[QUOTE=skipper_stu;6430658]
Quote Originally Posted by contessaman View Post
Oh! Well mine is about on a par with that at higher Rpm and barely moves at lower rpm.
Maybe I'm worrying over nothing. But my 2 previous boats had similar sized 4 cylinder diesels (perk 4108 and w.m. seapanther) and they didn't move much at all.

I was at the boat yesterday and marked my shaft where it emerges from the shaft seal with permanent marker. I made observations in neutral, in gear at idle, then at 1000, 1200, 1500 and 1800 rpm (by which time the engine is moving worryingly) and the shaft and engine combine IS NOT moving forward a measurable amount. Perhaps 1mm at the most from 1800 rpm in fwd to 1800 rpm in reverse, so those expensive r&d mounts I fitted are doing their job well.

I've come to thinking the problem has been caused by my inserting a flexible coupling in the drive train.
These engine mounts resist thrust very well but allow movement up and down. If I get in the engine room (easier said than done at 6'2" !!!) And straddle the gearbox I can easily grab it (the gearbox) and lift it or depress it an inch in either direction.

I was thinking that with the engine thus mounted, plus the flexible coupling, plus the floating shaft with flexible seal, that as soon as it spins its getting a tiny bit off centre, then the centrifugal force pulls it out even more on the flexibility if the system, and the problem becomes ever worse. The fact that my coupling weighs a ton is possibly making it worse. I think with the boat ashore I can take the prop off, slide the shaft back and remove the r&d coupling from the system to test it. If that was the culprit then order a new linger shaft and lower mass half coupling at the same time.

Any other thoughts or observations based on my latest findings?[/QUOTE
As my original post the big coupling. 10kilos you said?
Yep. Its looking that way. Gonna be a few month before I'm ashore to prove or disprove it now. Will update the thread when I do in case its of use to somebody doing a search in the future.