After putting the radiator back in the car while at the same time replacing all the belts and hoses (at least those I had access to), I finally arrived at the point of "main attraction": dealing with my V12 engine.

I don't really know what is wrong with it -- I never had cars with more than 6 cylinders in the past Only thing I know is something is amiss. So, this is just a first post to try to explain what I know and graciously ask the wonderful Jaguar community to help me and guide me in troubleshooting and, hopefully, zeroing in and fixing the problem. (The help I got while fixing my leaking radiator was invaluable and I am forever grateful to all who provided expert advice. I wouldn't have been able to do it without your support!!!)

So, about the engine. What I do know is the engine makes something like a pinging/knocking/tapping sound. I think (I believe) the noise is more pronounced on LHS (driver's side.) Maybe closer to center, slightly to the left. It is not that bad when the car is idling. But it becomes worse (stronger) when the car is driven. Note that I only drove the car once so far: from a garage of a previous owner to my garage. Previous owner was upfront about the issue. Which is why he did not drive the car either. The story goes that the engine started developing this knocking/pinging/tapping noise about 10 years ago and since that time the car mostly sat in a garage.

This is how the engine sounds when idling:
https://clyp.it/hcc5pw5d

By searching online, I learned that V12s by Jaguar are notorious for producing various sounds and noises, especially as they get older.

Unless somebody knows exactly what I am talking about and can pinpoint the issue, I am ready to start troubleshooting using principle of elimination. Starting with something easy, hopefully. (But I know that nothing is really easy with XJS!)

What should I start checking first? (Or ask me clarifying questions and I will try to get answers for you...)

Thank you SO MUCH!

 

Might be as (relatively) benign as a slight exhaust leak from a leaking manifold gasket or pipe-to-manifold seal. Such a leak often results in a tapping or snapping noise. I wouldn't go so far as calling it a 'knocking' sound, though.

If the sound is more like a rapid clattering or sewing machine type sound you might be suffering the dreaded dropped valve seat dilemma. This is not good; let's hope for something else.

The fuel injectors make quite a tapping or clicking sound but you wouldn't typically hear this inside the cabin while driving along.

"Pinging"...in the commonly used sense, such as you'd hear from using the wrong fuel or having incorrect ignition timing...is more of a metallic rattle. Not often heard at idle

Since the noise can be heard at idle, albeit not so pronounced, a mechanic's stethoscope would be very useful. Probe about, you might well hit pay dirt.

Mechanic's Stethoscope

Others will chime in.

Cheers
DD

 

Sounds are so difficult to describe. And not having a reference to compare it to you can't know what is normal.

Do you have a way of recording it? A movie would work. If you record from various positions it might help in isolating the location.

 

>> If the sound is more like a rapid clattering or sewing machine type sound you might be suffering the dreaded dropped valve seat dilemma. This is not good; let's hope for something else.

Keeping my fingers crossed...


>> The fuel injectors make quite a tapping or clicking sound but you wouldn't typically hear this inside the cabin while driving along.

I did hear it while driving. Frequency appears to correlate with RPMs. I did not push it while driving the car to my garage. Max speed I reached was about 50-55mph. But I heard the frequency of the "sound" varying with RPMs


>> "Pinging"...in the commonly used sense, such as you'd hear from using the wrong fuel or having incorrect ignition timing...is more of a metallic rattle. Not often heard at idle

If I did not know about the knocking sound while driving, and not knowing what the normal V12 sounds like while idling, I probably would just think that's how these engines behave. But I don't have any references to compare against


>> Sounds are so difficult to describe. And not having a reference to compare it to you can't know what is normal.

Exactly. I think I can record it on my iPhone. At least while idling. (I have the bonnet off and don't plan to take the car for a drive yet.) But need to figure out how to post it

 

post it up on Youtube and then post a link to the video here.

 

Here is the 20sec clip of engine idling:

https://clyp.it/hcc5pw5d

 

sounds like time for a compression test, try noisey side first!

 

How to conduct a compression test? (Scanned through Haynes book, but did not find it there.)

 

It does sound like valve train noise....but how close was the microphone?

Some valve train noise is perfectly normal but if this level of noise was picked up from 3-4 feet away I'd call it worrisome

Cheers
DD

 

I was standing on LHS, slightly leaning towards the engine. I'd say the mic was about 2-2.5 feet away.

 

Here's the most brief demonstration I could find:



Of course it's a lot more involved on a V12 because removing all the spark plugs is a bit of a chore in and of itself.

