this was two others that snapped higher up
the 15 studs which were not in the deeply-recessed parts of the casting came out cold without much drama
On another block (in better condition) all the studs came out easily with normal spanners using double-nut technique
Is this entire issue the result of poor coolant maintenance?
Studs through water is certainly suboptimal from the beginning, but without antifreeze or just letting it lose its rust-inhibiting properties as a consequence of lack of changes will have terrible results over 40 years …
Best
Jochen
75 XJ6L 4.2 auto (UK spec)
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This seems to be the older, ‘short stud’ engine, Foxy…
The usual problem of later, ‘long stud’, engines is that the studs corrode to the aluminium head, making the head difficult to remove. Or indeed corrode at the coolant filled bottom end to the extent that they just snap. Your situation was a bit unusual - but brilliantly solved…
Frank
xj6 85 Sov Europe (UK/NZ)
**
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Thanks Frank
I don’t know about short-stud/long-stud issue here tho as the studs were consistent on both the V12s I worked on (one is ealry carb version and other an HE).
Was it perhaps the E-type which had different stud lengths?
I have no real idea of the history of the blocks…
My project car (1974 Daimler Double-Six VDP) has a rusted-out coolant crosspipe and expansion-tank, plus the very stuck studs, so I guess the antifreeze was neglected
The other engine seems to have been crash-damaged early on in it’s life and put in a crate. Everything on this one looks like new
crash-damaged (?) HE engine was very easy to dismantle
Looks nice! Keeping my fingers crossed for you!
Best
Jochen
75 XJ6L 4.2 auto (UK spec)
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A very critical thing to do, to ensure longevity of aluminum blocks and heads.
It is not really an issue, Foxy…
In the early engines, the head was bolted to the top of the block, short studs - Jaguar then changed to long studs, anchoring the head to the bottom of the block. In fact, with a long stud problem, some replaced it with a short stud, threaded to the block - which actually works…sort of…
The reason was probably(?) that the short studs transferred the combustion stress to the block - and cast iron is not suited to tension. The long studs, suited for tension, are anchored in the bottom of the block placing the cast iron under tension.
I don’t really know if the short studs caused any real problems - but the complaint of the long studs are well known; being awash in coolant, they corrode. And indeed corrode to the aluminium head - all of which sometimes cause problems with head removal and broken studs…
Which were not supposed to happen with short studs…
Frank
xj6 85 Sov Europe (UK/NZ)
**
V12, Frank, not a 4.2!
Reason for the long studs in the 4.2 was indeed distortion of the block deck. Plus, longer bolts bring the stresses to the crankshaft area and the casting doesn’t have to stretch. The bores don’t deform. The increased length is good for more tension.
The same aluminium to iron corrosion will happen in the V12, I guess.
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A matter of wet vs dry studs ? Not sure why long studs have better clamping power than short studs. Unless the thread engagement was limited by the thickness of the block deck.
Carl
One advantage is, the torque applied to the fastener, on short stud engines, distorts the cylinder shape.
IIRC, longer studs clamp better because of a longer stretch, i.e., more spring tension.
I think…
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I think you’re right!
The third good thing is that the force is closer to the source. The cylinders push the crankshaft down and the head up. Long studs take the force down to the crankshaft area. Not that it matters so much on the XK but it does in more modern designs.
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I though the dry studs would cause less stud corrosion, Carl - problem free…
The clamping power would be the same for either stud type - but distribution of block stress would be different; with the long studs there is no tension on the overall block, just compression…
Frank
xj6 85 Sov Europe (UK/NZ)
**
Short studs equally corrode to the head given the “ right” conditions.
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They do, which why, around the base of each stud, in or through the block, I ran a fine fillet of RTV.
No coolant leaks up the studs, and less corrosion to the head.
Dead right. We used to cost the studs in “ neverseeze”
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Coat not cost! Damn iPhone keypad
V12 head studs were never any different.
Every single model had the same stud length.
The later engines I’ve stripped have mainly been a lot easier to get the studs out. I hot parts wash, and sonic clean the whole block prior to attempting tight stud removal.
We used to
Plead with production to alter their method of stud insertion! They never listened!
Maybe they DID at sometime after I left. Maybe that’s why the studs are often easier to remove from the later engines!
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