Hi,

I have owned my XJS for 11 years and have done around 110,000km in it. All up the car has done 220,000km. It is pretty much a daily driver.

The morning after a 400km drive I discovered it had developed an intermittent tapping noise on idle. It is more of a ‘tap’ than a ‘tick’. It sounded like it was coming from the front cylinder on the A bank (RHS from drivers view).

My first thought was dropped valve seat however the car had not been overheated. I run dual temp gauges, electric fans and a high efficiency radiator and am very conscious of monitoring the temp when driving. The car runs with the temp needle 1/3 of the way up the gauge. Also the noise is coming from the A bank where overheating problems tend to show up first on the B bank.

Also the noise was intermittent. You could induce it or stop it sometimes on idle just by moving the throttle a touch to change the idle speed.

The car was still running ok although every now and then it did seem to have a slight flutter out of the RHS exhaust. However I am near certain it had this long before the tapping noise developed.

After the tapping was first noticed I continued to use the car to see how the problem developed as I didn’t think it was possible to have a dropped valve seat. I probably covered another 1500km. Over this time the problem probably became a bit more noticeable and less intermittent.

Anyway, I have now started to investigate and have the cam covers off. Given the tapping noise I expected to have a wide valve clearance somewhere.

My results for cylinders 1 to 3 (area where tapping came from) are:

Cylinder 1 – Exhaust: 11 thou Inlet: No clearance!

Cylinder 2 – Exhaust: 11 thou Inlet: 11 thou

Cylinder 3 – Exhaust: 11 thou Inlet: 11 thou

On the valve where I couldn’t measure a clearance the cam lob is also shiny the whole way around so it appears my inlet value on the front cylinder is not closing all the way (which could explain the occasional flutter out the exhaust pipe on that side). But I can’t how this is contributing to my tapping noise or even how this problem could have developed!

Does anyone have any advice on what they think could be going on? I suppose I will have to remove the head but it would be nice to avoid that.

Regards
Mark

 

are those clearance values between the backside of the cam lobe and the solid lifter with the valve closed?

and why would you run dual dummy temperature gauges that dont read in *F/C?

 

Well the clearance being smaller than normal can be from a few causes. Ultimately the valve stem is higher than it was. This of course assumes it was within spec at one time.

1. The valve has tuliped. This is caused by a overheated valve. It does not necessarily mean you overheated the engine. It can be from a cylinder than was hot enough to allow the valve to tulip. A lean mixture is most likely the cause.

2. Valve seat recession. Not very likely due to the valve seats installed are hardened. More common in older leaded fuel cast iron head engines.

3. Loose valve seat that has been pounded into the head. This would should up on a vacuum gauge while the engine is running. Also start with a leak down test which may or may not show excessive leakage. Compare the results to the rest of the engine. That is more important than comparing to rules of thumb. If all cylinders are 10% except one and it is 15% than you need to find where the leakage is going. A rubber glove over the tailpipe can show if it is from the exhaust. A glove over the oil filler hole will show past rings. A stethoscope will be used to listen to the intake manifold. A vacuum gauge can be used to find a bad seat too. The needle will pulse in sync to the tick noise.

One thing you want to be sure of before dismantling an engine is what you are expecting to find. Your tests should narrow it down. If it is a valve seat then your options are to find a good head or send it out for new seats. If the valve is tuliped then you need to fix the root cause of that. Best bet is to check for what would make it lean. Vacuum leaks, faulty injector wiring, faulty or poor flowing injector. If It comes down to a tuliped valve I would send my injectors out for testing and reconditioning.

 

The clearances I measured were from back of cam lobe to the top of the bucket.

One of the temp gauges is the original factory gauge so why change it if its giving consistent readings in line with what is expected. The other gauge I fitted for the B bank measures in deg C. It sits on 90 deg C

 

Thanks Greg Edge. I have already sent my injectors over to the US to www.jaguarfuelinjectorservice.com He seems to specialise in the V12 injectors. I figured since I had all the injectors off it was a good time to get them tested and put on some new fuel hose.

 

Marke,

Good move. Did you happen to mark them so maybe Dave can tell you what they flowed before and after? Might give you some insight into what to look for with that valve.

 

After reading your post I wished I had! But no, I just packed all 12 into a box and sent them off which was pretty stupid in hindsight.

At the time I wasn't really considering the possibility of running lean as I hadn't got as far as taking the cam cover off and measuring the valve clearances. I was only thinking about my tapping noise and assumed I had excessive clearance.

 

how much does he charge for the injector service?

 

I am paying US$210 for 12 injectors to be tested and cleaned with new injector to manifold seals (excl shipping). I am also getting other bits done like a reconditioned fuel rail and hoses etc so I don't know if that brings the price for testing the injectors down a bit.

Overall though I thought the price seemed pretty good. Parts and Labour costs seem to be a lot higher in Australia.