You'd be looking for about 200 psi as a normal reading

If any readings are low it is common to test twice ...the second time being a 'wet test'.... wet being squirting some oil in the cylinders. If the reading increases you have a piston sealing issue. If not, some other issue: valve issue of some sort or head gasket failure.

Unfortunately good compression readings do not 100% guarantee that you don't have a valve seat problem as a valve seat can be loose enough to make some noise but not so loose that it changes compression readings.

Cheers
DD

 

Thank you! Very useful! I will start preparing for the compression test then. I guess my next goal would be to get to spark plugs... I think I will start a new thread on "how to get to the spark plugs." Surprisingly, Haynes repair book has almost nothing on 'how-to' on spark plugs. (But they did include tow pages of color pictures of how good and bad spark plugs should look like.) I also searched the forum and did not find any step-by-step instructions for how to check and replace the spark plugs.

 

I'm with Doug etc on this.

It "sounds" like 12 cylinders?????, so a dropped valve seat it may not be.

Extremely noisy tappets, but to do the tappets is a major task on a V12.

Lots of threads in here about access to spark plug, Pauling, Orangeblossom, are 2 I know of. It is NOT a fun task.

When you decide to get a compression tester gauge, get a "screw in" style. The cheaper "push in" will NOT do the task.

I would also be looking at the oil, if its crappy, maybe the supply to the camshafts is not good enough, hence they could be "dry running" , and that WILL be noisy, and eventually turn to "sqeaky" just before they sieze.

 

Noisy tappets, is it the same as "lifter noise"? For what it is worth, the previous owner's guesstimate of the engine problem was that it suffers from "lifter noise". But I don't know whether it is true and what diagnostic were run to determine this. (Most likely no serious ones -- as the health of the car started deteriorating, the owner decided not to throw any more money at it and simply kept it garaged.)

Will the compression test help determine (or rule out) if the clattering is indeed due to noisy tappets?

 

First....

Is there any way you can get the car to a shop familiar with V12s and have them listen? What I hear in the sound clip is suspicious, IMO, but I'm not 100% convinced there is an actual problem. It's hard to judge. It might be on the louder side of normal. I'd hate to see you go thru all this work for no reason.


Yes, the same. The two terms are often used interchangeably. It's an automotive semantics thing that we needn't get into at this point



Excessive lifter or tappet noise usually arises when the adjustments is too 'loose'; that is, the gap between the cam lobe and the tappet is wider than specification.

This could be checked but it isn't an quick thing. The cam covers must come off, which means removing the inlet manifolds, which means removing lots of other 'stuff'. Several hours work. The procedure to correct the clearances is time consuming as well...although certainly easier than pulling cylinder heads!

If the noise is indeed from excessive tappet clearance a compression test wouldn't indicate it.

I think your best bet is to perform the compression test on general principles. If the results look good, move on to checking tappet clearances. At the same time you'll be looking for any obvious abnormalities with the portions of the valve train that are visible with the cam covers off. If the clearances look good, and no problem is visibly apparent, it comes down to pulling the heads.

That's my take. Let's hear what others have to say.

Cheers
DD

 

Thanks all for your tips and advises!

Forgot to mention: I have a mechanic's stethoscope on order -- should arrive in couple of days. Will using the stethoscope help in anyway to confirm if the noisy tappets are the source of the problem?

But regardless, I am planning to get to spark plugs and do a compression test. This will have to wait until next weekend, though. My xmas/new year's holidays are over and I need to go back to my "normal" work

I did a more thorough search and found references/instructions on how to get to spark plugs. Here is one:
Accessing the Vee
Plus a few threads on this forum in the past. I will continue to study everything so that I can be prepared.

After reading the references, I split the job into five steps:
1. Disconnect/move out of the way the bellows
2. Unbolt move forward the AC compressor
3. Remove the ignition coil
4. Unplug the lead wires and remove the blue distributor cap (but not the distributor)
5. Unbolt and lift up the throttle switch

If I do these five steps, I shoudl have easy access to all 12 plugs, correct? Anything I missed?

One thing that was not mentioned in the link was loosening the tensioner bolt for the compressor belt. (Instead, it said about "prying the belt out".) Wouldn't it be easier to just loosen the belt first so that one can move the compressor forward without worrying about the belt?

A question about the compression test. Should I remove all 12 spark plugs first or can I do it one cylinder at a time (take out one plug, do the test, put it back in and move to the next hole)? I think in the youtube video it said to remove all plugs first. But I believe in the posts people mentioned doing it piecemeal.

