Head bolt torque

[dr_hunt]

Last night I was finally installing the head on the little DSM engine. I was getting ready to torque the head bolts and the guy that ownes the car said that the torque specs vary from 80 to 100. I didn't think so, so we checked. ARP says 81lb-ft with arp moly lube. A check of the DSM boards revealed that many people think that more torque on the head bolts keeps head gaskets from failing. Wrong assumption, here's why.

 

Fasteners need to be stretched to maintain proper integrity of the bolt, stud and nut from coming loose and providing the necessary clamping force. This is an elastic region of the bolt. If you over torque the fastener, you get it to yield and go into a plastic deformation which can lead to fastener failure!

 

The point is that you follow manufacturers spec, make sure your surfaces are flat, both the head and block, use proper lubricant and follow torque recommendations by the fastener manufacturer! Do it right, if you don't have what you need, wait until you do, getting done tonight won't help you when your doing it again tomorrow!!!!!!

[dj paul]

i find it amusing that people think that tightening them up tighter than spec makes them better.

[TimZ]

Last night I was finally installing the head on the little DSM engine. I was getting ready to torque the head bolts and the guy that ownes the car said that the torque specs vary from 80 to 100. I didn't think so, so we checked. ARP says 81lb-ft with arp moly lube. A check of the DSM boards revealed that many people think that more torque on the head bolts keeps head gaskets from failing. Wrong assumption, here's why.

 

I completely agree. One question though - 81 lb-ft with ARP Moly? Yikes, that sounds high - ARP's recommendation with the head studs for my Z was somewhere around 50 lb-ft with moly. Were these bolts or studs?

 

ARP seems to have modified their specs a few times, so it wouldn't surprise me that much, but ususally the spec is based on the size of the stud - maybe the DSM is 12mm? If these were bolts (you did _say_ bolts, after all) then that probably makes more sense, but it still sounds high with moly - probably equivalent to ~100 lb-ft with engine oil.

[dr_hunt]

You are correct, they are studs (my bad) and massive for such a little engine. Actually ARP says 81lb-ft with ARP moly lube, so that's where they are. The thread engagement in the block is like 1.5 inches!! And they are blind holes too!

 

This engine is a little stroker, 2.1L instead of 2.0, WOW! Being that it's a "stroker" it's supposedly only good for 7800rpm. The ports on the head are massive for such small displacement and look nice after I massaged them alittle under the vaves and did a port match. He went with Eagle rods, JE pistons, bigger manley and ferrea valves, crower springs, titanium retainers, custom ground comp cams, GT35R, custom exhaust manifold, aluminum flywheel, the list goes on and on. He has probably 7K or 8K in this little motor as it sits, maybe even more, that's just my guess since I don't know how much he paid for all the little extras.

 

The roller followers were pitted on the valve stem surface, so he has to get new ones from crower, like $260 or so, seems expensive for such a little piece of forged steel with a roller in the middle. But I guess I'm not rice yet, but now I can say I have done the ricer thing with a mitsubishi motor!