Hey everyone. This is my first post and its part therapy and partly an advice request.

I pulled the heads on my C6 Z06 and one of the small M8 bolts seized and broke off in the block. I could feel it galling and worked it back and forth, but it eventually broke flush with the block and left about one inch of the bolt in there.

This was the forward most M8 bolt on the driver's side, #15 in the shop manual: http://www.ls1howto.com/howto/fbody/...orquebolts.jpg

I was able to drill it out and remove it with an easy out. When I drilled it, I was off center just slightly to the point where my final bit took out the outer shell of the bolt and just touched the block threads enough to remove some aluminum, but not all of the block threads in the area. This was over about a 45 degree sweep of the threads. I really don't think it would have come out if I hadn't compromised the shell of the bolt anyway, so I don't feel too bad about it.

I ran a M8x1.25 tap down the hole and it cleaned the threads up fairly well. They still don't look great, but a new bolt threads up and down easily with just a little bit more slop than the undamaged M8 holes.

I'm planning to go back with ARP studs.

So, my questions are:

1) When I get the heads back, should I just try it and see if one of the ARP studs will hold 22 ft/lbs of torque without pulling out? Should I use some red locktight on the stud (would that help pullout strength any)? I guess the down side here is that if it fails, I could end up having to drill out the stud.

2) Should I just go ahead and install a time-sert? Is there enough meat in the block there? Any issues with a time-sert in that area?

3) How important is that particular bolt anyway? It doesn't look like it has much to do with containing combustion forces... it seems like it mostly seals the pushrod area against dirt coming in and oil getting out. If I can torque it to 10 or 15 ft/lbs, should I leave well enough alone?

Thanks for any input on this.

 

I would stack flat washers (thickness of head) under one of the old M8 bolts and torque it to 22 ft/lbs of torque to see if it will hold. If it does hold, you're good to go, if not, Time-Sert the hole.

 

I thought about doing something like that, but I was a little worried that it would cause a low spot on the block in the area... since the force wouldn't be distributed across the larger area of the head. Think that's anything to worry about?

 

Time-sert it and be done with it

 

22 ft/lbs is a very low torque (use large flat washers to spread the load), so I would not worry about a low spot. Did you measure the bolt hole depth? The bolt may have only damaged the upper threads and it's possible the lower threads are still perfect. Measure the bolt hole depth and the length of the bolt under it's hex head; compare.

 

I found a scrap piece of flat aluminum bar stock and made something to spread the force out as much as possible. The old M8 bolt wouldn't go as deep as it would in the other holes, so I picked up an end tap (I only had a chamfered one) and cleaned up the last 5 or so threads.

An old bolt threads all the way in now and will torque to 20# and still screws out as easily as it goes in, so the block threads didn't seem to move around any under the torque.

So, I feel pretty good about trying it with the head on.

Thanks everyone for the advice.