OK I seriously need some advice here, Posted last week about a potentially locked up V-12. pulled plugs & Starter motor & yes it is definitely locked up, will move about 2mm in either direction. Motor was not running when this occurred. Drove perfectly, parked for night, locked up in AM. Originally thought Hydro Lock (negative) next pulled starter ( negative)
Motor only has 30,000m on it
Any one have any ideas, Im thinking maybe timing chain or could a valve have dropped ??
Any thoughts are greatly appreciated before i pull it apart
Thanks in advance

 

In my opinion, that isn't common at all. I have built 3 Jag V 12s, and can't imagine what would lock the engine down with that little of movement other than maybe a valve spring keeper, and or stem broke, and the valve dropped down into the cylinder.
I have seen ads for a smartphone attachment that allows you to look inside the cylinder through the spark plug hole. Either way, sounds like a tear down is in your future.

 

Valve seats won't normally drop when cold. Normally they 'pound' loose when running...

If the chain jumps, it shouldn't lock up either, as the engine is supposed to be a noninterference engine...

 

OOPS.

One last suggestion that I thought of.

Mark and remove the distributor. There have been reports of the jackshaft gear jamming the distributor driven gear, but I have never seen it in all the V12's I have internally interfered with.

Then it gets messy. The oil pump is on the snout of the crankshaft, and if a piece of metal, God knows what or how it could get in there, has jammed that pump, that would give the limited movement you have. The pumps are not known to fail at all, they are huge, but things do go bang in the night.

 

When I'm faced with a situation like this I disassemble as much of the engine as I can in situ starting with the top end. Air cleaners, intakes, distributor, belts and so on. Once in awhile the issue will present itself before removal. This gives you a chance to find the problem. If the engine does have to come out many things have already been removed which can prevent breakage and perhaps make removal easier.

 

Although it isn't that hard getting the engine out...

 

The only thing that hasn't been mentioned so far is the 'Gearbox'

Maybe it got locked up in 'Park' or something, so may be worth a check before you pull the Engine to pieces.

If something in the Engine broke, I think you would you would have heard a noise or else noticed something was wrong before you parked her up.

Got to be worth a shot, I would have thought.

 

Thanks for the info guys
As for tans issue I put car in neutral & pushed it out of garage, so unfortunately thats not it.
Sounds like I am looking at a major rebuild no matter how I look at it.
If the heads come off I cant see reinstalling them with out rebuilding first.
If I have to pull motor, Drop pan & fish metal bits out, cant see not rebuilding lower end, SO
Now for the next question, what are thoughts on putting a SBC in instead of rebuilding the 12. cost & time would be less, what does any one think about handling characteristics with a cast iron V-8
NOTE: I would keep the numbers matching 12 & rebuild at a later date to possibly reinstall or sell with car in the distant future

 

Below is the text on the subject I posted in another thread linked below as this subject has been well covered.
https://www.jaguarforums.com/forum/x...al-v12-184209/

I have lots of experience personally and many others here do too. There are many advantages to doing a Chevy conversion. Less weight and more power in most cases, lower fuel consumption, and greater serviceability and reliability. The reduction in weight over the nose significantly improves handling, braking and acceleration. The torque of the chevy motor plays well with the tall gearing of the pre-facelift V12's.

There are many pitfalls with doing a conversion. The person doing the conversion must have good mechanical and electrical skills to get all the fine details like gauges and A/C working properly. If done well the conversion has the potential to increase the value of the vehicle significantly. If done poorly or incompletely the vehicle will be worth almost nothing.

At this point you have little chance of selling a conversion for more than the cost to do the conversion unless you got some of the parts and labor for free. The market for XJS' converts just isnt there...yet. Converts are most appreciated by someone who already has one so they have a somewhat muted appeal broadly speaking.

Currently, there is still a lingering stigma associated with converts among the purists. Some here have cowed those that have broached the subject like you have. Dont be deterred, the tide is turning. As time goes on the converted XJS' are becoming more tolerated as more of the die hard purists experience catastrophic engine failures. XJS converts are not yet as embraced as the converted XJ coups and sedans. The reason for this is rigid idealism combined with the fact that many converts are incomplete or very poorly done. There is something to be appreciated when it comes to originality and a conversion certainly destroys "originality" significantly. But, if your V12 is a spent bomb and the ability or willingness to fix isn't there, then conversions can keep these cars on the road and out of the crusher. That said... there are some people so rigid they sleep standing up and would rather see an XJS get crushed than converted. Wont be long till they make themselves "prone" in subsequent posts.

