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Clunks... What's going on here?

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So, the last two days of our cruise were a little marred by the following effect. Intermittent but can be reproduced sort of. Run motor and potter along the coast for 2-3 hours. sail for 3h or so, then start motor for manouvering. Does this in idle at neutral and when engaged in FWD but at idle, at least sometimes, then went away when increased to 1200 rpm...

It's not a sound and effect I enjoy so we stopped using the engine and only manoeuvred under sail after this. Called the Volvo service centre, they sent a tech, and of course we couldn't reproduce it. Didn't have the video to show him at that time. But recorded this after he left. Case now reopened but let's see.




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Starting to like the idea of 1000Ah of 48V Li and a DC motor slapped on the top of the saildrive...

Something big that require revs / centrifugal force is the prop, and one blade sticking will obviously cause balance issues. I actually wondered if you had a bucket wrapped on the prop. If it was a sh

The thing is with Camshaft, Cranks, Chains, Cogs etc etc and any other solid mechanical timed mechanisms, if they fail in anyway, the issue is not intermittent. They all cause major and even catastrop

1 hour ago, jim s said:

Hmmm it's very regular... and by the way the engine shudders on its mounts its not pretty. I suspect there may be issues with the injector pump. let us know what the tech finds - good luck!

Yeah the regularity and the shudder got me and I shut it down within 20 sec. I started it again 5 min later in Neutral to check and same thing so shutdown after 10 sec. In my experience, sounds like this warrant immediate shutdown.

Was thinking it could be a tooth on the timing catching, a cam hitting something, or a partial seize? I dunno. Considered the blocked injector or injector pump issue. I've relatively little experience with diesels, but the way it was kicking reminded me of an old escort engine missing on a cylinder or two, So I considered maybe those injection related issues. But  the tech eased each of the the injector nuts to depressurise each and she simply dropped down to two cylinders and ran smooth - no kick. For it to be an injector issue and regularly failing a cylinder I would expect the frequency of the error to be higher, perhaps 400 per minute (at 800 rpm). 

Tech mussed and fussed around for 20 minuted checking everything fuel supply related and eventually, grasping at straws, suggested that maybe we'd got some "winter coolant in the fuel line" (wtf!!) or drawn a little air into the fuel line when heeled over, as the fuel tank was only half full, to which I conceded might be possible if we were heeled at 90° and running the motor which we weren't. He left, satisfied the engine was fine, and then I got a call from the Volvo Action service centre telling me the case had now been closed be cause the tech had determined we'd run out of fuel!!! I told them in no uncertain terms that that certainly wasn't the case. But in a call this morning the call centre guy still referred to us running out of fuel. 

Now that I have a video of it I can re examine it a few times and make a different prognosis. The way it went away when gearbox engaged and up at 1200 rpm suggests that it might be something between the gearbox and the engine which is miss-aligned and trying to engage but missing...

In any case, a knock like that will certainly wear stuff out pretty quick.

46 minutes ago, Dtwo said:

What sort of prop setup do you have?  Coupling tight?  

It's a s120 sail drive ( I think that's the model). Standard drive leg and prop.


Motor was serviced at 38 hours (first service) a few hours earlier than the recommended 50 but it was the end of the season and the start of winter so not a bad idea to do it a little early. 

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4 hours ago, DrWatson said:

Was thinking it could be a tooth on the timing catching, a cam hitting something, or a partial seize

The Mechanic needs his rear projecting big end kicked. That is NOT a Fuel issue. He proved that by testing each cylinder. Air would have been bled out. 
It's none of the things you have suggested . Fault like those would not go away at a higher RPM. Plus a cylinder not firing is going to cause smoke issues. Rest assured that if the internals are making such a sound, then the fault is going to make itself very apparent soon. However, rest assured it is not the engine causing the problem.
In fact, I suggest it is external to the engine. The engine movement looks like it is being pushed around by an external force and the regularity seems like it is something trying to turn and hitting or something engaging or disengaging.
There is a flash of something in the background at the rear of the engine that is in time with the sound. Is it just a reflection of light in the screen on the phone? or is it something going on back there in the engine bay.
Dose it have a folding prop? Are you sure that the prop is totally clean?

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To be fair to the mechanic, it refused to make that sound and shake in his presence. 

Prop is two blades folding. Propspeed applied on 1july. Boat launched on 12 July. Worked fine for nearly the two weeks of our trip so I doubt it’s the prop. ESP as it doesn’t seem to happen once fully in gear and motoring.

I’m  going with something engaging or trYing to engage. Either way I expect an error like this could result in considerable wear  and damage if not rectified.


No flash in the back ground. It’s raining and some rain coming down the hatch. Maybe a trick of the light.

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Does look a bit like my engine when one blade of the prop wouldn't open, but intermittently.

Any sign of prop wash when its happening?

Prop slowly turning, blade flops down, somehow makes clutch cones grab, rests itself...

Clutch adjustment? 

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54 minutes ago, DrWatson said:

This is in neutral 

I realise that, doesn't mean clutch is not engaging a bit, would check anyway, is the prop definitely not turning at all.

Pretty easy for the various adjustments to be wrong, or something gone wrong in the gearbox letting the clutch grab

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Could it be the starter motor trying to engage with the fly wheel? Its the only thing I can think of that would make a noise like that. Possibly lectrical fault in the wiring loom. You know, when you go to start your car but its already running?

lectrical faults in wiring looms are a common cause of really random other faults. Especially if it came on while out cruising the boat. Sea air and wiring looms are diametrically opposed...

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