3QM30/KH18A

[mitchk]

Just finished reworking my engine and gear box. Removed the engine and gear box from the boat and while it was out I opened up the gear box to replace both front and rear seals. After re-installing it made a rattling sound in forward gear at low RPM's up to about 1200RPM then it smoothed out nice and quiet? Decided it was the damper plate so I replaced it with a new factory Yanmar damper plate. I am still getting a rattling noise at low RPM,s in forward gear? I am thinking it may be the shift fork? has anyone else had this problem. Damon from SV Bruadair was in town last month and we discussd this a lot but I am wondering if anyone else has ever replaced their shift fork or had this sound and figured out what it was? The symptoms all lead towards the damper plate but that did not stop the sound completely?

[chickenbone]

Mitch,

Did you ever figure this one out?

I have a very similar issue with mine. I have a Yanmar 3QM30 not sure of the gearbox off the top of my head (will check tonight). But shifting into forward is louder than reverse. And while in forward, If I run it up to about 1100-1300 RPMs quickly it develops rough, really rough vibration. I can back down and go slowly up to and past 1100-1300 RPMs no problems.

I cannot reproduce this in reverse.

The prop shaft is inline, tight, no wobble or play. And the engine runs smooth as hell if in neutral.

Thanks,

CB...

[mitchk]

Yes, I believe so, see my latest post, it involved removing the shaft, re-placing the cutlass bearing and prop, re-aligning engine (which I thought was perfectly aligned). Still in the middle of this project but I will post the results when she gets back in the water. www.hanschristian.org/bb/viewtopic.php?t=3456

[mitchk]

OK job is finished, ended up replacing shaft with a new 1 1/4" shaft, replaced prop with a Michigan MP20RH16, had to repair/rebuild aft part of stern tube, replaced cutlass, re-aligned everything and I still have the sound? It is driving me crazy!!! sound is bad at low RPMs in forward gear. I am considering buying a new tranmission and custom fabricating a face plate and footing bracket so it will attach to engine and have rear engine mounts?