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blue/gray exhaust smoke

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NutmegCT

NutmegCT

Great Pumpkin
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My 1958 Rambler American (196 cu in flat head six) runs beautifully. Smooth idling (no smoke), strong acceleration (no smoke), no hesitation nor miss under load, under no load, and at idle. Cylinder compression is even, about 150 150 152 150 150 150.

Climb a hill at 65, no problem.

But get to the crest of the hill and start down - grey/blue smoke is lightly visible from the tailpipe when I let up the gas pedal. Give it more gas, smoke stops. Smoke isn't heavy - just "visible". Similar to:

car_maintenance_tailpipe_smoke.jpg


What could cause this?

Thanks.
Tom M.
 
Sucking oil past the guides. Might be rings.
The last flatmotor in my 50 Tudor did that..long drag, stop at the light, take off and two full cars disappeared in the smoke cloud. Seriously.
Still have that block, hone will work, rings were wore...out. Guides were loose.
On yours....cannot remember Ramblers...but I think the guides are separate drive-in units, not cast in.
Trick on those was to pull manifolds, head, side cover(s), then all the valves (inspect stems and faces carefully) then lay rags in the lifter gallery, drive then down almost to the lifter, hit them with a chisel and hammer to break them off, drive the rest out.
Chill the new ones, know your installed guide height, drive them in (correct orientation), faced valves, quick lap to see if they grey up all the way around the block seat.

BTDT.
 
TOC - thanks for the details.

Just to be clear, I do *not* get smoke when I take off from the light. Smoke is only after I remove my foot from the pedal. So - no smoke under load at all.
 
Coasting on engine, oil bypasses guides.
 
My Tr6 does the same thing decelerating down a hill and puffing oil smoke when hitting the gas pedal. Valve guides were supposedly replaced when head was done and hardened valve seats installed two years ago. Compression is down in one cylinder however. Worn or broken ring maybe?
 
I remember those stories. Gus and the Model Garage. I don't understand how oil can work past the guides if they in fact were redone. I don't remember if I got the old guides back or not. I did get a few valves back that were replaced. The machine shop that did the work was upstate. Since the engine still runs great except for the oil, I'll keep putting in oil until there are other signs that a teardown is imminent. I still have more than 75 lbs. oil pressure and about 40 at idle. Runs cool too.
 
You may not SEE the smoke when you take off.
Trust me...if you come down a grade or long compression slowdown, and you get out and see the tailpipe burbling blue/grey, the entire system is full of smoke.
It will not miraculously all turn to clear air once you take off....combustion chamber, exhaust valves and ports, exhaust manifold, header pipe, muffler and tailpipe.
It will start clearing out once you start moving, but it has to clear out all of those places.
My cloud of smoke was the system doing exactly that...about two vehicle's worth.
 
Might take note: Had a Triumph GT6 that did the smoke thing only on coasting. Took a while then it did on take off and early morning start. Come to find out, when doing head, that no valve seals had been installed. Intakes were supposed to have seal, exhaust none. Back then seals for exhaust were not in parts book and you used a Chevy seal, now they are available at most parts vendors.
 
Thanks Larry. From the workshop manual, this 196 flat head six doesn't have valve seals. Maybe adding a heavier oil (10w40?) and/or Bardahl NoSmoke will cut down on the smoke, which now only occurs when coasting downhill while in gear. Back pressure from coasting, forcing oil up into the combustion chambers?

Tom M.
 
10W/40 is what I run in my older cars. All my old Jags get 20W/50. Only varible would be for winter contant driving would be 10W/40 in winter. If you ever tear it down, Chevy umbrella seals would be looked at, but the draw back would be less oiling of the guides and more guide wear.
 
Don't know that engine, but in the past I've installed umbrellas on other engines and cured the guide leakage, if that's the problem. Also make sure the lower end can breath properly with no restrictions. PJ
 
Thanks Paul. I'm concerned about "umbrellas", as Larry points out the likelihood of increased valve guide wear.

I just tested the road draft tube, and it's clear. Removed oil filler cap, blew air into the filler, and felt a strong stream of air coming from the draft tube.

Maybe try Bardahl NoSmoke to thicken the 10w40 oil?

Edit: here's a bit more about the engine, the "Super Flying Scot".

https://wildaboutcarsonline.com/cgi...tion=viewad&categoryid=9960481656952&viewad=B

View attachment 44621
 
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