The Stovebolt Site Forums The Shop Area Engine Shop Smoking on decel

Hi All,

My truck is '47 3100 with a 216.

I was driving at speed yesterday during my commute home (55mph on the interstate for about 5 miles). Truck sounds and runs great once warmed up and did not seem to smoke. Traffic got heavy and I had to slow down: foot off the gas and onto the brakes. The truck let loose of a large cloud of grey/white smoke during the decel and for a short while after it.

Given this happens under decel (as opposed to accel), I'm thinking valve guides instead of oil control rings. Given the age of the truck and the engine, it could be either.

I checked compression last fall and all six cylinders were within 10 lbs (after adding oil in the bores prior to compression check - it had not been run in a while)). Compression was 90 - 100 lbs. Also, I've been chasing a possible carb problem (won't take choke and idle fuel/air adjust is not reacting). I'm getting ready to change the fuel pump based on some prior suggestions and after confirming float level.

A full rebuild is not in the plan or in the budget. Any thoughts on root cause or potential reactions (short of a full rebuild)? Is it another symptom of a carb issue?

Thanks in advance for the help.

Bill

It is easy to check valve seals so do that first.
Under deceleration the vacuum is at it's highest. This means that the high vacuum helps draw oil past worn rings.

Hy BDammers47, the high vacuum condition caused by decelleration with the throttle closed will pull oil past worn valve guides and oil control rings, the resulting smoke is always blue however. You said your smoke was grey/white, that would indicate coolant/water getting drawn into the combustion chamber, do you have to top up the engine coolant a lot? As to the carb problem, it sounds like a rebuild is in order, that will verify the float level, and make sure all the passages are cleaned out, hope that helps.

I got to thinking and 1941-47 did not use valve seals originally.
They had a cap/hat that covered the top of the valve and retainer. This ran the oil off the outside of the spring.
Over the years these caps get removed. If the valves are not converted to a seal either umbrella or 1948 or later stem o-ring you will get too much oil down the stems.

Dave and 3B,

Thank you for your input.

I hadn't noticed any coolant usage, so I'll start monitoring it. I'll keep an eye on how and when the engine smokes and consider adding valve seals (or planning a rebuild).

I'll also re-check the float level on the carb.

Thanks again,

Bill

It may have been the fella didn't give enough clearance when he put the head together, but don't use the positive type seals on at least the exhaust, I tried it and had to pull the head and get new valves and guides after about 300 miles when they all started sticking open and dropping the pushrods. I left them on the intakes though. They are only meant to CONTROL the oil, not wipe the stems smooth clean, at least that is the theory as I understand it.

Thanks Brokenhead.

I'll keep you all posted as I monitor the truck's performance.

Regards,

Bill