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235 thriftmaster fresh rebuild. offy dual rottenchesters fenton dual exhaust.3000 miles since rebuild.
Ever since I've had the truck (54 1/2 ton) on the road I've noticed a real bad smell of burning oil when I am stopped and ideling. People behind me say the fumes are bad and they can see a very faint hint of blue smoke from the pipes. I know it runs a little rich from looking at the plugs. I thought it was maybe the road draft tube so I plugged that and put in a pvc breather in the valve cover and connected it to direct manifold vacuum. I just did a compression check and have 150Lbs across all cylinders. It doesn't seem to use any oil but then again I only drive it occasionally. Not to put ideas in your head but could this be a case of too much crankcase pressure? Thanks.

It runs rich.. wouldn't that also mean extra gas washing off oil from Cyl walls and burning it?

I suppose it could. Do you think going up 1 heat range on the plugs would help the rich problem? It's not so rich that it runs sloppy. I have good throttle response and am pulling about 20 inches of vacuum at idle.

I'm no expert... far from it. I was just offering a possible cause.
I seem to recall the Roch's having that problem with few solutions (if any) offered.
CarbKing has offered a lot of info here (and elsewhere)and is whose posts I look up when I have questions or just want to learn a bit more.

neswes,
Going to hotter spark plugs will not cure your rich fuel problem; it will only make the spark plugs look better. If you are seeing blue smoke, you have an oil burning matter to deal with; black smoke indicates a rich fuel condition. I doubt that crankcase pressure is the cause of oil burning. That is a possibility, but if that is the case, you should see oil leakage from seals and gaskets. Are all your spark plugs the same color? A good color is light tan to off-white, depending on the age of the plugs. Dark tan to brown indicates the spark plug temperature is a little too cold for your operating conditions. Possibilities for that are spark plug heat range is too cold, slightly rich fuel mixture, and slight oil burning. Spark plugs that are black but dry (sooty) are showing a more serious rich fuel condition. Black, crusty and wet-looking usually are the result of oil burning. And these conditions all depend on the mileage on the plugs- greater mileage gives better indications. From your description, it sounds like you have oil burning to deal with. With 3000 miles on the engine after a rebuild, the rings should be seated, but depending on the ring material, oil you are using, and the ring fit in the cylinders, the rings may take a little longer to seal properly. If your engine is a 1959 or later, the oil passage for the rocker arms is a passage inside the block and into the head. The head gasket was known to leak oil into the two center cylinders on those engines, although that problem was fairly infrequent. If your engine has the older oil tube that runs outside the block (but inside the side cover), and through a hole in head to the rocker arms, you won't have the head gasket possibility. Other possibilities include valve stem oil seals leaking (or maybe not installed, as would happen occasionally in the past), and oil dilution from the fuel pump leaking fuel into the crankcase (check your oil for the smell of gasoline and/or the oil level being too high). Anyway, running hotter spark plugs will only make your spark plugs look better, without correcting anything. After all this, my first thought, after checking for oil dilution, is to run the truck for a couple of thousand miles more and see if the oil smoke stops.

Hope this helps.

Harvester

Did the rebuild include a rebore? Only after a rebore should you use hard rings such as chrome or moly. If you did rebore, you need to make sure the machine shop cross hatched the cylinders after they bored them. If you used cast iron rings, then I agree that you just drive it and see if it gets better. Did you work the head too? It doesn't take much oil for blue smoke, and oil can get by worn valve guides.

150 psi in all CYL. may not be that good of news, Oil gets by the oil control ring, then helps the compression rings get good compression but still burns oil. That means something wrong with that ring seating in. Keep messing with the breather aspect also and experiment with different setups and drive a week or so on each and see if you notice any change, greater or lesser. May give you a tip off. Make sure the place you put the hose has good vacuum.

thanks for the tips I'll keep trying to diagnose the problem and see if I can find the cause.Right now I am in the process of switching from the dual carbs and dual exhaust to the more original 1 bbl and single pipe. I have the original intake and exhaust manifold and would like to find a manual choke carter carb to replace the Rochester.

Neswes am sending a PM.

Try re-jetting your Rochester Bs. Here is a resource for you:

http://quadrajetparts.com/rochester-1bbl-parts-jets-c-241_270.html

I am running a 50 jet instead of the original 56 to 58 that came standard on my Rochester B. I am getting around 20-25 MPG and have a dark gray tailpipe.

Walt Williams
La Verkin, UT