Rough spot

[Pandersen33]

Ive got my rebuilt 41T motor swapped into my 35 sedan. It seems as though there is a rough spot right around 2100 -2400 rpm. Is this standard on these flatheads? The original motor had a little vibration right around 2200 rpm as well so im not sure. Ive got an electronic ignition with 2x2. Ive messed with timing and fuel misture a bit but it doesnt seem to change. Is there a balancer i can add to the pulley or something? It idles so smooth i can barely tell its running while im at a stop

[rotorwrench]

The 41T designation is not common since it originates from wartime production (1944 221 CID). The T is definitely a truck designation. Is this a casting number from the cylinder head? Ford produced 41A blocks as replacements for agricultural purposes starting in 1944. They are a 221 block and many have the "59" casting mark on the back bell but not all of them do. The 59A 239 CID engines were produced starting in 1945 and both engine blocks likely shared the same outer mold in the casting flask.

Is this rough spot a vibration or is the engine running rough. Rough running during acceleration could be due to a power valve problem. Rough running during a steady RPM could be a problem with the main fuel metering circuit somewhere. What carburetors are you running?

Vibrations that are RPM sensitive are generally resonant vibrations than can come from anywhere in the vehicle. Wheel & tire problems are the most common cause of resonant vibrations. If the engine, transmission, or drive train vibrates then it can cause other things to resonate when just the right frequency (RPM) is reached.

[Fordestes]

Check to see if the rough spot will come in when vehicle is sitting still ,I had a 53 engine that was rebuilt and balanced that had a vibration like you are speaking of ,it seemed to be more like a surging ,it would peak and go away intermittently, Kind of like a wave ,never actually found the cause ,I swapped out the carb and ignition just because I had a spare sitting on the shelf, have you tried pulling the choke partly on while this is taking place, does it do this while sitting still and slowly revving the engine ?

[Pandersen33]

The 41t is on the heads. Nothing cast on the bellhousing. The vibrations happens in neutral or on the road. Had the flywheel balanced with the clutch cover before install. This happened wth both the stromberg it came with as well as the new speedway 97’s on a 2x2.

[cadillac512]

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I'd try removing the belt(s) and running it first. Could be something up front out of balance. As for a "balancer" for the front of the crank...not really since the engine is internally balanced and the only purpose an elastomer or fluid hub would serve is torsional damping,and likely nothing at 2200 rpm.
Might also try with clutch held down...that eliminates the clutch disk and transmission.