DT engine knocking

Ok, Got the P38 2.5 DT (203k miles R reg) so far it has run as expected (slowly doing approx. 700 motorway miles a week) since I got it, it has been difficult to start, I went out the other morning and it was turning over but refusing to start (getting just about there but not quite) and ran the battery down , so charged it up and eventually, after a fair bit of turning over it started, but there is now a knocking from the engine it reminds me of knackered big end bearings but coming from the top end and louder towards the front, this 'knocking' goes away at 1250 revs and it then just sounds like a normal diesel engine (well as normal as a 2.5 DT will get) also the knocking doesn't get any faster as the revs increase to 1250, I had already glow plugs so when they arrived I fitted them and now the car starts a whole lot better (but still the knocking) and, being the brave (stupid) sole that I am took it for a thirty mile run, where it drove as it usually does (slowly but gets your there) but knocking still there (a lot quieter with the bonnet down) any 2.5 diesel experts out there got any ideas?

Whats your oil pressure like? I'm no expert but id look there to start with. An oil pump failing/on its last legs may well not be getting much oil to the top end...??


Just a thought

Update, went out and released the tension on the auxiliary belt (alternator), and the noise goes away (aux belt starts slipping), so it is not the engine itself but something that is connected through the auxiliary belt

Littelwill said:

Whats your oil pressure like? I'm no expert but id look there to start with. An oil pump failing/on its last legs may well not be getting much oil to the top end...??


Just a thought

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Thanks, I did think about that, but there is no warning light on (or even flickering)

Probably crankshaft pulley disintegrated.

Water pump? Does the knocking stop when the belt is off?

N2O said:

Probably crankshaft pulley disintegrated.

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Think if the crank pulley was on its way out it would be not be driveable due to vibration. Take the belt off and feel the water pump, alternator,idler and tensioner pulleys for any roughness/ play.

When crank pulley is on it's way out it knocks only when there is load on it on low revs. Its simply dual mass pulley(harmonic balancer), no need for it when spinning fast, hence why it smoothens on higher revs.

N2O said:

When crank pulley is on it's way out it knocks only when there is load on it on low revs. Its simply dual mass pulley(harmonic balancer), no need for it when spinning fast, hence why it smoothens on higher revs.

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Don't want to get into a ****ing contest with you but when my mates started to break up the car was undriveable. Guess the op has to check everything that drives or is driven by the belt.

I'd go for the crank pulley as it quietens with more revs.

Datatek said:

I'd go for the crank pulley as it quietens with more revs.

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If it was the crank pulley shouldn't the noise continue when the belt tension is relieved? See post 3

tomcat59alan said:

If it was the crank pulley shouldn't the noise continue when the belt tension is relieved? See post 3

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It seems not, with nothing to pull against. It it were a manual, I'd go for the DMF.

Datatek said:

It seems not, with nothing to pull against. It it were a manual, I'd go for the DMF.

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Please explain

There is a possibility that the tension idler is fouling the the plate on the crank pulley.

When I refurbished my engine I started it up and the new tension Idler was just catching the plate and creating the most awful noise, from memory there are three or four raised castings on the crank pulley plate and these were bashing the tension idler.

It was a new part so I had a machine shop mill and few millimetres off it which solved the issue

Maybe your tension idler is tired and has developed play and is catching the plate as they over lap and there is a fairly close tolerance between them.

Worth a shot

tomcat59alan said:

Please explain

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With no pull on the belt, centrifugal force locks the 2 parts of the pulley together, at least that's my guess.

Without the belt tension I would have thought the outer part of the pulley will flop about like a cock in a three cornered hat. Wish the o/p would hurry up and have a look.

If the rubber separating the inner and outer is knackered the inner parts retention fingers could be striking the outer part causing a knock. But the torsional damper would have to be pretty well goosed for that to happen.

tomcat59alan said:

Without the belt tension I would have thought the outer part of the pulley will flop about like a cock in a three cornered hat. Wish the o/p would hurry up and have a look.

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Do you mean wobble about like a Whippets dick?

wammers said:

Do you mean wobble about like a Whippets dick?

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Not when referring to crankshaft pulleys Tony.. In his original post he said the knocking is coming from the top end of the engine. You been busy this weekend ? not to many posts.

tomcat59alan said:

Not when referring to crankshaft pulleys Tony.. In his original post he said the knocking is coming from the top end of the engine. You been busy this weekend ? not to many posts.

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Not specially busy just doing other things. Yeah the crank pulley is hardly the top of the engine. Maybe a sick tappet. But the crank pulley inner has three fingers on it that fit in slots in the outer. Basically so if the rubber between them becomes detached it cannot spin inside the inner and cause loss of drive. They can rattle about a bit i suppose if totally goosed. This may cause the tensioner to oscillate somewhat though, that would give a visual indication of damper on it's way out. You do get a gentle movement of the tensioner with a good pulley but with a duff pulley it would be very noticeable and rapid.