Yanmar Rattles in Forward Gear

[hneoman]

Dear All, I need help:
I have a Hunter 34 with Yanmar 3GM30 - 1988. The engine rattles heavily ONLY on the forward gear, not on reverse or idle. The mechanic checked the engine alignment, changed the transmission damper plate. The diver checked the shaft and prop, still happening. It gets worse after the engine heats-up.
When the rattle started 6 months ago it was not all the time, I would put the gear in reverse then forward and it would stop, now it's happening all the time when engine is on load forward.
I was told it's engine mounts, but they seem OK and why it happens only in forward not idle or reverse?

[Tar34]

Originally Posted by hneoman

Dear All, I need help:
I have a Hunter 34 with Yanmar 3GM30 - 1988. The engine rattles heavily ONLY on the forward gear, not on reverse or idle. The mechanic checked the engine alignment, changed the transmission damper plate. The diver checked the shaft and prop, still happening. It gets worse after the engine heats-up.
When the rattle started 6 months ago it was not all the time, I would put the gear in reverse then forward and it would stop, now it's happening all the time when engine is on load forward.
I was told it's engine mounts, but they seem OK and why it happens only in forward not idle or reverse?

Do you have a folding prop?

[hneoman]

No, it's a fixed 3-blade prop

[Sailmonkey]

Can you post a picture of your mounts with the engine in gear and revved up a bit while tied to the dock?

[brishear]

If your engine had a glow plug, occasionally they disintegrate and make their way onto the tops of pistons.

[Sailmonkey]

Originally Posted by brishear

If your engine had a glow plug, occasionally they disintegrate and make their way onto the tops of pistons.

On that note also, I've seen the precombustion chambers on yammers with enlarged holes that caused terrible sounds.

[hneoman]

The Engine doesn't have a glow plug,
I will post some photos of the mount laster on.

[hneoman]

The sound is not an issue, it is the physical rattle we feel in the cockpit under our feet (where the engine and shaft are). And I can see the engine moving heavily as a result.

[Cotemar]

Sounds like loose or broken motor mounts or twised or bent prop shaft.
Did the lifing strap end up on the shaft when they last lifted your boat?

[hneoman]

Thank you folks, the mechanic confirmed engine and mounts are OK, it must be the shaft or the cutless; becasue the noise comes from under the hull.

[GaryMayo]

Only forward, never neutral or reverse, leaves only one option I can think of. Something in the forward only powertrain.

The Transmission.

[Nemo55]

Thrust washer in the drive line excessive end play in forward, also maybe hair line crack only showing up in forward thrust of prop shaft to transmission.