Hello, the group: I am currently in the disassembly stages of replacing head gaskets, timing chains and tensioners and other miscellaneous items on the 4.0L engine of my 2000 XK8 convertible 50,000 miles, normally aspirated). I believe that while removing the crankshaft pulley bolt I might have inadvertently rotated the engine counterclockwise a few degrees. I discovered when preparing to install the crankshaft timing tool that the engine won't rotate by hand; with the timing cover off, it appears the chains are locked (some droop in the return side of the primary chain for the left bank; everything else is immovably tight).
My question is this: I believe I should be able to set the crank timing after the fact by installing the crankshaft timing tool when I'm ready to reassemble, but my concern is that the crank rotates twice for every single rotation of the camshafts, so it may be possible to get it 180 degrees out of time. With the cylinder heads off, can the correct setting be determined by looking at the position of the pistons?
I appreciate any recommendations.

 

Insert the crank tool with the heads off. It will accurately locate the crank. The cam positions are then set by the locking tools. That the cams rotate half speed doesnt matter as far as the bottom end is concerned.

 

Thanks, Quadcammer. Your advice caused something to fall into place in my brain - the pistons don't care whether they're at the top of the exhaust stroke or the top of the compression stroke, the camshafts look after all that. I appreciate your time and the fast response

 

I uploaded my STUDENT GUIDE 'Engine Course 168' I had converted from a 3 ring binder to .pdf years ago.
It is ALL OVER the internet and will have all the info for the V8 and V6 engines.

Gus has it on his site.

 

Here is a link to the Engine Repair Course motorcarman is referring to:

https://www.dropbox.com/s/vqpy3bbjzd...e_168.pdf?dl=0

 

I'd be concerned that the motor appears to be locked: a few degrees of crank contra-rotation shouldn't cause it to freeze.

Curious as to why you need to change the head gaskets - has the motor suffered an overheat?

 

you can turn them backwards all day long nothing happens. engine has to have a super worn out chain to do any damage

 

Good point, michaelh, and I am a bit puzzled. The engine was turning by hand (spark plugs out) before I removed the crankshaft pulley bolt. The only things I did afterward were to raise the front of the car about 18 inches and remove the crankshaft positioning sensor. I reinstalled the pulley bolt but became concerned when the crank didn't move while I was tightening it. I'm going to go ahead with the timing chain removal process and hope the crank can be moved afterward by nudging the flywheel. I might be too conservative about the amount of force I'm using on the bolt.
As for the reason for the gasket failure, it occurred - or became apparent - when I replaced the thermostat after owning the car for about four months. I think that's when the system became fully pressurized. My mechanic (a good one) noticed coolant seeping out the upper side of the left bank head at the frontmost corner. Haven't had any coolant in the oil. I think the gasket may have been defective when I bought the car but the defect became apparent only after the engine reached full operating temperature. It's something that should have been checked before purchase but the Jag was in splendid condition (no rust anywhere, fine interior, good driving performance).

 

motorcarman and NBCat, thanks for your help. I came across that guide a while ago and have the PDF sitting on my desktop. It's been invaluable.

 

I wonder if it might be hydraulic lock if the gasket is leaking - although I'd expect to see some coolant in the oil.

Since you're removing the heads, I would make no more attempts to turn the crank until they're off.

Incidentally, the techs on here recommend using the MLS gaskets from the 4.2 as replacements for the composition ones on our older cars. Direct fit, AFAIK.

edit:- I see you have the plugs out so unlikely hydraulic lock . Heads off should give you some clues, though.

 

For anyone still following this thread, I now have the cylinder heads removed and would like to share some of this experience.
I originally posted this seeking advice on my inability to hand-crank the engine (2000 XK8 4.0L N/A) after removing the crankshaft dampener. I discovered during disassembly that the secondary timing chain on the 'B' bank was locked up, and I managed to remove the tensioner, then freed the chain with a slight pry on the exhaust cam sprocket. I believe this occurred because I inadvertently cranked the engine slightly counterclockwise at one point while removing the dampener. After the heads were removed I was able to hand-crank the engine easily.
If anyone is wondering, I installed the crankshaft locking tool and discovered in the process that the keyway on the front of the crankshaft is matched to the tool-setting plug on the flexplate. If you get the keyway pointed exactly down, you'll be able to install the locking tool (with a bit of jiggling - you need to get it precisely right, and I found it useful to recruit my wife for the above-ground work in that enterprise).
I still haven't determined why the head gasket was leaking, but the machinist reconditioning the heads mentioned that the cooling passages in the upper part of the head are only thinly separated from the surface (less than 1/4" of metal) and this type of leakage is not uncommon with such designs. They're apparently very vulnerable to even a short episode of overheating.
I hope to compile a more complete post of this experience - I've seen many such accounts both in this forum and elsewhere on the internet, but I think I have a few things to contribute that might be helpful to others undertaking this work.