No point in using the stronger bolts if you aren't going to increase the preload.

Our machinist checked the align bore on the main caps with the ARP studs vs. the factory studs on the motor I just built for Rover - no difference.

did 65ish lbs on all arp miata head studs thus far and zero issues.

got mine a few weeks ago

PN 218-4701

200k psi 7/16

80ft/lbs

My engine builder measured the bore on the main caps with 50ft-lbs and then 45ft-lbs. It was basically perfect at 45ft-lbs and very slightly deformed at 50ft-lbs. What he didn't do is try to compare the ARP studs vs the factory bolts.

So what does the increased preload and clamping force do for us besides eventually forcing a line bore? How would we determine the trade-off between a slightly deformed bore vs clamping force assuming you didn't do a line bore?

I looked this thread up again because I’m building an engine again.

Again I think ARP is ridiculous on their specs for the Miata. The ARP main studs are the same thread size and pitch as the stock main bolts which have a torque spec of 40 to 43. It makes no sense to up the torque that much after switching from bolts to studs adding washers and ARP molly lube to make them clamp harder with less torque. 60 ft lbs would likely result in double the stock clamp force. I can’t see why that would be needed or even desired.

It does not suprise me things start changing shape with that much additional clamp force.

Bob

im in the 80ftlb club! but i did not fire up the motor yet, im actually going to pull the head off and send it to bogusvo for some work, do you think the damage has already been done? should i buy another set of head studs or call arp and advise them there instructions are useless and they owe me a new set?? how can they mis inform people?

ARP is kind of a crappy company to work with (as you can see in here) so I'd take anything they say with a grain of salt.

Recommendations from a seminar a while back that I sat in on for proper loading of a gasket using ARP's:
-Remove the black oxide coating from all friction surfaces (threads, washers, faces of bolts). It's a rust preventative and increases friction/variance when tightening.
-Throw away the ARP moly lube. The initial data on the hyperlube has been good, but the moly lube was crap. CMD #3 grease is a substitute for the washers/nut surfaces. A decent engine oil or CMD #3 on the threads.
-8 retorques is ridiculous. You can do 1 if you're really worried about it (it will decrease variance cylinder to cylinder) but that's probably unnecessary for this application.
-Check threads of studs/nuts with a thread gauge. A small burr can spike torque readings. If you have a bolt going in, chase the threads on the block to make sure the same is true.

A lot of those things are kind of OCD but they're things to think about.

Sorry... I can not count how many ARP rod bolts, main studs, head studs I have installed over the 20 years.

I have always used the torque specs ARP has included in the packaging of there products.

I have not ever recieved a call back, or had a come back, from going by ARP specs.

I do do a few things that is not part of ARP paper work.

All new fasterners I will take out the package and spin the nuts to the base by finger just to check for smooth engaugement.

Also I torque and relax new fasterners 3 times, this seats the threads to the block or rod and nut and removes any thread flex.

Now there is differance in the metalurgly between stock factory fasterners and ARP

But all fasterners have a "strech" to them, they have to so they can allow for thermal expantion, but keep clamp load.

Now when you torque a fasterner, you pull it into it's elastity range, over torque it and it over streches and can not return to its proper relaxed state, undertorque it it will not be in its elsatisity range, and will not hold proper clamp force.

The miatia 1.8 is a cast iron block with an alumium head, so is the Mitsu 4g63.
The 1g 4g63 has a 12mm head bolt and the ARP torque spec on the head stud is 90 ft/lbs

You can not undertorque a bolt and not be in the elastic range. Review some stress/strain graphs.
You're completely ignoring head geometry which is a huge deal (crushed bosses, screwed up gasket loading due to head deformation, etc.). You can't just apply a blanket statement that all aluminum heads can handle ___ ft/lbs of torque.

Over torquing can be as bad as under torquing.

njn............ I will be happy to look over any graphs you can point me too, and open to learn anything that can make me a better builder.

I was not making a blanket statement, I was poiting out the simular constructions,and stud sizes used between the 2 engines


I am not a collage educated man, as I am sure you can tell from all my misspellings and grammer mistakes.

I tend to try to apply my logic ,common sense and experance to an issue and find a fix for a problem.

At times they fail more often than not they work.

This is a good generic graph to explain how materials behave in tension:
https://www.miataturbo.net/attachmen...ine=1339265062
The stress is provided by the tension and the strain is how far it stretches.

All normal fasteners operate in the elastic region while torque to yield bolts operate past the yield strength point. Basically, my point was that steel acts very linearly in the elastic region and any load will put you into it.
Yeah, there's just a lot of things that go into it. If your bolt boss is too thin you'll collapse that with torque instead of adding additional load to the head.
Ha, don't worry about schooling. All my degree got me is a foot in the door of the industry. I basically started over on my education the minute I started working.

The studs are fine to 80ftlb or more and are reusable as they are in the elastic region with that torque. The head is iffy with that much clamp load however. ARP molly is incredibly slippery on threads.

When you tighten it down and it starts taking more revolutions of the nut to gain each 5 lbs of torque something is yielding and it is not the stud.

FWIW I have never blown a head gasket with a 350+ rwhp stroked track beast with head studs torqued to 50 ftlbs.

I just did mine to 55.

Bob

I had occasion to pull the head and found it was not cracked; but the washers definitely deformed the surface they clamped against. I am sure that this deformation under load relaxed the amount of clamping force over time and could be a reason that the head gasket failed.

I will reassemble with a new head gasket and torque to a lesser value.

Edit: For those of you that don't want to go back, the instructions were 80 ft lbs

How I understand it, this is what torque plates are designed to overcome. Torquing a head to a block will cause distortions that can reach a couple inches down. Torque plates are bolted to the block, in place of the head, before honing, with the desired head gasket and hardware, to create the distortions that are caused by the head being torqued down. When honed, the block will be "more" straight to what it will see when torqued with the head.

Any new information to share? I think I am going to torque mine to 60ft/lbs in three steps. Looking to make about 400whp.....

Is this thread still valid, although i am not sure what to make of it since some used 43, others 60 something and others 80, with ARP providing instructions with different numbers? I may stick with stock bolts as this seems all too ridiculous just to get boils that stretch less under heat but may very well cause a leak and or ruin some part of the engine if a magical # is not used. I don't have the engineering degree or know how to reinvent what a Mazda engineer derived decades ago. Is there any resolution to all this?

ARP updated their kits about a year ago to include a much larger washer and a reduced torque spec (65ft.lb).

Very good to know. Is there a part # to be sure I get the latest version? I also have to decide if the extra bite (less stretch) is worth paying $100 for studs instead of $25 for Mahle bolts, which I can buy new again when i rip the head off sometime from now.

Thanks for the advice.

The kit I just bought from Fab9 says 65ft lbs in the instructions. The washers look like OEM, but I have not tore down my engine again yet to check. They are a forum sponsor and have good prices.

I was figuring i would buy from Fab9 if i go with anything upgraded or anything they charge similar to advanced auto.