Flex Plate Failure

[a64pilot]

Yeah, once I get to Lake Worth that’s viable, but I’m pretty sure it would take a Yanmar part.
However where I’m at it’s not really an option, Maybe there will be a boat yard open in New Providence? I doubt it though, everything that’s not a gas station, medical or a food store is shut down here in the Bahama’s, nothing is open, and I don’t see end of that soon, but that’s a guess.
Plan is to sail when I can and motor when I can’t. My crossing window is this Wed thru Thurs, then it goes to North winds and waves in the Gulf Stream

[Davo1404]

Brand new one for a 2GM20F.

[Wotname]

@ a64pilot, do you have access to the service manual while on board?

If you are short on bandwidth, I can post the relevant pages from the my 4JH2 / KBW20 manual.

[LeaseOnLife]

We have almost the same engine/tranny here (4JH2-TE, KBW20). Do you have enough clearance between stuffing box and trans-coupler, to move the shaft enough back, to remove the transmission? I would say 3" would be good, 2" too tight. Then the removal of the transmission is not that hard, given decent access. From there you can check the damper plate for broken springs and rivets. It also gives you a chance to spin the freed shafts in the transmission, check for noises and axial&radial play.


Edit and correction: judging by my finger, 2" might be just enough to get the transmission shaft out of the damper plate.

[Frankly]

I would take a mask and check out the Auto Prop. Easy to check and replacing a blade a lot bigger $ than the Yanmar damper plate.


Frankly

[a64pilot]

Originally Posted by LeaseOnLife

We have almost the same engine/tranny here (4JH2-TE, KBW20). Do you have enough clearance between stuffing box and trans-coupler, to move the shaft enough back, to remove the transmission? I would say 3" would be good, 2" too tight. Then the removal of the transmission is not that hard, given decent access. From there you can check the damper plate for broken springs and rivets. It also gives you a chance to spin the freed shafts in the transmission, check for noises and axial&radial play.

Plan is to limp it home and then replace it there.

Frank, I should have, but I’ll run it gently today and see how it goes, I do have a spare prop on board and an Autoprop puller, just don’t know if I have tools big enough for the prop nuts.
I guess a hammer and cold chisel if I don’t.

Edit and correction: judging by my finger, 2" might be just enough to get the transmission shaft out of the damper plate.

Maybe, I figure worst case I’ll have to remove the engine mount bolts and slide the engine forward, I didn’t know it was only a couple of inches required, I figured you would need at least six to get the shaft to clear the bell housing.
I assume transmission comes first then the bell housing and that they aren’t removed as a unit?

[a64pilot]

Originally Posted by Wotname

@ a64pilot, do you have access to the service manual while on board?

If you are short on bandwidth, I can post the relevant pages from the my 4JH2 / KBW20 manual.

No, I don’t not the transmission end, figured R&R would be straight forward.
Have good band width now, leave in an hour or so, assume I will in New Providence.

[Davo1404]

I no that on the 2gm,you only have to remove the gearbox to expose the thrust plate. Hopefully your bigger motor is the same.

[Captain Bill]

I had a problem with my SD60 sail drives at about 1200 hours that was covered under warranty. When they had the drives out they noted that the damper springs were already loose and rattling around in the damper. The mechanic said that the current versions of the damper plate were rated at 1500 hrs and recommended replacing them since the drives were out and he would only charge me for the new dampers and 1 hr labor since the engines were already off the drive. The springs on the new ones were nice and tight. I don't know how long the original ones were rated for but they had to be replaced to accommodate the SD60 drives when I replaced my SD40s. In the literature that came with the install kit for the SD60's it mentioned the "new" style damper that meant that Yanmar had now standardized their style of damper plate across their small diesel product line. Apparently some engines used a synthetic polymer instead of springs and some used spring type dampers. If you read the service manual on the sail drives you will see a lot of parts have a service life rating of 1500 hrs, so I'm not terribly surprised that the damper plate would also be rated at 1500 hrs. My original sd40s did not have springs and seemed to be doing fine when replaced at 3200 hrs. I've also been told that low rpms are harder on damper plated than high RPMs. Apparently the power pulses they are designed to smooth out are far enough apart at low RPMs that the springs have enough time to decompress between power pulses and therefore move a lot, thus wear a lot. At high rpms the springs don't have enough time and essentially pretty much stay compressed. No movement, no wear.

