My 340 is blowing blue smoke

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Dadsdart340

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Melita MB Canada
So recently my 1969 dodge dart 340 started blowing smoke. Still runs great but the warmer the engine gets the more it smokes and the more oil it consumes. I did a compression test and six cylinders tested 150-155psi. The other 2 cylinders were 143 and 145 psi. It is a matching numbers car, I have quite a lot of plans for the car. Would I be better to throw the number matching 340 up on the shelf and rebuild it when I have time...and pick up another 340 somewhere that I can modify? If so, anybody got one for sale?
 
So my 69 dart is blowing smoke. Did a compression test and 6 cylinders were 150-155psi and the other 2 cylinders were 143-145psi. What should I look at next? Timing? Carburation? Please help!!
 
When does it blow blue smoke? start up, going down hill, all the time, tell us more.
 
On acceleration, rings, on deceleration, valve seals and or guides.
 
I put my nimbers matching 340 on a stand and built another 340 to have fun with , I guess could have done a 360 blah blah cheaper , blah blah , more torque , blah blahh blah , but I like the sound of 340 , and that's what came in the car originally .
Any of the 3 small blocks can be made to go , your choice , I just happen to really like 340's .
 
Pretty much all the time. If you let off the gas for a couple seconds and then get back on it it seems to really blow smoke but then blows less as the Rpms go up.
 
P.C.V /crank case evacuation set up? Seen this on new engines,not ventilated properly. Valve cover gaskets,a long shot.
 
Probably rings, but as Tim pointed out, the PCV system could certainly cause it and would be a CHEAP fix, so I would look at it.
 
Agreed, you'll have to bear with me, I am learning as I go. What exactly am I looking for when I look at the valve covers/breathers and PCV valve?
 
Take a picture or two, of your engine bay first. (Post them here..) Let's start there.
 
Having trouble uploading pictures abodybomber. Pm me you email address and maybe we can chat via email if you have some time. Cheers.
 
Do you get a puff of smoke at start up? Is it getting worse over time? If it was rings, wouldn't compression be worse? The two cylinders that are lower are within 10%.
 
I do get quite a puff of smoke at start up louie70dart. Ya I agree about the compression. If it was rings it would be a lot lower wouldn't it.
 
No idea , they pop up once in a while , but you really have to check them closely . Asking prices are high most the time because of the "340" reputation . Good luck , hope you find one .

Sounds like bad seals , but you never know , start with pvc and work your way down ,
 
Maybe, but a cylinder leakdown test can rule out rings as the problem. A good mechanic can read the pressure drop, if any, to give a better idea of what the situation is. Imo, only thing we can do here is give suggestions, without being there we can't really diagnose it. Hope this helps. Oh, I had a car that puffed smoke at start up that became worse over time. Performance was still there. But what started as a softball size ball of blue smoke became basketball size and bigger. Ended up going through a quart of oil each week. Didn't smoke until I let up on gas, but real bad when started and not when regular driving.
 
Cylinders could be gouged and it would smoke and have higher compression.

You could run heavier synthetic oil and it wont smoke as much.

Louie "above" had a classic case of bad valve seals. Oil drips on the valves while it sits and then at startup you get a puff of smoke.
 
Read the plugs,, if oil accumulation is on one side of the electrode,, it is likely a valve guide seal, if oil is evenly distributed around the plug,, - rings..

If you back-off down a long hill, then give it some gas,, and get a blue cloud,, Valve seals/intake gskt..

If you're on it hard,, and smoke's curling out the exhaust.. rings..
 
If it's anything like the 340 i had, or some other customer engines since then - some of the 2nd rings are broken. Either rebuild it now, or find/buy another one.
 
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