Hi,

my car is a 1977 Jaguar XJS coupe 5.3 V12 preHE. After a fire I am having the engine rebuilt in a workshop. The workshop owner said they milled 0.32 mm off the engine block to mate to the cylinder heads. Is this acceptable or is it a problem?
the workshop owner said I should send the timing plane cover with bolts so they can mill that also the same amount. They also said they mill the place where the liners sit, the same amount so the liners stand a bit above the surface of the block as required. He also explained to me that they made a customs steel part to put in placebof the crankshaft so the engine is held straight while on the machines.

If it is a problem, I thought the block was the same as any HE v12 so just the block I can swap? I am guessing HE V12 is easier to find only the pistons and the head are different while the block itself is the same.
What about the cylinder heads, how much can be milled off those before it's a problem?

thanks,
János

 

If the tappet plate is off, make sure that the surfaces are parallel.

 

I understood that the bell housing bolt pattern changed with the introduction of the TH400 transmission (which is why you need a custom bell or adapter to install a manual transmission). Otherwise you could go with E parts…

 

The 2 I have done were as follows:

Cars were both BW12, Pre HE Fuel Infected, minus engines, hence FREE to me.

Replacement engines, PreHE were both TH400 engines. So, later XJ12 or XJS units.

The only things I removed were the dowels. The BW12 bolted up just fine. Dowels are located differently on the clock face, and 40 years has passed so I have NO idea of what was what.

BUT

BUT

The spigot hole in the rear of the cranksaft is DIFFERENT.
BW12 and Manual are the same, but TH400 is a larger style hole, so an adaptor was needed. NOT available of course, so I made it.

 

OK, my take after too many years.

It appears he has DONE the milling, of the deck, and the liner seat, GOOD man.

The timing cover does need to be "trimmed" as he states.

That SMALL amount is OK in my opinion, and changes nothing of the base engine specs.

HE and PreHE blocks are the same, BASICALLY, as are the liners.

The TH400 trans adaption is the same. See my answer on that later in the thread.

BUT

Since he has gone this far, carry on, and enjoy the Beast.

Head milling, I would NOT go past 1mm, and that is SIMPLY based on Aussie Gut Feeling, nothing scientific at all.

 

Just to be clear about skimming the heads. If, repeat IF, the head is to be skimmed, you MUST remove the tappet block and having skimmed the head/block surface also check/skim the tappet block side of the head to be SURE the two faces (top and bottom) of the head are 100% parallel.
If not, when the tappet block goes back on the cam will not be/might not be, parallel to the head/block surface (ie at 90° to the valve stems).

I would skim the absolute BARE MINIMUM of the head surface, Grant's 1mm seems a lot to me!

 

Thanks Greg for the call on that.

YES,

Se, old age has its advantages, the Wing Man rings from France to tell the Fossil tp WAKE UP.

Gotta luv this Forum.1mm would be the ABSOLUTE MAXIMUM, on any of these engines.

 

Thanks!
I pay handsomely but at least it seems all is good then.
I have BW12 transmission.

 

AHA, so one of the very early XJS.

BW12 was rarer in them than the Manual Transmission.
One of my S2 was 6/76 and BW12.
The other was 12/76 and TH400.

Solid trans, LUVS fresh fluid, often.

About 450k kms is normal with that fresh drink from time to time.