Drilling and tapping a block for bigger head fasteners...

[RacinNdrummin]

I am drilling and tapping my 6.9 diesel block head fasteners from 7/16" to 9/16".

Ive done some testing on a spare block and its been successful (Several holes at 250+ lb.ft on the stud with a torque wrench, as high as the wrench will go), but I have some worries about one or two particular holes. They are really close to the back of the block, and After drilling for the 9/16" thread, may only have an 1/8" of wall thickness from the tangent of the hole to the back of the block.

I cant imagine any of the other bosses are any thicker on the other holes, but what is the safe zone for wall thickness on a cast iron boss assuming a top quality grade of cast iron? (These blocks are a very good grade)

Justin

[Toolguy]

Maybe 1/2" bolts would be safer?

[Joe Rogers]

If it is worth upgrading the fasteners for durability why don't you install studs?
Joe

[Doozer]

Are you torquing the studs into the block? That is never the right thing to do.
Or do you mean you are torquing the nuts on the studs at assembly?

-D

[strokersix]

You may already know this but in case you don't: Increasing fastener diameter is often the wrong choice when faced with a joint durability problem. Joint durability under service loads depends on fastener stretch and the relative stiffness of the parts compared to the fastener. Larger diameter fasteners change the relative stiffness in the wrong direction in terms of durability. Do some reading on bolted joint diagrams. boltscience.com is one source of information.

Best choice, if available, is higher grade fasteners (studs or bolts) of the same diameter. If you are going to increase fastener diameter, consider making custom hardened standoff bushings so you can use longer fasteners for more stretch.

Once you have chosen your fastener and modified the parts, I suggest testing the torque/tension relationship on the real parts. Get some extra fasteners. Measure length, torque, then remove and measure length again. Repeat, upping the torque each time until you achive yield, say .002 inch permanent stretch. Now you know what torque value to use, say 80% of the value that produced .002 yield.

Post back here with questions if you wish.

[RacinNdrummin]

Maybe 1/2" bolts would be safer?

1/2" 190,000psi studs don't have the clamping load necessary for what I am going after. I have tested a 1/2" stud, and the thread interference isn't an issue, so physically it would work, but like I said, its just not enough for the application.

[RacinNdrummin]

If it is worth upgrading the fasteners for durability why don't you install studs?
Joe

The 9/16 fasteners are 190,000psi ARP studs.

[RacinNdrummin]

Are you torquing the studs into the block? That is never the right thing to do.
Or do you mean you are torquing the nuts on the studs at assembly?

-D

This is the torque of the nut on the stud. Studs are installed finger tight and backed off a half turn.

[RacinNdrummin]

You may already know this but in case you don't: Increasing fastener diameter is often the wrong choice when faced with a joint durability problem. Joint durability under service loads depends on fastener stretch and the relative stiffness of the parts compared to the fastener. Larger diameter fasteners change the relative stiffness in the wrong direction in terms of durability. Do some reading on bolted joint diagrams. boltscience.com is one source of information.

Best choice, if available, is higher grade fasteners (studs or bolts) of the same diameter. If you are going to increase fastener diameter, consider making custom hardened standoff bushings so you can use longer fasteners for more stretch.

Once you have chosen your fastener and modified the parts, I suggest testing the torque/tension relationship on the real parts. Get some extra fasteners. Measure length, torque, then remove and measure length again. Repeat, upping the torque each time until you achive yield, say .002 inch permanent stretch. Now you know what torque value to use, say 80% of the value that produced .002 yield.

Post back here with questions if you wish.

Already been down that road. I tested the 7/16" and 1/2" fasteners to yield. 125ft/lbs of torque on the 7/16" studs before reaching yield (I lifted a head with these at half the fueling I am going to be running), 1/2" stud was 180ft/lbs before yield, and while that's right about what I am going to need for clamping load, If I am going to be drilling and tapping anyway, 9/16" are more stable in that range. Plan was to take to 200ft/lb's on the 9/16 studs. Im not worried about block structure other than lateral load on the thread bosses, the rest of the block is stout enough to take it, and the bolt bosses are tied into the bottom of the block, not the cylinder walls.

[RacinNdrummin]

The reason I didn't go with ARP+625's or something is that ARP wanted $1300 for a set of them. Being that a 7/16 +625 stud at 285Kpsi is still less than a 9/16" 190Kpsi 8740 stud, Id rather spend $400 on a set of those, and drill/tap the block.

[Bob Fisher]

If you would not mind, what are you doing with a 6.9 Diesel engine that requires that much clamping force? Bob.

[andywander]

PS it's ft-lbs or foot pounds, NOT feet per pound or ft/lb as you have written.

[RacinNdrummin]

If you would not mind, what are you doing with a 6.9 Diesel engine that requires that much clamping force? Bob.

350cc of fuel to 4000rpm

~105lb/min of Airflow

~50psi of boost pressure

Shooting for 600-700 horsepower at the wheels with a 3400rpm horsepower peak, and about 1300lb-ft of torque at 2600RPM...

8 cylinder Bosch P7100 injection pump
16:1 compression
94 IDIT connecting rods
Main Girdle/Studs
BW 60/68/.91 and 75/96/1.32 Turbochargers
Block Deck will be O-ringed

[Ironwoodsmith]

Your'e going to need a bigger boat!

[strokersix]

Already been down that road. I tested the 7/16" and 1/2" fasteners to yield. 125ft/lbs of torque on the 7/16" studs before reaching yield (I lifted a head with these at half the fueling I am going to be running), 1/2" stud was 180ft/lbs before yield, and while that's right about what I am going to need for clamping load, If I am going to be drilling and tapping anyway, 9/16" are more stable in that range. Plan was to take to 200ft/lb's on the 9/16 studs. Im not worried about block structure other than lateral load on the thread bosses, the rest of the block is stout enough to take it, and the bolt bosses are tied into the bottom of the block, not the cylinder walls.

As you say, more clamp force is required to withstand the applied loading. However: Did you study joint diagrams? Increasing fastener diameter should be accompanied by increased fastener length for a robust connection. If you have room, stout hardened standoff bushings (like 1 inch tall) to increase fastener stretch would help a lot. If there is enough meat in the bottom of the block you may be able to counterbore and tap deeper to increase the fastener grip length (and amount of stretch) as well.

If you don't believe or understand what I'm trying to tell you, boltscience.com has some good basic info.