Smoking??????

[Dusty1]

Brake-in doesn't seem to be taking. About 100 miles on the 340 and lots of run time getting ignition all adjusted, and it seems to be smoking worse now than when I first started it. It still has the cam brake in oil in it and I keep getting told to put miles on it, but it doesn't seem to be getting any better. Leaves a bad cloud especially on decelleration. Could the rings still not be seated? Thanks

[Chryco Psycho]

What rings were used , I had Chrome moly in one engine , the engine was still picking up more power with 6 k miles on it , no chance any of the rings were broken on installation ? or installed upside down ?

[cudabob496]

had similar symptoms once. Valve guides!

Or, intake not sealed well against heads, and oil is being drawn into
heads past intake gasket.

[Super Blue 72]

If you let it run and then let it sit for like 10-15 minutes and then restart do you see smoke come out on start up?  If so, it may be like cudabob said, valve guide seals.

When else does it smoke besides on decel? 

[Chryco Psycho]

With the throttle closed youhave very high vacuum on the intake side so it definatly could be intake gasket too or intake guides

[HP_Cuda]

Is the cloud a white dissapating one or one that hangs around awhile?

My guess is the rings haven't seated yet and you are seeing oil burn.

[Super Blue 72]

With the throttle closed youhave very high vacuum on the intake side so it definatly could be intake gasket too or intake guides

Cool!  So that's the science behind it!  Thanks! 

[Chryco Psycho]

Yup , the engine is turning fast / above idle speed , the throttle is closed there is no air getting in , the vacuum could exceed 20" easily

[cudabob496]

if heads or intake have had any machining, then that can set you up for leakage past the intake gasket.
I had to use two intake gaskets per side to seal things properly.

[KingCuda440]

I had a small block smoke like that after I changed an intake. It turned out there was a hole in the exhaust crossover and it was sucking oil. I would also check valve stem seals and valve guides.
Another thing to consider would be to run a compression test.  One last thing, when you say break in oil I'm assuming it's conventional oil as synthetic would cause the rings not to seat properly. 

[Dusty1]

Seal power rings, the heads are shaved and it does have conventional oil in it with cam breakin additive. Motor built by a good performance engine shop(anything can go wrong). Very little smoke when started up or on reving. When driving I can see that its leaving a slight smoke trail, I get out of the gas for a red light and on initial acceleration heavy smoke rolls up behind me, like it loaded up during decelleration. No blow by at the valve cover filler hole and no unusual oil in the pcv hose.

[cudabob496]

Seal power rings, the heads are shaved and it does have conventional oil in it with cam breakin additive. Motor built by a good performance engine shop(anything can go wrong). Very little smoke when started up or on reving. When driving I can see that its leaving a slight smoke trail, I get out of the gas for a red light and on initial acceleration heavy smoke rolls up behind me, like it loaded up during decelleration. No blow by at the valve cover filler hole and no unusual oil in the pcv hose.

Constant smoke down the road is usually rings.  Smoke during acceleration off the line is usually valve guides.

[Dusty1]

Maybe its just not seated yet(I hope). Engine builder said drive it?

[Chryco Psycho]

It would seem something is not right , after rebuilding , breaking in a Lot of engines you should not have that much smoke

[cudabob496]

Maybe its just not seated yet(I hope). Engine builder said drive it?

yep, I've heard the same thing from builders. Give it another 2 to 5 thousand miles.
Kinda baloney in my opinion. A well built engine should not smoke.

What work was done on heads? New guides?
If as you say, shaved heads, then were measurements taken before assembly
to show same gap all around head/intake area.
You can measure those gaps now to a certain extent.
Also, check all plugs. If only intakes oily, then maybe intake gasket leak.
Or if only one or two plugs oily, may help locate problem.

Only so much can be shaved from heads, until intake has to be shaved.