over torquing head bolts

[mobythevan]

In the past I have seen that turbo buick guys like to torque their head bolts 10-20lbs over stock ratings when running higher boost on stock head gaskets. What do you guys think about that? I am going to raise my boost some more on my stock 280zxt head gasket. Should I try raising the torque 10lbs over stock spec on the head bolts? Could that cause more harm than good to anything?

[2126]

From what I know, the torque of a bolt is based on the bolt design itself. When properly torqued, the bolt (or stud) will stretch a predetermined amount and at that specific torque, provide you with it's maximun safe strength. Going beyond a bolt's design limit overstresses the bolt and can lead to premature failure. If you want more torque on your head, think about purchasing a set of ARP head bolt...and use ARP's recommended torque...and of course a good head gasket.

[pjo046]

Or better yet, buy ARP studs instead of bolts, as studs are always far superior to bolts in strength!

[mobythevan]

on a side note, IIRC my motor manual lists two different torque specs for sbc heads. One from like 1975 specs 65 lbs, one from like 69 specs 90 lbs. Maybe I recall wrong, so did the two different years use different bolt grades?

 

Anyway, I bet the nissan head bolts have a 16% margin (10 lb more torque). So adding 10 lbs torque may stress them a bit more, we'll see if I break one. I'm betting they can support some more clamping pre-load.

 

If I put on new bolts I would put on a new head gasket and the whole thing would be a non issue, but I'm more interested in finding out if someone has tried it and still blown their stock head gasket at XXpsi boost. We know stock head gaskets blow out with stock bolt and stock torque.

 

Anyone tried it? Apparently helps on the GNs.

[mobythevan]

Are the stock nissan head bolts in 81-83 turbo engines toque to yield type? That would put a halt to trying to raise the torque. I did a quick search but didn't see if they are.

[mobythevan]

Here was a pretty good thread that shed some more light on the issue for me.

 

http://forums.hybridz.org/showthread.php?t=75965

 

I think I'll just leave it alone and see if it blows out

[cygnusx1]

When I pulled out the filthy ZX Turbo motor with 110K original miles on it, I cleaned it, changed all the external gaskets, and put about 10 more ft-lbs onto the head bolts. I have been running 14 psi in my Z for a over a year (10K miles) and it is still fine. No head gasket leaks or broken head bolts. Like you said, if one breaks or the gasket leaks, I will upgrade.

 

To clarify: I did not back off the original bolts at all, I just added about 10 ft-lb over what they were set to. Trial and error with the wrench to see what they were set to.

[mobythevan]

That is what I was curious to hear, somebody that tried it. Thanks.

[johnc]

Or better yet, buy ARP studs instead of bolts, as studs are always far superior to bolts in strength!

 

That's not true. A bolt designed for 180ksi (metric grade 12.9) is equal in strength to a stud and nut combination also designed to 180ksi. The advantage studs have over bolts is that assembly is easier (assuming you've got enough room), the head is properly located immediately when installed, and the torque readings are more accurate because the fastener itself is not being turned.

 

http://www.arp-bolts.com/media/pdf_files/CH_22-26_33-35.pdf

[Pyro]

I think studs are more uniform in clamping force as compared to bolts. Also having fresh threads and a lubed up nut will have less losses to thread friction and more clamping force/torque ratio as compared to a traditional head bolt. Especially an old bolt in an old block.

[akeizm]

I know one thing about headbolts, don't torque them up to 114 foot pounds. They will snap or worse strip the thread in the block.

[GHtokyo]

Yeah, I found out you can strip the threads in the block at about 30 ft/lbs with lubed up threads. Or maybe the threads were bad in the first place, but I thought my machine shop would tell me that. Ohh well, I have to piclk up some heli-coils. I've had good luck and never needed heli-coils before...any tips?

Also, does anyone remember the thread size and pitch of the head stud bolts.

Thanks,

[Guest bastaad525]

If I remember right I overtorqued mine either 5 or 10psi last time we did the head gasket. So... that's been about a year or more, running between 12-14psi of boost on a factory Nissan gasket and no problems so far.

[Synlubes]

One key note is to ALWAYS tap and clean the threads in what ever the bolts are going in.

In a "closed whole" use a (flat headed) bottom tap instead of a (pointed end) through tap.

I use a small amount of never seize on the bolt threads, UNLESS the bolts are going in a "thru whole" then use some type of sealant.

You don’t want the never seize or sealant to ooze out and get on the head gasket.

The (new) Nissan L6 turbo head bolts are plenty strong.

 

I do a 3 stage torque

(L6 engines) Torque all bolts at 35 ft lbs then go to 50 ft lbs and then go to 65 ft lbs.

I use both a spiral and X type torque method.

After the engine runs the first 30 min, shut it down and let it cool down for 24 hrs.

I then retorque all head bolts to 70 ft lbs (Nissan L6), again using both X and spiral methods.

[Guest bastaad525]

I should mention that the head bolts I used were brand new nissan turbo head bolts.

[Guest ON3GO]

what if you have a a few wholes helicoiled?

im afraid of torquing my ARP head studs to much and it just spin and spin.

right now i have it i think 50lbs and i havent started the engine yet.

 

whats your thoughts

 

mike

[materchan]

i remember my machine shop teacher telling me that a helicoil in steel is stronger than the original steel. i think i have my bolts set to about 75 ft. lbs.

[zguy36]

The advantage of a stud/nut combo is clear over that of a regular bolt. Much of the torque of a bolt is lost due to the friction of turning the entire fastener (more thread surface in block) and therefore less clamping force is translated holding the two pieces together. Both setups are equally strong, just the stud/nut combo clamps the parts tighter together.

-jeremy-

[johnc]

Both setups are equally strong, just the stud/nut combo clamps the parts tighter together.

 

You really think that?

[johnc]

i remember my machine shop teacher telling me that a helicoil in steel is stronger than the original steel.

 

Jeez, I need to go through this whole dang thread. Your machine shop techer is wrong; an insert that depends on the strength of the parent metal to remain in place is not any stronger then the parent metal itself.