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garrycol

Rover V8 - Head Stud Issue

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Hi I am building a 4.6 out of a top hatted 4.0 and have struck a problem with a ARP head stud pulling out of the block - looking for suggestions before I have to scrap the block.

This 4.0 block had a coolant leak and when the new head gasket was put in, the back outer head bolt (drivers side) was over torqued and stripped out. A helicoil was put in and the head put back on but in operation it started leaking coolant. When dismantled it was found that the metal between the hole and the outer block and coolant passage had developed cracks.

P5070058.jpg

The helicoil was removed and the block welded up.

Before decking the block

P8100129.jpg

After cleaning up and helicoil inserted

2014-03-02_13-12-35_960_zps5635aa05.jpg

When I got the block back I discussed with the engine builder the strength of the helicoil as the number of threads in the block that the helicoil locks into is only about 9 threads vs the 15-20 threads in a normal head stud hole. My thought was that while the helicoil was strong enough, as the helicoil is only half as long as the length of the normal threads that the aluminium in the block may not be strong enough. I was assured by two professional engine builders that it would be strong enough to take the torque of the head nuts on the ARP studs.

Today I decided to put the heads on the engine - the left head went on Ok - up to 90ft lbs (ARP say 100 ft lbs). The left hand one started OK - 30 ft lbs to start, then 60 ft ibs then 90 ft pounds but when I got to the damaged stud it failed at about 70 ft ibs as I thought it might and started to pull the helicoil out.

20150810_1507051_zpsyjanoicw.jpg

Tomorrow I have a mobile helicoil guy coming to put in an older style nut insert that is about 15 threads long rather than a helicoils 9 threads. When I put the head back on I will torque all the other stud nuts up to 90 ft lbs but only do this one to 70 as I am told that that corner stud should be OK at the lower torque. Nevertherless I am not optimistic but it is worth a try or else the block gets ditched.

If the repair once again fails, other than just ditching the block altogether I am open to other suggestions.

Thanks

Garry

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I thought with ARP's it was around 60lbft...

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I had an Arp kit on my 4.2 Turbocharged RV8, with a wet torque i.e. with the moly lube I did them to 60ft lbs as the lube gives an additional torque of 20-30%

Which would give a torque of 72-78ft lbs.

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And definitely don't follow the included ARP instructions, which say something ridiculously high like 100 IIRC.

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Yes ARP instructions are 100 ft lbs - I was going to do 90 and it is fine on all the other studs. When this head goes back on I will go 80 but not higher than 70 on the damaged stud.

I have tried contacting ARP on this a couple of times but they have not responded.

However on the assumption that it doesn't go well i am looking for alternate ways of securing the stud?

Cheers

Garry

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A Timesert would be a better solution than a helicoil.

If those aren't available then tap the hole out as big as you dare, insert suitably sized bolt (M14 etc), cut excess of bolt off, drill and tap bolt for ARP stud thread and proceed as before

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Ok I had the mobile thread repair guy around today - he put in a big threaded insert (not helicoil) that has 15 threads as against a helicoils 8 or so.

20150811_1513131_zpscivahu9s.jpg

On taking out the old helicoil we found out why the repair has failed - the supposed professional engine builder had not quite drilled the previous hole correctly so elongated it slightly and filled the gap with "liquid steel" so only a few threads of the helicoil were actually biting into the aluminium. In the last pic of my original post you will see what looks like metal sticking up is in fact the liquid steel.

So the new insert is installed but I need ot wait until the thread locker cures so tomorrow I will try once again to put the head on - this time 70 ft lbs will be the target. Here is hoping.

Garry

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That looks like a much better repair, fingers crossed for you.

I suppose as you've already TIG'd the block once you could always fill it with weld & re-drill & re-tap if all else fails. Or drill all the way through and use a reeeeeaaaaallly long bolt :ph34r: it works for the Rover K-Series :D

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Does it read 100ft lbs dry or lubricated threads? my set never came with instructions.

100 ft lbs with threads, washers and nut base covered in the provided grease.

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I suppose as you've already TIG'd the block once you could always fill it with weld & re-drill & re-tap if all else fails.

