Daimler VDP (XJ12) restoration: If Mohammed don't come to the mountain...

You know the expression. Think it was around before the current Islamic issues so you don't hear it as much now but I think it was saying - if something won't happen try another approach.

Well I'm taking the heads off my engine just now to see if I can get to the bottom of the seizure-problem. It's probably pistons stuck in bores.

You may know that V12 heads are know to be difficult-impossible to remove in the conventional way - ie take nuts off and lift head off block.

Problem lies with the ten 7/16" studs that run down the middle of the block. They live in the water-jacket (unlike the other 16 per head) and the shafts become bonded to the drillings in the head. Some say it is actually the Barrs coolant additive that builds up in there.

Anyway. Ppl have tried various methods to get them off. You can read in horror online if you wish but I'm going for the gentle approach. I figure if you take all the studs out the head can't remain stuck on. It's not easy to remove the studs but I'm getting there. I'm not in any rush tbh.

So there are 26 per head

12 x 3/8" thick (the plain nuts for those take 9/16 AF spanner)
14 x 7/16" thick (the domed nuts for those take an 11/16 AF spanner)

They can then be further subdivided into

likely to be corroded: the 10 x 7/16" that run down middle
won't be corroded: the 12 x 3/8 that run on either side of the head & the 4 x 7/16 at front and back of the head

Then there is sub-division for accessibility

ones that you can get to directly from above: all the 7/16 & the 6 x 3/8 that are on outer edges of head
one that you can't reach from above: 6 x 3/8 on inboard side of head

So how do you get them out? Well the easiest way is to lock two nuts onto each stud and unwind them but there isn't a great deal to get hold off on some groups and on others this doesn't seem to give enough purchase to unfasten them.

I got the outer 3/8 ones out and the clean 7/16 ones(2 at front and 2 at back of each head). So that's 10. I can't get sufficient access to the inner 3/8 studs but it's unlikely they'll pose an obstacle once all the others are out so I've given up on them. That leaves the ten water-jacket studs. I've got two out by welding a nut onto the top of them and them removing as if they were bolts. It works well but you waste a nut and a stud each time you do it.

Thing is that doesn't really matter as the studs are not in great condition and would be safer to replace them anyway.