CRACKED BLOCK TORQUING HEAD BOLTS

Man that sucks!!

I had a similar thing happen on the small block Chevy V8 in my dirt track car. After I finished (about 5 Min.) torqueing the heads I heard a "snap" sound. I found that one head bolt had broken while the engine was still just sitting there on the engine stand. They were just stock head bolts, but I had never seen that happen before.

Dennis

Former Owner of:
The Craig Breedlove "AERO AMX"

Still Owner:
SS/AMX #9 replica (THE BIG MENACE)
70 AMX 416, EFI, Nash 5 speed
70 Javelin 401, 727 (Wife's car)
72 Gremlin Autocross Project.

bvpotash1 wrote:

It was probably was iron head cracking in the usual spot at the sharp edge on the ends.

It is more probable to have either the head cracked or bolt snapped.

Heads will crack if un evenly torqued in a special sequence and torque range. Just because ARP or any other manufacturer states a torque range, it does not mean that the heads are to be torqued out of spec.

I will search for proper torque and pattern sequences for AMC v8 heads.

They have been posted here in a few threads.

As for bolts snapping... probably 1 in 100000 due to manufacturing defect, too small under inspection. Can be hidden by a few threads, though you will be taking the head off, so if any snapped you should be able to notice.

71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker

I will pull the head tonight and inspect.
Looked at the corners right after the noise was made but didn't appear cracked in that area. that was my first thought.
will let you know what I find out.

1969 SC Rambler
1974 Jeep CJ5 Dirt/Sand Drag Racer w/401 TH400
Tube Chassis Dirt/Sand Drag Racer w/401 Powerglide
"We are not here for a long time but we are here for a good time"

There have been reports like you'rs before, it turned out to be an inner (toward the lifter valley) bolt holes sheering off. I would go back over the bolts with the torque wrench, that should tell you what to be looking for.

One messy but important step that is often missed on older motors is to clean out the bolt holes. Unfortunately, most machine shops used to do this, but it is not nearly as common today.

Get a thread CLEANer/CHASER tap.. do NOT use a cutting tap!

http://www.summitracing.com/parts/arp-911-0005?seid=srese1&gclid=CKnfive2is0CFRNZhgod99QKZA

Use a good penetrating lube NOT a heavy oil (remember you are not cutting threads, only cleaning them)

Run the tap in a little... if you feel a lot of junk back it out, clean it off and repeat until you GENTLY reach the bottom of the hole.

Remove the tap.

Spray judicious amount of light penetrating oil down the hole.
If you have a bottle brush that fits in the hole run it down and spin it around (not necessary, but helpful).

Get a rag, safety glasses, welding helmet, body suit, breathing apparatus, etc. shield the hole and blow it out with compressed air. The most effective way is to have thin extension that goes all the way to the bottom of the hole and slowly bring it up while blowing out. It will shock you how much nastiness comes out!

Try to keep from getting anything on the surrounding block area or in the cylinder bores, but clean it all off before assembly.

What often happens is all that crud gets forced to the bottom of the thread bore and compressed. The Hydraulic pressure has broken many a block, though not as common with our engines

This sounds like a long process, but is not as long as it looks especially once you get it going... regardless, it is time well invested!

j2sax@yahoo.com
Plenty of FSJ's Eagles and other AMC's near Springfield, MO