I’ll try to keep this short
I acquired a 318 77 Trailduster, not running. It supposedly only needed an intake to run. Pretty much looked like the whole vehicle had been put together with spare parts.
Anyways, I bolted up an old 340 square flange intake and 4 bbl. It started but needed a timing gear and chain, so I replaced them. Afterwards it fired up and ran smooth. Seemed to idle and rev up just fine. But when I started going down the road, at about 13-15 mph, it started to vibrate, and would get worse the faster I went, at 30-35 mph, with my vision getting blurry, the vibration was so violent I could hardly hold the steering and about threw me out of the seat.
Once back at the garage, i found out the torque converter had the 360 weights on it, one on each side of the drain plug. I knocked these off and test drove. The vibration was much improved, smooth as glass to about 25 mph, but still started vibrating/shaking at 30 and would get progressively worse the faster I went. This time up to about 45-50 was about it. So I decided to go another direction.
A year later, I pulled the motor and installed it in a dart with a manual 3-speed. Resurfaced flywheel, new clutch, pressure plate, throwout bearing, and a roller pilot bushing/bearing. I still have the same vibration that I had when it was in the Trailduster/727 auto combo. :(
I am to understand that ALL 318s are internally balanced. The only thing left to check is the harmonic balancer. I looked up examples of both the 318 and 360. The one on this engine looks pretty much like the 318 piece as I see no counter weights or off set dimensions anywhere. It does however have 6 shallow holes drilled on the front of it. I have never seen them like this on a small block mopar. The back looks like a normal factory 318 dampener with the uniformed hollowed out section all the way around it.
Any ideas? Appreciate any information, and sorry for the long post.
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