Thanks alot for the explanation NBcat.

I'm hoping the valve timings are going to be okay but even without looking at the tentioners I'm pretty sure they have not been changed going by the cars many issues. 😆

 

I did a compression test on a 280Z a while back and all cylinders were within a few pounds of 155 PSI. The car had a compression ratio of 8.3 to 1 vs the 9 to 1 I think the AJ26SC engine has. It seems like the 100 PSI you are getting on your good cylinders is way to low. I wonder how accurate your results are.

 

I’ve seen plenty of zeros; all due to holed pistons. But that doesn’t happen that much anymore. A stuck open valve or dropped valve seat are more common these days.

typical Triumph 650cc with holes piston. I saw many of these in the 1970’s as people tried to get from Amarillo Texas to Oklahoma City in the summer heat with bad ignition timing.






Z

 

Thats an interesting comment David, what PSI should I be seeing on a good cylinder?

 

Sounds like a good candidate for cam chain tensioner problems.

 

At sea level the atmosphere PSI is 14.7. I believe that the AJ28SC engine in your car is at 9 to 1 compression. The AJ26 NA engine is 10.75 to 1.

So 14.7 times 9 give a base of 132 PSI. I think in real life the PSI values seem to be higher. I know on the Datsun engine I checked the values were higher than the math. But anything lower than 132 would indicate a low PSI for whatever reason. I think the basic routine for a reading is to remove all spark plugs, have a good strong battery and have the throttle body butterfly open. I have never done a compression test on a forced induction engine so that could be a issue.
If you have done these steps and got the 100 PSI reading then maybe try a different guage. I know it is a PITA to remove the plugs. If your PSI values stay the same I would consider talking with a experienced Jaguar mechanic, hopefully not at a dealer.

Good luck

 

Thank you guys.

 

Agreed I think it would be very sensible to take a cam cover off to have a look before doing anything else (the side without the dipstick is easiest). The pressures all seem low.

I would check this first before risking doing any more damage.

 

The above are pictures of piston 8 or right bank 4 which is the one with zero pressure, the pics are not great but the piston clearly has some makes/abrasions on it.

I've been advised to go with a reconditioned engine which I'm not that pleased to do as I want the car to be original plus its going to cost however if the secondary tensioners have gone I assume the engine has had it anyway?

 

That just looks like the area nearest to the spark plug ...the centre of the fire ,,small sign of valve touching the piston on the LHS...That could have bent it and thats your hole. Maybe you dont need a new engine just a head rebuild and those chains checking.

 

I think the biggest issue is the cylinder liner walls. If the Nickisil liners are damaged then the entire short block needs to be replaced. I think the advice of going with a reconditioned engine is likely the most cost effective way to go unless you are able to do a engine out tear down.

 

I would be tempted to do some further investigation before writing the motor off.

Agree with pistnbroke that there doesn't appear to be much wrong with that piston. Have you checked the cam timings yet?

 

I have very little experience stripping and rebuilding an engine to be honest but I can follow steps.

I've not checked the valves or tensioners yet.

 

If there is a dropped valve you will either need to look down into the area where the intake enters the head - don't know how easy or hard that is on a 99xkr... It's easy on an XK8 or NA car. If the valve did drop, went cockeyed and immediately got jammed back up into it's hole (soft aluminum) the valve could easily still not be sealing and sitting wrong in it's slot.
​​​​​​Hence NO EXTREME gouges and marring on the cylinder that one might expect from larger valve pieces bouncing around in a running engine...the valve seat is still there, maybe even with a big chip missing that got blown out with the exhaust.

If cockeyed but still there, valve may not be completing it's travel...Do you have a loud tapping at the valves in that cylinder when running?

Is there a way to get that CAMscope to point UP to the underside of the head? Maybe jam it down in there until you can get it to turn around and look upwards?

 

Another way of checking would be to look at the clearance between the cam follower and the back of the cam lobe. If the valve isn't closing properly (bent/stuck), then the gap between the two will be wider than normal (compare against one of the other cylinders).

Removing the cam cover isn't a difficult task, and it's a $0 job.

 

Yup, yup and yup.... ^^^^
HellO Michael!!!
France (and the driving) were amazing!
Jus say'n

 

As you are in the UK you could buy a whole xk8 for £2500 take out the engine and sell all the bits and make a profit..worth thinking about .....

 

I wouldn't be thinking engine out
I wouldn't be thinking engine tear down
I wouldn't be thinking nikosil engine problems
I wouldn't be thinking walls of the cylinder
that's just me...

I would be thinking about the 4 valves in that cylinder and their seats - only... Ya gotta get an eyeball on them and see what you see.

One of my first EVER jobs on my XK8 was to replace the LH head... Dropped seat... I had NEVER done anything like that before... Honestly, looking back, it was easy and kinda enjoyable - ESPECIALLY with help from the good folks here. Just took a bit of time. The heads can be had for less than 300$$$

One step at a time. You need to see the valves in that head and their seats. I would do what Michael said, use the CAMscope, you have the technology...

 

Hmm. I'm not jealous, much. Will PM you

 

If you do the replacement engine approach, how do you figure out if it's any good? Private sale (if it runs), do a compression test. Commercial (like Jagbits) based on the warranty? Seems like doing the rebuild is a much better approach since you know what you're getting (and how many miles are on the motor).