Damage Alert: How to Avoid Pulling Threads or Killing Head Bolts

[Sgt.Gator]

Interesting Article given my recent experience~

Damage Alert: How to Avoid Pulling Threads or Killing Head Bolts
By JEFF SMITH JANUARY 26, 2018

http://www.enginelabs.com/engine-tec...ng-head-bolts/

[redfogo]

Hope ARP plans to include this info in their directions going forward.

[DaveS53]

There's an error in this article.

"This friction assumes that the washer remains stable under load. But if that head bolt washer is smooth enough, it can turn as the load is applied. This effectively turns that washer into a bearing, reducing the friction. If this spinning washer reduces the friction by even a third, this applies another 10- to 15-percent of torque into stretching the bolt. As you can probably guess, this radically increases the actual amount of torque needed to create the stretch in the bolt. This additional torque then either fails the bolt by stretching it beyond its yield strength – or this additional torque pulls the threads out of the block. Both of these are situations best to avoid."

The word increases should be decreases. On critical rod bolts, there is a tool that can be used to measure bolt stretch, rather than relying only on a torque value. It can also show a defective bolt that stretches with too little torque. The real moral of the story is to be sure that every bolt is tightened under the same conditions, so the proper stretch is achieved and know what assumptions are made along with the bolt torque spec. If all of the washers spin due to the slick surface, using a lower torque would create the same stretch. How much of the torque put to a nut or bolt goes into creating bolt stretch isn't a very exact science.

[Sgt.Gator]

Hope ARP plans to include this info in their directions going forward.

My shop just pulled the threads out of a very expensive forged build Subaru closed deck block with 1/2" ARP studs. Neither the builder of the block nor the shop installing the heads could figure out why. Now I suspect this was the problem. And the TQ specs on the ARP 1/2" studs are quite a bit higher than the standard Subaru OEM specs which already probably had the block threads close to max, then when adding on the above problem it pulled out one of the thread holes.

Another: "Good Judgement comes from Experience. Experience comes from Bad Judgement" for me and the two shops involved.

So yes, ARP needs to include this in their packaging asap. Or how about designing new washers that have a slight surface friction built in for the block side?

[turbomacncheese]

Pretty sure my threads got fubar'd pulling the stock headbolts out. Shop had a slight bit of trouble threading in their studs, but they held. Mine pulled out somewhere around 70lbs. Just bang. Done. Now I wonder if I had slick washers on top of it. How much pressure is REALLY holding my heads in place? Makes me feel better about drilling all of them out, not just the ones that failed.

[Bob Cowan]

This happened to me putting heads on a Coyote motor. I wrote about it on the other forum. The ARP head stud snapped deep in the head, and was a real bear to get out.
The answer is to roughen up one face of the washer that contacts the head so it doesn't spin. I rubbed it on 80 grit sandpaper in one direction. I also put a dot of white paint on the washer so I could see immediately if it moved.

[SixStar]

My shop just pulled the threads out of a very expensive forged build Subaru closed deck block with 1/2" ARP studs. Neither the builder of the block nor the shop installing the heads could figure out why. Now I suspect this was the problem. And the TQ specs on the ARP 1/2" studs are quite a bit higher than the standard Subaru OEM specs which already probably had the block threads close to max, then when adding on the above problem it pulled out one of the thread holes.

Another: "Good Judgement comes from Experience. Experience comes from Bad Judgement" for me and the two shops involved.

So yes, ARP needs to include this in their packaging asap. Or how about designing new washers that have a slight surface friction built in for the block side?

IAG or Outfront?

[Sgt.Gator]

IAG or Outfront?

Rallispec racing block, Cobb Surgeline mating the heads and doing the tune.