Diagnose Engine Rattle

[SimonBrown]

Would anyone be able to help me diagnose an engine rattle I have had on the E since the engine was rebuilt 7 years ago and 3000 miles.
It is only from a cold start
Only at approx 1300rpm, quiet above and quiet below these revs
It disappears after approx 2 minutes running time from cold
From the top part of the engine, head or under cam covers
Valve clearances are correct for a late series 2, approx 10 inlet and 12 exhaust, parabolic 4 hole cams.
I have tried tightening the top chain, made no difference.
Difficult establish whether from inlet or exhaust side
I heave gently compressed each valve bucket and they all seem to have similar spring pressure, with no lateral play.
I am really at a loss with this one as I need to fix it but cannot find anything obvious
Any help would be greatly appreciated, YouTube link below
Many thanks
Simon

[mgcjag]

Hi Simon..dosnt sound good....your tapper gap should be 12-14 for both inlet and exhaust...check the tappets..are they rocking in the guides..I would check and set them all and look closely at the tappet guides...are they loose and hitting the cam lobes....close inspection will show marks on them....its not un typical to find dome cars have hold down kits fitted to stop them lifting......are you sure you have chain tensioned correctly.....just to eliminate waterpump/alternator then disconnect the drive belt....Steve

[politeperson]

Sounds like the timing chain might need re-tensioning to me.

[SimonBrown]

Hi Steve, James,
Thanks for coming back. I have tried tightening the top chain a touch too tight, this made no difference to the noise. I have tried rotating buckets with valves closed and can find no discernible movement. There are no witness marks on any of the guides.
What I really don’t get is that it is very rattly at a constant 1300 rpm, raise or lower revs and the noise disappears. Almost like a resonance.
Then disappears after only 2 minutes running time from cold.
Really frustrated with it as the engine runs fine apart from that
Simon

[mgcjag]

Hi Simon....remove drive belt to eliminate altermator etc.....Steve

[SimonBrown]

Thanks Steve, I’ll try that and come back tomorrow

[gtjoey]

First
BRUTAL RACING THE ENGINESTONE COLD....
Second and dont shoot the messenger,are you using BRAIDED oil feed lines on the back of the head?
Third , The REPLACEMENT timing chain tensioners are CRAP and fall apart.
Unless the BRAND NEW SNG ONES.....
I had 3 friends have this happen in the last24 months......
Yeah that good ole replacement part!
Good luck,I bet I know which it is.......
GTJOEY1314

[Jack the lad]

Please post another Youtube video with the engine running thoroughly warmed up. I can hear many noises, some appear to be coming from the crankshaft, do you have good oil pressure? Mechanics stethoscope is useful and not expensive, also remove the oil filler cap and listen in might help. Good luck with it, John.

[SimonBrown]

Disconnected drive belt as Steve suggested, readjusted top chain and started - no difference.
Compressions all good and even, oil pressure builds quickly from cold and maintains 55 psi at hot idle.
Braided cam oil feed pipes and plenty of lubrication. No rocking of valve buckets or witness marks.
I am at a complete loss
What I don’t get is that the rattle is very rev specific at 1300 revs, so 1100 revs it is quiet, and 1500 revs quiet.
It is there from cold start and disappears at around one and a half minutes later.
It appears to be coming from under the cam covers.
Could it be a resonance of some sort?
Appreciate any ideas
Many thanks
Simon

[mgcjag]

Hi Simon...your gaps are out of spec at 10 and 12...should 12 to 14....its something to consider rechecking them all....Steve

[nichmoss]

As James said, it sounds like the top chain adjustment. The noise is very apparent when the revs fall after you raised them - this is a classic symptom of a loose chain. Obviously, check those gaps again first but I would then recheck the top chain.

When you make the hot engine video, try blipping the throttle to 3000 rpm and immediately release. If you hear that noise again, the first place I'd look is the top chain adjustment.

