Head Bolts

Technical advice Q&A

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colinevans
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#1 Head Bolts

Post by colinevans » Fri May 10, 2019 5:11 pm

Hi All
Just made a schoolboy error. I undid one of the long head studs (centre bottom one in the image). Stupid I know (I’m a rank amateur on a steep learning curve!) but I couldn’t work out how to remove the plug leads as they are snug in the protector sleeve that is held down two of the studs.
As soon as I realised what it was I re-inserted and tightened it but it’s now leaking. I’ve read another post that says these long studs go through the water jacket, so I’m hoping it just needs undoing and resealkng maybe with a hylomar type product. I’m crossing fingers here!
It seems to be running OK but I only ran it for a couple of mins as I didn’t want to do more harm.
Appreciate any advice, this forum is fast becoming my first point of reference (and my sanity saver!)
Many thanks.
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Colin
Series 2 OTS, 280SL

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mgcjag
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#2 Re: Head Bolts

Post by mgcjag » Fri May 10, 2019 5:32 pm

Hi Colin......i wouldnt go undoing it again....you dont want the stud comming out and water getting down in its threaded hole...asuming the nut is now seated down correctly then just put some leak seal in the coolant...bars leaks etc...Steve
Steve
1969 S2 2+2 & Building a C type replica

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colinevans
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#3 Re: Head Bolts

Post by colinevans » Fri May 10, 2019 5:46 pm

Hi Steve
Water would definitely have gone into the threaded hole first time round when I took it out right out of its thread and lifted it. Would Bars be good enough do you think, and is it a permanent fix? It seemed like more than a weep, so it maybe that it didn’t seat properly even though it nipped up ok. I’m letting it all dry out tonight and I’ll have another look in the morning.
Thanks for your help.
Colin
Colin
Series 2 OTS, 280SL

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mgcjag
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#4 Re: Head Bolts

Post by mgcjag » Fri May 10, 2019 6:06 pm

Hi Colin....ok didnt realise the stud had come right out....the problem with this is that not just water but sludge will go down into the threaded hole....making it possible that the stud wont go back down completely.....the nut could feel tight but not actually tightened down......have a real good look at the nut and ensure the washer is fully down and tight against the head....if so your lucky and then just use the leak seal...i have known others to use it and permanantly seal the leak....Steve
Steve
1969 S2 2+2 & Building a C type replica

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colinevans
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#5 Re: Head Bolts

Post by colinevans » Fri May 10, 2019 6:12 pm

Will do, thanks Steve.
Colin
Series 2 OTS, 280SL

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PeterCrespin
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#6 Re: Head Bolts

Post by PeterCrespin » Fri May 10, 2019 6:33 pm

You must assume the stud has not seated, given it now leaks. Barr’s Leaks will not produce the required 54 ft/lbs of torque/head clamping.

Clamp stud in vice and remove stuck nut. Clean out crud inside nut and check threads. Drain all coolant completely, ideally using the tap or drain plug hopefully fitted at lower left rear of block. Blow crud and water out of blind threaded stud hole in block.
Do not assume it is clean and dry, VERIFY it.
Lock two nuts on the top end of the stud and do a trial run to see it screws fully home. Remove and repeat with some thread lock on the lower end. Allow to cure.
When fully home, remove lock nuts and check the plug wire bracket plus head nut washer are considerably thicker than the gap under the nut when loosely tightened down.
Refit them and torque down head nut.
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

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christopher storey
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#7 Re: Head Bolts

Post by christopher storey » Fri May 10, 2019 6:39 pm

I would just add to Peter's advice that if all else fails and the stud will not go fully home , it is worth a. cutting a single slot vertically in the bottom thread of the stud ( a dremel or similar will do it ) which will then act rather as a tap does, without significantly compromising the strength of the stud , and b. grinding the boss at the very base of the stud to give a little more vertical clearance from the bottom of the hole

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colinevans
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#8 Re: Head Bolts

Post by colinevans » Fri May 10, 2019 8:04 pm

Chris - thanks, i’ll pick this up again with you if all else fails. Peter, why do you say it’s a stuck nut? I just undid the stud normally? Also what’s the best way once I’ve drained down to clean out the threaded stud hole? An air blower with a long nozzle?
Thanks
Colin
Series 2 OTS, 280SL

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PeterCrespin
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#9 Re: Head Bolts

Post by PeterCrespin » Sat May 11, 2019 12:33 am

Undoing the nut normally requires less torque than unscrewing the stud from the block - thank goodness. This is partly due to less thread overlap (approx 1/2” vs 3/4”) and less corrosion up top than down in the coolant.

If it were not so, it would be normal for the studs to unscrew. The other reason -rotted studs- thankfully doesn’t apply here.

So if the stud unscrewed then the nut was tighter than designed on the stud unless the stud was looser than designed in the block (rare, but you may just have repeated it inadvertently). A common reason for tight acorn nuts is when they are too short or the stud too long, which means you can see 54 ft/lbs but have a leak because it screwed home before it clamped the head. There are a few reasoms it can happen but something like it was involved. If everything is loose then great - just check everything and clean everything and assemble it all correctly.
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

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colinevans
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#10 Re: Head Bolts

Post by colinevans » Sat May 11, 2019 11:31 am

Morning guys, managed to drain it and blow out the stud hole. Torqued up and dry now. Thanks for all the advice!
Colin
Series 2 OTS, 280SL

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