Technical Rhythmic Vibration

This '48 stock flathead powered coupe has had a vibration since I bought it. I've been involved in estate matters and haven't had the time to really check it out until now. It starts and there is an immediate vibration that gets faster on acceleration whether sitting still or driving. Before I go through pulling the trans to check the flywheel bolts, is it possible that the vibration is the result of a dead cylinder? It's raining here today so pulling the plugs and checking compression seems a good way to spend the day. Maybe something as simple as a fouled plug?

 

>>immediate vibration that gets faster on acceleration whether sitting still or driving>>

Loosen belts to see if vibes change.

 

I have heard of cracked fan's with the same symptoms, Before they throw a blade..

 

Yep, take the belts off, then the dampener (balancer thingy).

 

Since you aren't able to rule out a miss, I'd try removing the plug wires one at at time to see if there is one that doesn't make any difference. Once you find the cylinder you need to determine if the problem is mechanical (low compression) or electrical. Running an 8 cylinder engine on 7 cylinders does set up a rythmic vibration.

 

Look at it running at night, in total darkness. You may see a bad plug wire arcing. I like to do the free and easy stuff first.

 

Did the previous owners wife leave a device plugged into the auxiliary power port?

 

How about motor mounts. Are they possibly collapsing or collapsed. Trans mount too.

 

OK, what I did first was pull the plugs. They were Autolite 216s, all sooty and all gapped too tight at .025. I pulled out some new Champion H10Cs and gapped them at .030. Before they went in, I ran a compression test on all the holes, and I was pleasantly surprised to see readings from 115 to 120 PSI. I thought I was doing good with 100 to 105 in the engine in my RPU. After installing the new plugs, I ran the idle mixture screws all the way in and then backed them out one and a half turns per specs. My daughter hit the starter; the engine fired immediately and is running smooth. I'll get a few miles on this setup and check the plugs again. There is very little vibration.

I did notice that the belt driving the water pumps and alternator was running not quite true, so I laid a straightedge across the alternator pulley and one of the water pump pulleys. There is almost an eighth inch gap between the straightedge and the water pump pulley. As for the motor mounts, I replaced all three at the same time I replaced all the rubber bushings in the suspension.

Edit: Finally got the compression check video to work.
https://photos.app.goo.gl/Tfq65YoRRVUv8AeM6