Ready to Mount the Head Studs

(Lou) #1

Now that the holidays are over, I can get back to some serious work; reinstalling the head on the Jag :slight_smile:

As discussed some weeks ago, I have drained the coolant and blown out the head female thread where the studs screw into the block. And I will grease the end of the studs before installing them.

However, there is one issue that I am still not comfortable with. Some of the studs are still “loose” after tightening them as much as possible. By “loose” I mean that I can move the studs in a circular motion, down to the bottom the block, even though they are as tight as possible. Stud four is the loosest, studs three and five, less so, Studs one, two and six are tight.

I was wondering what I could or should do? Maybe some low strength loc-tite on the block threads.

(Pete55Tbird) #2

Lou, can you clarify loose? Are you saying the OUTSIDE DIAMETER of the studs
is SMALLER than the INSIDE DIAMETER of the threaded hole? If not what? Pete

(tony) #3

imo, you should make an inspection of the suspect thread

in Hammills book, he outlines the following method of checking whether the thread union is strong enough.

place head with no gasket, torque bolts, remove nuts, check height of each stud
repeat…if any have moved up, that is a fail

(Lou) #4


Sorry for the vague description. Let me clarify if I can.

After double nut installation and tightening a stud for #2 cylinder, but before installing the head, I pull the top of the #2 stud towards the front of the car as far as the opening in the head permits, and let go. The stud springs back to its original position immediately.

If I do the same thing with a stud associated with the #4 cylinder, the stud does not spring back to its original position but instead, remains in the new position. The stud is tight and cannot be tightened further, but can be moved backward or forward, as much as the opening in the block permits.

Hope that helps.


(PeterCrespin) #5

How can you pull a stud as far as the head allows if the head is not fitted?

Are you threading into the deck or the base of the block?

If the former, are the loose holes blind or open? Blind hole studs should jam at the base with a thread or two left visible. Open hole studs will jam on the last stud thread and might wobble in a shallow hole but it doesn’t sound good.

Are they OEM rolled threads or machined threads?

(Frank Andersen) #6

Such tightening ‘as much as possible’ is pointless, Lou - when the studs bottom, metal to metal in the block, it is as tight as it gets…

The reason for the ‘wobble’ is thread erosion, rusting, of the block threads - to be expected. Given new studs; the question is whether the there is enough threads remaining to take the strain. In addition to testing wobble; how much ‘up and down’ play is measured. Slightly loosening the stud may give a ‘better’ indication - but Is still inconclusive as to holding strength. Unless considerable force is exerted, near the expected load - a ton or so…

There is no certainty; you may inspect the block threads visually, of course - and compare the respective ‘loose’ and ‘firm’ studs. But unless massive corrosion is clearly observed, my guess is that you will be OK as is…

Adding lock-tite is pointless, it is only meant resists unscrewing - the holding force is dictated by the metal strength - amount of thread metal remaining.

The only viable option is to use helicoil inserts - which will give the original holding strength. It has provided a complete cure in cases where the threads have utterly failed - but whether the effort is necessary, or worth while, in your case is questionable…

Be aware that the torque applied to the head nuts is not the stretch force. The nut torque is the amount of friction between the treads and friction between the nut and the head. The torque read on the free, double nutted, stud is just the twisting of the stud…

xj6 85 Sov Europe (UK/NZ)