S1 Series 1 3 XJ6 engine knock


Simply wished to ask, and I am not probing for some miraculous answer.
This car is a keeper and as such will need to be rebuilt otherwise I will not be satisfied.
But I just may not have the time sadly…i hate to let it go. These cars are so rare and special.

It’s a series 1 with a series 3 motor.

Knocks are tricky to trace. Such a subtle thing I need to go out again and again to try and get a fresh idea of what I have or feel.

The car is a mess of vacuum leaks and although I have cleaned out fuel system, rebuilt carbs, there is much to do, however unrelated to knock condition.

Solid compression of 150 across all cylinders … although #5 yields 130. a spot of oil brings it up to 150.

Remove the lead to #5 and the sound goes away…

the ole tube to the ear seems to point to the sump area…so I’m thinking rod knock…but who knows. Hard to tell, it’s subtle, sound travels easily, etc.

this car has been sitting ages, is really in super shape otherwise … but it has been sitting within garage for ages. 2 lines from header tank blocked off by PO as radiator connection is welded shut and overflow tank has pinhole leak…

Some oil sludge existed prior to flush with vinegar, etc…either oil or bars crap.
I have 2 complete heads with the car. PO either replaced an d did not flush out cooling system (absolutely probable) or it is overheating or bars leak crap.

Won’t feel comfortable without new radiator, hoses, water pump…still deciding whether I should get a newer model or stay with this. This is a keeper that’s for sure, a bit of a dream car for me, but although eccentric and a die hard nut, as an everyday, well, I’m beginning to have second thoughts…

I patiently went through it all, lubed cylinders prior to turning, used seafoam a couple times to clean valves hopefully…if sticking. Shot sprays of water too while idling…completely cleaned fuel delivery.
Patiently and cautiously bringing her to life. I’m a perfectionist.

Simply searching for other thoughts.

Could it be a valve issue? Sticking valve? Would a head gasket issue cause this sound? Can a sticking valve remedy itself?

Again, this car has not been run for a long time.
I have driven it around the neighborhood for 15min or so only.

The Facts:

Compression 150 solid on all cylinders except #5 at 130. Oil added to cylinder brings it to 150.

Disconnect #5, sound disappears.
Oil pressure very good.

After running a while when attempt to start again seems like it is missing, as if incorrect spark plugs attached to wrong cylinder. Was it overheating? Can’t be sure. Infrared thermometer said no.

Sound disappears with increased revs.

First starting attempts yielded black plugs…they seemed wet actually. not fluffy black.
another new set of plugs reveals a cleaner running condition.

Is it a result of my processes, shooting water, using seafoam, etc to de-gunk the the cylinders and valves, or is it water in cylinders? I dunno.

Overheating past…before me. Possibly sat for a while with water in oil, ruined bearing?

Valve tappets ok. Clearances need to be rechecked since determining #5cylinder, but if anything they were all a bit too tight.

Attempted to use screwdriver to push down cylinder through hole to determine any rod slack. nothing.

Replaced oil, wires and plugs with high end NGK recommended in ETtype forum. very clean…too clean if I remember. Water in cylinder? dunno.
At 130psi should not be head gasket issue?

that’s all that comes to mind at moment to cover bases beforehand.

I have not yet replaced hoses and refused to run it until pump, radiator, hoses replaced.

When I drove it, and tested it idling, it did not overheat as per infrared thermometer. however it did not have thermostat I discovered!
Thermostat since installed, yet again, although pump seems ok, all gunk discovered makes me want to replace everything, and hoses are crunchy.

So I don’t know if it was removed due to overheating issues, which seems probable. Engine replaced rather recently per dumb PO.

Any thoughts appreciated.
I’m not searching for a magic answer, I simply have nobody to talk to who knows these cars like we do…

Thank you.

