ARP tech advice

[JT68]

These photos are the poster child for why you should be very careful who you listen to about torque specs for ARP head studs and bolts as well as general technical information.

One notoriously incorrect site recommends 70-80 ft-lbs WITH ARP lube. This is a serious mistake.

80ft-lbs with ARP lube is equivalent to over 100lbs dry-which is madness with a 60's Nissan cast block.

These two blocks show the results of exceeding the tensile strength of the block deck. The little lines are cracks shown with magnaflux.

Note all these cracks go straight to the water jacket, they are now scrap iron.

For the U20, R16 and H20, using the factory headbolt specs with ARP LUBE is plenty.

A busted matching numbers U20 block will really ruin your week.

[redroadster]

They're not stretch head bolts ? They/ some look like the stretch type ...usually torque to 35 -40 then a 90 degree slow turn ...then another they stretch on the turn some
Seems illogical
After say 40 k they do not stretch as much or at all and you just guess it ( they're recommend to be replaced )
I didorder new once but only received 70 % of them

[JT68]

Yes, the head bolts do stretch/are stretch type which is normal. the stud kits won't stretch nearly as much.

With either style if you go nuts with excessive torque, the block deck can definitely fail. We've thrown out 3 U20 blocks this year and one R16. Ouch!

tip: if you are buying a used block, no matter what the history, make it conditional on passing mag-flux, otherwise you may buy a very expensive lump of scrap metal.

[redroadster]

Not with stretch head bolts
They 1st came into being with the deckless head designed engines ( 420a chrys & others, ...the cyls are installed later by a bronze compression fitting with seal, most are not poured but made from red hot BBs pressed )
Torqueimg 15 lbs over the recommended setting they only stretch up to a quarter inch

[JT68]

The photos show what happens when you exceed the tensile strength of the block. The studs (especially) will not yield, but the block will.

Yes, 15lbs over as a dry spec may be workable for a stretch type fastener.

80lbs (or more) with ARP lube and studs is asking for deck failure. It’s a very poor recommendation.

Very unlikely that a ARP head fastener will break, the photos show what will.

[spl310]

I don't have ARP studs. What is the proper torque?

[JT68]

for the 1600 ARP Studs- 45-50 with ARP lube is more than enough.

for the U-20 ARP Studs- 65 with ARP lube is more than enough.

Remember AL grows WAAAAY more with heat than steel, so with the engine at temperature the clamping load is really, really high-much higher than cold.

If you can't keep a head gasket on it with these torque values, there is a technique issue, bad surface quality or something isn't flat.




also, more helpful info:

45ft-lbs for the 1600 OEM headbolts DRY

65ft-lbs for the U20 OEM headbolts DRY

It's typically ok to use "antiseize" compound on the OEM bolts too. If you do that, subtract about 5-10lbs.

1600 OEM bolts won't take much more than 45--if you feel one go into yield. STOP and back off a few pounds or replace it.

The "large head" OEM u20 headbolts are very strong, if you feel one of those yield, throw it away.


You should never feel one of the ARP fasteners yield during torqueing.

[SLOroadster]

This is exactly why I still use the stock head bolts and torque them properly, dry. 20 years and I've never had an issue with the stock bolts and correct torque.

[70MTRoadster]

Thanks for your info Jt68. I'm going to pull my aluminum head on my Stroker engine and check the block visually for cracks. I bought my ARP head studs from Dean and torqued them to 80 lbs because that's what his site says and, I believe, ARP too. At any rate, the engine is out of the car and in its place is that free U20 so I can do it without too much pain. It has never blown white smoke or loss of coolant or funky dipstick oil but it has always run hot.

[JT68]

Right, so if ARP actually did or were to suggest a torque spec, it would be (or is) based on limitations of the fasteners- not the tensile strength of a 1967 Nissan block.

One thing you can count on, no one at ARP has any experience with rebuilding roadster engines or has any idea about the limitations of the roadster blocks. ARP makes superb fasteners, but that is their knowledge base, not 60’s Nissan engines.

The photos are conclusive and just back up decades of roadster experience here. (Actually rebuilding and servicing engines, not just peddling parts)

I can tell you from years of experience that the roadster decks can almost always withstand moderate increases in the dry torque spec.

80lbs WITH ARP LUBE is another matter. That’s like basically exceeding the dry value by about 60%!

Any competent engine builder will tell you that is asking for failure with most engines. It's a roll of the dice on the particular casting strength of your individual block.


70MT-With your engine specifically, if it wasn't using coolant or blowing white smoke or actually leaking-not coolant mixed with oil, good chance you didn't have a HG failure to a water jacket. Most likely just another cooling system issue-very common.

[JT68]

This is exactly why I still use the stock head bolts and torque them properly, dry. 20 years and I've never had an issue with the stock bolts and correct torque.

ARP fasteners are very good, but this mirrors our experience as well.

The large head u20 bolts work great if everything is flat and correctly prepped.