Smokin... and I don't mean in a good way

Chris Larkin

Chris Larkin

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Sooooo... I've been waiting to ask, hoping it'd cease on its own (as if?)

Following a top-end rebuild, maybe 400 miles ago, my ’73 850 Commando has begun smoking at start up (left side only). White smoke, kinda heavy at first then fades to gone as engine warms… less than two minutes. Starts and idles fine, runs very well.

I’m unable to go back to the shop where the rebuild was done, they’ve moved (unrelated, I’m certain). One post pointed to me popping the top and look at the valve guides for a leak(?). I have the tools to do the work, capability too… but have never removed a head from a motorcycle. Will someone please point me to a YouTube tutorial, or other guide? My wish is to have a “look for this” plan before I crack it open… which I really don’t wish to do. Ugh.

Thank you for the assist.
 
The Workshop Manual and Parts Catalogue are great resources to add to the tools. The Manual is well written and has good illustrations and in my opinion a must-have for these machines.
 
Chris Larkin said:
Sooooo... I've been waiting to ask, hoping it'd cease on its own (as if?)

Following a top-end rebuild, maybe 400 miles ago, my ’73 850 Commando has begun smoking at start up (left side only). White smoke, kinda heavy at first then fades to gone as engine warms… less than two minutes. Starts and idles fine, runs very well.

I’m unable to go back to the shop where the rebuild was done, they’ve moved (unrelated, I’m certain). One post pointed to me popping the top and look at the valve guides for a leak(?). I have the tools to do the work, capability too… but have never removed a head from a motorcycle. Will someone please point me to a YouTube tutorial, or other guide? My wish is to have a “look for this” plan before I crack it open… which I really don’t wish to do. Ugh.

Thank you for the assist.
Click to expand...
So has it smoked since being rebuilt?
Or has it started at 400miles ?
Is it definitely white smoke and not blue?
Does it smoke on declaration IE going down the gears with the throttle closed?
You'll need to diagnose if it's too end or rings
Best outcome would be if an inlet seal has come off the inlet guide
Probably the worst would be a cracked head
The 850 head can crack easily if the valve guides aren't fitted properly
But usually the smoke would just get worse as it warms up
Does the shop do a lot of commando work?
 
Yes, I have the manual, and I use Andover's website to search parts. I've looked through the manual and can visuaize the work... yet hoping a "how to" videos is out there. My searches have been unsuccessful so far. Thanks for the reply Bert.
 
baz said:
So has it smoked since being rebuilt?
Or has it started at 400miles ?
Is it definitely white smoke and not blue?
Does it smoke on declaration IE going down the gears with the throttle closed?
You'll need to diagnose if it's too end or rings
Best outcome would be if an inlet seal has come off the inlet guide
Probably the worst would be a cracked head
The 850 head can crack easily if the valve guides aren't fitted properly
But usually the smoke would just get worse as it warms up
Does the shop do a lot of commando work?
Click to expand...

  • It started smoking somewhat recently. I don’t recall it smoking prior
  • Yes, the smoke is always white. It stops smoking either after a few high revs on the throttle, or after it's idled for two to three minutes. There is a ghost remnant of smoke after a 20-minute ride... yet very, very faint.
  • Smoke never gets worse as it warms up, always disappears – mostly, maybe a vapor like density after fully warm, if at all.
  • The mechanic at ‘OC Motorcycles’ was well schooled in British bikes. I don’t remember his name but remember researching his credentials. I believe I was in capable hands.
Thank you Baz
 
I do not understand why it is white smoke and not blue. Oil makes blue smoke.
White (in cars) means coolant is being vapourized.
What sort of oil are you using?
 
DennisMo said:
I do not understand why it is white smoke and not blue. Oil makes blue smoke.
White (in cars) means coolant is being vapourized.
What sort of oil are you using?
Click to expand...
Not always blue.

Modern oils, and HOW HOT it gets determines the color of smoke. (Depends on where it is coming from) intake valve stem, rings, exhaust valve)

One poster here dumped white smoke for the last four seasons, saw it again & again.
 
Last edited:
Chris Larkin said:
Yes, I have the manual, and I use Andover's website to search parts. I've looked through the manual and can visuaize the work... yet hoping a "how to" videos is out there. My searches have been unsuccessful so far. Thanks for the reply Bert.
Click to expand...
There is SO MUCH MORE than YouTube videos.

I would respectfully suggest you need a talented mechanic to help you.

50 years repairing engines, including fixing work the "pro shops" porked.
 
Long shot, could be 'Wet' sumping.
Wet sumping is when the oil drains into the crankcase from sitting, then pumps up into the cylinder on cold starts.
Before you do anything. Drain the sump, pour it back into the oil bag and start it.
If it starts up relatively clean. There's a start.
The Wet sumping could from a pourly set up pump, or a pinched or missing cone seal from pump to cover.
Regardless, I would probably pull the timing cover to confirm proper cone seal before any tear down.
If the seal is compromised or worse, missing, oil just pours into the crankcase.
If convinced the seal was good, I would pull the pump and troublshoot.
Like I said, may be a long shot, but I would proceed here before any tear down.

