The engine in my new-to-me '89 convertible was not running when I bought the car. After confirming that I had spark and fuel I began to look at the timing.

I set the crank to TDC and looked at the distributor rotor. They were in correct alignment but the engine refused to run. If I sprayed starting fluid into the engine it would not ignite even though I had spark.

I determined that the engine must be out of time so I removed the distributor and rotated the rotor by one tooth. The engine would then run but was not yet perfect.

I suspect that the balance has failed or that the assembly has rotated on the crankshaft. I seem to recall reading that this has happened to others.

I'd be grateful to anyone who can describe their experience with this issue and what I need to look for to perform a correct repair.

Thanks!

Mark

 

What ignition system is it?
If it is Lucas ignition the the damper has no bearing on the timing, other than the timing marks are no longer to be believed.
If it is Marreli ignition moving the distributor can only make a change to the distribution of the spark, not the timing. The timing function of the damper would only be effected if the woodruf key has sheared as the timing fingers are part of the hub NOT the outer damper ring.

 

Yes, it is Lucas. The timing marks do not correspond to the correct rotor position.

If I set the timing marks to TDC or 10 degrees BTDC and then align the rotor with plug #1 the engine will not run. I had to rotate the rotor counterclockwise by one tooth to make it run.

I plan to pull the pulley and balancer off to find out why the alignment is wrong.

Mark

 

Mark the balancer with chalk or spray paint a stripe on it, fire up the car , give it a few revs then see if the stripe in not aligned.

 

Good idea. I will give that a try and report.

Mark

 

The 2 keys in that pulley area are well known to shear, coz the pulley does come loose. Usually associated with a "strange" knocking noise, BUT, not always.

The tapered mounting collar is also known to come out in more than one piece.

Once the rubber drives integrity is confirmed, do the folowing.

Remove 1A spark plug, use your thumb over the hole, and get your MATE to wind the engine over BY HAND, until you feel the "push" of compression, then insert a "soft wire" probe, and continue BY HAND until the probe ceases its movement, YOU ARE NOW AT TDC COMPRESSION #1A, now set the distributor, and look at the timing marks down below and remark accordingly.

One caution here, DO NOT ROTATE THIS ENGINE BACKWARDS, timing tensioner damage CAN occur. If you go "past" the mark, go around 2 more rotations and take more care.

Timing chain "stretch" on the V12 is real, and resetting the actual cam timing is fact, at about the 100K mile mark for us purists. The plastic chain tensioner breaking and upsetting the cam timing is also real.

 

Hi Grant,

That too is a good idea. I will set the #1 piston at TDC and then see where the crank is. If the timing mark is way off then I will know I need to service the pulley and balancer.

Mark

 

Dont foget the JD, it is mandatory for V12 timing, keeps the nerves under control, and the concentration spot on.

 

Quick question....

Assuming that the #1 piston is at TDC and the rotor is properly pointed at plug #1, should one spoke of the reluctor/star wheel also be aligned with the pick-up?

 

In a word YES.

The rotor and star wheel are a fixed item on the same shaft.

I usually transpose the #1A spark plug post of the cap onto the casing of the distributor. A simple file mark will do.

Then when the reluctor is aligned, the rotor MUST point at that file mark to be correctly timed at TDC on 1A Compression Stroke.

Make sure you have plenty of adjustment in the "advance" direction when installing the distributor at TDC. You will not need anymore "retard" but you will need "advance" adlustment.

Some light reading attached.

Refitting the V12 distributor.doc

HE Tune up.doc

 

Thank you for all of the help.

I did get the engine to start but for some reason it's running very rich. I'm pretty sure that I accounted for all of the vacuum hoses but I will take another look tomorrow.

Maybe time to start a new thread.

Mark

 

Jaguar XJS Series 3 XJ12 V12 Pulley Crankshaft Damper | eBay

 

I had a similar issue with my 91 Classic where the car would misfire occasionally and 'stutter' while driving down the street when all the power disappeared at once! I discovered that the front crankshaft pulley/balancer actually has a rubber 'bushing' between the inner and outer parts and this had somehow broken free allowing the two halves to rotate freely of each other which screwed up the ignition position sensor. My first attempt was to replace the TDC sensor but it still kept missing occasionally and didn't cure the problem. A new crankshaft pulley/balancer was the fix.

 

The crankshaft has a woodruff keyway machined into it on the front, where the lower pulley/damper mounts. I've had this Woodruff key bend laterally, causing the lower pulley to slip on the crankshaft, and change the timing by several degrees. When this happens, the potential for catastrophic damage is high, but, keys are inexpensive, and this is a somewhat common failure, so I bought a spare, just in case it happens on one of my other motors.

 

That is confusing since the timing fingers which trigger the sensor are firmly attached to the hub of the balancer and not effected by breakdown of the rubber. The only way for them to move so as to alter timing is if the woodruff key or keyway become damaged. I suppose it is possible the loose outer section of the balancer moved to such an extent that the fingers were bent out of range of the sensor.

 

I had a similar problem where I could turn the engine damper about a 1/4" either way by hand and I had an oil leak from the seal, turned out it had not been tightened properly and the cone had broken, the movement had caused the key slot to become baggy in the crankshaft slot, I got a new key and cone filled the oversize slot in the crank with liquid metal fully tightened it and its all been fine since,

 

Dizzy mechanical advance seized ?

 

Baxtor, the inner and outer halves of the damper can move independently of each other hen the rubber breaks down, so while the sensor remains in the same place on the outer part, the inner part that is connected to the crankshaft is in a different position, several degrees out of alignment. When I dismantled mine, the woodruff key was in excellent condition so I reused it with the new balancer.

 

If you suspect the damper has movement there is a way to check. Use a felt pen and draw a line from center to outside. Run engine a bit, rev it a couple time then check to see if the line is still straight. If not you have a bad balancer.

 

Assuming we are talking about a marelli V12 the sensor trigger fingers are attached to the inner hub with three bolts and a pin, not the outer. This inner hub is also firmly attached and keyed to the crankshaft. If the rubber breaks down the only thing it will affect is the alternator drive. Even the additional pulleys out front are bolted to the inner hub.
The motor will happily run in time with the outer part of the balancer removed altogether.