Leaky Head Nut. Options?

[maxstu]

Number 5 nut on cylinder No. 1 has a slight weep. Nothing staining the driveway. But the coolant needs topping up with half a pint every 500 miles or so.
I did a top end rebuild on this engine, and its covered about 3k since fitting in my camper in Jan this year. The engine performs well.
When replacing the head seals l used a beam torque wrench on the head nuts and set them in two stages according the manual.
I was startled how loose it had become. Yet the nut wont simply torque up again because the threads are (head stud and nut) wet and stopping it from gripping.

Options....
I will need to drain down the right bank and dry off the threads'. Then add yellow sealant on the nut surface and torque to 50nm in one hit.
Or.....
Should l do all eight nuts on the right side again? Singularly or take all off in one hit and do the complete torquing procedure once more?

Your views please.

Thanks and regards
Stuart

[ajsimmo]

If only one nut has come loose there must be a reason. It just doesn't happen if all was correct at the time of assembly, but I wouldn't like to guess the cause.
The yellow stuff is a non-setting sealant, so you won't need to clean it all off, just add a bit of fresh. I'd take off one nut at a time, quick clean, spin up and down the threads to make sure they run smoothly, then a bit of yellow and torque back down. Only do one at a time because you don't want to reduce the clamping force on the fire ring. Be interesting to see if any others are loose. I've repaired a few that have come loose, usually Engine Shop builds - partly because they put gunk under the fire ring which burns off potentially leaving a void, and also they only torque to 35Nm ish (or so they told me!). It's an air-cooled builder's thing.

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[maxstu]

Thanks for your reply and advice...
Perhaps, just perhaps, l missed going to the second torque setting on this one head nut? Tea and a bit of cake time. It was that loose!
I did thoroughly clean all threads with a dye and tap at the rebuild. Then wiped them with 100% alcohol well before the initial torque setting.
I was wondering whether this particular head nut is bottoming or topping out against the stud before it get to the correct clamping pressure? How do l check?
Lastly, what method would you use to drain coolant from the right bank only? Or just drain all?
Regards
Stuart

[ajsimmo]

Perhaps, just perhaps, l missed going to the second torque setting on this one head nut? Tea and a bit of cake time. It was that loose!
I did thoroughly clean all threads with a dye and tap at the rebuild. Then wiped them with 100% alcohol well before the initial torque setting.

It's easy to miss one, we've all done it. This can be avoided by going round them again as a check. I often go aound three times. If one doesn't feel right I back it off, clean and check, then torque it down again. Then check again. Also I go down in 4 or 5 stages. 10 to 50 is way too big a jump for my liking. I add 20, 30, 45 in between, but it's really easy as they're preset in my digital torque wrench. Also pull and hold and feel the nut. It's amazing how long a nut will continue to creep round when held at the set torque. When you hold it at 50 for a few seconds and it doesn't move it's there. Quite tricky to do accurately with a beam type wrench (and impossible with a clicker!).

I was wondering whether this particular head nut is bottoming or topping out against the stud before it get to the correct clamping pressure? How do l check?

Good point. You can measure (or count) the threads exposed. Try running the nut down a standard m10 bolt until it bottoms and count the turns/measure the depth.

Lastly, what method would you use to drain coolant from the right bank only? Or just drain all?

Park on a slope.



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[maxstu]

Okay and thanks. On it during the week.


Regards
Stuart

[ajsimmo]

How did it go?

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[maxstu]

Thanks for reminding me... Did it earlier this week

I drained off enough coolant to stop it coming out of the head after removing the nut. Then thoroughly cleaned and dried threads inside nut and on head stud. No photos unfortunately.

I added yellow non setting stuff to the face of nut only, making sure none went inside it. Then did three stages. However the final stage at 50nm still has the nut running back just a tad when l release pressure on my bar wrench? So lm assuming the nut or stud (or both) has a weak thread.

Undoing the nut again confirms this. Tightened to 50nm. Releases at about 39-42nm. At this stage and with hindsight, l should have taken the nut off and tried a replacement using the black stuff instead.
Still learning

30 miles later no issue. No pink staining or water loss. Yet the real test comes tomorrow. 300 miles to Yorkshire dales and hot, hot, hot.



Taking a few used eplacement head nuts, a small tube of K2 black silicone...and recovery card.

Wish us luck.

[cobblers]

Sounds like the head stud is elastically twisting a bit, my a*** would be going like a rabbits nose if I could feel that happening!

[maxstu]

Sounds like the head stud is elastically twisting a bit, my a*** would be going like a rabbits nose if I could feel that happening!

Just a bit. Not said anything to Maxine, though.

If it's been like that for 3k then not too worried. We've been towing a caravan for about 1000 miles since rebuild too. That surely would have found the weak spot.

Will keep you posted...

[ajsimmo]

Tbh when you've done plenty you stop worrying about the twisty springy feeling. Every engine has a couple that feel that way, and a couple that feel like they stay put at 50. I just go around them again, and hold for a few seconds. The springyness often lessens each time round, showing they've gone up a bit more. On the basis that the specified torque on early engines was 35Nm, then 45Nm, before finally being increased to 50, I reckon one or two nuts being one or two Nm shy of 50 won't result in failure. It's still way more accurate and reliable than using a clicky wrench once and calling it done!

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[maxstu]

Thanks.

[maxstu]

Our grand tour is done. A 1000 miles later, driving in extreme heat at times we travelled Margate to N Yorkshire, just above Scarborough. Then 400 miles touring the area (better than the west country in our opinion). And NY to Margate today covering 320 miles.
The camper drove faultlessly, and the auto box got some rough abuse in and around the moors. One steep hill saw her in first gear and crawling at a poorly 15mph. Very worrying
But still losing coolant around the head nut. Used about 2 pints of fluid. Fridge worked well though!
Averaged 22mpg.

[slowcoach]

Good you made it home

[maxstu]

Good you made it home

Thanks slowcoach.