Lotus Elan

ARP stud torque

PostPost by: Plus2soon » Tue Dec 19, 2017 2:09 pm

Hi,
I have installed ARP head studs and think the recomended torque 80ft is very high.
Does any one have experience what torque to use? I have read Lotus never retorqued
the heads. I use the standard copper gasket.

Thanks a lot for any input

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PostPost by: 2cams70 » Wed Dec 20, 2017 2:19 am

Yes I agree the head nor the block were originally designed for this torque figure. It could lead to distortion of the the block/head face and the bores. That's why I decided to use the ARP bolts instead. Others with more experience using the studs may have different opinions.
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PostPost by: rgh0 » Wed Dec 20, 2017 9:11 am

The standard 60 to 65 ft-lbs will be fine for a standard or tuned road engine. This torque actually will give a higher bolt tension load than the original design due to the finer UNF thread the nut runs on the stud compared to the UNC thread the bolt runs in the block on and also less surface friction of the nut to the stud compared to the bolt in the block..

I use 70 ft-lbs with the ARP studs on my race engine for a higher bolt load again. Keeping the head gaskets sealed on race engines can be challenging so the additional torque and resulting stud tension load helps.

I don't believe you need to use the full 80 ft-lbs the studs are capable of for adequate sealing in any circumstances I have experienced. The heads suffer enough from head bolt recession without needing to much extra help from excessive head bolt loads.

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PostPost by: 2cams70 » Wed Dec 20, 2017 12:14 pm

Personally I'm not too keen on using any fastener at a torque less than that it was designed for. Doing so means it has less "spring" and therefore more likely to come loose due to the gasket compressing slightly in service. That's why stiff fasteners are sometimes designed with a necked down diameter to give them more "spring" for any given applied torque. It may be ok or it may not. At the very least I'd be checking my tightening torques more often for reassurance. If you use the ARP bolts rather than the studs you don't have to ream out the cylinder head bolt holes for clearance and the standard torque value is fine.
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PostPost by: Craven » Wed Dec 20, 2017 5:04 pm

Torque figures are to ensure the bolt or stud is working within the elastic region of the material, under the given figures you are relying on just friction over torque may move the material into the plastic region where permanent stretching occurs.
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PostPost by: rgh0 » Wed Dec 20, 2017 7:42 pm

I think you misunderstand the engineering basis for design of bolted and gaskets joints and the multiple factors that go into the design. I will write it up in more details when I get a chance. You asked for experience which I gave you now you ask for the technical design basis and I can you you that also

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PostPost by: Panda » Wed Dec 20, 2017 10:09 pm

Hi Johan,
I agree entirely with Rohan's comments. I also use 70ft lbs on my current race engine with Arp studs and Cometic mls gasket. The same as on my previous race engine with an Ajusa composite gasket. Never had any sealing problems. On a road engine with a copper gasket I would use 65ft lbs and retension once.
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PostPost by: Craven » Wed Dec 20, 2017 11:20 pm

By ignoring the advantages of a head bolt operating in its ?Yield Phase? ( elastic ) denies optimum uniform and consistent clamping force, especially with high thermal expansion aluminium heads and composite gaskets.
Design of the Lotus head bolt a long and waisted shank suggests a bolt working in this Yield Phase way.
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