Unfortunately as we already know, when RV8 heads and blocks overheat the metalurgy of the aluminium changes and becomes a bit porus and soft. While this engine has not been overheated the TIG process provides plenty of heat and though not visible there is some evidence of the heat so the heat involved in fulling the bolt hole and and the the fill may cause major damage.

I really want to avoid that if possible - I have another 4.6 block but it has two slipped liners and to prepare it with top hat liners would be quite expensive.

Cheers

Garry

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If you didn't manage to anneal it with that bead up the side then you shouldn't worry about filling that hole if the need arises.

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That's the same fix I just did on my winch. Yours looks great !

First thing to note is that a helicioil doesn't spread the load like an insert does. Also the helicoil puts down some uneven forces as the thread tries to roll. Nut inserts don't do that, so that looks a cracking fix :)

The weld could be high silicon. This reduces the chance of the weld cracking, but it would have meant that helicoil number two was in softer metal?

If that doesn't do the job I'd keep drilling until I hit oil. Then I'd seal the thread.

I hate helicoils, but we use them a lot at work and they are better than bare ally, even if it high magnesium alloy.

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I dont disagree at all.

The head bolt holes in the block are just over an inch deep and have about 20 threads in them. Irrespective of whether studs or bolts are being used they have about about 20 threads as well, so the 70-100 ft lbs torque is spread over these 20 odd thread in the aluminium block.

A standard size helicoil only has about 8-10 threads so irrespective how strong the helicoil is or how strong the stud/bolt is the 70-100 ft lbs torque is spread over only 8 threads - surely in effect the the helicoil as a repair is only half as strong as the original arrangement. The insert is twice as long as the helicoil so has about 15-20 threads biting into the alumium block.

Increasingly I am finding advice from so called experts is suspect and not trust worthy - I was reassured by two seperate engine rebuilding companies that a single helicoil in alumium would take the required torque - despite me discussing the issue at length with them but I was not reassured. I even sent a message to a friend just before I started putting the head on that I didn't expect it to hold even though professional advice was that there would be no issue - and I was right.

Garry

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Head now on - all studs torqued up to 75 ft lbs - no issues. I guess the issue was the bodgy helicoil in the first case.

Garry

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Hmm.. I don't know what the Original torque for head bolts is?

BUT: the studs have fine thread (UNF) @ the end where the nuts go and the are torqued up. They need a lower torque than the bolts with the corse thread (UNC) for the same clamp down force!

The number of threads are limited to 9 turns when you use helicoils? Use longer ones! ;-)

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There's a chance the original helicoil would've held if it had been into solid ali rather than a badly drilled hole filled with putty, I'd blame that rather than the helicoil.

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Hmm.. I don't know what the Original torque for head bolts is?

BUT: the studs has fine thread (UNF) where the nuts go and for that they need a lower torque than the bolts with the corse thread (UNC)!

Indeed. This makes the ARP recommendation even more ridiculous. Sticking to the original torque with ARPs is more than plenty, and does work.

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There's a chance the original helicoil would've held if it had been into solid ali rather than a badly drilled hole filled with putty, I'd blame that rather than the helicoil.

Absolutely!

And I agree, 60lbft should be more than enough :)

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Not taking in account the difference of torque needed for UNF and UNC is quite a blunder for a (in)famous Nuts, Studs & Bolt company!!

And this is happening for years... :wacko:

I found some time ago similair treads about striped threads for mainbearing caps in combination with ARP studs & nuts, wrong torque advice and short threads... Shame on ARP... :-S

Well, I have to say also: I never had them in my hands yet....

My impression till now is that they make great stuff with wrong dimensions and bad advice... :blink:

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The ARP stuff is proper quality, and fits well, just use some common sense when following the instructions...

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Exactly but it is annoying when you try to contact them to clarify things on a few occasions and they do not respond.

The 100 ft lb torque may be fine for a new block that has never been used but in relaity the studs are going into used blocks that have had stretch bolts previously in them and have been in service. While still quite serviceable I am sure the threads in the block would have deformed just a little albiet at the microscopic level.

Clearly 100 ft lb is far higher than what is actually needed.

Garry

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I wouldn't trust 100 ft lb on fine thread in any aluminium block tbh... If you really want extra strength, I think I've read about some people fitting bigger studs.

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The thread in the block, yes. The thread on the other side of the stud is UNF ;)

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