I have finnally solved the vibration problem in my 250. I worked all fall and into the winter tring to solve this. I pulled the engine at Christmas time and looked it over. I installed Rhoads Lifters and a different cam with new gears. I had the intake/exhaust machined flat, replaced the broken shifter mount, replaced the tail shaft bushing, added a torque strap from the head to the frame, rejetted the carburaters, replaced one rear axle, and none of it worked. It still had the vibration at 65 mph!
I was out of ideas, the only thing left was the head. In the first post I didn't say any thing about changing heads, figured no way it could cause a problem!
I had changed it two years ago when I thought it was leaking water, turned out the block was cracked at #1 head bolt. Anyway, the head was modified with expoy to simulate lump ports. The exhaust valves were inlarged and ports cleaned up. My dad has a flow bench so we new what kind of improvements we made. The intake flowed the same up to .350" then gained from there up to .500". The exhaust out flowed the stock port from all the way to .500" .
Over the last few days I changed the head back to the stock '68 250 head. The truck runs great, not quite as responsive at low rpm, but the vibration is gone! It will run any speed now, I was out today running 70 mph with no problem. We have no idea what is wrong with the other head, we plan to reflow. We know the intake to exhaust ratio is off slightly, but something else has to be wrong. At least using epoxy, I can chip it out and still have a good head to work with. I do miss the small intake ports, it idled better and was really quick right off idle.
Anyway thanks for all your suggestions and ideas. Joe
