Been having a subtle deep knock from the front of my motor that can only be heard/felt in the A bank cylinder head right over cylinder 1. Used a stethoscope to pinpoint the knock, one hundred percent certainty that's the only place it could be heard and felt. Suspected there was a loose rod bearing. It was a super deep sounding knock that could be felt in the shifter. Oil pressure is 70 psi cold, 30 psi hot and in gear without the car moving. Had extremely faint sparkling stuff in my oil that was non magnetic. So went into my motor inframe to start looking at bearings starting at the front and going back suspecting to find the problem immediately upon taking 1a rod cap off. All I found was a good looking bearing with a few light gouges from something foreign getting in. I took off the front 6 caps and found the same story on all of them. Good looking bearings with just slight amounts of foreign material damage. But nowhere near enough to cause knocking, unless gouges can do that. The top halves look fine, with minimal copper exposure, not enough to cause knocking. So I pulled the 3 front mains, I can only attach one picture, don't know why. But here is the most worn bearing. Supposedly I can't use plastigauge right because it says this worn out main pictured is running a .002" clearance. Yes I wiped oil away and the main cap side, there was oil on the other side of the bearing, but that should take a MAX of .001". I'm not sure what to do next, the cheapest car with a 6 liter is $2,800 in my area. The next best option is to pull the motor and check piston skirts and wrist pins, although the knock is way too deep sounding to be a skirt or wrist pins. Is there anything else that could cause deep knocking that isn't bearings? It's a 96 xj12 but the xj12 forum is dry.

 

I am no expert at all on engines, but that bearing looks pretty shot to me.

 

Yes Greg! You are correct. Visible copper always means bad bearing. Now why are all my bearings worn? I got the car with 5 extra quarts of oil. And the oil light would come on at idle from the possible excessive foaming of the oil. I just talked to my most trusted guru and he said visible copper always means the bearing is in usable. My crank is perfect, so its time for new rods and mains! So, problem solved!

 

Are you sure? there should be white metal there surely?

 

Very interesting - more pictures.
Did you have to pull the engine? or is that a dumb question.

 

Like Greg I am no expert but that bearing looks tired to me.

 

Why not use new bearings of the standard size that is available?

 

That bearing is tired, and I would not use it.

Causing the knock, NOT convinced. That would mean the HUGE crankshaft must be flexing, and that I doubt seriously.

Not sure on the 6ltr, and I will look at my books later, but on the 5.3, SAME engine for what we are discussing, the front crank bolt, the BIG SUCKER comes loose, the pulley rocks on the cone, mainly from ON/OFF of the A/C compressor, this wears the keyways and keys, and eventually the cone will split in two.

THE KNOCK HERE IS IDENTICAL TO A BIG END. It matters not if the A/C is used now, the damage be done.

I have heard a few, and I 100% hung my hat on big end bearings, NOT so.

Worth a look, but DO NOT rotate that engine Anti-Clockwise.

 

OK, the 6ltr has NO cone. The pulley/harmonic balancer slides on the snout, and held with the BIG bolt, and key way.

Same as the AJ6/16 engines, and they DO come loose also, both mine did, and the knock was horrible also.

 

It was a knock that was surely dependent on oil pressure. When I fired it up in the morning it would be THUMP THUMP THUMP then oil would come and it would go away until it got hot. The knock was very faint and subtle. All of the top halves of the rods in the front 6 cylinders had visible copper. I'm not even going to waste time trying to plastigauge them to determine if they were loose. I'm just going to put in rods and mains and see if it fixes it. And if it doesn't, then I will live with the knock until it gets worse and then I'll address it. But now, I must ask. Can I pull off the rear main cap without pulling the motor?

 

Ivan,

Never gone into a 6ltr.

On my 5.3, YES, as I did so to seal the cap to the block for an oil weep.

BUT

Mine was the Pre Marelli engine, with the 2 halve rope rear seal. Yours will be the full circle "flaseal" style.

The oil supply and suction pipe o/rings sound like they have failed, easy task to replace with the Viton spec rings.

 

GREAT! What makes you say my oil suction and supply pipe seals have failed?

 

Yes, your slow oil pressure rise etc is classic o/ring failure. At least on the 5.3, so i see no reasons for the 6ltr to not have issues eventually. Failed is probably a tad strong, they shrink, sometimes split.

ALSO

Take a look at the snaps here:

https://www.jaguarforums.com/forum/x...l-seal-234222/

They clearly show the full circle rear seal you will have. It is recessed into the block and main bearing cap. Removing that cap would be simple, as things are, refitting, and keeping that seal in place, dunno.

 

Good point! I always remembered it taking a little too long for the oil light to go away! So sad Jaguar had to do it that way! Also, I guess I'll liberally use anaerobic sealant! Thanks!