Thread engagement

[70MC]

I bought a used GM 572 crate motor 4 years ago and changed a few things, one of them being the heads. I bought a set of AFR's and the bolts ARP recommended. What I noticed is that the bolts thread engagement is close to half as to what GM used for their heads and their fasteners.
I know to get max strength from the fastener that you need the same amount of thread engagement as the diameter of the threads, which I have. But I was worried about the thread life of the block, and was thinking also that longer threads in the deck of the block might be better for bore distortion?

With the factory heads and bolts I had about (i am guessing from memory) 7/8 to an inch thread engagement and now have 1/2 to 5/8.

Would you get longer fasteners or use studs or run it?

[mag2555]

If you need to have atleast .750" of thread engagement to be golden with course threads if you ask me.

[David Redszus]

The thread engagement is a function of bolt grade and threaded material and is measured in multiples of bolt diameter.

Assuming a cast iron block, the engagement depth will range from 1.0 to 1.4 diameters depending on bolt hardness/tensile.

The depth of the bolt into the block will have a pronounced effect on bore distortion, both ovality and taper.

[novafornow]

Yes, get longer bolts.

[jake197000]

i always thought thread engagement should generally one and one half bolt diam,at minimum

[dfarr67]

Whats the cost between ARP bolts and their studs?

[BillK]

Just for grins why don't you call ARP and see what they say ???? I have found that some of the kits they list for specific heads are not always correct. Personally I would certainly want more thread engagement than what you have.

[arlancam509]

i always thought thread engagement should generally one and one half bolt diam,at minimum

agreed. have always gone with 1.5 times the diameter for ferrous metals and 2.0 times the diameter for the non-ferrous metals. it is a fairly safe 'rule of thumb'.

[David Redszus]

The thread engagement is a function of bolt grade and threaded material and is measured in multiples of bolt diameter.

Grade .....................8.8 ..8.8. 10.9. 10.9. 12.9
Dia/pitch ratio........ <9.... >9.... <9.... >9.... <9
Heat treated steel.... 0.80. 0.90. 0.90. 1.00. 1.25
Med carbon steel..... 0.90. 1.00. 1.00. 1.20. 1.50
Low carbon steel...... 1.00 1.25. 1.25. 1.40
Cast iron............... 1.00. 1.20. 1.20. 1.40
Aluminum ............. 1.20. 1.50. 1.50
Hard plastic............ 1.50. 2.00

Engineering fastener rules. No thumbs allowed.
A higher grade bolt requires increased thread engagement.
A finer pitch bolt requires increased engagement. <9 = coarse, >9 = fine
A softer threaded material requires increased engagement.
High grade bolts cannot be used with soft threaded material or soft nuts.

Note that a high grade (12.9) bolt cannot be used in a cast iron or aluminum block.

[arlancam509]

Engineering fastener rules. No thumbs allowed.

i guess where i come from, i need my thumbs. it is the only thing that sets me apart from my friends at the zoo.

[allencr267]

Also, like a nut doesn't have a fully formed thread on either end, so reduce its width by 1 pitch for engagement measuring purposes.

Bottoming stud for a Lotus Ford Twincam cam cap & cover.
qedmotorsport.co.uk/product-images/lotus/twin-cam/cylinder-head-components/cam-cap-stud-long.jpg

[Kevin Johnson]

So then no more bottoming out studs then.

...
Bottoming stud for a Lotus Ford Twincam cam cap & cover.
qedmotorsport.co.uk/product-images/lotus/twin-cam/cylinder-head-components/cam-cap-stud-long.jpg

"Thus it has been demonstrated."

Good choice of picture.

[70MC]

Whats the cost between ARP bolts and their studs?

Bolts $75.00-80.00 and studs $175.00- 200.00.

[70MC]

Just for grins why don't you call ARP and see what they say ???? I have found that some of the kits they list for specific heads are not always correct. Personally I would certainly want more thread engagement than what you have.

When I called them 3 years ago, they did not like what I had and said the bolts in the kit was not right. I sent mine back to arp and they sent me another kit, it was the same, so we tried again with no luck. So I used what I had, even though I was not happy.
I called today and the tech said 1/2 inch engagement was sufficient. That was without me telling him I had 1/2 inch engagement. So I am going to use studs.

[Newold1]

Read some of the technical information from ARP. Especially how good threads make a difference and how the bolts must do certain things to create the proper clamping strength and hold. Also read and understand why head studs are much better for even clamping and torquing.