Top end clatter - diagnosis help please!

[kingzetts]

I fitted a brand new "military" cylinder head from SNGB to my 3.8 over the winter.

I put a couple of hundred miles on it when winter receded, and all seemed well. Then last week I drove down to Nice - 1000 miles on motorways. By the time I got to Nice there was a terrible clattering noise. It appeared to come from around #1 cylinder (rearmost) inlet valve area. It sounds very like a massively loud tappet noise - and I mean really, really loud, not the "loud" you get from excessive valve clearances.

It is definitely engine rpm related. At idle it would occasionally disappear altogether but reappear immediately once revs increased, and it is definitely not from the gearbox or further back.

I decided to press on rather than have the car recovered, and luckily made it back OK, the noise maybe getting slightly worse but not massively so.

My tentative diagnosis was a loose tappet guide. Not so. I confirmed the noise as arising near the back of the inlet side of the head by stethoscope, so I pulled the inlet cam cover off today and could see nothing amiss - definitely not cam lobes hitting anything. Plenty of oil everywhere.

What I did find was that there was zero valve clearance on #1 inlet valve. The other 5 were normal. I checked the clearances when I fitted the head and at that time #1 inlet clearance was normal (I didn't keep the measurements but it was in the same narrow range as the others and all were in spec for parabolic cams).

So I pulled the camshaft and used a depth micrometer for a quick and dirty check by measuring how far below the rim of the tappet guide the top of the valve collet retainer was sitting (I couldn't get my depth micrometer to fit to directly measure onto the valve stem tip). Based on this it seems #1 valve is sitting between 0.7 to 1.0 mm higher in the head than all the other 5 valves.

Now normally I'd think that reduced valve clearances would quieten the top end, not make it noisier. So far the only theory I've come up with to fit the symptoms is that I have a loose valve seat which is causing the loud clatter and causing enough recession of the seat into the head to close up the clearances.

Next step is to pull the head, but before I do I thought I'd see if the collective wisdom of the forum could provide any other diagnoses or thoughts.

[mgcjag]

Hi John....when i first got my E it had bad tappet noise..on checking there was almost no gap on the inlet side, set them correct and made the tappets much quieter.......so reduced gap can make more noise.. Steve

[christopher storey]

I agree with you that the valve seat probably has something to do with it , most likely that it has receded, although why it should do that is something of a mystery. The other possibility that occurs to me is that the valve has stretched. This sounds a most unlikely occurrence but it is, I suppose, just possible particularly if the valve springs are stronger than they should be. (? is the military spec different from road specs), and has someone been doing "pick and mix" of valves, spring seats, and springs?. If that were the case it could possibly explain the noise, being the sound of the valve hitting the seat much harder than is intended

PS Just thinking about it further, if the clearance has effectively disappeared, it may be that the bucket is now transmitting the noise of the valve hitting the seat to the back of the camshaft itself, which is telegraphing the noise

[Hugo]

Don't like the sound of this one bit. But how do you know it's not a loose tappet guide (although this wouldn't account for your vanishing valve clearance)? If I were a betting man I'd say it's a valve seat that has fallen out & been hammered back into the head. But you should now have a hefty misfire - do you? Or maybe it just landed back in about the right place enough to give some sort of seal.
Frankly I would have thought if that had happened you'd be lucky to make it all the way home - normally they break up & go through the piston.
Anyway, always eager to be the bearer of good news, I reckon that you are going to see a very unpleasant sight when you take the head off - I would keep a sick bag handy - the head and the piston are not going to look pretty, but you might be lucky & find it has spared the cylinder bore.
I might be wrong, and I truly hope I am.

[andrewh]

I must say Hugo, that I had similar thoughts about the valve seat. I also like Christophers observations on mixed valves being a potential cause. I reckon before taking the head off it may be worth you doing some further checks. I would be doing a leak down test or at least a compression test and using my borescope to have a look inside the cylinder. with some careful wiggling you should be able to see the valve seat when the valve in question is open. I would still be hopeful that this is a head problem and has not damaged the rest of the cylinder.

[Hugo]

I must say Hugo, that I had similar thoughts about the valve seat. I also like Christophers observations on mixed valves being a potential cause.....

Too esoteric for me I'm afraid

[kingzetts]

Thanks for the various replies, chaps.

Hugo, I understand that the noise from loose tappet guides is due to impact between the cam lobe and the edge of the guide. With 1500 miles of the noise behind me, I would expect to see witness marking on the cam lobe and the edge of the tappet guide and there is absolutely no marking on any of the guides or lobes - and as you say a loose guide would not account for the lost clearance - so that's why I don't think it is a loose guide.

There is no misfire, backfiring or obvious loss of performance (although I was not exactly thrashing it on the drive home). And if the seat had broken up and fallen out totally I would have thought the valve would have come up rather more than 1mm.

