714 mustang
New member
i am using the ARP head stud kit and noticed that the thread pitch is a fine thread on the one side not going in to the block wont that double the amount torq being put on the head thearefore overtorqing the head? 
head torqing?
- Thread starter 714 mustang
- Start date
nope
think about it, there's no torque wrench for fine threaded bolts Vs coarse threaded bolts
where torque readings are concerned, threads is threads, you're setting your wrench for a certain amount, when it gets there it lets you know (either by clicking or through the dial)
there are a few posts and threads that go into better explanation than that, i'll try and find them
think about it, there's no torque wrench for fine threaded bolts Vs coarse threaded bolts
where torque readings are concerned, threads is threads, you're setting your wrench for a certain amount, when it gets there it lets you know (either by clicking or through the dial)
there are a few posts and threads that go into better explanation than that, i'll try and find them
714 mustang
New member
yea thats what i was kind thinking thats why we use a torq wrench in the first place thanks
'68falconohio
Well-known member
Asa":pbk57id9 said:
I disagree, it matters how many TPI the bolt is. The torque wrench will indeed only read how much force it takes to rotate the nut but the amount of tensile force(clamping force) exerted on the stud will be different between a 10 TPI and a 20 TPI both torqued to 10 ft.lbs.
The threads are like a ramp around a mountain.... If you try to go up a mountain in one revolution, you have to exert A LOT of force over a SHORT distance to reach your goal. If you go up the mountain in a spiral with 20 revolutions, you exert a a SMALL force over a LONG distance to reach your goal. With a fine thread bolt, you exert less force(lower torque) over a longer distance(more TPI) to get the same clamping force as a coarse thread bolt(higher torque, less TPI)
I suggest you contact ARP and ask them for the torque specs for their studs. Their studs/nuts may very well be able to take the extra tensile force of torquing to the coarse thread specs but you're exerting more force on the block.
Addo had a good picture showing what happens to the cylinder bores when you torque the head down. Extra force is more deformation of the cylinder bores.
Asa":5npyeces said:
This sounds right to me. Thread count is only going to affect the rate of change...that rate at which torque is applied. Finer threads will allow for torque to be applied in smaller increments and will allow for more discreet torque settings. Whereas coarser threads will apply torque at a greater rate, and not allow for as precise a measure...eg one revolution on a fine thread will mean the bolt is traveling less distance than one revolution on a coarse thread...but torque reading from one to the next is basically equivalent.
Not sure this is not tangenting off here, since the original question really appears to have more to do with the fact that head bolts are coarse threaded and studs are fine threaded on the end where the nuts hold the head down. I think the question really has more to do with if studs had coarse thread on both ends would that equate to less torque than with the fine thread...75ft/lbs on a coarse stud/nut is the same as 75ft/lbs on a fine stud/nut. Total surface area shared between the two is a different matter.
'68falconohio":5qz3r0jz said:
This is correct, fine threads with the same torque applied will indeed result in higher clamping force, all else being equal. A screw thread is nothing but an inclined plane wrapped around a shaft, so your analogy of the mountain road is good as well.
Joe
8) technically everyone is right. even is right that torque is torque in that it doesnt matter whether you use fine or coarse threads, 10ft/lbs is 10ft/lbs. however with fine threads the clamping force is greater, which is why racers use studs rather than bolts to secure the heads and main caps to the block. using studs you want to still use the stock torque specs. with the arp studs you can bump that spec by 5ft/lbs with no problem, but even arp does recommend going higher than that. in fact these days arp recommends using the bolt stretch method of tensioning the bolts rather than a set torque spec.
rbohm":s4qi0lwf said:
Yup. And since the whole purpose of tightening a bolt is to achieve clamping force, it behooves us to have a clear understanding of just exactly how this is accomplished.
A bolt applies clamping force because it actually stretches slightly when it is tightened; a typical rod bolt will be stretched several thousandths of an inch when properly tightened. Notice I did not use the word "torqued", even though it is somewhat correct. Think of a bolt/stud as a spring that exerts its "springiness" in a straight line.
The problem with relying on torque wrenches is the fact that torque is merely an INPUT, and NOT a result. We are looking for results, and even though we may apply the proper input, the result (output) can be skewed by certain variables, with friction being the main culprit. This can be affected by dirt, rust, burrs, etc. Also thread condition (wear). Another factor is manufacturing tolerance of the stud to the nut. Proper lubrication is crucial, and of course thread pitch has an effect as well.
So why even bother using a torque wrench? Because it is about all we mere mortals have available, the system has been in use for a long time now and is generally accepted as a reasonable method for we members of the un-washed masses. In a stock or mildly modified application, careful use of a torque wrench will yield satisfactory results, but in highly stressed situations or very critical places (such as airplane engines) it is common to use the bolt stretch method.
I won't be throwing my torque wrenches away any time soon.
Joe
The only way to accurately measure the clamping force of a head bolt or stud is to put a Strain gage in between the two surfaces you are clamping together. This however is impractical mostly for reasons of cost ( you would need one for every head bolt) and possible gage breakage ( if one breaks you have to start all over).
So we are left with the humble torque wrench. Prep is everything to getting a good reading. All threads must be clean enough to eat off of and lightly lubed and the surface that the bolt or nut will tighten against must be clean lubed and free of defects. This will give results that are predictable and fairly consistent.
So we are left with the humble torque wrench. Prep is everything to getting a good reading. All threads must be clean enough to eat off of and lightly lubed and the surface that the bolt or nut will tighten against must be clean lubed and free of defects. This will give results that are predictable and fairly consistent.
69.5Mav":2zvrbh2u said:
True.
But measuring bolt stretch gets you pretty close, certainly closer than a torque wrench.
However, in the grand scheme of the cosmos, very little practical difference will be noticed if the original poster uses fine thread studs and torques them to stock specs; the head will be clamped a bit tighter, but that's about it. Getting the specs from ARP would be the best bet.
As we say in the sawmill business "Calculate to an angstrom, measure with a micrometer, mark it with chalk, and cut it with a chainsaw".
Joe
A
Anonymous
Guest
Due to the design of the headgasket sealing ability, i still see the typical headgasket seeping on the left side of the engine, regardless of using studs or just stock headbolts.
I have had better luck with victor headgaskets than felpro. Outlaw
I have had better luck with victor headgaskets than felpro. Outlaw
'68falconohio
Well-known member
My grandpa always said, "Close enough for government work, right boy?"
Similar threads
