Head Bolt Problems (Torsion and breaking)

[MarkSud]

After a week of research and a close inspection of the head bolts I've decided that it would be ok to reuse them when rebuilding from the head up. After cleaning the threats on the bolts and in the block I started the process of torqing the down. I went in increments (25, 55, 85), and when it came time to start the 85 round the bolts would get up to somewhere around 78-80 and then the torque would start going down. I thought that was weird and decided to keep tightening them down to get to 85 (hindsight bad decision) and ended up breaking on of them. Luckily it didn't shear completely and I was able to back the whole thing out. My questions are, did I do something wrong in the process or was this just a case of old, stressed out head bolts? Also, when I order my new set (Anyone know where to find a set of 7/16 inch head bolts for a AMC 258 i6 / 4.2l ?) can I reuse the new head gasked that I just slapped on before starting to torque down the head? Any help would be great.

 

[Torxhead]

Your guess about why that bolt gave out is correct. I would not recommend reusing that head gasket as it is already compressed. You could probably try a big 4wd outfit like Morris or 4wd hardware for those head bolts.

 

[red dog seven]

I agree I wouldnt use that gasket. Better to just put a new one on than to not and end up with an issue after it's all back together. ARP makes just about every bolt for every engine out there, good quality too. Chase the threads in the block with a tap, dirty threads can cause havoc. Old bolts, dirty threads, all of this impacts touque and altimately the sealing of your gasket. Use some torquing compound as well when installing and torquing your bolts and you will get a true torque.

 

[tarry99]

I agree I wouldnt use that gasket. Better to just put a new one on than to not and end up with an issue after it's all back together. ARP makes just about every bolt for every engine out there, good quality too. Chase the threads in the block with a tap, dirty threads can cause havoc. Old bolts, dirty threads, all of this impacts touque and altimately the sealing of your gasket. Use some torquing compound as well when installing and torquing your bolts and you will get a true torque.

Like he said go the ARP route.......chase your threads in the block, If you can & want put studs in it, if you use studs check your block thread entry holes for a slight chamfer to set the studs ......much better program for torquing down heads.........pay attention to the recomendations for lube and the torque values.

 

[MarkSud]

Thanks for all the help fellas. A few issues I have run into. I can't seem to find a Tap that for a 7/16" x 14 thread, in the past I've used a wire brush (bore brush that will fit hole size) and just used brake or carb cleaner and some enthusiastic brushing followed by a blast from compressed air. Will that work good enough? Also, I've found the head bolts only at 1 web site (headbolts.com) for $89. Will ARP custom make a set for less if I call them to tell them what I want?

 

[tarry99]

Thanks for all the help fellas. A few issues I have run into. I can't seem to find a Tap that for a 7/16" x 14 thread, in the past I've used a wire brush (bore brush that will fit hole size) and just used brake or carb cleaner and some enthusiastic brushing followed by a blast from compressed air. Will that work good enough? Also, I've found the head bolts only at 1 web site (headbolts.com) for $89. Will ARP custom make a set for less if I call them to tell them what I want?

7/16" x14 is pretty standard.......most hardware stores should have that. The point in cleaning and restoring the threads in the block is to allow the bolt or stud to be able to grip the block and be able to torque to the proper tightness.............any debris or damaged to the thread will not allow that to happen.........I would get or borrow that tap so you can chase each thread..........
You can call ARP but for the most part the likes of Summit or Jegs or Headbolts.com may be cheaper.......my Catalog says for Studs on the AMC 258 i6 / 4.2l I6 the part # is 112-4001 & Head Bolts #112-3601 of course you should verify those part numbers.

 

[Purple77CJ7]

1985 AMERICAN MOTORS Parts and Accessories - SummitRacing.com

This is a good place to buy parts from.

 

[MarkSud]

I haven't done too much work with a tap. Any advice? I don't want to ruin the threads completely in the block.

 

[Torxhead]

Try and do some online reasearch on how to use a hand tap, maybe on Youtube. A tap handle can help you here. Practice on some existing threading prior to going on engine parts, using oil will help also. After you are done an air hose and a q-tip will help clean out the hole. Follow the existing thread, as you are just basically just cleaning out the hole.

 

[red dog seven]

7/16" x14 is pretty standard.......most hardware stores should have that. The point in cleaning and restoring the threads in the block is to allow the bolt or stud to be able to grip the block and be able to torque to the proper tightness.............any debris or damaged to the thread will not allow that to happen.........I would get or borrow that tap so you can chase each thread..........

X2....you really want to do this right the first time

 

[tarry99]

I haven't done too much work with a tap. Any advice? I don't want to ruin the threads completely in the block.

Any through holes into the water jackets should be done with a standard tapered starting tap..........any blind holes should be down with a Bottom Tap!......Again, don't over think this..........I use a Mikita cordless on the slowest speed and a low torque setting........get the tap started & straight, use a little oil, take it in slowly and back it out.........Walla your done if you have air available blow them out.........this is normally a procedure that is done prior to the block being cleaned , boiled out bored or surfaced......... If your on the back end of the assembly Just keep everything clean........
Again it you go to studs you'll want to put a slight chamfer at the thread entry point......that is not even a bad Idea on Bolts as sometimes that top thread gets pulled up a little after being used for a period of time.
If you have through holes into water jackets make sure during assembly you seal the threads with a proper sealer. All others need a lubricant to attain proper torque.

 

[rlitavecz]

I have used this website in the past. Good service and they had what I needed in stock.
Jeep 4.0 4.2 258 Cylinder head bolts / fasteners

 

[MarkSud]

Once again, impressed with the help and the speedy responses. Thanks again!

 

[MarkSud]

New Headbolt set ordered from HeadBolts.com. Hope they come in fast, I need to put this guy back together so I can tune my new Carb and get on the road!