[roadmaster_56]

Hi All,

I'm having an engine vibration problem with my 48 Chrysler 8 with Fluid Drive that has about 26k original miles on it.

The vibe is related to the engine and not to the drivetrain or wheels as it is not effected by road speed.

When stopped with the gear selector in neutral (clutch can be in or out) I get a vibration at about 1200 RPM, as the RPM increases the vibration subsides a bit but is still there. At about 2000 RPM I get an occasional misfire. Other than this, the engine runs great.

I'm wondering about the vibration damper. Mine appears to be ok, I based that on the fact that the timing mark on the pulley lines up with the pointer at TDC. I don't know how else to check it....any suggestions?

Below are the things I've done or checked.

Has anyone changed a vibration damper......what's involved?

Thanks
David

compression test, one low cylinder 90lbs, the rest about 110lbs.
valves adjusted
timing ok, 2 degrees ATDC
dwell 30 degrees, points appear ok
checked the level of the 10w oil in the fluid coupling
checked the manifold heat riser...operates freely
vacuum test....at idle I get about 20 degrees vacuum and the needle is steady.
spark plugs look good and are adjusted to .025
new spark plug wires
engine temp about 165 to 175
idle mixture adjusted to highest rpm at idle, choke working properly.

[hchris]

I wonder if that low cylinder has a valve not seating properly ??

[roadmaster_56]

I've been thinking about that valve as well. My exhaust valves were set too tight and I just re-adjusted them. Tomorrow I'll try another compression test, maybe it will come back up a few pounds.

[hchris]

Ouch!! perhaps you might be better off carrying out a leak down test on that cylinder

[DeSoto Frank]

All the shop manuals from the 1930's - '50s suggest that a 10-lb variation in compression between cylinders is acceptable.

Your 90 lb cylinder is 20 lbs below the rest... that could be enough variance to cause vibration.

Would suggest testing that cylinder again, "dry" and with a couple squirts of oil, directed towards the distributor side of the engine ( getting the oil over the piston, not the valves), to seal the rings. If the compression comes-up, sounds like sticking rings (would not suspect broken rings at only 26k miles).
If the compression does not inmprove w/ oil, that indicates that one or both valves are not sealing.

I think a cylinder leak-down test on all eight cylinders would be a good step.

Could also be a plug on its way out, failing coil, or bad condensor.

Run the engine after dark, looking for "leaking" spark-plug wires (along the metal loom), mist with water from a spray bottle to double-check.

Good luck !

I have a '48 New Yorker that was my daily driver from 1988 through 1993, clocking about 40,000 miles in that interval. Once I got the initial cobwebs cleared-out, it was a fine runner.