Rebuilt V-12 smokes on startup

What kind of smoke? Any other symptoms?

 

What tim said....and Time to go testing. start with the very basics. If the smoke is not much with a bad idle they could be related. Sometimes they are both a symptom of more bad news. Either way continuing to tweek is just hoping the problem will go away. If they are a smart shop you don't need to hunt for ideas here. They will make it right. OTOH If you get the feeling this is dragging on and on then the problem is either ineptness or hope (hope it goes away or hope you go away).

 

You mentioned carbs are not adjusted right. If the engine smokes on start up when hot I would bet the smoke is black in color and due to the carbs being to rich on that side.
Blue smoke is oil and of a bit more concern and might change with ring seating.
But you have not mentioned the color of smoke so we have very little to go on.

 

No smoke accelerating and no smoke decelerating means the rings are sealing well. Good power up top means little other than the mixture is acceptable. Good power at tip-in and at low RPMs is indicative of proper sealing of the combustion chamber (rings, cylinders, valve seats.)

Note:
Black smoke: overly rich mixture
Blue smoke: oil being burned in combustion chamber. Indicative of oil seaping past guides, or excessive blow by that is then being consumed by the intake and combustion processes (unlikely in a car this old.)

Smoke on startup, then goes away quickly--indicative of valve seals.

It may take a lot more than 400 miles to fully break in a motor when using modern synthetic oils especially when a dose of ZDDP was added to help with breaking.

 

Blue or white oil smoke on startup could be a valve guide seal.

I don't know the inside of that engine you speak of, but you should check to see if it has neoprene valve guide seals, if so that could be the source of the oil causing smoke at start-up.

I don't know what shop did the engine rebuild, so I can't comment on their competence, but even the best shops can make small mistakes in assembling a complex engine and here's hoping they will make good on it for you.

 

I don't buy this at all. While textbook correct a 12 is so smooth many will drive on 11 cylinders and never notice it. Even me a racer and skilled DIY'er could not detect misfires on my 12 that obd2 picked right up. The OP needs real hard data not subjective impressions. The builder is on the hook and the longer one's lets this linger the more likely what you see is what you get.

 

I looked at an exploded diagram of the Colombo V12 on the Ricambi web site and it does appear the engine (if yours is a SOHC rocker arm Colombo V12) uses typical valve stem seals.

I agree with previous posters that the shop is on the hook to make it right, not sure what your contract says, but it sounds like a rebuilding error of some type, and they should make it good.

Diagnosing the problem is the first step, and replacing the valve stem seals on the one bank and running it, should be conclusive.

Is the shop uncooperative or are you just reluctant to go back ($$$$$) ?

BTW, if oil seems to be seeping into the cylinder after shutdown, and smokes on hot restart, what happens when you do a cold start ?

 

Guys,
No mention of the color of smoke by Zanny1 who has the problem.
Zanny1 did say there is a carb adjustment issue, back firing popping.
He did say the car makes the smoke hot (big hint here) over rich would show it's self more hot than any other time.
Valve guides usually leak down cold or hot, the smoke is noticed while engines is hot.
With out knowing color of smoke the most logical conclusion that can be drawn by the little information given is a carb. problem, maybe just linkage, one side dragging the other side a little?
Why jump to worst case scenario's right off the bat? oil control , when we have a known problem with fuel delivery?

 

To the OP: You said that the shop "will make it right," but you didn't say whether you took the car back to them, and what they found / told you upon examination.

Your options are basically limited to one: return the car to the shop, and with the engine still warm show them the problem.

Leave the car there, and tell them to repair it and call you when the repair is complete.

Of course, do so with grace and with a smile, but they'll understand: it's a dreaded "come back."

It happens, and they are on the hook 100% to make it right.

 

the OP has had this car for over 10 years, he should be comfortable with the engine and has seen all of its' quirks during that time... a little fogging wouldn't bring him to this forum with his concerns... the concern is about the amount ( excessive ) of smoking along with a few other issues... a new rebuild should run clean, without any issues, nothing should be happening that would set off ANY alarms from any where... it needs to go back to the shop ASAP and stay there until they get it correct... rebuilt Ferrari engines run clean and without issues

the more time passes before it goes back to the shop, the risk of fault shifts more to the owner and away from the shop

 

One quick and easy idea is to check the plugs. The color MAY give an idea as to what is happening by cylinder. The tips may be grey, brown, black, wet, etc and give you a clue.

