Broken Head Bolt Question

Eldoninoz · Post by **Eldoninoz** » 17 Apr 2013, 16:26

I had a bolt broke off 2 inches below deck where the treads engage the bolt. Finally managed to remove it but have damaged about 1/4 inch of the threads on one side in my first drilling attempt. Will the remaining good threads be good enough to not have to repair. This is on an engine that the bolt had been broken for quite some time before I had to pull the head to rebuild it. The damaged threads from the drill bit account for almost 25% of the threads of the broken piece removed.

Thank you ahead of time for your thoughts

Post by **JDS60R** » 17 Apr 2013, 16:40

Is this a head bolt ? If so , use a Time-sert to replace the threads.

Eldoninoz · Post by **Eldoninoz** » 17 Apr 2013, 17:01

Here is the pic of the bolt fragment I removed

I was using a 7/32 bit when I did the damage. And yes, this is the head bolt from between 4 & 5 on the back side of the motor.

Post by **JDS60R** » 17 Apr 2013, 22:27

Can you post a pic of the damaged threads in the block? I see about 2mm by 10mm damage to the bolt.

Eldoninoz · Post by **Eldoninoz** » 17 Apr 2013, 22:40

I'll try, but the treads are 2 inches below the deck of the block so we will see how the pics turn out in the morning.

Eldoninoz · Post by **Eldoninoz** » 18 Apr 2013, 12:18

Unable to get a pic of the treads due to lighting, looks like a dark hole when I use the camera. I took the fragment to a mechanic friend and his advice was to make sure the threads were clean. I took one of the other bolts and ran it through a few times without any problems.

Post by **JDS60R** » 18 Apr 2013, 14:22

Without knowing how much of the threads in the block were damaged its difficult to give an opinion.

Eldoninoz · Post by **Eldoninoz** » 18 Apr 2013, 14:35

The only damage to the threads was from the drill bit in the area where you can see on the bolt, otherwise the threads were unharmed. I am leaning towards making sure the threads are clean and installing the new head bolts. It has to be better than driving with one that was broke off like it was when I pulled the head. If the threads were more compromised I would probably go for the Time-sert option. Never heard of anything other than Heli-coils and knew that was not an option in my situation.

Thank you JDS60R for you input, I appreciate your willingness to comment and help me think through my options.

donis222 · Post by **donis222** » 18 Apr 2013, 17:35

I have a different view on this matter. The % of threads that were lost is way below 10%. The damage is 25% down, but only 15% of the circle, i.e. 85% of the threads in the damaged area are intact. If the bolt threads well on the first section of threads, just go ahead and torque the head.

I might leave a tiny bit of the torque off of that bolt although theoretically it is not necessary.

Post by **JDS60R** » 22 Apr 2013, 20:26

If the threads in the block have damage the same size as the bolt fragment, I would chase the threads and install new head bolts. Remember to clean them well and use a proper torque lubricant like ARP ultra torque.