Yanmar shuddering when put in gear

[Blueboatman]

Ah, been here, done that. I had exactly those symptoms. I have a 4JH. You can be pretty confident that it is the cone clutches failing. Sorry, it’s not good news. I replaced the gearbox with a new one because it wasn’t much more expensive than the rebuild cost and much quicker. I was fortunate to find a new old stock gearbox on the shelf which I bought for about £1,500, that was very lucky.

I am fortunate to have an excellent engineer on site, he diagnosed it in a flash after I’d spent months trying to understand what was going on. It is caused, commonly, by poorly adjusted gearbox control linkage which causes the cone clutches to be held very slightly open at all times. Failure is only a matter of time.

Interesting direct experience, good to tuck these bits of stuff away..

And at the same time probably replace the 4 engine mounts too=future proofing

 

[Bobc]

Sorry for the delay in replying.

Does it happen the same going into forward and reverse, or is it just going into forward?

 

[Sea Change]

Sorry for the delay in replying.

Does it happen the same going into forward and reverse, or is it just going into forward?

I think it only does it going in to forward gear.

 

[Bobc]

I think it only does it going in to forward gear.

Ok. I suspect it's the forward clutch cone that's the problem. It might be "grabbing" when it's engaging.

First thing to try is to change the oil. Drain the old stuff out, put new in, drive it round for a couple of hours, then drain and renew again. That might sort it out. If it's still the same, then it probably needs a new set of cones.

 

[Sea Change]

Ok. I suspect it's the forward clutch cone that's the problem. It might be "grabbing" when it's engaging.

First thing to try is to change the oil. Drain the old stuff out, put new in, drive it round for a couple of hours, then drain and renew again. That might sort it out. If it's still the same, then it probably needs a new set of cones.

This is good info, thank you. I know you can lap the cones, which sounds a bit like servicing a Blakes sea cock to me.
How bad do things have to be for me to be considering a reconditioned gearbox instead?

 

[Bobc]

This is good info, thank you. I know you can lap the cones, which sounds a bit like servicing a Blakes sea cock to me.
How bad do things have to be for me to be considering a reconditioned gearbox instead?

Have a look into the costs. Once you've costed a new set of cones along with the bearings and seals, you may find that a new gearbox is not much more money.

 

[Alex_Blackwood]

I can categorically rule this out. It's been behaving like this ever since we launched, and I've dived under the boat almost daily in clear water since then. I'd have noticed if there was something in the prop!

No idea whats wrong, but! What was it like before you lifted out and what did you, or a yard, do whilst it was out?

 

[Sea Change]

No idea whats wrong, but! What was it like before you lifted out and what did you, or a yard, do whilst it was out?

The boat was on the hard when we bought her. We launched, cruised for about a year, and then lifted out. No idea if the previous owner encountered this issue.

We've just avoided putting on sudden bursts of power so the juddering doesn't happen. If we were in the habit of needing to manoeuvre in tight spaces it would be an issue but we live at anchor so it's not really a big deal.

But obviously I want to get to the bottom of it before we launch!

 

[Boater Sam]

Something horrid on the prop or shaft.
Something horrid hanging on the rudder or P bracket and getting wrapped on the propeller.
A loose or broken flexible drive coupling twixt gearbox and shaft.
Sheared drive plate on flywheel.
Lets have a photo of the whole of the shaft inside the boat.

 

[Sea Change]

Something horrid on the prop or shaft.

Nope. I've been diving under the hull most days since we launched, I would have seen that.

Something horrid hanging on the rudder or P bracket and getting wrapped on the propeller.

See above

A loose or broken flexible drive coupling twixt gearbox and shaft.

I'd have expected that to be a bit more consistent? It only happens when I engage hear and then apply power straight away. If I wait a few seconds, it doesn't happen.

Sheared drive plate on flywheel.

The drive plate is definitely a potential suspect. But it's looking like the clutch cones are more likely, unfortunately.

Lets have a photo of the whole of the shaft inside the boat.

Not currently possible, the boat is about two thousand miles away. Returning early April.

 

[noelex]

The Yanmar 4JH5E was availble with a number of gearboxes.

What model gearbox do you have?

 

[Sea Change]

The Yanmar 4JH5E was availble with a number of gearboxes.

What model gearbox do you have?

I think it's the KM35P, but I'm not 100% on that at the moment. I'm going to see if the survey recorded it.

 

[noelex]

I think it's the KM35P, but I'm not 100% on that at the moment. I'm going to see if the survey recorded it.

That is a cone gearbox so Bobc is likely on the right track having suffered an identical issue.

The engine was also delivered with a number of other gearboxes (disc and hydraulic), including a larger cone gearbox, the KM4A.

The KM35 gearbox has a good reputation for reliability (unlike the cone clutches in some of the Yanmar saildrives), but Yanmar only offered the larger KM4 gearbox on the more powerful TE series, suggesting the KM35 gearbox was close to its horsepower limits in the 4JH5E.

 

[Sea Change]

Further thought on this, I've been nursing the issue along for several months. How likely is it that I'll suddenly lose drive completely? And what can I do in the meantime to minimise further damage?
I've been treating it very gently, not applying power too quickly, presumably that's the way to go?
I'd like to get this fixed before we launch but we are very much constrained by tides so we'll be launching mid May regardless.

 

[Bobc]

Further thought on this, I've been nursing the issue along for several months. How likely is it that I'll suddenly lose drive completely? And what can I do in the meantime to minimise further damage?
I've been treating it very gently, not applying power too quickly, presumably that's the way to go?
I'd like to get this fixed before we launch but we are very much constrained by tides so we'll be launching mid May regardless.

If it is what we think it is, there's not a big risk of you losing all drive. It's likely to just get worse.

Ways to minimise this is to keep the oil fresh and clean, and keep doing what you have been doing when putting it in gear.