.
Another possibility ?

Have fun !!

Hi Rohan
The crankcase is standard at this stage, also still running the original breather system, I did notice during that anything above 65-75 mph constant speed, that quite a few oil leaks appear around the crankcase mating faces, might be time to carry out some mods. I doesn't appear to be breathing hard back into the tank at all.

I am pretty sure I have the rocker spindles in correctly, and it didn't play up until after a 1,100 miles.

I did note tonight that when I checked the return to the oil tank that the flow seemed to be relatively constant, i.e. at idle the oil flow was nearly constant out of the two witness holes, something that I haven't noticed before, just seemed too much in my opinion, I do have a new pump, so I may fit it and I might also take the breather off and check there is no problems there as well!

I haven't checked compression but it appears ok as it still needs easing over compression before giving a full kick, starts easy though, I have fitted a compression plate as it was too high for my 10 stone.

The engine itself is still performing well regards acceleration and also runs out to speed with no problems, little bit of a hesitation if I open the throttle too fast, but just ease it on a bit then once cam starts to work it runs quick, possibly a lean on the pilot circuit as it spits back out the carby when opened up too quick.

Best Regards
Burgs

I'm sure you have already thought of this .... but are you overloading the oil tank with oil .... ? sometimes it is the simple stuff .... my '72 Combat is very fussy about oil level .... doesn't take much over fill to get lots of smoke and oiled plugs
Craig ...

Is 80 thou. a bit far to go ? . Might be a bit thin in places and distorting when its HOT .

Whdus it feel like to push over compression just after it stopped like you said ?
Pay to have it thoroughly warmed up for the Comp. Test - If its distortion causing the grief .

Hi Matt
Plenty of compression hot or cold, first time I stripped down, bore looked to be worn evenly, but did look a bit glazed, pistons looked fine, although I have been looking for a spare set of cylinders, just in case, if it was distortion I would have though it would have showed straight away when first put together.
There is that much oil coming out the engine is coated from the exhaust nuts right around the head over the primary case, covering the air filter and back of the cylinders.

Hi Craig
I usually run with the oil level just on the bottom of the dip stick, this time I filled about halfway up to the full mark, I am going to go right through the breather system today, it seems funny that after a run when I check the return flow to tank the oil is pumping out, flat out at idle?
May be I should take it for run, come back and drop the oil out of the sump and see how much is in there, or just bite the bullet and fit the new pump, then do it as it is wet sumping bad at the moment?

Best Regards
Burgs

I fill oil tank just a tad less halfway up on dip stick when sump is empty .... take it for a good run and take a look when I'm back and add a bit if needed .... my bike also returns oil steady to tank at idle .... I thought this was a good thing ? .... I always check for return flow on start up before leaving for a ride ...
Craig

Hi Craig
At idle it is returning to tank two full steams except for small intermittent bits of air hardly discernible, maybe that is good enough, just looked like too much oil and not enough air after a run?

Best Regards
Burgs

Craig said:

I fill oil tank just a tad less halfway up on dip stick when sump is empty .... take it for a good run and take a look when I'm back and add a bit if needed .... my bike also returns oil steady to tank at idle .... I thought this was a good thing ? .... I always check for return flow on start up before leaving for a ride ...
Craig

Click to expand...

The dip stick is 3.5" long. The "L" mark is 0.5" up from the tip. The "H" mark is 1.5" from the tip. I believe most of us agree after running the engine fill the oil level to the "L" mark or between the L and H. Above the H is too much oil.

When I rebuilt my bike I had an experienced shop overhaul the head. Guides, valves and springs.
I noticed almost immediately I had smoke coming out one pipe.
Figured I'd messed up the rings so put in new ones. Still smoked.
Figured I'd messed up again and put in new pistons and rings. Still smoked!!
Decided it must be the head. Took it back to the shop that did it and it turns out the brand new intake valve stem seal had split.

I know you've had the head off. Did you confirm seals ok?
However having both sides fail at same time would be rather odd, unless wrong type/size or put in backwards.

Hi There
Valve stem seals are OK, also no sign of oil at all in the inlet ports, both valves ports both clean, and no smoke on the over run, on the other hand both exhaust ports very wet.

Today I have removed the timing cover and found a spare nut floating around, looks like an oil pump nut???? no obvious damage.

Fitted the new pump for if no other reason but to slow wet sumping down a bit.

