Undoing Two Cylinder Head Bolts/Nuts ?

[DavidH]

I have recently fitted the red conduit (part number C2351) to correctly channel the HT leads to the spark plugs on top of the cylinder head.
I now need to attach the conduit to the cylinder head which will mean undoing two cylinder head nuts and am wondering what the best way to do this might be ? Currently I am thinking that I will need to remove the black paint on each bracket of the conduit so there is metal to metal contact between the bolt washer and bracket and then remove the two nuts one at a time, place the bracket underneath and then re tighten them to the correct torque.
My thinking is that undoing the nuts one at a time wont be much different to when they are undone to remove the head, so its unlikley to do any damage to the head particularly as the head will also be secured by the others..... however am not 100% sure ?
Any thoughts/comments/advice on the above appreciated before I attempt it in a few days time.

P1010972.JPG (154.5 KiB) Viewed 2651 times

[Heuer]

I removed both nuts, plonked on the conduit and tightened them up. It only takes a couple of minutes and they are both on the same side so no harm will be done. Nor did I remove any paint from the brackets. Obviously you need to thread the cables into the conduit before hand which is not easy if you are using copper ones. Start with the cable furthest away from the conduit outlet and use a pick to ease the cable through the holes.

[christopher storey]

David H : you do not say what engine you have. With any 3.8, and with early short stud 4.2 engines, there is unlikely to be any problem in your method. If yours is a long stud 4.2 ( recognisable by 5 core plugs on the exhaust side ) then there is some hazard in disturbing any cylinder head nut, as there is a possibility that the stud may unscrew with the nut, and there can then be considerable difficulty in getting the stud back into position, because cooland and/or crud can flow into the block thread and cause hydraulic locking of the stud

[mgcjag]

Or even worse the studs snapping due to corrorion where they screw screws into the block...yes this can happen on a long stud engine even when just undoing a head nut....Steve

[Heuer]

Guys: If you read DavidH's post carefully you will see he is fitting the red conduit which is designed to only fit early 3.8 engines without the lifting brackets. Can't be fitted to later engines as the lifting brackets get in the way, unless they are removed. So no long stud problem.

DavidH: Please add your car details to your signature as it will help members answer questions

On another point it looks like the very original 1965 S1 currently for sale has a red conduit with the later fixings to accommodate the lifting brackets.

[christopher storey]

Guys: If you read DavidH's post carefully you will see he is fitting the red conduit which is designed to only fit early 3.8 engines without the lifting brackets. Can't be fitted to later engines as the lifting brackets get in the way, unless they are removed. So no long stud problem.

There you are : the benefits of encyclopaedic knowledge - interestingly I don't ever recall having seen red conduits - only black ones

Also - David Marks of JEC is very much against fitting any conduit - he says that they are one of the commonest causes of misfiring/crossfiring as plug leads age

[Heuer]

The conduits were made from Vulcanised Fibre a chemically pure cellulose product (used for suitcases and Spitfire long range fuel tanks). Although the product was available in many colours black or red is seen from the XK's on-wards to the S2 cars. Jaguar specified black but supply limitations meant the red had to be used and whoever made these up decided to paint them black. Unfortunately the properties of Vulcanised Fibre mean nothing will adhere to it so, much like the diffs, the black paint fell off leaving the red showing. In some cases they did not even bother with the black paint and red was used. So we see a mix of red, black and red with black paint usually oxidising off. With the help of Tadek and several others we were able to convince Julian to make the early red version with its unique brackets which could be used on all saloons and sports cars up until the lifting eye's were introduced. Some owners paint the red black whilst others leave the conduit red.
More info here: viewtopic.php?p=59237#p59237

David Marks is wrong - the commonest cause of misfiring/crossfiring is plug lead ageing, not the conduit!

[christopher storey]

David Marks is wrong - the commonest cause of misfiring/crossfiring is plug lead ageing, not the conduit!

Weeell... both of you are correct, in that the trouble only manifests itself with age, but it is the close proximity induced by the counduit that enables, in particular, crossfiring to occur

The history you gave is very interesting - I had never realised they wre painted black

[DavidH]

Many thanks to all for the useful information.
I am installing the conduit on a 1963 3.8 litre OTS.

I plan to just undo the two bolts, place the brackets underneath and then re torque them to 58 lb.f.ft (circa 78 Nm) which is the value shown in my Haynes manual.... I'll also check that the other bolts are tightened to the same torque - if anyone thinks I plan to use the wrong torque setting please let me know !
I read a post a while back that advised that no paint should be on the cylinder head at the point where the bolts tighten but will probably just use the painted brackets and recheck the torque after a few miles.

For information, I see some questions about plug lead lengths. I used the lengths suggested by Michael B in his post from 25/9/16 which were 0.7, 0.8, 0.9, 1.0, 1.1 and 1.2m which I think will work out OK. If you look at the picture at the top of this post however you can see that the holes are not evenly spaced along the conduit so leads 3 and 5 are slightly shorter than the others. I think if I ever do it again (hopefully unlikely), I'd use 0.7, 0.85, 0.9,1.05,1.1 and 1.2m and then just trim them as required when finally installed.

[Heuer]

To be clear, they are acorn nuts not bolts so don't panic if you think something has sheared off!

As for lead length it rather depends on when your car was built as there were three routes and different means of retention. More info here: viewtopic.php?p=69517#p69517

Best method is to install extra length leads into the conduit, route them with the correct fixing's and then trim to length.