Convert combustion deposits on intake valves

[bigbikerrick]

Hi Folks, when I removed the intake manifolds on my Convert last night, I noticed quite a bit of black carbon deposits all on the underside of the intake valves. It reminds me of how the bottom of a well used, old cast iron frying pan looks. Poking it with a screwdriver does not remove it. Its pretty hard stuff! The exhaust valves show some light soft carbon coating on the same area, but nothing like the hard burnt on deposits on the intake valves. Is this normal on an engine with 14 K miles ? I dont recall seeing this on the intake valves on other Guzzis I have owned, with more miles.  The bike runs very well, and the plugs look a nice tan color as they should.
Opinions?
Thanks
Rick D.

[Shiny Hat]

Blast with walnut shells. There’s a kit to do this or you can make one.

[moto-uno]

  Spend much time with the choke on ?
  Are the actual valve seats (and valve faces) still shiny ? Peter

[bigbikerrick]

  Spend much time with the choke on ?
  Are the actual valve seats (and valve faces) still shiny ? Peter

I dont know about previous owners, but in all the time I have owned the bike, I never have needed the "choke" for cold starts. It fires right up after a couple of twists of the throttle. I cant see the condition of the seats, but compression is good. I had no idea walnut shells can be used to clean this up in situ. but as easy as it is to remove Guzzi heads, it may be better in the long run to take apart and clean up properly as well as lapping the valves. It just surprised me to see so much carbon on an intake valve. Where in the world does it come from?  I would think that fuel air mixture flowing past the valves underside,would keep it clean. Could it be caused by oil from worn valve guides?
Thanks
Rick.

[Shiny Hat]

Could be worn seals, guides, does it smoke when starting after sitting then clear?
Hot crankcase vapors come in contact with the valve (which are cooled by the entering fuel) condense and turn to baked on deposits.
You see a lot of posts in threads about cleaning throttle bodies, the cause is oil vapors being vented to the air box. Some remove the hose, add a filter and vent to atmosphere.
Then again I have no idea what a convert is (something was changed from original?) 14k seems low for a lot of buildup but this is a Moto Guzzi and I’m finding they aren’t the best designed machines, intriguing none the less.

[Wayne Orwig]

I never have needed the "choke" for cold starts.

Maybe then the idle mixture is too rich if you don't need the choke.

Or the valve guides are leaking.

Maybe inject some water when hot.

[Wayne Orwig]

Then again I have no idea what a convert is (something was changed from original?)

https://en.wikipedia.org/wiki/Moto_Guzzi_V1000_Convert

[Don G]

 Here is a pair of valves out of a new to me Convert that has 19K on the speedo, the exhaust guides are loose but the intake guides are still good to go. This engine had an appetite for oil so I honed the cylinders and gave it a set of rings, also a set of rebuilt heads that were on the shelf. I wondered if the odometer was correct, perhaps 119,000 K? DonG

[Shiny Hat]

https://en.wikipedia.org/wiki/Moto_Guzzi_V1000_Convert

I’ll be darned, Motomatic. I had a few Hondamatics which used a torque converter (two speeds, pick either one).

[cliffrod]

..... Could it be caused by oil from worn valve guides?
Thanks
Rick.

Very likely worn guide, worn valve stem or both.  With no other sources of origin in that otherwise closed tract, thick deposits on carb side of the valves are typically the result of oil drawn through worn guides that is slowly carbonized onto the valve surface.  The result looks exactly like build-up in the outside and bottom grandma's old cast iron skillet.  The more deposit present, the easier & faster it grows- especially on hotter exhaust side.  It can fill the entire valve pocket , have chucks break loose to pass into combustion chamber, hold valve open.....  not cool. 

You can clean in place but that wont solve the source of the problem.   If it were my bike and a keeper, I would pull heads and do a proper valve job.

Edit- as far as deposits from not choking?- no.  You may have some soot in the intake tract, but there will not be thick deposits.

Later dellortos (those without a tickler to flood carb) use an enrichment circuit to benefit cold starts, not a proper choke with blade like other carbs to limit airflow to provide the same enrichment of fuel mixture.  A properly adjusted & tuned dellorto should easily start with a couple of twists to provide the same enrichment.  My old V7 Sport and even this CX also start fine without the "choke".  They will not idle without throttle attention until the engine warms.  When left activated, the enricher (what some consider the choke) simply supplies extra fuel to eliminate the need for throttle attention while warming.

[Shiny Hat]

So I was looking at a parts diagram for a 03 Stone, don’t they use valve seals on these engines? At the very least on the intake or am I just missing it?

[Moparnut72]

The radials I tore down in the shop I worked in were notorious for the deposits on the backsides of the valves. The intakes were especially bad with buildups, if I remember correctly, could be as much as a quarter of an inch. The seating surfaces would be fine though. The valve stem to guide clearances would be pretty bad though. We installed a lot of guides. The bead blaster would clean up the valves quite readily. I spent way too much time on the bead blaster and solvent tank.
kk

[EldoMike]

make sure you are running it in low gear enough...lot of people use the high gear and it doesn't run enough rpms to keep everything cleared out...

