Myanmar ym30 vibration in forward drive

[Lupton to]

Need help with this vibration problem as I am totally out of ideas. Bought the boat, a Beneteau 343 last year. Due to reasons that do not matter now I did not do a sea trial prior to purchase. On first driving the boat from the marina it was clear straight away that there was a vibration . The vibration only occurs in forward gear, it's not that bad, but is still noticeable up to about 1800 rpm. From 1800 rpm onwards it gets worse, and it is very noticeable, makes the teeth chatter as the revs increase up to a max rpm of 3400. There is no vibration in reverse and the engine will rev to 4000rpm. Work done so far, 4 New engine mounting, New cutlass bearing, prop removed and checked for straighteness and its ok, the propeller, a 2 fixed blade checked for uniformity on both blades and balance, both ok. prop alignment spot on and the shaft turns freely. Cone bearing removed, not an expert on this but the grooves were good on forward and reverse faces with no glazing. Engine has had the valves reground and 3 new injectors and runs well although it's a bit lumpy till it gets to 1000rpm, that's assuming the rev counter is accurate. Looking at the engine and propeller turning when driving the boat both look the same in forward and reverse minimum engine vibration, but there is no vibration through the boat in reverse. Would appreciate any suggestions of where I go next as at the moment I am out of ideas.

[a64pilot]

Assuming your sure engine alignment and shaft run out are good, I'd borrow a prop somehow, even if it's the wrong pitch etc. just to be sure, I know you have had the prop checked, but sounds once you eliminate engine alignment and a bent shaft, what's left?


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[charliehows]

wha?!? thought yanmars came from japan, not Burma...