Le Mans II smoking conumdrum...

[clivecookie]

Hello all,

My first post ! Hope you maybe able to help get my Guzzi back out where it belongs ? Sorry it's a bit long !


The problem is my Le Mans 2 has developed a smoking problem. On a cold start, large (very large) amounts of light grey smoke pour from the left hand pipe. This continues for approx 2 min (by then my whole road is choking) and then clears, and runs absolutely fine for the rest of the day (which may involve spirited riding for a couple of hundred miles). Riders following have not noticed any more smoke (on the over-run or on full throttle openings) during the ride.
I have changed the head gasket (twice) O rings and had new valve guides fitted to the effected cylinder - no difference noted. The bike has a believed genuine 20 odd thousand miles under its belt and I always use the centre stand.
Spark plug is ginger bread man.No oil comsumption problems to speak of.

I have had some heavy breathing problems (on long runs) but this has inproved since the addition of a deep sump extension - oil capacity kept as standard.
Oh, just a last detail, once in a blue moon, it won't smoke on cold start up at all (well very very little) !
This weekend, I have taken the plunge and removed the l/h barrel - all looks absolutly fine - rings,piston and bore (pre-nikasil, I think).
Any ideas on how I can solve this problem would be much appreciated. Thanks

 

[ghezzi]

Re: Le Mans 11 smoking conumdrum...

You could try Nicotine patches, :lol:

Is oil return from L/H blocked?
Where are the crank case breather tubes connected to?
Do you have standard airbox and filter system?

 

[Rafael]

Re: Le Mans 11 smoking conumdrum...

I bet it's the oil ring.

Have you check it to see if it/they still meet specs?

 

[PP-1753]

Re: Le Mans 11 smoking conumdrum...

Might also be a valve guide - just putting it out there...

 

[ghezzi]

Re: Le Mans 11 smoking conumdrum...

If it was an oil ring broken/damaged or installed upside down, I would expect it to smoke all the time.
Even if smoke wasn't visible, anybody behind would smell the burnt oil.

As it only seems to burn oil on start up, it has to be either leaking down valve guides or from the air/oil seperator in the crank case ventilation system, but then it should smoke both cylinders.

Could the head or a guide be cracked/porous below the seal?
Have head checked by vaccumn leak down test.

Could it be a loose tolerance that closes up when engine warms up? Pissed and slapped anyone? :silly:
Check bore and piston for ovality and taper. Any decent engine machine shop should be able to do these.

What mods, reco work etc has been done?

 

[clivecookie]

Re: Le Mans 11 smoking conumdrum...

Hi Guy's,

Many thanks for this. Still getting used to 21st century communications ! This might catch on you know...

I'm gonna head back down to the garage in a mo, I'm happy the oil pipe and breather pipe are all clear. The bike is mechanically standard (apart from the aforementioned sump ext) so has open carbs (well the mesh that may stop a bird from being sucked in) and the small breather pot sitting on top of the crankcase, vented to rear of bike.

I will inspect the rings to the best of my ability ,although as ghezzi has said you would have thought it would smoke all of the time ? It is such a marked difference - honestly if you saw how thick the smoke was pouring from the silencer you'd think it was cream crackered. Then 2 min later everythings huncky dory...

The valve guides have just been replaced (and the mechanic said the old ones were well within tolerance) although he would have visually checked the head -maybe a vacuum test would be prudent...

Could it be a oil pressure problem ? To much pressure perhaps ?

I will attempt to take some measurements tonight on the bore etc, and report back. Only 2 weeks till the TT and I don't want to take the BMW ! Yikes ! :S

 

[Morizzi]

It is unlikely but check to see the mechanic didn't put the base or head gasket on backwards. Do this by placing a thin wire probe down the small return hole at the bottom of the rocker area and ensuring it goes all the way down to the crankcase.

Late LM II's had nigasil bores, earlier had iron. Different ring sets required for each. I'd check to see you got the right ones for you. Use a magnet on the inside of the bore to test then check with the ring supplier.

Once that is done, re-torque the heads.

Rod

 

[clivecookie]

Hi Rod,

Thanks, yes gaskets were all on ok (now at present stripped down again). I can now confirm I have the iron bores. Current rings have been fine for the previous 6 months (since I purchased it). It is now looking like I will have to try a new set of rings to see if I can eliminate the problem (I'm happy the top end is all good to go).

Will let you know how I get on.

Many thanks, Clive

 

[Morizzi]

Clive, this is not the first time I've read of your symptoms. Its not common but it is not unheard of.

Funny how it always seems to be the LH side. :? That's the side that works less. Only responsible for 270 degrees of rotation.

I'm guessing you will get it back together and it will be better, then return after a while. Re-torque the head.

I've got a theory about it. Slightly mismatched mating surfaces between the head and barrel. The smoke doesn't start right away but takes a few seconds to start pouring out? I think it takes that long for the rocker oil drain to fill and as the oil travels down it can be sucked past the gasket into the combustion chamber. As the barrel and head warm they expand and close the gap after a few minutes.

