So the only head bolt hole in the block not pre-checked by me seems to have an undersized insert installed in it - the story of my life...

I guess I must have skipped it checking it by accident when the short-block came back from the machine shop. The first head went on just fine, and the 2nd head was going well until I got to the last lower (shorter) bolt (one of the middle bolts). The bolt wouldn't catch at all, so I lifted the head back off and saw that it had an insert in the bolt hole in the block. Testing different bolts that I had, it takes a 7/16" x 14 bolt. As you all well know, the typical head bolt is a 1/2"x13 bolt.

So the million dollar question is: do I drill this insert out and install a 1/2" insert? Or buy an ARP 7/16" head bolt which says its good for 80 ft-lbs and trust that it can go to 90 ft-lbs (13% more)? Or is this a time and a place for a head stud?

Things were going so well too...I could smell the finish line...

Geoff

 

Strange it would have that. You can look at McMaster-Carr, they have high strength 7/16-14 screws.

 

Thanks for your reply. Most likely stripped during a previous cylinder R&R. The source of my concern is that it seems as though the strongest 3" long 7/16"x14 bolt I can get is about 180,000psi steel. Looking at the recommended torque values for a bolt of that material and size is about 70 or 80 ft-lbs. I need to go up to 90 ft-lbs. Doesn't seem like much more, but will that be the straw that breaks the camel's back? On another forum, a guy took a 7/16" bolt and when up to 120 ft-lbs before it yielded, but I don't know if that's what I should be hanging my hat on. I guess I get the strongest bolt I can, torque in steps to 90 ft-lbs, if the bolt fails or the insert pulls out, then I'm back to option #1 which is drilling out the insert and going with a 1/2" one. Is there anything I'm missing?

Geoff

 

Well I called up ARP and they told me that using a 7/16" head bolt is not something I should be doing. They recommend getting the 7/16" insert out and installing a 1/2" insert. That being said - is there any danger of breaking through the sidewall to a coolant passage or something? I'm just a little concerned that the person who installed the 7/16" insert, did so for a technical reason...

Geoff

 

That is a big concern. Are you going to do the repair yourself? If you are having a machine shop do it maybe they can advise. It may be possible to heli-coil it and not have to go way bigger.

 

With discretion being the better part of valor, I pulled out the insert today. Used one of the Harbor Freight stout hooked tools (not the skinny ones) and tapped the point into the loose end of the helicoil. As soon as that moved away from the wall of the bolt hole, I was able to get a needle nose locking pliers on the loose end and pull it out like a big spring. I have the kit coming from EB that has everything I need to install the 1/2"X13 helicoil. I think I found why they installed a 7/16" insert instead of the proper 1/2" - once I pulled the old insert out, I looked down the bolt hole and saw some rusty, smooth looking threads. I took a 1/2"x13 original bolt and was able to thread it into the bolt hole. They clearly used the 7/16" insert to get away from having to overdrill and then tap the stripped hole - they just threaded the insert in. Would be nice (and somewhat scientific) to know what kind of torque they were able to achieve with that. Anyway - my only concern is keeping the drill bit nice and straight in the bolt hole. I'm thinking of bolting in an old head to use it's upper hole as a guide for the hole in the block.
Geoff

 

Yes, that would be a good idea. If there is any gap around the bit and the head bolt hole you might be able to get a 1/2" diameter pipe that would fit in the head bolt hole and make the drill bit a tad tighter. Good luck with it.