P38 with machine gun sound at 2,200 revs

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amongstit

New Member
Posts
44
Location
Rutland
My 1998 P38 diesel auto is making a machine gun sound from what seems the top of the engine as it goes through the rev range at around 2,200 revs.
It's without vibration and disappears with a change of gear or when I reach around 2,700 revs.
If I very gently go through the rev range the noise isn't there but even with a normal driving pace on the road the noise is present.
I've revved it hard with my head under the bonnet and no noise,I'm hoping it's a common loose part in the bay but as yet I can't find anything loose though I've only had a quick scan,any advice would be greatly appreciated.
 
amongstit said:
My 1998 P38 diesel auto is making a machine gun sound from what seems the top of the engine as it goes through the rev range at around 2,200 revs.
It's without vibration and disappears with a change of gear or when I reach around 2,700 revs.
If I very gently go through the rev range the noise isn't there but even with a normal driving pace on the road the noise is present.
I've revved it hard with my head under the bonnet and no noise,I'm hoping it's a common loose part in the bay but as yet I can't find anything loose though I've only had a quick scan,any advice would be greatly appreciated.
Click to expand...

Could be a sticky tappet or check there is no delamination on the fan belt. A delaminated thread hanging off can cause this sort of noise as it slaps against a part.
 
wammers said:
Could be a sticky tappet or check there is no delamination on the fan belt. A delaminated thread hanging off can cause this sort of noise as it slaps against a part.
Click to expand...

I've had somebody rev the engine while I listen for the sound with my head in the engine bay and the sound isn't there.
It seems to be worse when going up a hill for example,going down that same hill accelerating the noise wont be there so its when it needs to move it's own weight with a bit of effort
 
amongstit said:
I've had somebody rev the engine while I listen for the sound with my head in the engine bay and the sound isn't there.
It seems to be worse when going up a hill for example,going down that same hill accelerating the noise wont be there so its when it needs to move it's own weight with a bit of effort
Click to expand...

Find yourself a decent mechanic and get him to listen to it. If it is only making the noise under load it could be something blowing. But have a look at the EGR valve if it's a sort of tinkling noise it could be that. Make sure all the connections to it are sound and whip it out and give it a clean. Sorry can't be more specific without hearing it myself.
 
Are you sure it's coming from the engine?

A machine gun sound is commonly associated with a stretched and slipping chain in the transfer box. If your vehicle has over 100k on it then it is likely to be stretched.

If it is the chain then I would expect it to only do it under heavy load ie hard acceleration. You won't be able to replicate the problem while stationary.

Just a thought...

Guy.
 
kooky_guy said:
Are you sure it's coming from the engine?

A machine gun sound is commonly associated with a stretched and slipping chain in the transfer box. If your vehicle has over 100k on it then it is likely to be stretched.

If it is the chain then I would expect it to only do it under heavy load ie hard acceleration. You won't be able to replicate the problem while stationary.

Just a thought...

Guy.
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Definitely the engine area,it reminds of the loose manifold cover sound from cars that used to have them,my vehicle has done 90k.
 
He did say there was no vibration, would think a prop spicer on it's way home would vibrate just a little. Unless he has one of those Jap none vibrating on failure UJs were the first indication you get is when the prop comes through the floor between your legs.:D:D:D
 
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It's an odd thing, but I have had a bearing cap eject itself from the spider after the bearing siezed and wore the circlip away, there was no discernable vibration but it made a curious clattering sound when under pressure and no sound on light loads.
 
Well another possibility is that it is actually a heat shield although it's hard to see why it would be tied to a specific engine speed.

One of mine just fell off into the propshaft and was making some very unpleasant noises - I thought the prop had gone again or the front diff was breaking up. Some of the others don't look that steady either. They're only attached with flimsy clips.

Guy
 
kooky_guy said:
Well another possibility is that it is actually a heat shield although it's hard to see why it would be tied to a specific engine speed.

One of mine just fell off into the propshaft and was making some very unpleasant noises - I thought the prop had gone again or the front diff was breaking up. Some of the others don't look that steady either. They're only attached with flimsy clips.

Guy
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Sympathetic resonance.

They are retained by the circlips. They are supposed to be a tight press fit into the prop, if they are loose going in the prop is knackered.
 
wammers said:
Sympathetic resonance.

They are retained by the circlips. They are supposed to be a tight press fit into the prop, if they are loose going in the prop is knackered.
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Hmm. Mine's a new prop although it's only a britpart one so I've kept my original so I can change the joints when I get round to it and replace it. Where is the best place to get new joints from?

My damaged heatshield has been stuck back on with big washers and nuts but I assume they didn't use nuts originally for a reason so I'll sort it properly when I replace the cats.

Guy.
 
kooky_guy said:
Hmm. Mine's a new prop although it's only a britpart one so I've kept my original so I can change the joints when I get round to it and replace it. Where is the best place to get new joints from?

My damaged heatshield has been stuck back on with big washers and nuts but I assume they didn't use nuts originally for a reason so I'll sort it properly when I replace the cats.

Guy.
Click to expand...

Any of your local motor factors should have them. There is no reason the Brit part prop should not give you years of good service.
 
Problems with a worn/loose chain in the transfer case are almost always described as a "machine gun sound". I came into this thread expecting this to be the case but I don't see anyone pointing to it?
 
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Not had chance to look at any of the areas mentioned but I did take it out for a 80 mile run tonight after adding 2 litres of water to the cooling system.
After the first 20 miles the noise had totally disappeared along with the dash creaking I've been getting(I'm aware this had nothing to do with topping up the cooling system),at the end of the run I popped into a local field to test my low gears and suspension,everything was fine so I left the field and dropped it back to the normal ride height(solid line setting on dash) and once again the machine gun/chatter noise appeared but not as loud and still certainly from the top of the engine,the dash creaking was as loud as before if not louder,so I ask again,any ideas?

I think this may be the least of my worries though as I think I'm losing water,tonight I added 2 litres and had to get rid of an air lock,I can see it's had a new rad so I'm hoping the tosser who fitted it didn't bleed the system of air,it wouldn't surprise me,yesterday I found a rad pipe that was rubbing on the side of the rocker so the last owner or his backwards mechanic had rubbed grease around it to delay the friction from damaging the pipe,I've since loosely zip tied it with success
 
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