RE; Foley Engines
"Damper plates lead a tough life
They work in the dark, are often soaked in salt water, and are never checked, let alone maintained. They are the marine equivalent of a mushroom! The damper plate is bolted to the flywheel with a half dozen or so small metric allen bolts. Into this clutch like plate slides the splined input shaft of the Hurth or Borgwarner gear. The damper plate acts as coupler between the engine and the transmission and all torque is transmitted through it.
Noisy damper plate
Sometimes these hard working clutches rebel and their springs loosen up and even fall out. Or one or more of the allen bolts back out and the plate become loose and moves around. Symptoms of this will be a rattling sound from the bellhousing area when in neutral. Engaging gear is often difficult and the Hurth gear is hard to shift. Often loose or missing springs is the only problem. People often think that they need a new transmission when all they need is to replace the damper plate.
What to look for
If you suspect that your damper plate springs are loose and rattling around and that you have damper plate problems here is what to look for. First check your linkage to ensure that everything is tight and working properly. Then check that the bolts holding the damper plate in place are present and installed correctly. Verify that the Hurth or Borgwarner gear is not mis-aligned. Use a dial indicator to check for this. Finally, if the damper plate is worn and/or springs are missing, check to see that your Hurth or Borgwarner gear's front bearing hasn't failed. Worn damper plates can often cause the transmissions' input shaft to wear and result in front bearing
What they look like. It's the springs that rattle