If we could hear the noise like you do, Demian - we may be better able to offer more…

Is it a’ thump’, is it ‘clicking’ is it a ‘rattle’ or whatever? There are two types of noises; the harmless but irritating ones - solved by turning up the radio while searching for answers. And the destructive ones - which eventually gets to a point were remedial actions is necessary to keep the engine going. The unsolvable problem is what’s what…:slight_smile:

The lower compression on #5, increasing in the ‘wet’ compression test imply bore wear, or possibly failed rings - the latter may or may not be noisy. No way of finding out except piston removal - but a borescope inspection in situ may show telltale bore scratching. Measuring bore wear requires head removal - which of course also allows closer bore surface examination. The long standing may have caused bore rust, which may have affected rings/bore. A head gasket issue will not affect compression in a ‘wet’ compression test…

Clicking may be an uneven shim - which tends to come and go, but is unaffected by plug lead disconnection. And head gasket issues make no noises…, .

‘Heavier’ noise may be big or small bearing wear, on a single cylinder possibly caused by a block in the oil feed to that one which would cause excessive wear there. Again, patient must be opened up for clarification and remedial action. However, sloppy bearing will not cause such a large drop in compression - bore/rings is more probable…

Hypothetically; one can detect excessive bearing wear byt precision measurements. remove #5 and #2 plugs for comparison - they are moving in tandem. Measuring to piston tops while slightly turning the engine both ways - in theory, bearing play will show up as reduced or delayed movement of pistons. May be detectable as a difference between the two cylinders. At the worst it will be inconclusive - even audible bearing wear is in the range of thousandths or may be hundredths of inches - but beat pushing with a screwdriver…

Anyway, nothing with the cooling system will cause noises as described - but cooling system faults may of course cause overheating, which may cause engine harm. However, the cooling system has its own failure symptoms - usually easily detectable. Blocking vent-lines is an absolute no-no - whatever the intention…

Keep talking…:slight_smile:

xj6 85 Sov Europe |(UK/NZ)

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I hope my contribution isn’t counter productive. I have had my share of connecting rod failures. Even with my seriously compromised ears, I think I could recognize the special noise that
a failed rod or rods. makes. In all but one event in my past, it was all 4, 6, or 8!!! Only one with a failed single rod bearing…

An odd given, slightly loose rod bearings are quiet under load.
So, a rough test usually works. Let the engine idle a bit, the rev it up to about 1500 or 2000. Close the throttle quickly. A rod bearing/s will rattle like shot in a tin can.

In the instant case, something is clearly wrong in #5. But, I suspect not bad enough to be noisy.



Yes, keep talking, solve one problem at a time.
Get the overflow tank fixed, or rig up a plastic aftermarket one. The purpose of these is to allow the excess anti-freeze to run out when it gets hot and expands, and back in when it’s cold, keeps the main system always full.
You mentioned listening for noises with a tube in the ear. A mechanic’s stethoscope would be better, or a long screwdriver in the ear.
This change when disconnecting #5 plug lead suggests to me a fault in the distributor cap, possibly internal tracking.

Thank you all for taking time.
I don’t know what the heck I’m asking.

Thank you Frank…as always. yes, I know it is a no no.

@ Rob: it was done before me, for obvious reasons. I don’t run it for long. It is said it can be run that way, keeps water from atmosphere and therefore boiling…but the pressure eventually?

Distributor cap , wires, and rotor replaced. going in to replace points and condenser and other stuff today, go through the distributor.

Haven’t run her in a while. Although parts very cheap, I’m undecided if i should keep it, go the whole show and spend what i shouldn’t at the moment and use it towards a later model and sell this one.

These are so rare and in this condition. I always keep eye out and yet to find one not butchered, if found at all.

Anyway, it’s a helluva thing. I have these thoughts, then remove cover and get in it again and can’t sell it.
Can’t beat old jaguar smell…

Anyway, also the sound is so illusive, vague, i can’t seem to get a handle on it, requiring to go out again and get fresh perspective, which i will now.

New cap and rotor installed.
Want to pull distributor for refresh anyway.

That wiring needs redping too, and lt lead cotton wire wrap from side to to points is flimsy as can be, can’t imagine a wire within.

Wasn’t arcing between points, but i have new everything for replacement which I’ll do today.
Not issue, but should be done.

Yes, stethoscope is needed.

Will hook all up for now and start again briefly to get fresh idea and report.

Maybe take vid.

Considering just swapping for another s3 motor. Would prefer to rebuild/refresh myself, but i just haven’t any space.

Found ad locally selling one w 85k that had overheating issue…for $100…complete.
Considering just rebuild it, then swap, or may as well rebuild what i have…nevertheless, extra parts would be nice to have at that price.