Anyone know if the Hemmings Videos are around?
 
DennisMo said:
I do not understand why it is white smoke and not blue. Oil makes blue smoke.
White (in cars) means coolant is being vapourized.
What sort of oil are you using?
Click to expand...
Castrol Motorcycle oil 20/50

Sure looks pure white... I'll start this afternoon and try to see blue.

Thanks Dennis
 
If the bike is stored after a ride on the side stand, and the oil drain hole in the head is partially blocked, oil could be
pooling around the valve guide. The inlet oil seal could be dislodged from the guide. I don't think pulling the head
is a particularly difficult task requiring an expert mechanic. There are a few tricks to insure there are no oil leaks
after reassembly.
 
MichaelB said:
Long shot, could be 'Wet' sumping.
Wet sumping is when the oil drains into the crankcase from sitting, then pumps up into the cylinder on cold starts.
Before you do anything. Drain the sump, pour it back into the oil bag and start it.
If it starts up relatively clean. There's a start.
The Wet sumping could from a pourly set up pump, or a pinched or missing cone seal from pump to cover.
Regardless, I would probably pull the timing cover to confirm proper cone seal before any tear down.
If the seal is compromised or worse, missing, oil just pours into the crankcase.
If convinced the seal was good, I would pull the pump and troublshoot.
Like I said, may be a long shot, but I would proceed here before any tear down.

Anyone know if the Hemmings Videos are around?
Click to expand...

Yes. The bike does sit for 10 to 14 days between starts. (work n chore interference)

I rode yesterday, got it fully warmed up. I'll start it when I get home to see if the quantity and density is less?

Great triage suggestion.

Thank you Michael
 
Well,.... take the least invasive measures to INSPECT first. Pull the plugs. Are they oily? pull the exhaust pipes and rotate the engine. Are the exhaust valve stems stained with burned oil? Is there burned oil around the seat of the guide?

Do you know that the intake side of the head has a drain hole that has to be carefully aligned on reassembly with both the barrels and the crankcase? If it's clogged then the intake side of the head drowns in oil until it spills over to the exhaust side and drains down the pushrod tunnels... soooo,... Remove the intake valve cover, then put it on loosely, start the bike and once it starts blowing oil smoke, shut it down, put on your oven mitts and remove the intake valve cover. Is there a lake of oil on the intake side? if so, you need to poke the oil drain hole on the intake side of the head...

As was said, and inspect the intake valve seals while you have the intake valve cover off...
 
Block the oil feed to the head and see if it goes away.
You can safely do a few cold starts and a 10 min. ride.
This will determine if the oil comes from the top or from below.
 
First confirm if the bike is wet sumping during shutdown periods. Check oil level in tank after running, then again before next fire up to see if level is lower than after running. Never top up tank without first running engine to return any accumulation in sump.
Check the drain port on intake rocker floor is clear. It is quite difficult to see, half covered by the spring seat on right hand side...maybe about the 5 O'clock position? Try pouring in a bit of oil to see how fast it drains down. I managed to poke a length of wire down all the way to timing chest 90 degree bend, then spray wd40 in. Seemed to speed up the draining test.
The intake guide seals can be renewed without removing head. When mine went, symptom was puffs of smoke on throttle blip roll offs on left side only.

Another point, when my engine had a rebore, it took maybe 500 miles before light smoking disappeared. Perhaps your new guides, valve seats need to wear in a little?

There quite a few youtube videos out there showing the full head remove/reinstall procedure. Will post some links shortly.
 
If I can add my two cents, left side smoke when starting is caused by valve guide seal. I have seen these improperly installed and they work loose.

They kinda snap over the guide's groove. It may have not been pushed on properly when install. It might be as easy as pushing it in place. Once they come off they will stay on the valve stem, moving up and down with the valve.. Worse case is they can act as a pump and force oil around the valve stem. Take a look, I hope it's this easy
 
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Oh, wait a minute...what headgasket did the shop use, copper or composite? The composite needs to have head bolts re-torqued after first start up, then at 100 miles, then a few more times up to 500+ miles....because it squashes down a lot. Copper only needs a re-torque once or twice by comparison.

Here is one video showing the head re-install process in much detail (owner didn't set it to be watchable on other websites, so just click link to watch on YouTube directly):


Be sure to see in the video at 38 min mark the check for light permeating though a crack in the forward stud holes....quite a common situation I gather (I've seen it on a block locally that the very experienced owner/mechanioc didn't know was there).
 
I just did a seal replacement in situ . It takes a while the first time as you really tend to be cautious of every move . It saved tearing down the bike . The tooling cost me $0.50 cdn. which would be $0.17 US . There is more information on this site on how to do it.
 

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