The Stovebolt Site Forums The Shop Area Engine Shop '48 3600 with a 235 - top speed engine issue

For some reason or another the 235 in my 1948 Chevy 3600 doesn't like to work too hard. Once I get to a certain road speed (43mph in 4th gear and some unknown speed in 3rd gear) the truck will only take maybe 1/2 throttle or it'll start running a bit rough, make some popping noise under the hood (But not from the exhaust like backfiring) and surge a bit.

From what I know the 235 engine was built in 1957. The flywheel and starter on it are from a 6-volt truck.

Right now I'm working on setting the ignition timing as setting it has been suggested to me. After putting a new vacuum advance unit on the truck I set it per The Chevy 216/235/261 Tuneup Guide found on Deve's Tech Net online. This morning I went to check that the #1 plug should fire with the cylinder around TDC. I hooked my light from the points/coil wire on the distributor to negative to read when that wire is powered, and I'm finding that power comes on when the piston is around TDC. Shouldn't power be shutting off around TDC?

This Chevy has been my first adventure setting timing on an automobile, but what I remember from magnetos is that at the proper timing setting the points should break open, shutting off electrical flow and causing the coil to induce electrical current from the primary winding into the secondary winding which is then routed to the correct spark plug by the distributor itsself.

I checked my timing really roughly by marking the crank pully when the points open and then moving the #1 cylinder to TDC and it looks like my static timing is around 15 degrees BTDC, so I'm going to do some research and figure out what it should be.

the popping is most likely from the carb, and it's a sign its leaning out, i would check the float level.
Jay D.

Popping through the carb can also be sign of sticky intake valves. Run a heavy dose of "Sea Foam" additive in the gas for a few tankfuls to try to dissolve any carbon deposits or varnish on the valve stems. Did the truck happen to sit unused for a while with gas in the tank? If so, stale gas can, and usually does form a gummy residue that can stick intake valves to the point of bending pushrods.

Some of the information in the tech article you mentioned can be misleading or downright wrong- - - -research other sources before accepting it as gospel. Stovebolt engine timing is set by a dot on the flywheel and a pointer visible through a window above the starter. Most (but not all) engines time by aligning the dot and pointer with the engine stopped and turning the distributor housing counterclockwise until the points just barely open. (static timing). That's approximately 5 degrees before top dead center.
Jerry

Spark occurs when the points open. So your test light should come on when the points open. Look elsewhere.

I did reset the float level when I put a new gasket in the carb and I'm pretty sure I did it right, but maybe I'll recheck it.

The truck did sit for ~20 years before it got fixed up in 2019 and I bought it this year. The PO said he went through the whole fuel system and cleaned everything out, and the gas seemed alright when I bought the truck. I s'pose I could also pull the valve cover and visually check the valves, correct? Though I've never done anything with the valvetrain of an engine before I do need to put a new gasket on the valve cover anyways to fix a couple of leaks from it. I have a few cans of seafoam on the shelf so I'll run one through the truck.

The static timing was set so the points open just as that dot aligns with the pointer. I haven't checked how far BTDC that is, but I realized that I my understanding of the operation of my light was wrong when I made my 15-degree BTDC claim.

Okay, I finally figured that out. For some reason I was thinking that as soon as the points open electrical flow would cut off and my test light would turn off, but I was forgetting that my light is wired in before the points. So, from my understanding now, normally electricity flows through the closed points and the test light is off, but when the points open the electricity instead flows through my light to ground, illuminating the light.

There's a sneaky trick to minimize valve cover leaks. Stovebolt cylinder heads are flat where the gasket sits, so oil can puddle behind the gasket and seep underneath, unless the gasket is glued down to the head. It's also necessary to assure that the valve cover flange is completely flat- - - - -overtightening the 4 bolts that hold it down can dimple the sheet metal and result in uneven clamping along long sections of the gasket. I like to use weatherstrip adhesive to glue the gasket to the head, and a thin layer of grease on top to allow the valve cover to be removed periodically for valve adjustments without damaging the gasket. Gluing the gasket to the head builds a dam to discourage seep leaks.
Jerry