But i really haven’t time for any of this. I’m not 16 anymore and not retired…so…

But so easy to pull this motor. Seems it was just installed and left.
All hoses cut. No ac stuff at all.no air pump.
My god a car with space to work and you can see the ground!

2 engine mount bolts and trans mount, prop shaft connection, that’s it!

Thx again…will tell what i find.

@Carl: Oh, and i recall your thought on revving then dropping fast to hear noises…noise goes away at higher rev. and no noises upon closing.

And that #5 alone would hv bore wear would be weird. Why made me think/hope sticky valve issue.

Thought that md me consider head gasket, water in bore causing noise was due to poor combustion as spark plug is near white on #5.

Uncertain and couldn’t rwmember if a blown head gasket creates engine noises, knocking due to possible water leaking in a cylinder…or something.

Yes, verified that sound went away when HT lead disconnected from #5.

All leads getting spark. Good spark i don’t know. Why wish to do distributor.

Ok, will go out and see what i see again.

In the end I feel rebuild.
I don’t feel comfortable just pulling head as I don’t think any of the work done was done well. Certainly not to my standards! … especially if I intend to keep it.

PS: Frank, it is a faint knock.

And for record, valve timing and upper chain adjusted. All tappets look fine.
Did quick clearance check and all seemed too tight rather than loose.

As it had been sitting in an arizona garage for ages, poured combinations of sea foam and marvel mystery oil on all valves and let soak week at a time alternating to help eliminate any possible sticking valve issues…fwiw.

You say the noise is ‘vague’, Demian - does that mean faint, or just difficult to locate…?

Too ‘loose’ valve clearances are harmless - too tight may cause valve burning or worse, However, Sticking valve is NOT the noise problem. A valve not moving properly will promptly bend against the piston - and the ensuing compression loss will not react in the ‘wet’ test. The same goes for a head gasket leak - adding that a bent/sticking valve will cause very large valve clearances. Whether whatever concoction you used prior to starting the engine helped; valves work works…:slight_smile:

Incidentally, and referring to Rob’s comment on coolant expansion as it heats up; the force of expanding coolant is on an atomic level and is very, very powerful - measured in tons rather than pounds. So it is very important that the vent lines are open to the expansion tank - which, as Rob says collects the expanding coolant, to be ‘reused’.

At first fill, cold and to the brim, excessive coolant will be expelled at first heat cycle through the vent hose at the expansion tank filler neck. Later heat cycles, after cool down, will expand against an air cushion - pressurising the system to 15 psi, the opening pressure of the expansion tank cap. This pressure will raise the boiling point of the coolant to some 120C - coolant boiling point is otherwise some 100C. If the pressure is lost, due to any coolant system leak, it will not interfere with cooling - the pressure just raises the boiling point. If overheating; steam will form, forcing coolant out of the system - and the ensuing loss of coolant will further increase overheating, a cascading effect, until… :slight_smile:

You are obviously a competent DIY - but do not get too focused on one issue, the reported engine noise; drive the car for a wider experience of what is good or bad…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

@ Frank both vague and seemingly difficult to locate. Yes, I understand cooling system concepts well. Thanks for excellent writing though.

Well…here it is…

Drove around neighborhood today which as fun. second time since ownership and after flushing everything at least twice.
Oil was ok when purchased but as it had been siting for god knows how long, i spent much time and effort flushing it and coolant and fuel system. Again, carbs rebuilt.

Ran seafoam again via brake vacuum line…wow does that make a cloud around the car!!! holy smokes.
last time I simply poured over valves and let soak a week.
Took some time to burn out. Also no doubt oil deposits from sitting.

Now then, the noise here is quite pronounced. Although warmed up, it was not driven in ages.

I did check tappets with valve covers off once before, all good. Clearances must be checked again.

Anyway, upon driving around all afternoon for a while the noise seemed to be largely clearing up, and frankly, it seems more like exhaust valve tappet side…or top end there.

However why it would clear up when plug cable removed I am not quite seeing yet.

Also, there was no overheating. Remained around 180F/ 80C max. per infrared thermom. at head valley.

Any thoughts?

Just wanted to post this.

