Bore distortion: headstuds and head bolts - Dodge Cummins Diesel Forum
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post #1 of 18 (permalink) Old 05-21-2018, 05:35 PM Thread Starter
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Exclamation Bore distortion: headstuds and head bolts

disclaimer: I AM NOT A MACHINIST

so i had a conversation with a machinist about headstuds, headbolts, clamping force of aftermarket studs etc and he brought up something that i dont think is considered much in the consumer end of it.

so when these blocks are machined from the factory, they are machined with the intent of using head bolts with a certain amount of clamping force. I dont know if our 6.7 are machined this way, but usually when a block is machined and honed, a torque block is used in place of the head when its getting machined. the purpose of that is to replicate the clamping force of heads so that bore distortion gets factored in.

so from what i was told, studs and bolts will have different bore distortions. usually blocks are supposed to be machined with the same type of fastners you will be using on the head install. if your heads are going to be bolted, you machine it with bolts with the same amount of torque. same for studs.

now you throw headstuds into an engine that has been machined with bolts, (supposedly) you will now create distortion, one factor being studs instead of bolts, other being additional clamping force and im guessing the fact that headstuds sit deeper than headbolts will also play a factor.

so i asked the machinist what he thought of doing studs on an already assembled engine. his thought was, the little bit of extra blow by and worse ring seal is overshadowed by not blocking headgaskets.

so...all this being said, what do you guys think of it? would be cool if an engine builder/machinist can chime in


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post #2 of 18 (permalink) Old 05-21-2018, 06:10 PM
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Quote:
Originally Posted by chknkatsu View Post
disclaimer: I AM NOT A MACHINIST

so i had a conversation with a machinist about headstuds, headbolts, clamping force of aftermarket studs etc and he brought up something that i dont think is considered much in the consumer end of it.

so when these blocks are machined from the factory, they are machined with the intent of using head bolts with a certain amount of clamping force. I dont know if our 6.7 are machined this way, but usually when a block is machined and honed, a torque block is used in place of the head when its getting machined. the purpose of that is to replicate the clamping force of heads so that bore distortion gets factored in.

so from what i was told, studs and bolts will have different bore distortions. usually blocks are supposed to be machined with the same type of fastners you will be using on the head install. if your heads are going to be bolted, you machine it with bolts with the same amount of torque. same for studs.

now you throw headstuds into an engine that has been machined with bolts, (supposedly) you will now create distortion, one factor being studs instead of bolts, other being additional clamping force and im guessing the fact that headstuds sit deeper than headbolts will also play a factor.

so i asked the machinist what he thought of doing studs on an already assembled engine. his thought was, the little bit of extra blow by and worse ring seal is overshadowed by not blocking headgaskets.

so...all this being said, what do you guys think of it? would be cool if an engine builder/machinist can chime in
It's true, but they don't care.
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post #3 of 18 (permalink) Old 05-21-2018, 07:57 PM
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I think that might matter for rockets and maybe racing engines. I bet the difference in clamping force is much much smaller then the inaccuracy of auto torque wrenches used. Add to the inaccuracy of a torque wrench would be difference in friction depending on how clean the threads are and the surface of the head and the bolt. Then what is the torque on these, I think the older ones was 66 foot pound then an extra 90 degrees. And someone thinks the difference in head studs vs bolts is going to make any difference in this.
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post #4 of 18 (permalink) Old 05-21-2018, 08:18 PM Thread Starter
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Originally Posted by cjgoode View Post
I think that might matter for rockets and maybe racing engines. I bet the difference in clamping force is much much smaller then the inaccuracy of auto torque wrenches used. Add to the inaccuracy of a torque wrench would be difference in friction depending on how clean the threads are and the surface of the head and the bolt. Then what is the torque on these, I think the older ones was 66 foot pound then an extra 90 degrees. And someone thinks the difference in head studs vs bolts is going to make any difference in this.
i would imagine it matters for on road diesels as well since bore distortion even .001" will cause new wear points on the cylinder that didnt exist with headbolts.

