Yanmar 1GM10. Fore / aft vibration - banging.

cwstard

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19 Jul 2010
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Pembrokeshire
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At anything over half revs, get a violent banging from engine. Jumps forward / backwards along line of propshaft. Fairly irregular but round about once a second.
Only happens in forward, reverse is fine and engine revs smoothly in neutral. Engine alignment is perfect - just rechecked it. Propshaft is straight and propeller is balanced.
The engine mounts are non standard and about 6 years old but don't think the type of mount is at fault since the engine has been fine with them for the last 5 years. They
still look good but I've decided to change them anyway. I've a feeling that new mounts aren't going to solve the problem though.

Could this be a gearbox fault? I've seen the problem described in another thread but the thread drifted off without any clear answers.
Anybody got any clues?? Boat's a Hunter Horizon 26.

Cheers in advance.
 
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