Why have the head nuts come loose?

[ukkid35]

I've had to pull the heads after the engine started over pressurizing the cooling system

This was also accompanied by lots of moisture coming out of the exhaust on cold startup, presumably it had been sucked in when cooling

Thankfully it never hydrolocked

I found many of the head nuts could be turned 90 degs before reaching say 80 ftlbs

What is the most likely cause?

(hint - I did replace the head gaskets myself three years ago - so no doubt I did something wrong)

[227bhp]

Did you replace the studs?
Did you re-torque after x amount of engine running time/miles?

[ukkid35]

227bhp said:

Did you replace the studs?
Did you re-torque after x amount of engine running time/miles?

No - because I assumed they can't be TTY studs

No - because that never occured to me, and one of them is behind the timing cover and requires an engine pull to access

[227bhp]

Well there you go, assume nothing.
Next time use new studs & nuts, correct sequence, lube and check them after a few heating and cooling cycles or a couple of hundred miles. Basically mark them up, back off 1/4 turn, retorque check alignment marks.
If the ones you can reach are ok then the ones you can't get to will be too.

You've underestimated the destructive force of detonation, it breaks, deforms, bends and melts pistons, rings, rods, heads, con rods, studs, bearings etc. I wouldn't be surprised if there is more damage which hasn't surfaced yet.

[Boosted LS1]

The studs have been stretched and need retorqueing. It may be worth replacing them or you could suck it and see.

[ukkid35]

Having rechecked the assembly manual, looks like I failed to "lubricate the threads of threads of each head nut with hypoid gear oil and fit"

Probably a stroke of luck that I didn't otherwise I probably wouldn't have found out about the loose valve guide until there was a catastrophic failure

I will also make sure I clean the threads on the studs more thoroughly this time

Ironically it was the nuts on the good head that came loose, those on the damaged head were ok

[Mr2Mike]

Aluminium heads that have been overheated can get soft enough that after re-fitting the material under the head nuts/bolts slowly creeps and reduces the clamping pressure. Is there any evidence of this happening i.e. a significant depression in the spot faced area under the nut?

[ukkid35]

Mr2Mike said:

Aluminium heads that have been overheated can get soft enough that after re-fitting the material under the head nuts/bolts slowly creeps and reduces the clamping pressure. Is there any evidence of this happening i.e. a significant depression in the spot faced area under the nut?

Thanks, very useful to know

Ironically the head that came loose was not the head that had obviously suffered from pinking

Also, the pinking was mostly resolved once the faulty injector was replaced, which about the same time I pulled the heads three years ago - I messed up the cam timing then so it did continue to pink badly until I fixed that some months later

[ukkid35]

Mr2Mike said:

Is there any evidence of this happening i.e. a significant depression in the spot faced area under the nut?

I don't think so but I will take and post pics once I get the heads back from the engineer

[Boosted LS1]

Have you fitted hardened washers under the nuts? Also, rub them with sandpaper underneath to stop them rotating when you torque the nuts down.

[ukkid35]

Boosted LS1 said:

Have you fitted hardened washers under the nuts? Also, rub them with sandpaper underneath to stop them rotating when you torque the nuts down.

I have done a first pass a cleaning up the washers with 400 wet&dry

I am not sure they are quite good enough

The washers have two sizes for these 12mm studs: width 3.3mm, OD 19.5mm and 21.0mm

If I put them shiny side up will that be good enough?

If not where can I get some from?

[stevieturbo]

If there is any doubt as to condition of the studs/nuts/washers...it might be sensible to replace the lot and torque correctly as per instructions with a known good calibrated torque wrench/sequence.

As for washers, pretty sure ARP and others would sell such washers separately, or surely a main dealer for same vehicle could supply whatever washers are used normally ?

You dont state what the engine is, whether it used studs originally, bolts, or anything really. I'm sure Reinz or countless other brands might also sell suitable washers.

[ukkid35]

stevieturbo said:

You dont state what the engine is, whether it used studs originally, bolts, or anything really. I'm sure Reinz or countless other brands might also sell suitable washers.

TVR's AJP8 has limited support

Replacing the studs seems mad, why are they studs if they are a use once item, makes no sense to me

Surely there's no such thing as a Torque to Yield Stud?

[stevieturbo]

ukkid35 said:

TVR's AJP8 has limited support

Replacing the studs seems mad, why are they studs if they are a use once item, makes no sense to me

Surely there's no such thing as a Torque to Yield Stud?

Studs are not indestructible. By all means measure, check for true, check threads are not stretched etc etc. If all good then yes they would be fine to re-use.

Washers are washers...nothing will be unique to your application...all you need are dimensions.12mm...plenty here.


http://arpcatalog.com/124/#zoom=z



http://www.streettunedmotorsports.com/parts/arp_he...

[Evoluzione]

Judging by the state of those and the overall lack of er, professionalism seen so far i'd be putting new studs, nuts, washers and possibly refacing the seating area of the washers too.

I wouldn't be happy putting any of those components back on again, learn by your mistakes and don't cut corners.

[ukkid35]

Evoluzione said:

Judging by the state of those and the overall lack of er, professionalism seen so far i'd be putting new studs, nuts, washers and possibly refacing the seating area of the washers too.

I wouldn't be happy putting any of those components back on again, learn by your mistakes and don't cut corners.

Obviously I'm showing the worst examples

Refacing the seating area of the washers will be very difficult indeed, as there is no line of sight for most of them

The machinist told me that it would have been originally done from underneath using a tool he doesn't have

Lack of professionalism is absolutely right, I am a home mechanic with a parking space, not a workshop, I am most definitely an amateur

[adam quantrill]

I've had gasket problems over the years with my Rover V8, eventually went to AJP studs which helped but still failed after a while (supercharged, see).

In the end I found Elring gaskets, fitted them, and never had a problem since.

Dunno what options are available for your block/heads, but the gasket seems to be the key.

With the studs yes you have to retorque them after a few heat cycles but for the one you can't reach, just ignore it. In my case I didn't back off 1/4 turn and retorque, I just went over them all on the same setting and if the wrench cracked immediately, left them alone.

The oiling and washers are quite important because they reduce the friction and allow most of the torque to pull the head down, instead of being more variable where friction "uses up" some of the torque applied, so yes replace those dodgy washers with the correct thicker shiney hardened ones.

[mighty kitten]

Probably worth checking that the stud threads in the block aren’t pulled up .

[ukkid35]

Following up on this

I made a concerted effort to resurface the washers as I could not find a supplier

I cleaned up the studs but didn't replace any of them

On completion I found that the head gaskets didn't seal, which was disappointing to say the least

I had pull the engine to remove the timing cover and re-torque all the nuts

I then let it rest overnight and did it again

And let it rest overnight and did it again

Only then did I find there was no more to be gained

It's not practical to put it through heat cycles and tighten them again because of the nut hidden behind the timing cover

I'm concerned that if I tightened all the others and ignore the hidden nut it might twist the head

The car has now done nearly 1000 miles, 30 of which were on the rollers, without any coolant loss, so I'm confident that they are sealed now

[Elliot2000]

“It's not practical to put it through heat cycles and tighten them again because of the nut hidden behind the timing cover”

I think you missed the point some of the posters were making- if you had retorqued the ones you could get to easily -either by marking up and backing off before torquing or just by checking that they are still tight- then if they all lined up with the original marks or were all still tight then you needn’t worry about the one u can not access.