Vibration When Shifting Kansaki (yanmar) KM3 Transmission

[F10]

Sometimes when shifting my Yanmar/ Kansaki transmission from neutral to either fwd or rev I get a high vibration. If I give it high throttle the vibration will be gone. Or I can shift back to neutral and back into gear and it will usually disappear. I know the vibration is in the gear, as once underway under power no matter what rpm, I have no vibration. Seems the vibration has to do with the transmission engagement. I recently rebuilt the engine (Yanmar 3gmd) and replaced all engine mounts with oem yanmar, and did engine realignment. The cutlass is new. I understand the transmission has cone clutch and damper plate. Don't really understand how these work, but could they be the problem.
Thanks

[a64pilot]

What kind of prop? Although my initial guess is slipping cones, it could be a feathering / folding prop problem too

[F10]

Originally Posted by a64pilot

What kind of prop? Although my initial guess is slipping cones, it could be a feathering / folding prop problem too

The prop is a fixed 3 blade. I inspected after the vibration started and the prop is clean, and the shaft tight in the cutlass bearing. Seems like some type of clutch engagement problem. It does not always happen, just intermittent. I inspected the transmission shifting linkage and cable control and all the adjustments look to be within spec. I just looked at the transmission drawing and the cone looks to be a possible cause of the vibration, maybe it does not engage well.

[Ramjet60s]

Mine does (at times) the same.

[ErikFinn]

Is the prop foul free and un-damaged un-corroded and balanced?
Was the alignment done while boat on the hard or on water? If on the hard the hull has a different flex than when floating and must be done again when boat is on water.

I would start with these before venturing into gearbox internals.

[bsurvey]

damper plate springs have a tendency to rust and loosen. did you check it during the rebuild. it s more of a rattle than a vibration

[Boston Blackie]

There is another recent CF thread on rebuilding KM3A transmissions. The forward or reverse end of the splined male drive cone can become worn and slip in the hard conical pocket of the respective driving gear. The cones can be easily lapped to remove glaze and the transmission reassembled. It is a straightforward DIY project.

[Boston Blackie]

The Yanmar Service Manual has detailed instructions.

[Matsubob]

First check alignment. New engine mounts may not be well adjusted. (did it do this before they were changed?)
Possibly the damper plate, but it seems it would vibrate all the time.
The cones in the transmission are massive. This one piece is slid into the receiving gear for forward and into the other one for reverse. Then, torque from the engine forces it tighter against the inside of the gear. It is hard to imagine enough imprecision there to cause vibration.
To do a simple visual inspection on it, the transmission will have to be removed from the rear of the engine and flipped onto its side, to keep oil from coming out. Then, removing the side cover will expose the inner workings.
The main thing to watch for with reassembly is that the shifting "fork" is oriented in the same way as it was when removed, and that the shifting lever be in the "neutral" position before the fork is slipped over the shifting collar.
When inspecting the cone, look for signs of "scoring" or excessive wear.
To avoid transmission damage, of course, NEVER slam through neutral to engage the other gear! The momentum of these big gears will cause the friction serrations to shear.

[F10]

Thanks for all the replies. To answer some to the questions the engine was aligned after install of new engine mounts and it was done in the water. The alignment was checked again after 20 hours of running and found to be good. The prop and shaft are bronze and not corroded or bent and is balanced, and they are not fouled. I am thinking as a few of you have mentioned that it is probably coming from the cone part of the transmission. The transmission is actually a V drive KM3V, same as KM3 but with the change in output shaft direction thus the "V". I am very careful with shifting between N and fwd and Rev and also going between Fwd and Rev gears. The vibration does not always happen, and say I shift it into gear and it starts vibrating (sounds like chattering) if I bring the revs up the chatter will disappear. Don't really like doing that as it does not seem like the thing to do with a gear box. So I normally bring it back to neutral and shift again, and in most cases the chatter does not occur.

[F10]

Originally Posted by bsurvey

damper plate springs have a tendency to rust and loosen. did you check it during the rebuild. it s more of a rattle than a vibration

When I rebuilt the engine I left the transmission connected. The rebuild was upper end only (head). The sound is like a heavy vibration and chatter, but never occurs once in gear no matter what the throttle. Vibration only occurs when trying to engage in either Rev or Fwd, no slip or chatter/vibration when successfully in gear.

[notiesbob]

Following this. We have similar problem with same engine/transmission (not V drive). Mechanis suggested shaft whip because there is 1" between back of strut and front of prop hub (Flexofold prop) or shift cable adjustment.

[galynd]

Same problem with km2p on 3gm 30f, beneteau 36cc. It's not as bad since I raised idle to about 950. Was very bad with idle at 700. I've also thought it to be shaft whip. Also 1" between back of strut and front of prop hub.

[F10]

Originally Posted by galynd

Same problem with km2p on 3gm 30f, beneteau 36cc. It's not as bad since I raised idle to about 950. Was very bad with idle at 700. I've also thought it to be shaft whip. Also 1" between back of strut and front of prop hub.

Since the vibration only occurs during the initial transmission shift, I would not think it would be due to shaft whip. Also, from what I understand 1 inch clear between strut and prop front should be ok. My 1 inch shaft has about 3/4 inch clearance to the strut.

[yalnud]

Originally Posted by F10

Thanks for all the replies. To answer some to the questions the engine was aligned after install of new engine mounts and it was done in the water. The alignment was checked again after 20 hours of running and found to be good. The prop and shaft are bronze and not corroded or bent and is balanced, and they are not fouled. I am thinking as a few of you have mentioned that it is probably coming from the cone part of the transmission. The transmission is actually a V drive KM3V, same as KM3 but with the change in output shaft direction thus the "V". I am very careful with shifting between N and fwd and Rev and also going between Fwd and Rev gears. The vibration does not always happen, and say I shift it into gear and it starts vibrating (sounds like chattering) if I bring the revs up the chatter will disappear. Don't really like doing that as it does not seem like the thing to do with a gear box. So I normally bring it back to neutral and shift again, and in most cases the chatter does not occur.

Must be a pain in the arse to handle that beast when docking