I know this subject was discussed many times, but I need one question cleared - how many teeth on camshaft sprockets must a chain jump before valves hit pistons?

My story is very similar to others . 1999 XK8. SToped at the farmers market yesterday after eventless drive. The car would not start 309 minutes later. It was a hot day so I thought first about some kind of vapor lock, later about flooding. Full throttle routine did not help. I pulled plugs - right cylinder bank - all cleaned, left cylinder bank - oily, and black. While starting a lot of backfiring int the intake manifold which got almost immediately hot. I think that a timing chain jumped. The car is still sitting there waiting for being pulled home tomorrow. Before I remove a valve cover and invest in secondary timing chain tensioners, I would like to now what chances are that valves are bent. I don't think I would be able pulling head off the motor just on the street in front of my house. I am also afraid that the Nikasil cylinder wall might get scored when I was trying to start the car and washing the cylinder walls with fuel...In the worst scenario - what engines I can install instead this 1999 4.0 - there are some newer on ebay and in local junkyards - even 4.2l...thanks for the help...this is not a good weekend for me...

 

I do not know if there is a specific answer to your 'number of teeth' question but based on plug condition a valve cover removal and view of the cam timing would be a very good place to start. The flats on the cams should be 'almost' parallel held off only by the valve spring pressure on the cam lobes.

If you determine that the cam timing is off, replacing the tensioners while aligning the cam timing may be the least cost option at this point. After that you can do compression and leak down tests to determine where to go next.

Don't buy a replacement engine yet but the '99 through '02 are AJ27's and while there will be issues to resolve they are good matches. Anything else is going to be a significant labor situation from a financial standpoint or time if you plan on the swap yourself.

 

^ and sounds like oil is leaking from the valve cover on the left bank (I assume passenger side?) Get that fixed and new plugs on that side, be prepared for a bad coil or two, but see if the new plugs work. Tensioners eventually go, sorry you weren't more lucky.

 

HI, I consider the drivers side as a left side of the vehicle and en engine as well.There was not any oil accumulation in the sparking plug well, which is another confirmation of my fear that the timing chain jumped or snapped...

 

I seem to recall reading somewhere... jump 1 tooth = Okay. Jump 2 teeth = new engine.
George

 

I hate to say it but if the car won't start, and the cause is the timing chain, you have bent some valves, killing the compression. Since bad secondary tensioners is a known fault, it will pay to ghone in on this. I have heard little of skipped teeth, the chain is usually broken due to the severed tensioner shoe going through the gear.

 

You were right, a broken secondary chain....not sure whether I can handle it on the street in front of my house..and I have to start to look for some other source of parts than Jaguar dealer....

 

you can see what I have found. I guess a head needs to be removed. I also don't know if the cylinder walls were in any way affected by my stupid prolonged starting procedures...perhaps that is the heat affecting a clear thinking, but I dealt, in the past, with cars with broken timing belts and engines usually did not spin, or did with a distinct clunk---nevertheless, now I have to decide should I tackle it myself, or not....

 

Dneu,

Ouch. But maybe not as bad as you think. If it were mine, I wouldn't worry so much about the cylinder wall as the valves being bent, and you don't have to remove the head to check the valve seal.

At a minimum you are looking at a complete front cover-off timing chain, tensioner and guides replacement. But you want to see if the valves are ok before spending the money on this stuff.

So, remove the spark plugs. Squirt a *little* oil in each cylinder. Remove the exhaust cam on that side to allow all the exh valves to close. Then do a leakdown test on each cylinder of that bank, turning the motor a little each time to close the intake valves of that cylinder being tested. This should show you the condition of the compression.

If all is good, then do the timing chain job.

Dan

 

Sorry to hear this. I'm not sure, but if any valve damage has been done, I think it would have happened on the first failed start, so don't feel too bad about cranking it too much.
Of all the failures i've seen reported, yours let go in a big way.
That engine looks like it's been overheated at some point, no doubt contributing to the failure.
Unfortunately, a poor design, which Jaguar only corrected after many a ruined engine.
They knew for many years that it was a weak point, but never made customers aware of the problem, thus never giving them a chance to catch this early.

 

Agreed, but IMHO overheated at some time doesn't necessarily mean trashed engine. If the compression is still there, I would bet that this is a good candidate for timing chain replacemement (AND water pump AND thermostat).

 

...I agree that it is a flawed design and I would expect that a reputable manufacturer of higher class automobiles would address the problem and recalled cars affected. I even question necessity of having a tensioner on a such short chain. My car has only 92k miles and worked fine. A coolant temperature never raised above safe level.
I am a little puzzled with the amount of deposit on the inner surface of the valve cover and on rotating parts as well. Because this is not a non-interference engine I expect at least two valves bent.... anyway, I will keep adding reports as I progress with tests and eventual repairs. Still looking for a cheap source of parts...

 

The Lincoln LS used a modified version of the AJ27 engine and their tensioners are consistently 40% less expensive than from a Jaguar parts supplier. My Ford parts boxes said 'JAG' on them. FelPro has a Lincoln LS valve cover gasket set for less than half any Jaguar source.

 

I had a metallic whirring sound develop coming from the right bank of my 2000 XK8 engine, and inspection revealed that the upper valve timing chain was rubbing against the inside wall of the engine block. Bad tensioner and chain was replaced which took care of the noise, and likely spared me from chain failure which could have resulted in a swallowed valve and serious engine damage.

Sounds like a similar senario to what dneu experienced regarding the tensioner.

Rusty in NC

 

Any update on this? im thinking I have the same problem (hopefully not a broken chain) but I have decided to replace everything, both sets of chains and tensioners due to the high mileage of my cat and im wondering how difficult it is.

 

Excellent step-by-step pictorial in the FAQ above. Secondary pretty simple, primary somewhat more difficult.

 

I did not read anywhere that you checked compression leak down. Are you sure you have good compression leak down all around? It seems that you are making a decision without enough information.

 

I did a compression test w/o oil (tho the spark plug holes had some oil in them) compression is 140-150 left side and 120-130 right side, lowest compression in hole closest to driver at barely 120(this one took longest to reach compression, maybe 3 or 4 cranks)

 

Well at least it sounds like you do not have any bent valves, which is excellent!

 

so i finally found a manual that works and an old Dell to use it on.. now im wondering which to tackle first? the primary chains and tensioners or the secondary ones first? and can i do one side at a time or do i have to switch back and forth doing both primarys followed by both secondarys?