Head Studs Vs Bolts

[Ken(Ark)]

So the head studs are coarse on the block end and fine thread on the nut end . Head bolts are coarse .

When a stud is installed there is no real force on the cast iron block threads , which is good .

A coarse thread head bolt is what the system changed to and is sufficient .

So my question is , what would be wrong with installing coarse studs with coarse nuts ? Seems like you would not stress the block and a coarse nut would get as much clamping force as a bolt . Or should I say sufficient clamping force , not trying to split hairs , unless Y"ALL want to go back and forth on the technical issue , I am just looking for the simple answer .

Seems like a man could inexpensively get / make stainless steel studs , that would have enough clamping power and not rust to the block . Studs would be much easier to seal a coolant leak .

 

[TheOldHokie]

(quoted from post at 18:02:44 09/09/18) So the head studs are coarse on the block end and fine thread on the nut end . Head bolts are coarse .

When a stud is installed there is no real force on the cast iron block threads , which is good .

A coarse thread head bolt is what the system changed to and is sufficient .

So my question is , what would be wrong with installing coarse studs with coarse nuts ? Seems like you would not stress the block and a coarse nut would get as much clamping force as a bolt . Or should I say sufficient clamping force , not trying to split hairs , unless Y"ALL want to go back and forth on the technical issue , I am just looking for the simple answer .

Seems like a man could inexpensively get / make stainless steel studs , that would have enough clamping power and not rust to the block . Studs would be much easier to seal a coolant leak .

When you torque the fastener - stud or cap screw - you are creating a tension in the body of the fastener. Torque is simply an indirect way of measuring that tension. The tension needed is an engineering parameter that Ford determined was needed to clamp the head securely to the block. Regardless of what combination of fasteners you are using you are trying to get the same tension or clamping force - let's call it T.

The stress on the threads in the block is the same in all cases. It is the result of the tension T and the geometry of the threads in the block. What is pulling on the other end doesn't change the strain on the threads in the block - it is always T.

If you switched to studs with coarse threads on both ends you would use coarse thread nuts on the studs and the torque value needed for those nuts would be the same as for cap screws.

Stainless steel has a lower yield strength than carbon steel studs or cap screws and could possibly be inadequate for the tension T needed to clamp the head. You would need to do the engineering math on that to see where the number fall. The torque value needed to produce that tension T would also be different as the modulus of elasticity of stainless is different from carbon steel.

TOH

 

[FarmerDan2018]

Would vibration be a consideration? Coarse threads seem to vibrate loose faster than fine threads.

 

[TheOldHokie]

(quoted from post at 21:12:11 09/09/18)
Would vibration be a consideration? Coarse threads seem to vibrate loose faster than fine threads.

Fine threads are more resistant to vibration and have a higher pullout strength. In this case you have coarse threads in the block so you are gaining nothing at the other end.

In practice modern OEMs have come to the conclusion that the advantages of fine threads are so small as to be negligible. Coarse threads make assembly easier and the use of fine threads has all but disappeared. Coarse threads are used in all but a few very specific applications.

TOH

 

[Tim PloughNman Daley]

You can use whatever you want -just be sure you know and if you sell the tractor that the new owner knows so keep it noted somewhere handy. It's like the guy below who posted -had 15 studs/nuts and 3 hex bolts. No qualified mechanic would ever do something like that. Most likely some shadetree guy taking a shortcut. Dan has explained torque as well as any engineering textbook. The important factor is that each fastener, hex nut or hex bolt, applies EQUAL clamping force. If uneven, when things get heated up, it may cause the head to warp worse case or by a lesser case, leak. I've worked on N's with snapped off studs, stripped ends on studs, with boogered up broken studs that have broken drills or easy-outs in them, and/or the head hole is boogered up from drill walk trying to extract the broken stud, all because some guys just don't know the how's and why's. Studs are hardened steel. You aren't going to be effective using a cordless or 1/64 HP hand drill trying to extract a broken one. Those simply do not have the HP to do it. Plus, trying to hand drill/extract a broken drill, bolt, or easy-out is asking for trouble due to drill walk. If you get into the block tapped holes, you are going to permanently muck up the threads. It is best to take the block to a reliable machine shop/engine rebuilder as he has all the right tools to do the job.

Tim *PloughNman* Daley(MI)
TORQUE VALUES