Thread: Broken Bolt in Cylinder Head. Ouch!

Did a post recently on rocker shaft bolts/studs, factory torque specs are ok with NEW bolts/studs and NEW threads but not with bolts/studs and threads that may have been removed and replaced 1/2 a dozen times. Just do them up till they are tight and a mickey hair more, torquing up old bolts/studs to factory specs. is asking for trouble, regards Frank

Originally Posted by Tank

Did a post recently on rocker shaft bolts/studs, factory torque specs are ok with NEW bolts/studs and NEW threads but not with bolts/studs and threads that may have been removed and replaced 1/2 a dozen times. Just do them up till they are tight and a mickey hair more, torquing up old bolts/studs to factory specs. is asking for trouble, regards Frank

Yeah I'm starting to wonder about the value of some of these torque settings outlined in the WM. I JUST BROKE ANOTHER BLOODY BIT ON MY CYLINDER HEAD!! Grrr

This time it was 25Nm on the injector clamp nut - sheered the stud clean off! The first clamp clicked the torque wrench and felt good, second clamp just cracked it on a couple of turns.

I'm having serious doubts about my torque wrench now. After number 2 snapped I moved it back to injector one and it clicked as expected so maybe I'm just having bad luck with worn out studs/bolts. If my wrench is over tightening it can’t be by that much. I’m relieved I didn’t have any issues with the head bolts… probably thanks to the majority of the sequence being tightened by angles.

When the stud snapped off I almost had a heart attack because I was convinced it was a cast stud, part of the head... I can’t tell you how relieved I was to find that they are in fact fancy looking screw in studs that are replaceable!! I can just take one from my old CH.

So no more torque wrenching for me.. I’m doing feels good tight from here on in and sending the wretched wrench off for a calibration certificate.

Broken Bolt Extracted!

I phoned the 'Thread Doctor' and explained the issue over the phone - he recommended hammering in a flat head screw driver with a V cut into it.

First try didnt work because I misunderstood and made a pointed V and hammered that, which would have only worked if the bolt was very soft and allowed the full arrow to penetrate. Not likely!

Second try I got a two prong bit (snake-eye) from my screw driver bit set and used a grinder to sharpen the two prongs. You could use a standard flat head and cut a V into it. The bit needs to be small enough to fit comfortably in the middle of the bolt without being too close to the edges.

I put the bit into my cheap plasticy ratchet screw driver and hammered it into the bolt with a couple of sharp blows whilst pushing down with my holding hand... kept the downward pressure on whilst very slowly turning the thread and out it came! Very little resistance - the two prongs only need to penetrate the top of the bolt slightly to get enough grip.

So there you go, if you break a bolt by over torque in cases like this you dont need any special tools or expertise!

Cost = nothing - releif!