 

You might consider valve guide seals/ valve guide clearance. Common problem on rebuilt cylinder heads if the machinist did not make allowances/clearances correctly. Same for checking oil return holes.

 

This is the 4390cc DOHC engine.

 

Bingo !

i don't know the shop and i hope i'm wrong...but...

 

This right here is why I cringe when I hear people say that they don't pay any attention to their gas mileage. A sudden increase in fuel consumption for given driving conditions can be one of the first red flags that you just MIGHT have a problem.

Obviously this info wouldn't likely help the OP after a fresh rebuild & I didn't mean to get the thread off track - just hoping some owners of these fine machines might take notice & save themselves some grief over time.

 

LOL! Many men also think their wives leave them all of a sudden...Some just plain fail at understanding "context clues".

 

Hi

Here is a system for determining if there are gas in the engine coolant. This system you will find here:
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allowed me to know that the dysfunction of my 400GT engine did not come from a broken head gasket. Even if the smoke is blue, do not underestimate all the causes of dysfunction. For my part, thanks to this unit I saved a lot of dollars in unnecessary repairs.
Here is where we talk about:
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Theodore
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So nothing new to say about the smoke on start, Oil is likely seeping down the valve stems when the engine has been shut down and gets "Burnt when you start it". Agree - check the plugs for signs of oil - is it all 6 cylinders on the one side - might be only one or two, which would be good to find out.

Regarding the miss-fire on idle - Yep, I had some of that and it took me a while to figure out how to dial in the carbs. The carbs can be set up so it does not miss-fire at idle or stumble on slow acceleration and at lower speeds, (under 75) it can get pretty good mileage. If things are running right, a C4 will tootle down the freeway with the throttle just barely off the stop.

On the technical side, I discovered mercury columns, which I got at the local Honda Motorcycle shop. They come in groups of 4 used on the old 4 cylinder Hondas. They have really worked for me to synchronize the carbs. Also - disconnect the linkage between the two banks and synchronize one side at a time. I may have a written about this on the C4 site. Anyway, good luck.

 

after rebuilds if there is smoke as described it would be logical to have the cam timing re checked before anymore time is wasted...
after THAT is established, to be 100% on the money, and the distibutors have had the curves, phaseing, and dwell(least important!) DOUBLE CHECKED AND PLOTTED, and timing checked, then a leakdown is in order-when hot, then cold

Did your machineshop use original Ferrari nylon guide seals-if so this is 50% of problem-NOBODY uses that junk anymore...
viton metal cases at base with a soft shoulder on the stem is the modern methodology...
if nylon ones used, diminsional clearances will be a real problem potential...

When I do guides, I use a CNC Okuma lathe to make the guide to each bore in the head-after first precision honing said bore round and FREE of galling marks.
The bores are almost ALWAYS damaged by caveman removal methods-beating them out with hammers, or, GOD forbid, air hammers!
Proper removal is to slowly drill them out from ABOVE-AFTER MILLING THE TOPS OFF, so that they peel out from the bottom, causing almost zero damage.
OH MY GOD does this take time....but the heads never require repairsize guide manufacture!
Oil sucks down the guides between the head and the guides far more frequently than most think, it usually manifests as hi rate of useage, with out much smoking

Smoking usually means something is ill timed by a small yet significant amout(4-12 degrees) can be largely unnoticed by "most owners", and the car seems like its DOA...smoking 1-2 packs a day...
The smoke MIGHT abate if suspected tuning issues are verified off, the consumption is an "organic disorder" which cannot be "tuned away" if problems as described above are true...
LASTLY, if a broken ring is guilty, there is a big problem.... see leak down above...

In any event, its probably more likely than not that its going to come down again...
PS-done these before(several of them)...hardest street motor overhaul car they ever made...by a mile. Daytonas WAY easier...

DONT waste alot of time on carbs, they dont really "go bad"-you had car for 10 yrs right?
think about it carefully, and scientifically....then it will become more clear-emotionally charged perhaps-but clearer...