Thank you all.
Kind regards

It sounds like either a valve tappet clearance too loose, or a timing chain too loose.
The hydraulic lower chain tensioner is a frequently mentioned problem with XK engines that have been idle for long periods and with gummy oil.
The upper tensioner oil feed cup can also get gummy and full of crud.
Try the long screwdriver, handle in your ear, tip against the cam cover near each tappet. Then at the front where the chains are. Above and lower down if you can get there without being too close to the moving parts.
I see someone on the Saloons forum is dealing with a lower timing chain tensioner problem and has pictures.
Glad you didn’t get shocked pulling that plug wire. #5 is obviously working.

I noted two three related to the #5.

  1. White spark plug tip. Suggests, "steam cleaning by water injection. Slight leak at the head/block joint attributable to the gasket. Modern crystalline sealers, not Barr’s. can postpone the eventual failure for quitter a spell.

  2. The noise goes away when #'5’s plug wire is pulled. Translates to no combustion load removed. That coupled with PSI gain on oil injection could mean a busted ring or ring land.

I have never heard of water in a cylinder causing a knock. As water does not compress, a lot of it can do a lot of mechanical

So, buy that “cheap” busted engine? I gave my busted I6 away. It included a healthy BW65. The “Happy wife” thing.
Build the spare, hoping it has no really bad bores or crank,
and swap it in. Drive what you have gingerly in the mean time.


Cleaned up the carnage of tools all over the bench left from the fixing of my daughter’s Passat and my Jeep. Huge amounts of leaf matter on th floor and on the drive!!! Allergy enabling stuff. Fired up my leaf blower. Blasted breezeway, shop and drive clean. Street not so much. The sweeper is due soon, so that will fix that. Awoke with sore shoulders and back? Why ? Oh the blower packing + 87 years!!!


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@Rob: It seems to be a valve clearance knock, however why disconnecting plug would make a difference? nah…dunno about that, yet I will remove valve cover & verify best I can with head on.

@Carl: Thank you for thoughts.

Yes, my simple thought on water entering, clear plug, was perhaps a sort of pre-ignition condition caused as a result.

Again, the sound goes away when at higher revs, and later in afternoon driving became much better.

The key clue is the removal of plug wire causes sound to disappear.

Yes, rings or rod otherwise. Only possibilities otherwise.

Again, excuse all, not asking for some magic answer or what I want to hear as many do. It isn’t healthy and worse case must be rebuilt/taken apart to discover.

Perhaps all of this will help others as I have seen it posted elsewhere without response or solution.

When/if resolved I will make point of returning to post result.

May drive around neighborhood for a while see what happens, while in meantime buy a used XK engine to tinker with and rebuild.

kind regards

PS: Although I will not contact PO bcs he is a bastard, it seems a clue perhaps the extra head was included with intention to replace present one?

It is entirely intact with valves, springs, stakedown kit installed??


am in the process of fettling in a S2 engine to replace my sicky original 420G engine, which I will strip down…my PO turned into a bastard when he found out he had sold me a fully rebuilt engine for $300!

I have a mate that has been a mechanic 60+ yrs, runs his own business, and was an engine builder for at least 10yrs, and knows Jags…a very experienced mechanic like that can usually tell if that noise is a rod knock in a few minutes…if you know such a person/s, have them listen

a rod knock (should) be able to be differentiated form other internal knocks if you know what to listen for, I would keep trying to narrow it down with a stethoscope or metal rod.

if it is a rod knock, one would expect it would get worse.

may be worth removing cam covers to check clearances, possible contact with buckets, and chain tightness

Sure sure…no doubt. Wish I did know someone.
I’ve had Jaguars all my life, never once ran into or heard of a bottom end problem with these XK motors … so I dunno.

although having purchased sight unseen, never anticipated a bottom end issue (therefore)…
Yep, need stethoscope.

It bear all the hallmarks of a failing big or small end bearing, Demian - but only confirmation of that is a stripdown…

…which is a major operation - and more extensive outside causes is worth while pursuing, the sound of the sound is not all that distinctive. And ir seems too related to #5 to lie elsewhere - there is nothing else related to the engine that would react specifically to #5 manipulations. You have not mentioned if removing any other plug lead has any effect…?