[bigbikerrick]

Moparnut,and Cliffrod, I think you guys hit the nail on the head as far as the cause of the deposits. Its gotta be worn intake guides. The bike does puff a tiny bit of smoke when revved high, and the let off the throttle and rev it up again. Its not much,and when riding behind the bike there is no noticeable smoke when going through the gears. Its just a little "puff" when revved at a standstill, with the clutch pulled in. It just surprises me this wear occured with only 10K miles. This bike did sit in a museum for about 20 years. Would this have anything to do with the oil coming through the guides? Would a "top lubricant" like marvel mystery have prevented this?

Are the valve guides something an automotive machinist can just press into the head, or is any special procedure required?   I plan to pull the top end sometime this winter, for a  proper valve job,and re sealing.
thanks
Rick.

[bigbikerrick]

make sure you are running it in low gear enough...lot of people use the high gear and it doesn't run enough rpms to keep everything cleared out...

Thanks Mike. I do run it in low gear quite a bit, around town. I love the rapid acceleration from stoplights in low gear. I only use high , if I anticipate speeds above 50 mph. I used to leave my previous convert in high all the time,and just let it "loaf along", but not so much any more. The engine seems happier around town in Low, and Im sure there is less heat generated by torque converter slippage.
 Rick D.

[Moparnut72]

The symptoms you describe point to valve guides. I don't know much about these models as to whether MG used valve guide seals or not. If they did sitting for that period of time would harden the seals and be the cause of leakage of oil into the cylinders. If not then there are a couple of remedies, some better than others. I once had the tops of the guides on an old Studebaker V8 machined for seals. You could have the guides knurled, cheapest but longevity is a ? Best but most expensive is replacing the guides completely. One thing to consider is how much you are going to use the bike to decide which way to go. there may be other options that may be brought up by better minds here than mine.
kk

[Frenchfrog]

No seals on the big bloc guides

[Shiny Hat]

Unusual that they don’t use valve seals and I can see an urger to source and install on the intakes but you would need to know more about the engineering behind this decision. They might want some oil for lubrication and feel the benefit outweighs the negative. Installing seals can create bigger issues, tough call.

[Frenchfrog]

Some people used to do it Shiny...not very common though

[cliffrod]

Moparnut,and Cliffrod, I think you guys hit the nail on the head as far as the cause of the deposits. Its gotta be worn intake guides. The bike does puff a tiny bit of smoke when revved high, and the let off the throttle and rev it up again. Its not much,and when riding behind the bike there is no noticeable smoke when going through the gears. Its just a little "puff" when revved at a standstill, with the clutch pulled in. It just surprises me this wear occured with only 10K miles. This bike did sit in a museum for about 20 years. Would this have anything to do with the oil coming through the guides? Would a "top lubricant" like marvel mystery have prevented this?

Are the valve guides something an automotive machinist can just press into the head, or is any special procedure required?   I plan to pull the top end sometime this winter, for a  proper valve job,and re sealing.
thanks
Rick.

Marvel mystery wouldn’t have made a difference.   

Any number of issues could contribute to such wear.  Sometimes it’s just the part or assembly.  Everything is manufactured with an accepted statistical rate of failure.  One of my college professors told us if a company produces machine that costs $1M with a .01% rate of failure, that basically means for every 10,000 machines produced there will be at least one complete throw-it-away failure that cost somebody $1M. 

The wear may not even be that significant.  It’s not uncommon on older automobile engines using umbrella seals on valves to have seals harden, fail & crumble and the resulting debris block oil drain back holes so head is flooded.  At that point, even ok valve guides and stems can draw oil into the combustion chamber.    When replacing seals on those engines in the car, it’s necessary to also ensure the oil drain back holes are thoroughly cleaned and working properly..

Before any serious disassembly, check the oil drain back holes to make sure oil isn’t pooling under the valve cover to facilitate the creation of the deposits.  That’s a lot cheaper remedy (aka Guzzi content…) than a full valve job with new guides

[bigbikerrick]

Thank you, Cliffrod. I will pop off the valve covers and check for any oil pooling there.  Its easy enough to do.
Thanks
Rick.

[pressureangle]

Probably loose intake valve guides. Very common in all engines, particularly those not used hard frequently. My solution, absent the time or desire to disassemble and clean them, is to run a pint of Marvel Mystery oil through, a couple tankfulls, and you'll see it go away. It takes longer depending on severity, and it will also help if you take some highway miles.

[John A]

Probably loose intake valve guides. Very common in all engines, particularly those not used hard frequently. My solution, absent the time or desire to disassemble and clean them, is to run a pint of Marvel Mystery oil through, a couple tankfulls, and you'll see it go away. It takes longer depending on severity, and it will also help if you take some highway miles.

^^^^^ wot he said.

[bigbikerrick]

I have been using Marvel Mystery oil in my eldorado for years, when I remember, I will add a few ounces per tankful, mostly as a "Top" lubricant. I got used to doing that from my MGB,and Triumph days.  I will do the same on the convert. I dont think it will hurt anything, and Ive never heard MMO added to the fuel causes detonation,or pre ignition.
Rick.

[Moparnut72]

We always added MMO to the fuel when we started and broke in our overhauled radial engines. Of course with 5:1 compression ratios detonation wasn't a concern. 
kk