Good luck, Chris

[SimonBrown]

Thanks Chris,
Inclined to agree, it does sound chain like. However the chain has now been adjusted three times, once slightly over tightened, then slackened correctly and these different adjustments haven’t altered the character of the noise.
I am sure there is no noise when blipping the throttle hot, but will produce a video to confirm.
Unfortunately I have noticed a leaking fuel pipe so need to fix that before running it again. Aftermarket parts🤬
Appreciate your help
Simon

[christopher storey]

The fact that it disappears when hot , and the oil is therefore thinner, leads me to suspect the lower timing chain which is tensioned by a piston type tensioner which is actuated by oil pressure. Unfortunately, there is no way of checking this without removing the front cover. What I would do first is rather drastic , but may work. Change the oil for a mixture of about 40:60 diesel fuel to lubricating oil, and run the engine - gently - for about 15 minutes . Then replace with normal lubricant ( 20-50) and see if it has made any difference . If it has, then job done. If not, then it is sump and front cover removal time

PS the other possibility, which these ( 4.2 rather than the smaller sizes ) engines are subject to, is piston slap, which often, for reasons that I do not understand, can often be most readily heard from directly in front of the engine . This would fit most readily with the fact that the noise disappears as the engine warms. I should also ask whether by any chance your engine has originally come from a mark 10 ( 7D engine prefix ) as these had the cranks ground with slight ovality to eliminate resonance effects in the bodyshell of the mark 10

[SimonBrown]

Thanks Christopher,
The noise is right at the top of the engine, at top chain, camshaft valve level, and disappears after about one and a half minutes from cold. I can’t see the oil thinning in that time?
I did think of piston slap, but my experience with piston slap was of a much deeper knock, rather than a tappet type noise. It is the original engine to the car (7R8682), and although 6 units before the change to 4 hole cams, it has the latter
Simon

[SimonBrown]

Apologies for going on about this, but I am determined to sort it🥱
Is it possible I have a slightly loose valve seat, rattling when stone cold, but warming up enough to stay in place after one and a half minutes running?
Thank you
Simon

[christopher storey]

Ah, now my experience of piston slap on XKs is that it shows up as a light tinkling noise which lasts for a very few minutes until the pistons themselves warm up. I have to say that it is very easy to become paranoid about noises on these really quite complex engines, ( we are inclined to foget that they are just as complex as a 1920s Bugatti ) and if the noise disappears completely after a short warm up, as it seems to do in your case , I would be inclined to ignore it unless it manifests itself at other times or in other situations . I have to say that unlike another contributor, I could hear nothing which suggested crankshaft noise, which usually is rumble in the case of main bearings worn, and a throttle sensitive knock in the case of big end trouble

[christopher storey]

My last post crossed with your latest. No, I think a loose valve seat is very unlikely , because warming of the aluminium head is likely to loosen the chilled cast iron seat rather than tighten it, and if it was loose enough to be trapped by the valve and therefore cause significant noise, then almost certainly it would be accompanied by rough running because of loss of Compression, and in a very short space of time the brittle seat would be likely to break up . A loose bucket guide is more likely, particularly on the exhaust side , and you can fairly easily check for this by removing the cam covers and looking for witness marks on the bucket guides/ the buckets themselves/ the cam edges

[SimonBrown]

Thank you Christopher, appreciate your advice. I think I am going to leave it unless it gets worse. If I run it at under 1300rpm for a couple of minutes before driving it is as quiet as I could expect. I have had the cam covers off and could see no signs of loose buckets or any witness marks. Although all clearances are approx 2 thou tight I can’t see this making too much difference.
I am concerned I will remove and strip the head still finding nothing.
Thank you again for your help
Simon

[Jack the lad]

Just a thought, when you adjusted the top chain device did you turn the adjuster the correct way (direction) as told by the Jaguar workshop manual? Its possible to turn the adjuster in either direction to tighten the chain but only one is correct, well worth a check. I never found the video with the engine running when hot, have I missed it? Do not under any circumstances run the engine with anything other than only 20/50 motor oil, the suggestion to add Diesel fuel will leave an amount in your engine and fill oil galleries to cause problems later. I would love to know where to obtain oval crank bearings for the MK10's, none listed in my extensive catalogue collection.

[christopher storey]

The bearings are not oval : it is the crank journals which ( however strange it may sound ) were ground to an oval . This is dealt with ( IIRC) in Roger Bywater's extensive commentary on the development of the4.2 XK engines and the mark 10