Have you tried it under load - in gear? And instead of just disconnecting #5; hook up a spare plug, plug body well grounded, to #5 lead - just to eliminate sparking noise as a factor. Observing the engine room in the dark may reveal sparking - which is not noiseless. any port in a storm…:slight_smile:

However, there is no way the noise relates to valves; they don’t react to plug disconnection - and valve clearances would be way off with a hanging valve. Also valve clearances narrows as the engine heats up - so test should be repeated with the engine hot, which may also affect bearings. Oil flow through bearings increases with increasing rpms - your video did not show reaction/noise with increased, steady idle…

The ‘seafoam’ introduce into a running engine just burns off carbon - usually introduced in carb air intake at high rpms. But it is not an ‘innocent’ remedy…

xj6 85 Sov Europe (UK/NZ)

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Thanks for thoughts again Frank.

It is no doubt related to #5.
I did actually rev it…

At higher rpms, say over 1500 and at speed or load it goes away.

Nevertheless, needs work and inspection to know for certain.

Never encountered a bottom end issue on an xk engine!

Indeed, Demian - the xk bottom end is considered ‘indestructible’…

However, it only takes a muffed bearing installation or indeed clogged oil passages, sloppy overhaul to defeat even the best engine bottoms. And rogue parts or assembly issues will show up occationally …:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Indeed, we will all learn allot. One way or another!

  1. Drive it til the issue magnifies. My vote is for a busted piston.

  2. Take it apart and examine. My vote remains the same.

  3. Memory thing. Way back when, I decided my 34 Chevvy
    was not only done for, but wimpy. So, off to the local Ford dealer’ s used lot. Limited college kid budget. Selection, (?)
    came down to a 37 Ford four door V8. Looked decent, started and ran well. But, it had a “click” or knock. $200 bucks and it was mine. Teen pals and I decided it was a busted valve spring. We pulled a head and we got it right. Valve assembly and gasket within my teen budget. Done. Wowee, was it worn!! But, a full out valve job or more not in the $'s.

Considerably better, no noises. Raggedy idle, questionable starting in the cold. But once fired it did a lot.

Curiousity abounds…


gosh, hope you are not a doctor! Busted piston … jeez … how gloomy can you be. Just tell me I have cancer with 2 weeks to live why dontcha! J/K
Maybe you mean rings or wrist pin?

Actually been driving around neighborhood, Italian tuneup sort of thing.
Will not shift out of 2nd, no vacuum hose(s) connected and/or perhaps linkage screwy.

Someone just slapped this motor in here, and while i have gone over everything I can on the exterior and there is nothing to it, easy to remove again therefore, I am am uncertain what the heck to do…

It HAS become better driving around, but in end must be rebuilt or replaced.
These sure can be daily drivers though. Gas mileage would be terrible though. Were way ahead of their time that’s for sure.

BUT I am uncertain what the hell to do, in that, I have not the space or time for this now.
Considering an XJ40 (never thought I would) with super low miles and a cream puff, but I would have to sell this one.

I have had great cars in the past, Mk2, Mk7, 3.8s saloon, E type…sold them. Often for later models, WHICH in time of course diminished in value and do not compare now.

this S1 was a dream car for various reasons. Feels like more modern Mk2 with the short wheelbase…best of both worlds, etc.

Ah shucks, decisions decisions…

Can’t really see this a busted piston, Demian - it would be highly unusual with no other symptoms than those described…

At this stage, the noise is a sign that something is amiss - but not necessarily more of an irritant rather than instantly catastrophic. Ie, OK to drive. while you are musing decisions - and observe developments…:slight_smile:

If you have the BW12; with no vacuum connection to the gearbox, or a faulty/maladjusted vacuum modulator, it will not upshift out of first without serious reving…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Frank and Demian:

I don’t see it clearly either. But, the evidence points that way. Isolated to #5. Not a rod knock. Not a valve noise. Compression anomaly allayed by the addition of oil.

My vote remains, busted ring or ring lands or both.

Apologies for the poor prognosis. Naah, a Dr. I am surely not.

Side bar. I did fix my lethargic shop vac!! Removed about 12" of Coco fur from the intake pipe. Good and bad. fixing tools delays doing the intended task. In this case, vacuuming out the Jaguar’s foot wells. leaves and mud from a wet winter…