Drilled the hole below the oil pump as in previous information, with much care as possible, now to check the breather system to make sure I can at least get air through it freely, as I mentioned before there appears to be bugger all smoke coming out of the tank to indicate excess blow by, that is at idle at least.

Best Regards and thanks all for suggestions.
Burgs

One thing to note is once your exhaust system has been flooded with oil as you describe, it takes a long time for all the oil to burn away. Especially the oil that has migrated far back into the mufflers. This oil may only smoke when you're running hard and putting a LOT of heat into the pipes. I guess the point here is you might have already fixed the cause, but you are still seeing the symptoms. Just a thought...

Hope it clears up soon.

Don

Since the bike cut out at high speed and high temperature under excelleration I wonder if a partial head gasket failure allowed oil to be pulled in from the push rod tunnels.
I know you have had the head off and put back on but did you re use a copper head gasket.
If a new flame ring type not likely to reappear though.
If oil definitely not coming into intake ports and highly unlikely through new rings unless forced from below with excessive crankcase pressure and due to exhaust gas direction not possible through exhaust guides how else could it get into combustion chambers?
Cracked head, but you've looked careful I assume.

The suddenness of it happening under high temperature and load sounds like somdthing let go due to them.

Hi Don
One thing I didn't mention was that the plugs were both oily as well after the run, I had to clean them to get it to restart, so problem is still there.
The exhaust system will definitely take a while to clean out, running a light throttle opening and cruising around 60 mph there is very little smoke as far as I can see out of the mirrors and occasional glance back over the shoulders.

RK7171
The head gasket is copper and looked fine both times, as well as I annealed it both times, there doesn't appear to be any leaks externally from the gasket either.
I have checked the head very closely for cracks, valve guides seals ect. May be I should have heated the head up when I checked?
Having now fitted the new oil pump I will modify the breather and fit a check valve, take a pocket full of spark plugs and spanners and put a few miles up and see what eventuates, in the meantime I am on the look out for a good set of barrels, as I am running out of easy stuff to check and as Matt said quite possibly the bores are deforming under hard acceleration.

Best regards
Burgs

Re: COMBAT Blowing Smoke

Have previously diagnosed oil pump with bad scavenge side. After a long run, immediately drain sump. Check sump oil volumne. This is more likely on combat with no filter in sump. Really hard on scavenge side.
New pump in friends bike and all was well....no more smoke.
IMO combat breather gets blamed yet a marginal or bad scavenge is at times the problem....you state STEADY return oil ... again possible bad scavenge....should be blowy and pukey.

OK see you have new oil pump now....not better????

I wouldn't expect to see two streams of oil returning to the oil tank at idle. Just a bubbly trickle. That would indicate that there is too much oil getting into the crankcases. It would also explain the excess of oil in the cylinders and you may consider getting the bores measured properly. I didn't think it was advisable to go beyond 0.060" oversize and infact I didn't know you could get pistons that size. How the extra oil is getting into the crankcases is a mystery. The stray nut in the timing cover might mean that the pump is not tight against the cases and oil is leaking (pumping) out into the timing cover and then into the sump. Thats my two-penneth

Re: COMBAT Blowing Smoke

If it came on suddenly, could it be the timed breather? I seem to remember a recent post where there was suspicion of the disc's drive ears shearing off, no longer running in sync with the cam.

dynodave said:

....you state STEADY return oil ... again possible bad scavenge....should be blowy and pukey.

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Granted, I'm playing with a '74, but, at idle, the scavenge return line runs mostly air back into the tank.

Nathan

Re: COMBAT Blowing Smoke

Nater_Potater said:

If it came on suddenly, could it be the timed breather? I seem to remember a recent post where there was suspicion of the disc's drive ears shearing off, no longer running in sync with the cam.

Click to expand...

A "1972 Combat" won't have the timed breather.

The .80 overbore is an issue as I've not heard of this big a size and yes the walls could be thin and subject to warping from heat with hard accelerations. Sounds like you've checked over other logical things well enough.

Re: COMBAT Blowing Smoke

L.A.B. said:

Nater_Potater said:

If it came on suddenly, could it be the timed breather? I seem to remember a recent post where there was suspicion of the disc's drive ears shearing off, no longer running in sync with the cam.

Click to expand...

A "1972 Combat" won't have the timed breather.

Click to expand...

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