A Chevy conversion is a GREAT way to turn the XJS into the sporting GT it could and should have been. A LT1 with a 6 speed is an awesome and low cost way to create a very refined and unique GT experience that offers a very high level of performance. The LT1 or LS with a 4l60e is great for those who dont want to row. The TPI /700R4 package offers a vintage performance feel which still performs well and is still appreciated by many and a good low low cost approach if you already have one. The 350/350 conversion or SBC with carburetor and 3 speed TH350 transmission is passe at this point.

So... if you're going to do one... do the car justice and do it as right as you can. Unless you're an accomplished fabricator, it would really help to speak to Andrew from Jaguar Specialties. If you follow his program and kit you will have a greater chance of completing a well sorted convert that is reliable and a joy to drive.

Dont get carried away...unless you really want too. You could easily spend 7 to 15 grand on an LS engine alone... This type of conversion can overwhelm a stock suspension and chassis and put a big dent in your wallet. This type of engine can also offer a high level of over all performance if you are willing to spend the additional monies necessary on larger wheels and tires, suspension, brakes and so on. An LT1 conversion can cost as little as $3500 and is a great match for the capabilities of the stock suspension. The Lt1 offers a few more horsepower than the V12 but far less weight, therefore over all performance is much higher. LT1's can be massaged to make almost the same HP as entry level early LS1's. The LS and LT1's with their sequential fuel injection offer levels of refinement very close to the v12. Basically if your conversion is an exercise in frugality the LT1 is the way to go. If not the any LS is a great performer and would have more refinement and a higher resale becasue, these days, almost anything with an LS is sexy.

 

Had funky issues starting when parked on an incline as well, with a loose parking brake cable. Had to get a slight nudge to relieve the pressure, properly engage the gearbox, then good to go. Cheap to check.

 

Hard to imagine something causing so little movement without being catastrophic. Possibly the transmission pump jammed? Not that I've ever seen it. I have seen pistons seized in bores but it always happened after overheating.

 

Ok so I pulled the starter & heard a loud clack upon removal. I figured eureka that was it. Now motor will turn counterclockwise but still won't budge clockwise.
Starter was holding it from going counterclockwise.
Now going to tear it down & see if I can find out what happened. My bet is a valve, anyone else care to wager as to the culprit??

 

Hi Burger

Oh No!

If you turned the Engine in the Wrong direction, then it sounds as if you've Broken the Timing Chain Tensioner.

So I will give Daim the pleasure of talking you through the fix, in the event that this may be your problem.

 

Moved it CCW only 10mm to avoid the chain tensioner. Olso did test with oil filler cap off so I could observe chain & it only moved a couple of mm.
It's locked solid in clockwise rotation. Are there any gears that could have broken or if a valve let go could it be jammed in the jug.
Remember the motor was not running when this occurred

 

That makes sense.

Counterclockwise with a broken tensioner will need to take up the slack before the LH cam will move, and that 10mm for a 1mm or so at the cam is a tensioner gone AWOL, and jamming the chain in clockwise direction.

If it were mine, i would be spending the time removing the timing cover, either in the car or out (removing that engine is simple), and then IF there is nothing there, move deeper.

 

Hi Burger

I very nearly accidentally 'almost' turned the Engine over the wrong way myself, when changing the Fan and pulling on the belts.

So that I could manage to get to one of the nuts I couldn't get at underneath but I was very lucky and got away with it but only just.

As all hell seemed to be breaking loose when I tried to start her up.

'Daim' has got some great Photos which I'm sure will be of help, in explaining the best way to go about doing this job.

 

I've turned my engine a few times backwards. Around 45-50° with no worries...

 

I'm in S- fla riding out Irma
As soon as it lets up I'm going to crank this thing CCW for a little & see if it frees things up. At this point I have nothing to loose
Next option is either pulling motor or tearing it down in place

 

Stay safe big fella.