Head bolt keeps breaking

[diamondback21]

I have a 1979 Johnson 35 HP. Trying to replace the head gasket. The middle right bolts a broke twice while torqueing. All other bolts torqued to 216 in. lbs. but that one just twists off and breaks. Luckily the stud was sticking out enough to grab with vise grips and turn it out. What could be causing this?

 

[Silvertip]

Re: Head bolt keeps breaking

Better check for debris in the hold and then use a bottoming tap and chase the threads. The bolt is probably bottoming in the hole. Use a piece of wire or a phillips screwdriver to verify the hole depth is the same as the other bolts. If it is noticeably shallower, you either have the wrong bolt length or there is debris in the hole.

 

[fireman57]

Re: Head bolt keeps breaking

For some reason I was thinking that they only torque to 105ft lbs. I better recheck.

 

[glenn property of pam]

Re: Head bolt keeps breaking

216 in lbs is 18 ft lbs (i dont have a manual to know what they shoud be set to) . Are you using bolts designed for the motor or are you buying bolts off the shelf as a head bolt is a higher grade

 

[diamondback21]

Re: Head bolt keeps breaking

It's the bolts for that motor. The bolts break before getting to the required torque. I tighten ALL of the bolts to around 200 in lbs then set the wrench to 216 and go around again and that middle/right bolt never clicks the wrench. It just turns and breaks.

 

[Silvertip]

Re: Head bolt keeps breaking

I repeat. Check bolt hole depth and run a bottoming tap then blow out the hole with air. That bolt is apparently bottoming or binding and breaking at a torque somewhere between 200 and 216.

 

[gordwa]

Re: Head bolt keeps breaking

streched bolts...might have been overtightend once before ????? make sure you antiseze them when reinstalling