I put a new motor in my '40 sedan about a year and a half ago. Least expensive Chevy 350 crate motor ($1300) , completely stock. It seemed to smoke on start-up so I replaced the positive valve seals with umbrella types since I had this problem with these engines in the past. I didn't notice any other unusual smoking. It seemed to be leaking oil out the back and I couldn't pinpoint the source (rear seal, pan, casting flaw) so Chevy said to take it to the dealer for warranty inspection. They said they cleaned it and couldn't find a leak but they added some UV dye to the oil while checking. I didn't understand this because I clearly saw oil coming down the rear of the pan and the distributor and valve covers were dry. Then I noticed it smoking while idling, revving, general running for about 100 miles. Couldn't understand it. Finally decided to check the oil and it was 4 quarts over full. I can't imagine any way I could have done this but I can imagine a lot of ways the dealer could have. Changed the oil with 20-50 and it won't stop smoking. The plugs are black and very sooty. I tested the compression in one hole and it was 133 with one gauge and 128 with the other. It went to 138 with oil added. The smoke doesn't change with the PCV valve and the trans modulator disconnected. I had complained about the oil leak when the motor was under the 12-month warranty and I finally took it in after the warranty was up. It's been quite a while now. I can come up with a lot of theories about this but I'm basically lost. Anybody got an idea? All thoughts are appreciated.
when you put it in did you break in the motor properly? those target 350 crate motors are not run (to my knowledge) before being crated and shipped. You may have never got the rings to seat properly. Being that over full with oil wont help that either. Trying running it up and down the road holding it in 1st or second gear and then left off the throttle letting the motor slow the car down under compression. My Dad told me to do that years ago on a motor I re ringed and it took care of the smoking issue on that motor. His claim was that when you close the throttle off at speed and coast down under compression, the vacuum spikes and in turn pulls the rings out against the cylinder walls helping them to seat in faster. Is that true? I don't know, but made sense to me at 20 years old and it worked.
I think you'll find they have moly rings, and the rings seat just fine without any special effort. If the carb is acting up, it will do strange things...and might damage the rings/bores if it's flooded, I hear. I've never seen it, though. I recently had some fun with a fresh rebuilt 350, it was burning a lot of oil, the intake was not sealing well at the ports. I don't know what is wrong with the intake, but I replaced it and it seems to be fixed, for now. There are a lot of places for a 350 to leak oil from. The rear of the intake, the oil plugs in the back of the block, the pan gasket and seal, cam plug, the rear main seal, there's another oil plug under the driver side head at the back, the valve covers, etc. And you could easily have two different issues, the oil leak and the smoking might be unrelated. Viva Mexico!
If the thing is that rich, you may be thinning out the oil.. hence the smoke. Give the dipstick a whiff.
What carb and intake are on the engine? Does it have a working choke? Is it getting up to full operating temperature? What was your break-in procedure? What is the manifold vacuum at idle? At a steady cruising speed? Is the crankcase properly vented?
Are you sure that extra oil wasn't gas and oil. You may have a carb flooding causing the smoke. Check the carb and take it out and see if it smokes more on acceleration or de acceleration.
You need to finish your diagnostic steps. Take a compression reading on all 8 cylinders. If they vary by more than 10% you likely have a ring or valve issue. 128 pounds sounds low. but we'd need to know more about which 350 you have to compare it to specs. My impression is that normal compression is more in the 160 psi range if you have an 8.5:1 engine. Carb problems don't cause low compression in themselves.
I would think if engine oil is diluted because of a carb problem than it could have an effect on compression.
Fuel pump could be leaking gas into the crankcase. That is more likely than a carb putting a gallon past the rings. Gas in the oil will also cause smoking issues.
if the rings are bad/cylinder walls are scuffed, no amount of carbuerator manipulations will cure the smoking or raise compression back to specs. This certainly could have happened from diluted oil, but, if it did, the damage is done. Unfortunately ring/cylinder wall issues are explanations for both low compression and smoking. Better to eliminate them as possible causes at the start rather than investing time in tinkering.
If the carb is flooding fix it change the oil run it to temp and then run a leak down test maybe one would get lucky.
Most embarrassing . . . I guess I was way out in left field. I started checking out the Edelbrock carb and the more I got it to lean out the less it smoked. I don't have an air/fuel gauge. Eventually I got it to smoke least and run best with the idle air screws all the way in. I took the carb apart twice and cleaned and checked everything. I didn't test the fuel pressure because it wasn't really easy to do as I have AN hose all the way to the fuel pump but I finally found some extra fittings and made a gauge setup. 10 psi. Obviously way too high for the carb to control. I ordered a pressure regulator and some AN fittings. I plan to set the pressure to about 4 psi - I think that will be enough to run OK. Stupid aftermarket stock-type fuel pump has been on there for years. Thanks a ton to those who suggested looking at the carb instead of the rings, etc. Saved me a lot of mental torment and time!
I find that fresh built engines can be very forgiving, they'll give you a sign that something is not right, the trick is to pick up on those signs.
EXTRA 4 qts! The dealer should have found that...oil issue (besides ADDING the 'high visibility purple'!) Funny, with all the hype ASE training does for the Newby Techs...Who's grading those sheets?
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