Anyway, all the ideas so far point to having to remove the head to do further investigations, so I think this will have to be the next step. I'll let you know what is found (with suitably gruesome pictures of Hugo's optimism proves correct!).

[Hugo]

I've been in this game long enough to always assume the worst - that way you're never disappointed! My guess is that you might be lucky & the problem lies with the valve seat, which as you say is obviously still there, although it may have bashed its way further into the head. If that does turn out to be the case, I'd say that is a better result than most people could expect, and you might get away with just repairing the head. But I'm speculating way too much, which is not really helpful.

[JagWaugh]

...
Anyway, all the ideas so far point to having to remove the head to do further investigations, so I think this will have to be the next step. I'll let you know what is found (with suitably gruesome pictures of Hugo's optimism proves correct!).

It might be a broken spring a bit of which has worked itself up into the area of the keeper. It's a long shot, but if the compression is ok on that cyl you might just manage to hold the valve in with compressed air, or possibly even rope, take the cam out, remove that bucket, have a look. and if that is what it is change the springs.

(me, an optimist?... hardly, but it's worth a try)

[Hugo]

You reckon?

[JagWaugh]

You reckon?

I have trouble imagining that a "brand new head" would have the seats so poorly fitted that they would knock back 1mm after a decent run in period. I would expect a poorly fitted seat to make itself known audibly pretty early on (after a few heat cycles).

I've seen lots of pictures of dropped seats, never had one myself, but judging by the pictures of the damage it causes I would say it must make such a racket that you'd have to be mad or deaf to risk driving home from Nice.

Besides... a broken spring would be easier and cheaper to fix....(always look on the bright siiide of life, dedum, dedumdidumdidum)

[Hugo]

I don't think it 'knocked back' - I think it fell out & then got hammered back in, sort of. That's just a guess, of course, but better than yours I reckon Bet on it?

[JagWaugh]

I don't think it 'knocked back' - I think it fell out & then got hammered back in, sort of. That's just a guess, of course, but better than yours I reckon Bet on it?

I only bet if I feel the need to take your money.

Besides... there is a land which the seat is pressed home against. The chances of it falling out and getting hammered back hard enough to shift the land back by 1mm are pretty slim.

I wonder if military heads have deeper seats and someone fitted the wrong seats?

All conjecture until we see pics of the dirty bits.

[Gfhug]

OK, I'll ask the question. What is a military head?
Would a late head as fitted to the XJ6 S3 be similar, though that uses the later cams with the larger (12-14 thou) clearances.

Apologies, not trying to move away from John's problem (sorry for your problem, John), just trying to understand.

Thanks
Geoff

[Hugo]

I thought you'd chicken out Whatever has happened, the chances of it happening are slim, as it's pretty rare.
C'mon Mr Kingzetts - whip that head off & put us all out our misery!

[ralphr1780]

John, sorry to read about your troubles.
Did you examine closely the spring of the subject valve with a magnifier? It could be broken but yet still complete and well seated, and while engine is running it would just split and slam.
I had this once on my Alfa engine, took us quite some time to figure it out.

[Hugo]

Doesn't explain the vanishing valve clearance though.

[kingzetts]

Geoff, a military version of the XK engine was used in certain British Army armoured vehicles such as the Scorpion light tank back in the 1970s. SNGB bought up a large number of ex-military XK engines - some used, some unused and lots of spares - some time ago. At one time recently they had a chap employed full time dismantling these engines and putting parts into stock.

The military version used basically a standard 4.2 head (the later long version with the extra cooling ports at the rear of the head and parabolic cams, but not the big valve injection type) but the exhaust valves and exhaust tappets were beefed up to provide greater robustness against iffy fuel quality. From memory the exhaust tappets are larger and have a sort of bearing under them which causes them to rotate to even out wear, and the valves are sodium cored.

Those differences weren't why I bought the head - I got a brand new crated fully assembled head (cams included) from Barratts for much less then the cost of having my old head fully overhauled.

I will try to look at the spring and may stick my borescope down the plug hole tomorrow......

[Hugo]

Cam followers will rotate anyway. All engines do it - generally the cam is ground a bit 'off' so it applies uneven pressure across the face of the cam follower, or else the contact point is offset.
Sodium filled valves huh? The last engine I saw those on was a Wolseley 6/80 OHC which was derived from a Hispano-Suiza aero engine which I think dated back to WW1! (yes One).

[JagWaugh]

Sodium filled valves huh? The last engine I saw those on was a Wolseley 6/80 OHC...

Sodium filled valves are quite common. Most turbos and high perf engines use them, Audi, Alfa, Mazda. I asked a long time Alfa mech about that just last week.