[Jeff Niceswanger]

I spent 30 years in a fleet garage (Ralston Purina) working on forklifts, power workers, semi trucks, bobcats,lawn equipment,aerial platforms, even locomotives. I can remember fighting this issue several times and finally figuring out how to cure it. These were not modified engines with aftermarket flywheels and such, but we did have similar issues. If you're sure the mechanics are correct, and your starter is fine, you might try this. We started putting a nice sized remote continuous duty solenoid and running 10 gauge wire to it, and then over to the starter solenoid, which in these engines were a part of the starter as they were GM engines. We used the original starter lead to trip the soleniod.It cured it every time. Must be some type of voltage issue, but on a meter everything showed normal. I always thought the solenoid must not have had enough force on it to hold it in tight and the working of the pinion in and out makes racket and severe vibration under load.. But all I know is it fixed it .It's a pretty cheap fix if it works. We ended up with every Clark Lift Truck in the place having one of thoses Hot Starts installed.