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Clunks... What's going on here?


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Looks and sounds like a sticking valve - sometimes a valve not completely sealing and blowing out compression via the intake system. When the tech got it to drop to 2 cylinders it was the same regardless of the cylinder stopped? Be interesting to see what volvo say...

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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

10 hours ago, Island Time said:

Looks and sounds like a sticking valve - sometimes a valve not completely sealing and blowing out compression via the intake system. When the tech got it to drop to 2 cylinders it was the same regardless of the cylinder stopped? Be interesting to see what volvo say...

It dropped down the same regardless of the cylinder. But it didn’t make that kick.

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one other left field possibility to check, because I had this happen to me - a faulty alternator. 

In my powerboat days with a big Perkins had the situation where the engine was trying to jump off its mounts when warm. Zeroed it down to the alternator and on 3rd visit to the auto leccy insisted they open it up and they found one of output wires had come loose and was intermittently disconnecting.

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12 hours ago, DrWatson said:

I’m starting to think we should run a poll,...

Haha! I think you’re right the honest answer is that we’re all pretty clueless and hopeless and helping you aren’t we?

Be v interesting to see what the verdict is.

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haha, 

well I don't think "Hopeless at helping" is accurate :) but we might soon be exhausting our reservoir of explanations.

The breadth of experience here on the forum is exceptional, and each suggestion has been based on a member's previous experience. Some of those experiences include the strangest things which others of us would never have considered, but the suggestions are made on first hand examples, and all made with reason. It's not like people 

To date:

  1. Buggered injector pump/buggered injector (not being a mechanic this was my first guess)
  2. Burnt or sticking valve
  3. Broken crank
  4. Obstruction on the prop
  5. Broken engine mount
  6. Broken/occluded cam
  7. Alternator
  8. Wiring loom issue (Lordy I hope not, there's about 2km of wiring on this boat)
  9. Black box
  10. Clutch cone grabbing 
  11. Oil level in gearbox
  12. Morse cable adjustment
  13. Engine drive plate
  14. Starter motor/flywheel
  15. Engine dampner plate

 

One thing to consider is that it only happens when the whole set up is warm and restarted... (might happen when it's warm immediately, but I normally don't leave it running in neutral after I've finished motoring somewhere.) It also didn't do it earlier in the trip when we ran the motor in Neutral for 40 min or so to charge batteries while making water - so when the motor is warm and the gearbox not.

So it's intermittent and very regular... about once every 12th revolution (Thanks JimS for counting), so it's likely to be geared issue, but not something related to the engine firing or engine timing itself? I'm guessing a sticking valve would not occur "exactly" every 6th action.

8 minutes ago, Island Time said:

If it does not do it down a cylinder, what happens if you remove the air cleaner?

haven't tried...

 

 

 

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The sail drive is 2.3  : 1 or thereabouts so that becomes less likely.   a warm engine will react to (ignite) a stray amount of fuel much more readily than a cold engine. Pity you aren't in NZ we could have a Crew barbeque with a sweepstake while we sort it...

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18 minutes ago, jim s said:

The sail drive is 2.3  : 1 or thereabouts so that becomes less likely.   a warm engine will react to (ignite) a stray amount of fuel much more readily than a cold engine. Pity you aren't in NZ we could have a Crew barbeque with a sweepstake while we sort it...

Hahah, we could still do the sweepstake, and the winner gets to sail Firefly to Jersey and back to France at the end of October... 

She needs to leave the EU for at least a night, and what with various quarantines and work commitments, I'm not sure it's gonna work out.

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