Just my theory.

Good luck.

Rod

 

[ghezzi]

Hey Morizzi, that makes sense.
Every conceivable problem I came up with also had question marks.
ie. It should happen on both cylinders, or all the time.

 

[Chuck in Indiana]

I'm clueless, too.. my old 1000 SP used to occasionally do that.. only on the left cylinder. A leak down showed nothing. Didn't burn any oil between changes. Well, not noticeable on the dipstick at any rate. I used the sidestand a lot, and *assumed* that had something to do with it.. apparently not.

 

[clivecookie]

Hi Guys,

Thanks for the time. Rod you may have saved me £90 (for rings), a days work and a period of frustrating running in...

Looking at the head / barrel joint surfaces doesn't immediately show a problem (a straight edge placed across the surfaces looks good) although I guess it might be difficult to see a little warpage by eye ?

You are right when you guess the smoke takes a few seconds to reveal itself.

Just of note, I have checked the ring gap (only on the compression ring at present)and this is within tolerence. There is a slight gap (0.10mm) between the top of the liner and the top of the barrel (liner is sitting low) not sure if this is normal ? Also Inlet valve (inside the combustion chamber face) is wet with oil - problably no surprise there ?

Hmm, think I will re-assemble this weekend -with care, fresh gaskets, o-rings. Would anyone suggest me trying a little gasket sealant :angry: or torque down the head a little tighter :shock: To help with a seal ?

Cheers again, Clive

 

[john zibell]

I'm not a big fan of gasket sealant in modern applications. I do use it on head gaskets on antique cars. That product is copper coat and is easily removed with lacquer thinner. That will be your call. Use 35 lb-ft for torque (recommended to me some time ago by the service rep at MGNA). Don't forget to go in stages (I use 15, 25, then 35). Also re-torque after a heat cycle, and again at 500 miles. Also take the time to clean up your combustion chambers while she is apart.

 

[lucky phil]

Funny how it always seems to be the LH side. :? That's the side that works less. Only responsible for 270 degrees of rotation.

Eh?
Ciao
Phil

 

[Series4]

I'd suggest if the inlet valve is wet on the stem then that's where the main issue lies, either leaking down the valve stem or between the guide and head. Also if there's a mismatch between head and barrel I'd expect a compression leak until the engine warmed. It only takes a small amount of oil to make a big cloud of smoke and the symptoms you describe sound as though there's oil pooling on the piston. During normal running not enough oil will get down the valve per revolution to be noticeable, and it will also be washed away/diluted by the incoming fuel charge

 

[clivecookie]

Hi all,

Lucky Phil, there is only oil on the face of the inlet valve (and not the stem) so not sure if this tells us anything (other than there is oil present in the conbustion chamber ?) Just of note, the last time I went to use the bike (10 days ago now) if failed to start (after a fair bit of cranking). This was traced to a faulty ignition switch (talk about kick a man when he's down) - just thinking - oil pressure would have built up and possibly the leak (wherever it is coming from) would have started ?

Thanks John for the advise on Torque settings, I just off down to the garage to re-assemble - at least gaskets are inexpensive...

Cheers, Clive

 

[lucky phil]

Ok just had a thought,if this is a cold start issue have you checked the l/h side carb choke.If the choke is allowing way to much fuel into the cylinder it will wash all the oil off the bore and cause OIL smoke.As a quick check borrow a decent carb or swap carbs and see if it cures the problem.Naturally with a hot engine you wont be using the choke so the issue wont occur.
Ciao

 

[davidguzzi]

I had a problem with my choke sticking on the left carb, I took the cables off and its running well now. Worth a try, could be unrelated.

 

[lucky phil]

I had a problem with my choke sticking on the left carb, I took the cables off and its running well now. Worth a try, could be unrelated.

Most certainly worth a try.When the engine is cold the fuel doesnt atomise as well this is why you need a choke in the first place( engine heat help atomise the fuel mixture)
So when the engine is cold a lot of the fuel falls out of suspension and washes the cylinder walls of lubricating oil.Wont be such a problem when the engine is hot because the fuel stays in suspension due to engine heat.
Also check for the l/h carb leaking fuel into the cylinder/inlet when the engine is stopped.IE poorly seating float valve.
Ciao

 

[clivecookie]

Gents,

Progress, I think...

After re-assembly , started her up - fair bit of smoke. Was expecting this due to the 'extra' coating of oil applied on build up. Took her out for 20min. Let her cool right down, then re-torqued head. Started her up - not a puff of smoke. Went out for a ride (30miles) no problems.

Have just re-torqued again (the next day) - so will try tomorrow to see if it is sorted. All being well, this was my mistake all along - not to go back and re-torque once the gaskets have settled.

If though, the problem re-surfaces - looks like its the chokes turn for a little TLC ?

Thanks for the continued support - much appreiciated.

Will keep you updated, Clive