[rbk]

Originally Posted by a64pilot

Maybe, I figure worst case I’ll have to remove the engine mount bolts and slide the engine forward, I didn’t know it was only a couple of inches required, I figured you would need at least six to get the shaft to clear the bell housing.
I assume transmission comes first then the bell housing and that they aren’t removed as a unit?

Just the tranny, bell housing can stay in place. You may be able to leave your engine in place if you have the room and can slide your shaft back a few inches.

[FPNC]

Drive plates are a wear item. There is a good chance that they will not last the life of the engine.

Some drive plates are designed to provide a 'weak link' that will fail in lieu of one of the more expensive drive components failing should the shaft overload from say a line wrapping around the propeller and suddenly stopping the shaft from turning.

The spring type drive plates are notorious for becoming very noisy prior to failure.

Anyone considering sailing to very remote areas should be proactive and identify the particular drive plate that is on their engine and possibly any alternative vendors. This will give you the ability to source one more easily or better yet, keep a spare plate or elements on board in case of failure.

[Frankly]

Because of the much larger mass/inertia of that AP, not hard to imagine that damper plate takes a licking shifting into gear. That would be a the top of my list of suspects. But you are not in much of a position to do anything about that.

Lot of moving parts in that AP and loosing/ damaging a blade is a pretty big financial hit. Bahamas water might still be a little cool but it is pretty deep in the Florida Straights to try to find a missing blade. I change mine out in the water every year (dockside). If you happen to go that route just be sure to have a line on that prop. You ain't going anywhere but to the bottom when that prop comes off that shaft


Frankly

[LeaseOnLife]

Originally Posted by a64pilot

Maybe, I figure worst case I’ll have to remove the engine mount bolts and slide the engine forward, I didn’t know it was only a couple of inches required, I figured you would need at least six to get the shaft to clear the bell housing.
I assume transmission comes first then the bell housing and that they aren’t removed as a unit?

The bell housing stays with the engine, together with the aft motor mounts, that would avoid re-aligning the engine, if you have the space. 10 bolts hold the trans to the bell housing. Not hard for a motorhead!


Pics shows tranny removed. You likely will see some loose springs in the damper plate, hopefully nothing broken. You can't do much about it but explain the noise and give you confidence to cross the stream.

[Captain Bill]

On my engine (sail drive so may not apply to OP) the transmission end of the bell housing opening is definitely not big enough to pass the damper through. The bell housing must be removed from the engine to mount the damper. Mine is a 3jh3 which is pretty much like the 4jh series except for the extra piston. Definitely check the size of the opening at the transmission end of the bell housing. It only requires about 2 inches of space to clear the shaft but I need an extra inch or so just to have some working room. If you can get the transmission out of the way with 2 inches of clearance, you're good. Given my sail drives I can do it in the water, but I have to move the engine forward about 4 inches to take the bell housing completely off. I can't move the transmission back, but then again I don't have to re-align the engine when I put it back together.

[CassidyNZ]

Originally Posted by a64pilot

Bill, If they are like clutch springs and I strongly suspect they are, they are the connection between two parts of the plate, all torture is transmitted through the springs.
The rattle occurs because when the engine is at low RPM, it’s actually jerking, not a smooth rotation, but actually many quick jerks.
If the engine RPM goes high enough it smooths out and the jerks are very much less apparent. It’s also why many engines will shake at idle, but visibly smooth out at high idle or higher.

That is why I’m thinking it’s the springs.

Almost certainly the springs. And you’re right on the money with vibration at idle, many diesels do that and the springs in the drive plate will chatter accordingly.

Unless a spring breaks there is no failure issue and these springs can go on literally for years without breaking. As an example, my pick-up truck has loose springs in the drive (clutch) plate that chatter loudly when running against compression (down hill) and have been doing that for years, perhaps 50,000 kms.

Motoring your boat at constant RPM will not precipitate a failure, IMO.