Flathead smoke

[guy1unico]

It is kind of a long story but I'll describe briefly what was and what is.
My engine is a 49 - 53 hipo with Merc crank and 3 3/8 bore. The motor has about 2000 miles on it since completely rebuilt. it ran great with no smoking until i put in synthetic oil. When it started smoking out of the passenger's side tail pipe my friend told me to go back to 30 weight non detergent oil, because synthetic is a horrible break in oil. He said to put on about 800 miles with the 30 weight and the smoke should go away. Well after 200 miles it only smokes when the engine is warm and when I rev up in place. As i drive on the highway the smoke goes away. The second spark plug in from the front on the passenger side is always wet and I think it is fouling out but dont know for sure. All the other plugs are clean and dry.

Do you think if I keep driving the situation will continue to get better or am I going to have to pull the motor and break it all down...damn I hate to think of this?

Thank you,
Guy

[Brendan]

would not run synthetic oil, get a good grade of multi viscosity oil.

[Mike51Merc]

Sounds like it's getting better, so why disrupt the healing process?
I bought a new Audi in 2003 and after the first 800 miles the low oil warning came on. I filled the oil and after 800 miles it came on again. I freaked out and complained about it but they said oil consumption on a new engine was normal. The periods between losses increased, but it took 10,000 miles for all oil loss to stop. Ran the car for 100,000 more miles with never any loss between oil changes.

[JWL]

Check the compression in the cylinders. If there is mechanical damage it won't improve with age.

[Charlie ny]

I like Shell Rotella from Walmart. You might try one heat range hotter plug in the
smoker cylinder. In my experience synth oil in a Flathead is a no no, clearances are
too great.
OMHO
Charlie ny

[flatheadmurre]

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If compression test doesnt show any big differences i would check the ignition for that cylinder.
Might be as simple as a bad plug/wire/connection.
Check cable switch plugs between cylinders.

[Walt Dupont--Me.]

Swap the plug with a clean one in the engine, see if that same cyl gets black. Walt

[Lawrie]

I had the oiling up two plugs on my 33,always the same two,only on deceleration,turned out to be loose valve guides.
Lawrie

[guy1unico]

Lawrie...that is interesting.
I may pull the head of that one side and have a look see.

[flatjack9]

I don't see a problem with using synthetic in a flathead. Probably not on an old well worn engine. But we build these engines today with pretty close tolerances, just like any modern engine. And I don't like using diesel oil in a flathead either. It is not formulated like a gas engine oil.

[Lawrie]

Guy, It took me many miles to work out the problem,my 33 would run all day at any speed up hills or on the flat, no miss fire UNTIL i let of the gas to slow down for road works or an intersection, ,always after had this small misfire,.always the 5 +6 cyls plugs oiled,,finally looked out the back after coming down a big long hill and just as I got on the gas a pile of blue smoke out the back.
good compression and leak down on ALL cyls,
these two cylinders had really bad stuck guides when I put the engine together,and like a DUNCE i used old valves and guides, so have some other good ones to put in later.
Other than that I could not fault the engine.
Lawrie

[guy1unico]

Lawrie,
Yes that sounds just like my situation.
So you think I have to stuck guides?
Guides are just basically a tube that the valve slides back and forth in.
Guides stay put so how can they stick?

[Lawrie]

When I stripped the engine to rebuild it those two guides were really stuck in and I had to make a drift to bash them out,I think that either they had some rust in the block where they sit or the valves where loose in the guides that I used.
lawrie

[guy1unico]

Ok, thank you
I think i'll put about 450 total miles more on this engine. Right now I'm at 200. If nothing changes I'll bust her down.

[Mike51Merc]

If you're running cast iron rings on a new bore job, you should not run synthetic oil during the break-in because synthetic oil can actually prevent the break-in process.

[flatjack9]

I don't think synthetic oil will affect the break in. I would not use it simply because it is expensive and you shouldn't leave the break in oil in for a real long time.

[Bored&Stroked]

Me, I run straight break-in oil until I know the rings are seated . . . then I switch over to whatever oil I'll run for the long term. Back in the day, we ran non-detergent 30 weight for the first 500 miles or so, then switched over to a multi-viscosity oil with detergent. I wouldn't run a synthetic oil during break in - unless it was specifically formulated for the break-in period. With that said . . . I'm sure it has been done a thousand times . . .

[Bored&Stroked]

Also, as some noted - you may just be having a misfire in that one cylinder . . . causing partially or un-burned fuel to create a bit of smoke. I'd definitely do a leak-down test if you have access to the tools - will tell you if the overall cylinder is in good shape. If you put a new plug (maybe a step hotter for now) in that cylinder and it still stays wet, then you might explore your ignition a bit. If the plug is oil-soaked, that is one thing (rings or guides), if it is fuel soaked (wet), then it is probably somewhere in the ignition system and/or associated wires.

[moefuzz]

Bored and stroked has got it right.
Run the Correct break in oil,
And switch to Synthetic after the rings have seated if you wish.

[FireEngineMike]

Guy, how many miles were on the rebuild when you switched to synthetic?
Everyone else, how many miles do you run break-in oil before switching to what you run long term?