should max revs be obtained when

davierobb

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My mates sunseeker has been experiencing fuel problems. When tied to pontoon would you exesct engine to reach normal cruise revs, i.e about 3500 revs? The most we get in gear is 1200. We dont want to venture out of the harbour at present to see if it can reach full revs when unleashed.

Its fitted with a new kad32.
 

kashurst

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I am assuming it has two engines - are both affected?
have you checked /changed all the fuel filters and bled the system right through?
have you checked all the fuel pipe joints for tightness and or leaks?
are the engine(s) easy to start?
when running what is the exhaust smoke like?
are the air filters clear?
do KAD 42s have super chargers fitted ? if so check all the belt tensions and the supercharger clutch
try to resist revving the engines when not in gear - it knackers them! understand your worries about going out, very sensible, potter about in the harbour whilst sorting it, a quick/brief burst on one engine at a time will reveal if you have cleared the problem.
 
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Viscount

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Testing tied up can be misleading. My top end is 3,900 but would struggle to get more than 2,000 in gear when tied up. Are you in Troon per chance?
 

[2068]

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try to resist revving the engines when not in gear - it knackers them!

I'm really not sure why this would be the case, given that it's properly warmed up first, and you keep within operating range.

The only differences I can see would be a bit more exhaust back pressure from outdrives not moving through the water, and less forced cooling water induction from the pickup.
 

moonraker 36

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must put the boat and jetty under a lot of stress test engines this way....
glad its not my boat being stressed like that...
 

PCUK

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As engines are tested up to max idle revs as a matter of course, the only damage would be to an already fragile engine!

Test running while moored will never achieve anywhere near max revs in gear.
 

Latestarter1

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As engines are tested up to max idle revs as a matter of course, the only damage would be to an already fragile engine!

Test running while moored will never achieve anywhere near max revs in gear.

Exactly, could not have put it better myself.

'An engine under no load = minimal pressure on rings. At high revs ring can chatter in groove and break. It has to be said this is more likely on an older engine. Big ends can suffer similairly.
Also torsional oscillations in the crankshaft gan be set up. The load on the engine acts as a damper to the oscillations.

It's not a disaster to do it, just best practice not too.'

Never heard of so much gobbodygook. High idle testing is standard part of any manufacturers sign off testing (which is why figure is included in engine spec sheets) and certainly key element in dynamometer testing. You let the governor stabilise out on the droop, just letting the engine sing to you before you you apply test load. I am not aware of any diesel engine that is so poorly designed that it has a published health warning.

Unless you are dealing with an electronic motor high idle test MUST be part of any engine survey.

Also agree that running up loaded engines whilst moored is pretty pointless.

When testing at WOT if vessel is clean with 50% tanks should make published rated speed plus a margin of around 100 rpm in order to avoid engine overloading later in the season.
 
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tinkicker0

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An engine under no load = minimal pressure on rings. At high revs ring can chatter in groove and break. It has to be said this is more likely on an older engine. Big ends can suffer similairly.
Also torsional oscillations in the crankshaft gan be set up. The load on the engine acts as a damper to the oscillations.

It's not a disaster to do it, just best practice not too.

Never heard of ring flutter on a governed diesel engine. Piston speeds are just not high enough IMO. Maybe on a very well used petrol with piston land wear, but the alfin insert on most diesels pretty much stops ring groove wear, unless the air filtration is not up to the job.
Even a petrol engine has to accept WOT with no load without going pop if it is to pass a dyno test.
Doubt a diesel would achieve the 50 -60 m/sec piston velocity that would set up ring flutter.
Of course I could stand corrected.

I have measured and assessed probably in the region of 1000 diesel pistons in my customer specified class 2 (overhaul rather than remanufacture, class 1 being new pistons as matter of course) repair career, and rarely have I come across groove clearances that are out of specification and those usually on construction equipment motors, not automotive. Usually cracks in the skirt or underdimension / ovality / heat damage are the causes for rejection.
 
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The engineer

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I stand well and truly corrected by you 2 gentlemen! It was something I had been taught and believed. Pretty bloody obvious when you think of high idle figures.
 
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volvopaul

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You cannot possibly test the engines that way, the engines, drives and prop sizes are calculated and tested by manufacturers before any model hits the sales pitch.

You must carry out a sea trial in both directions against the tide and record rpm and speed attained figures, speed and rpm varies boat to boat, but as said you must achieve max loaded rpm if possible, but before you do this make sure the engines are serviced and are safe to put to sea.
 

Peanuts

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I notice in true forum form a complete tangent from the OP. In the first post the engine is a KAD 32, by the 2nd one it has become a KAD 42, or have I missed something?

In the OP it is mentioned it is a new KAD 32, now if it reaches the 'unloaded' RPM but not when underway to me I would be looking at the props, unless of course there is more to this story!

I always stand to be corrected!
 
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