 

Mmmm, inlet valve issues on a v12 are rare indeed.

If the inlet valve is not closing for any reason, then I would have expected the compression pressure to cause a blow back into the intake system, like a back fire thru the aircleaner.

The exhaust valve doing the same is dampened by the exhaust system.

A mis-fire is always the result.

Staying away from the inlet clearance for a moment. I have had many of these with very OLD spark plugs in 1A and 1B due to access. Also I have had brand new spark plugs drop the centre electrode, which usually goes OUT the exhaust without damage as it is so small.

Just because, is the 1A spark plug TIGHT. I have had them loose/cross threaded/stripped, access again, and they leak compression, and it sounds just like a tappet noise, and of course there will be a mis-fire due to compression loss.

I know it is outside of box thinking, but pulling the engine to get the heads off is not fun.

I would give that cylinder a comp test (screw in tester please), and see what it reveals.

 

I am with Grant. Compression is always the place to start. A vacuum gauge can tell you a lot too. If you can also perform a leak down test.

 

Thanks guys. I changed the plugs a couple of years ago but haven't checked them since.

The car did not have a noticeable misfire when I parked it up just the occasional flutter out of the exhaust on that side. So I suspect the inlet valve must only be staying open a very small amount.

My other thought was the inlet seat is loose and sometimes it drops down and gives me a tapping noise and sometimes it pushes up too far and I lose clearance as the tapping was intermittent at times.

I don't have any equipment for checking compression so will have to see what's available. I'm away this weekend so probably won't get to it until the following week.

 

Things move slowly with my XJS issue but today I removed the camshaft. It appears I am not the first one who has been there.

I removed the tappet / bucket on the number 1 inlet valve (the one that has no clearance) and found the valve stem has been cut to size at some point. And it is too short. The shim has been touching not only the valve stem but the valve collar.

On removing a few more tappets I found most of the valve stems appear to have been cut although only on cylinder 1 is the valve stem so short that the shim touches the valve collar.

Head will have to come off it seems with new valves fitted.

On the plus side jagaurfuelinjectorservice.com checked my injectors and apparently they were all working within spec

 

DAMN.

You are so lucky that the shim has not pushed the collar far enough to release the collets.

I hope new valves is all you will need, unless some fool has cut those seats sooooo low, the cutting of the valve stem was required???.

 

Not nice on the part of whoever did the work. But on the plus side of the ledger, it did last 11 years and 110K.

 

Yes I was thinking lucky I got 11 years out of it without the valve falling out!

Grant, you might be right. I wonder if there is a reason the valves have been cut. Maybe I will need new seats as well.

I will remove the exhaust manifold after work today. A real shame because I only replaced the exhaust manilfold gaskets less than a year ago to fix a leak. Hopefully I will get the head off in the next week or so.

 

Things move slowly but another update and question....

I purchased new valves and found they sat too low in the seat, which explains why they were cut in the first place.

So after considering new seats etc I purchased a brand new head which already had new seats and valve guides. Total cost delivered to Australia from the UK - A$400. Cheaper than buying seats and paying a workshop to fit them into my old head. I also purchased a new tappet block complete with bearing caps.

Which leads to my next question...While playing around and doing a few checks I noticed once I tighten down a single bearing cap on the camshaft it becomes very tight and hard to rotate by hand. If I tighten up a second bearing cap I can't rotate the camshaft by hand (despite being well oiled). So I tried the same thing with my old tappet block and bearing caps and it is similar. Is this normal? Am I correct in assuming the alloy bearing caps expand with heat so they must be a tight fit when cold?

 

Mark,

You have progressed well, and some good pick ups there also.

The camshafts should still rotate fairly easily with ALL the caps installed. It will NOT spin as such, but rotate with some caoxing by you.

The few I have done have all been that way, BAR 1 (mine) which turned out had a bent camshaft, B bank. Only 0.012", but enough to cause grief. Nothing around at the time, so took to my "old engine reconditioning" shop and straightened it. That took me about 2 hours, and then linished the journals, and all sweet. Still running today.

I did see a looooong time ago a "workshop" with webbing straps around the camshaft trying to lift the head off, and I reckon that would do the camshafts NO GOOD at all.

Only way would be set it up on 2 "knife edge" V plates and roll it with a dial indicator.

The more I read the more I reckon this engine has been HOT at some time in its life.

 

Grant,

Unfortunately I think you may be correct. I removed the camshaft prior to pulling the head so I haven't done anything that would bend the cam but it is clear dodgy work has been done before me so who knows what has gone on.

Finding a new camshaft looks like it might prove problematic. Does anyone here have an A bank V12 camshaft they would like to sell? Obviously I would like a straight one!

 

No I dont.

I will ask around in the next few days.

Check out JagDaim (Bill or Doug or Brian) in Melbourne, or Prestige Spares (H & H) (Phil or Herb or Matt) also in Melbourne.