Leaking coolant after Cylinder head dress-up kit (Chrome head Bolts) fitment

[markc555]

I purchased one of these kits from SNG Barratt and attempted to fit it yesterday.

The car is a US spec 1969 S2 Coupe. It was running fine (no water leaks).

I figured (wrongly?) that I could simply swap the chrome nuts and washers (D shaped) one by one torquing (54ft/lbs) the new nut up as I went. I drained a few pints of water out of the radiator to stop water spilling out of the nuts when loosened. I replaced the nuts in an order so that the next one was always at least 2 away from the last one replaced. All the old nuts came of cleanly and easily however they where all round washers, no D-washers at all. I cleaned up the head surface under each old nut/bolt as I went. All seemed to go well and I finished by re-torquing all the nuts, several times. I re-filled the system and fired up the motor.

Almost immediately noticed 3 or 4 of the new nuts weeping fluid! I left the engine running to get some temperature in it and used kitchen roll to catch the fluid. The fluid trickles continued.

I've since read about cylinder head bolt problems, where they don't "screw" all the way down in the block so the domed head nuts bottom out before locking down properly.

Have I ruined the head bolts/studs so that I'll need to remove the cylinder head to repair/replace them?
Is it likely that undoing the old nuts unscrewed the studs slightly so that the nut now bottoms out?
Should I just try a liquid gasket to ensure they new nuts seal? (I've seen Permatex 300 mentioned on some sites)

Any help or advice will be greatly appreciated.

Thanks

Mark

[cactusman]

There is another thread on here where someone did the same thing. Think he had a combination of nuts bottoming and an issue with the studs. Be worth finding it....was within the last six months or so

Others here will know more but the General advice would be not to release those nuts unless you plan to remove the head. As you have done so the worse case scenario would be the head gasket won't re-seal and you need to remove the head. Also, some of the studs go through into water ways I believe which may be where your seeping is coming from....hope you get it sorted...

[christopher storey]

I'm afraid that this is a known hazard with the long stud engines, which yours will be ( recognisable from 5 core plugs on the exhaust side. It may be that some of the studs have partly unscrewed, but it is also a known problem that many of the new nuts produced do not have sufficient depth, and that the stud bottoms out in the new nut, and thus although you think you have torqued them down , you are not in fact achieving the required clamping force on the gasket/head interface

What I would do is this : select the worst leaker, and with the engine stone cold, remove the nut again. First, with a depth gauge ( you can get decent electronic ones from e.g. Aldi for about a tenner if you have not got one ) measure a. the internal depth of the nut ( which needs to be compared with the internal depth of the old ones if you haven't thrown them away , to ensure that the new ones are at least as deep as the old ones ) and b. the depth of the stud protruding above the head, and c. the thickness of the washer. a+ c -b should be a positive figure, and at a guess I would say that you need it to be at least 100 thou /2.5mm to have adequate clearance - others may suggest that a greater clearance is needed. If the new nut is sufficiently deep, but you have a very small or negative figure for a+c-b, then I am afraid that the stud has unscrewed, and you need to come back to the thread when I can suggest to you how to tackle the problem . If , however, all is well , then I suggest that you use some silicon sealant round the annulus between stud and head, and reassemble. This exercise of course needs to be repeated for each stud presently affected, and if it turns out that the nuts are of insufficient depth then they will all have to be replaced

[chrisfell]

As well as checking the threads in the nuts, I'd also check the thickness of the washers that were taken off. If they are thicker than the new ones there is a possibility that a PO has had this very same problem, and thicker washers were the solution.

[288gto]

Interestingly while disassembling my spare XJ6 4.2 Series 3 engine for the head and other parts I noticed the head nuts were actually taller than my E type ones. I assumed this was a production alteration to overcome the problem mentioned above.

E type nut on left.



Simon

[PeterCrespin]

I assumed this was a production alteration to overcome the problem mentioned above.

Correct. And because the longer nuts on the XJ 3 are not chromed, people go for for the shiny ones, not realising the nuts will likely jam on the studs rather than clamp the head fully tight.

[markc555]

Thanks Christopher,

I'll run through those checks next weekend or when I next get back in the garage properly.

Quick comparisons suggest that the old and new domed nuts are externally identical. The old washer may be a tiny bit thicker but only by a few thou at most.

I'll report back how I get on.

Cheers

Mark