Well I finally got the alternator belt replaced, and I got to go for a drive and perform somewhat of an "Italian tuneup" (hey it was styled by Pininfarina, right?). I noticed that the engine has a ticking noise (which I noticed before, not bothering me too much), but then today after I went for a drive (maybe 3-4 miles) the engine sounds like a diesel engine when revving it under load and even in neutral! I will post a video of it sometime soon showing what it does.

The car did start up without much cranking, which was great!

Do you have any idea what this could be? I notice that from a standstill if I mash the gas pedal the engine revs up to maybe 2000 rpm and gives decent acceleration. However, if it's already moving about 5 miles an hour or so, it seems like it just doesn't want to accelerate too much (rpms stay around 1000 and slowly climb until it gets into the powerband) which seems normal I suppose, but it makes sort of a rattling sound that almost sounds like an exhaust leak or a loose heat shield. I didn't notice this so much before--I wonder if this happened due to the belt change I just did. Maybe I accidentally disconnected something?

 

The tappet housings pressed into the head can work loose and then the cam wallops them as it comes around. If found to be loose there is a kit available to clamp them down, which however needs some drilling and thread tapping to be done so the clamp plate can be secured.

You may ask why Jaguar didn't secure them this way, and it is a good question, but they didn't do an awful lot of things they should have done when this engine was in production !!

You can check using the screwdriver stethoscope trick on each cam cover near each valve. Also do a compression test to make sure you haven't bent a valve, 'coz this will make a big tapping noise with the increased valve clearance.

 

Hmmm... thanks for the possible causes. I'm hoping it's not a bent valve. I doubt it is, because wouldn't I be seeing a lot of blue smoke coming out the rear?

I think I'm going to start off with an oil change, after putting a little seafoam in the crankcase and driving it for maybe 25 miles (that's the distance to the Jag dealership!). I'm a little bit nervous to drive it that far, though, so I'll probably do a few more test drives to give me enough confidence to drive it out there for an oil change. The last couple of drives haven't given me any reason not to believe that it is capable of driving that sort of distance.

Is there any reason that I can't use a couple ounces of Seafoam in crankcase to drive 25 miles?

 

Well I gave it another shot at an Italian tuneup. Now the acceleration is great! It's not fast by any means, but I can floor it all the way and it will rev and accelerate as I think it should. Shifts are surprisingly smooth when you give it the goose!

I'm pretty sure the tapping sound is the tappet guides--I'll try not to drive it TOO much until I can get those secured. But there is still that groaning sound when giving it gas at lower RPMs. I'll try to capture it on video sometime.

The climate control works!!!! And the A/C seems to work (it was about 50 degrees out and it seemed to be blowing air that was colder than ambient temperature), which is a miracle! How do the rear climate controls work? There are two knobs back there but I can't figure out what each of them does!

 

Hmmmm... now that I think about it, the groaning sound could definitely be the sound of the flex plate which apparently an infamous issue for these cars. Has anyone else experienced this groaning/clattering sound when starting from a stop?

 

Before you consider the flex-plate, inspect the motor mounts for loose fasteners and separation as the rubber/metal bond may come apart over time or in the presence of an oil leak. The rear gearbox mount may also be separated, which will allow the gearbox to move under acceleration thus creating different types of interesting noises.

To check the condition of the engine mounts, place a floor jack having a wooden block on the saddle under the sump and VERY CAREFULLY AND SLOWLY raise the engine to see if the mounts are separated. If the jack moves easily and raises the engine, then the front mounts should be replaced.

NBCat

 

Good suggestion, thanks. The transmission was apparently replaced about 30k miles ago in 2004 (I think). I'll have to check the records. But I would presume they replaced the transmission mounts along with that.

If the motor mounts check out, what sort of noise do loose flex plate rivets end up causing? The noise I hear seems to only occur when the engine is "under load". However, this can be when it's in drive pulling away from a stop light or if I'm blipping the throttle in neutral. I don't seem to notice it once I'm at speed or not accelerating anymore.

 

From your description, it sounds like the engine or gearbox mounts are the problem. Loose rivets on the flex-plate may cause a rattling sound when the starter engages the ring gear or the starter pinion may miss the ring gear and make a high-pitched, grinding sound as it strikes the ring gear that will certainly get your attention.

NBCat

 

I have replaced the torque converter drive plates for the 'rattling' noise (common fault back-in-the-day). I have also seen tack welds in several places and the rivets 'bucked' to tighten the plate-to-ring gear.

Look closely at the rivets for signs of movement. If you see rub marks on each side of the rivets, then they are loose.

There are several ways to fix the noise.

bob gauff

 

It seems as though buckling the rivets is a common thing to do to stop the flex plate from rattling.

However, I'm going to try to take a video of the noise--perhaps when the car is next to a brick wall so you can hear it well. It's hard for me to diagnose the noise from outside the car because I'm only one person.

Who knows--it may just be a loose exhaust heat shield.

 

Flexplate Clatter

FYI somebody wrote a procedure for doing this on Jag Lovers.

 

You can certainly make a video, but save yourself time and check the engine and gearbox mounts for loose hardware or separation.

NBCat

 

It appears that the motor and transmission mounts are OK.

I found this picture of the flexplate (is it for an XJ6?) and ring gear.



Where are the flex plate rivets in this picture? Or is this not the right flexplate?

 

Or perhaps this picture is more correct? (Taken out of the Jaguar FSM, but for the XJ12--don't know if the flexplates are different?)



Are the rivets those circles near the edge of the drive plate?

 

Completely left field, I guess, but possible.
Years ago I had a Rover SD1 V8 that had similar symptoms: took off well from a standing start, but on the road the acceleration dropped away, particularly heading uphill. They were not record setters anyway, but it was still a great road car to travel distances here in Aus. Eventually the problem was traced to the torque converter, which had two broken vanes. Unfortunately I cannot even remeber how I traced the problem (hey, it was almost 30 years ago), but if your performance doesn't quite come up to scratch for no discernable reason, it might be worth a look.

I've also experienced similar more recently from a MAF that went crook. It did give a clue in that the upchanges gradually ocurred at higher & higher speeds on light throttle settings.

Cheers,

Languid

 

Hmmmm... very interesting. I don't think that the car has any real acceleration problems--just annoying clattering.

 

I got my chance today to put divots in the rivets holding the starter ring gear to the flex plate and now the clattering sounds are GONE! I actually could only reach 9 out of 10 divots but that did the trick. (Seems the flex plate stops in only 3 or 4 different positions no matter what and we lost patience.)

The engine still doesn't sound all that great with the ticking (still need to do the tappet stakedown kit--think I will have it done professionally next month) and possibly an exhaust leak, but this has definitely increased my enjoyment of the car by at least 50%!

 

You MUST install the tappet hold-down plates as soon as possible to avoid catastrophic engine failure.

As a point, the Bosch/Lucas L-Jetronic system fitted to the Series III XJ6 functions on air volume moving the air flow meter flap unlike modern MAF sensors reliant on differences in temperature based on air flow volume.

NBCat

 

The flex plate may be rotated by using the teeth on the ring gear to reach all the rivets.

 

Yup, next month is as soon as possible. I am trying to keep this XJ6 project on budget. Fear not, the car will probably not be driven more than 10-20 miles in that time frame. Heck, this whole time I've had it, I've only put about 30 miles on it!

I would install the tappet guide kit myself (I have the parts already from Coventry West) but it seems like there is so much hysteria over getting the bolts straight and measuring clearances and whatnot.

I still think it's pretty amazing that the car runs so well and I'm only $1400 into it so far!