P38A Tapping noise from bottom of engine on '99 4.0

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rangie1998

rangie1998

Active Member
Posts
279
Location
Leeds
Evening all,

My friend has very recently purchased a '99 P38 4.0 SE with the Thor Engine.

Really nice car, quite jealous!, but has this tapping/knocking noise which appears to be coming from the bottom of the engine near the front (certainly more evident when looking under the bumper at the front).

It drives fine with no issues, i.e, its not overheating or down on power.

The noise seems to prevalent when the car has warmed up. My friend isn't too concerned as he got the car at a very good price but it would be nice to know what is causing this noise and if left is there the potential for something serious to happen?

He's not yet a forum member, but I said I would post on his behalf as if you guys don't know what it might be it really is an odd one!

Thanks in anticipation of your wisdom!
 
Take the fan belt off ,start it and see if the noise is still there. The diesel crank pulley can give problems but I don't know about the Thor. Get a stethoscope or a long screwdriver and try and locate the source of the noise. Is it down on oil pressure? Timing chain? I'm sure there will be other suggestions but they will be guesses. Can you upload a video it may help.
 
Possibly a slipped liner. If it's a later block with the steps at the bottom the noise can come from the top & bottom as the liner hits both the fire ring on the cylinder head & the step at the bottom of the block, almost like a double tap. Mine did this.
 
Colthebrummie said:
What mileage is on the engine and has it got a good service record?

Col
Click to expand...
It's done 129k and does have a good service record. The previous had it 7 years and has kept it in good condition. No problems in the way it drives.
I'll try uploading a video of the noise today.
 
martynv8 said:
Possibly a slipped liner. If it's a later block with the steps at the bottom the noise can come from the top & bottom as the liner hits both the fire ring on the cylinder head & the step at the bottom of the block, almost like a double tap. Mine did this.
Click to expand...
Thanks, doesn't sound like a 'double tap' more of a 'rattly' tap and appears to be only at the bottom of the engine. Will take a closer look today and try to upload a video.
Other than the tapping noise I think its a great car. Hopefully nothing too serious.
 
Just a guess but if it's ok when cold then taps when worn my guess is a slight big end knock. Mine did this for years. Before a rebuild. As the oil thins out it allows contact on one big end. I thought mine was because water was getting into the engine oil. It could also be leaking manifolds exhaust pipes.etc
 
tomcat59alan said:
Take the fan belt off ,start it and see if the noise is still there. The diesel crank pulley can give problems but I don't know about the Thor. Get a stethoscope or a long screwdriver and try and locate the source of the noise. Is it down on oil pressure? Timing chain? I'm sure there will be other suggestions but they will be guesses. Can you upload a video it may help.
Click to expand...


wakey wakey alan.. its a 4.0 (petrol) no fan belt.. a serpentine belt
 
possibly a crankshaft bearing, . can I just eliminate something obvious.... look at the back of the viscous fan coupling.. are the 4 bolts in there and tight? mine lost a bolt and it gave a rhythmic tapping noise. new bolt.. tightened all 4 up to torque.. problem solved.

what you can do, is get the longest screwdriver you can, lie underneath and put the pointy end against the sump in the area of the crank bearings and the handle end to your ear.. move forward and back the sump and see where the noise is coming from.. Saint V8 did a walkthrough on big end bearing replacement if I remember correctly
 
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For me the tell tale is if the knocking happens when the cars properly warmed up on tickover. Amazingly when the engine is coldish the oil is thick enough to stop the rattle(10/40)! Also when slightly higher than tickover the oil pressure will prevent knocking. These things point to a big end problem. Jb
 
Thank you for your replies, very much appreciated. Didn't get chance to have a look yesterday as it was raining most of the day (typical Yorkshire weather).

Will check out the things mentioned and do a video, most likely tomorrow as off to collect another classic project today.....

Thanks again, great forum as always.
 
Crawled under the car today with my phone and long screwdriver! The noise appears to be coming from the rear/bottom of the engine where it meets the auto box, but I couldn't pinpoint it with the screwdriver.

Only does it when warm and on tickover, when you rev it it stops, and then starts again when the revs have settled.

Have done a video but having a few problems uploading it to the message, what's the best way?

Thanks
 
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I had an XJ6 years ago that tapped on tickover and it turned out to be the drive plate had fractured around the torque converter mounting holes. Is there an inspection cover on the bottom of the bellhousing? If so take it off and see if the T/C is loose. Question to members, are the torque converters known to excessive wear.
 
There is indeed a little cover bottom of the b/housing. A torch and a sturdy screwdriver to turn the flywheel will reveal any problems. Leave it in neutral/engine off.. of course!! ;)
 
That is indeed a common problem on p38s to! On mine I undid the cover and several parts of the drive plate fell out. Tricky job to replace though.
 
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