 

All plugs out for compression test and you want the same number of piston strokes for each cylinder as you test.

 

Hi v1rok

Its easier (relatively easier) to slacken off the Adjuster, so you can take off the Aircon Belt easily, because at some stage when you put it back, you are going to want to adjust the tension anyway, though you may as well fit a New Belt/s, while you are about it.

Just be careful that the Spanner doesn't slip and put a hole in your New Rad Core, if the Rad is in the Car protect it with some Cardboard but what you really want to do is make sure all those adjusters are easily un-doable (wire brushed off and greased with Copper Grease)

Don't take the Pipes off the Aircon, as you can lift it out of the way in order to get to the Plugs and don't undo the Big Bolt on the end of the Aircon, as that is under Pressure.

It took me Three Days to Change the Plugs, because you need to work slowly and some of those plugs were a hell of a job to get out.

If you are going to take all the Plugs out, cover each hole in some way because its all to easy to drop something down the hole (a piece of crud or an injector clip) if you do its virtually game over.

Mark any leads you disconnect and preferably take photos, as by the time that you have finished dismantling everything, it is all to easy to forget how to put it all back.

You could also clean the Injectors, as has been suggested which is very easy to do, with no Special equipment required.

If it turns out to be a dropped valve, then you may have bought a Parts Car, so be aware of throwing good money after bad, as you could end up spending enough to buy another car in good running order.

Buying yourself an XJS is usually the least expensive part, as you could end up spending double just getting her up to snuff.

This is how I did mine on my 1990 Marelli Car.

https://www.jaguarforums.com/forum/x...-122634/page8/

 

Does it have to be all 12 out at once, or can I do each side at a time (6+6)?

 

Just because I own a Jag doesn't make me an expert. But I've been a successful backyard mechanic for 40+ years. That being said let me suggest somethings you can do to check your engine out and determine the source of the noise, assuming the noise is bad or unnatural for your Jag.

First, When you first start the car, that first 5 seconds, do you hear a rattle? That could be a timing chain or bad adjuster.

Have you checked the timing? Find a shop manual and check the timing of that V-12. If its not at factory specs, take note of where it is and then reset to factory specs. At the same time check to make sure the plug wires are going to the right plug and terminal on the distributor cap. If any are wrong make a careful note of how it was and then make it right according to the service manual.

Start the car and listen again. Is it the same? if not take it for a run and see if there is a change. Put some good tier 1, 92-93 octane gas in the car. Find a hill a drive it up the hill. Is it pinging? Its possible you have old / contaminated gas that is does not have enough octane in it. Don't drain the gas just put some good gas in and run the car. When you fill it put good gas in it.

Still pinging or making a noise? You could have carbon fouled heads. There is a bunch of snake oil out there for carbon fouled heads...everybody has a favorite or an opinion. I like a good tier 1 gas and an Italian tune up. Give a good high speed run varying the engine speed with your right foot.

Ran through tank or two of gas and its still making noise? Now do a compression test. One cylinder at a time. Pull the fuse for the fuel pump. Start the car and let it stall. No fuel going to the cylinders now. Pull off one plug wire, pull the plug, look at it. tan or black? (more on that later) check the gap. Record what you find, one cylinder at a time on a pieces of paper, Screw in the compression fitting by hand. Crank the engine over with the starter. ONE THOUSAND TWO THOUSAND, release the starter. Record the compression on your piece of paper. 165 to 200 is good but don't worry too much about what it reads. Gauges can be off. It more important that when your done doing this on all 12 cylinders that all the cylinders read about the same. Say within + - 10% of each other. Any more then that and you might have a problem. Spring for a new set of plugs at this time. Set gap to factory spec and reinstall the plugs and put the wires back one cylinder at a time.

All the plugs should be tan or light grey, Any that are excessively black or fouled are not burning right and require further investigation.

All this is assuming its a pinging sound.

Pull off the valve covers and look at the valve train. Broken or bent parts are what you are looking for. You don't have to be an expert. You'll know what's wrong when you see it. Checking for bad lifters on this car is deeper then I can go without a service manual in front of me.

The next step would be to drain the oil through a filter cloth / painters mask, right out of the crank case. Your looking for shinny stuff in the bottom of the filter at this point. That would be bad. At that point its time for another V12 or a 75% of one. LS3's are nice.....

Everybody, feel free to comment but I think this is a good start that anyone with moderate skills and equipment can accomplish. You can borrow the equipment you need from Pepboys or Autozone.