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post #5 of 18 (permalink) Old 05-21-2018, 08:20 PM Thread Starter
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http://www.irdindia.in/journal_ijmer...l1_iss2/14.pdf

potentially a good read

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post #6 of 18 (permalink) Old 05-21-2018, 08:44 PM
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Quote:
Originally Posted by cjgoode View Post
I think that might matter for rockets and maybe racing engines. I bet the difference in clamping force is much much smaller then the inaccuracy of auto torque wrenches used. Add to the inaccuracy of a torque wrench would be difference in friction depending on how clean the threads are and the surface of the head and the bolt. Then what is the torque on these, I think the older ones was 66 foot pound then an extra 90 degrees. And someone thinks the difference in head studs vs bolts is going to make any difference in this.
I don't assemble engines with " depending on how clean the threads are ". And, my torque wrenches are checked annually for calibration, as per my employer.
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post #7 of 18 (permalink) Old 05-21-2018, 09:12 PM Thread Starter
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if someone is putting heads on my truck the threads on the bolts or studs better be clean. ARP gives you their own assembly grease for their studs and the torque specs they give you accounts for that grease in the threads.

there is a lot more engineering and science to putting an engine together than "if's" and "maybes"
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post #8 of 18 (permalink) Old 05-22-2018, 10:04 AM
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Originally Posted by chknkatsu View Post
i would imagine it matters for on road diesels as well since bore distortion even .001" will cause new wear points on the cylinder that didnt exist with headbolts.
I doubt the difference between head studs and bolts is enough to cause .001 more distortion in a bore.

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post #9 of 18 (permalink) Old 05-22-2018, 10:41 AM
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Cummins uses a Torque Plate when honing these engines new at the factory.
Excessive clamping force generated when using aftermarket head studs DOES distort the cylinder bore.
There are companies making torque plates designed for the 12-24 valve engines. Keating Machine, BHJ, ZRM, and few others.
During the build on my 6.4 Cummins, I searched every machine shop in South Texas, and could not locate one with a Cummins honing torque plate.
And purchasing my own was not in my budget... And it still bothers me.

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post #10 of 18 (permalink) Old 05-22-2018, 10:43 AM
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I believe Industrial Injection has a YouTube video out about cylinder distortion, and torque plate honing.

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post #11 of 18 (permalink) Old 05-22-2018, 12:29 PM
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Quote:
Originally Posted by chknkatsu View Post
i would imagine it matters for on road diesels as well since bore distortion even .001" will cause new wear points on the cylinder that didnt exist with headbolts.
1 thousandth of an inch is a lot. No way there's that much distortion. No way.

At most, I'd say less than 1 one hundred thousandths of an inch. Maybe more in the 1 - 2 millionths.

The cylinder bore gets distorted more when the crankshaft spins than you might think. In fact, the whole block twists under torque. It's why SBC's have to have 4 bolt mains if they're gonna routinely turn over 4500 RPM. They'll prematurely wear or even grenade on you because the castings were made for lighter weight as a priority over strength.

One reason why the 351 Windsor isn't used more for performance is that it has 3" Mains as opposed to the SBC's 2.25" (Doing this from memory so please feel free to correct me) Add to that the lack of roller lifters (except in the Lightning for a couple years and Cobra R) and.......

The Windsor was built for strength, not for RPMs. But you take it up to higher RPMs and the 3" mains can't take it very well.

It's a thing. It's about block distortion/twisting

But homey ain't buying the stud vs torque bore distortion theory or the align-honed distortion theory. Not on these blocks. (I'd be more apt to buy the align-hone distortion theory than the bore theory, but I ain't buying either)

I wouldn't give it a second's thought.

On a 20,000 RPM F1 engine? Oh yeah. On a Cummins? Not even.

I could be wrong, as usual but I need more evidence than some unnamed individual's opinion.

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post #12 of 18 (permalink) Old 05-22-2018, 04:32 PM
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On a 20,000 RPM F1 engine? Oh yeah. On a Cummins? Not even.

I could be wrong, as usual but I need more evidence than some unnamed individual's opinion.
Unnamed individual ??? Cummins themselves uses a Torque Plate when manufacturing these engines. And just about every single big name Cummins performance engine builder uses a Torque Plate.

That's just a fact. Try Google. It can help you learn easily.
There are more than a few videos from the Cummins factory floor, and from performance builders.
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