Cylinder head - broken flange bolts

[loxley007]

Hi all, i am tearing down a 1979 CB750 (RC01) engine and the person I bought it from has secured all bolts with something fairly strong. This has resulted in 4 broken flange bolts when I was removing the camshaft cap holder bolts in the cylinder head

I’ve removed one of them but messed up the second and drilled into the threaded insert in the cylinder head when trying to remove it with a bolt extractor.

My question is whether and how I can recover this? Is it possible to drill out the threaded insert and replace it or have I junked the whole head?

Photos below for reference - shows one of the stuck bolts.

All help greatly appreciated.

 

[loxley007]

Bumping this just in case anyone has any insights??

 

[SenseAmidMadness]

The factory didn't use inserts for those bolts and just tapped M6 threads into the aluminum casting. Are you seeing steel thread inserts in this head?

Also, can you point out which particular bolt you're worried about in those pictures? It looks like quite a few are broken.

It sounds like whoever put those in previously used a threadlocking compound...would've been nice to know that beforehand as heat and acetone both solve that problem rather easily.
These bolts are NOT supposed to have threadlocker when installed. In fact, the factory torque specification is considered a bit too high and often results in stripped threads or broken bolts. I've had the factory bolts snap both during head installation and removal when torqued to the factory spec.

Some folks go one step further and drill out all the factory bolt threads preemptively, and replace them all with coiled steel thread inserts. Those threads end up stronger than the original aluminum and the risk is lower.

Whoever put those bolts in there in such a way that they won't come out might be the one who junked that head.

 

[loxley007]

Thanks, that is super helpful. I’ll have a look tonight when I get home. Cheers.

 

[Chrisraven]

I would agree that when you initially had a problem with the bolts coming free you should have stopped before breaking the bolt. One thing that has worked wonders for me is a infared heater coil, you can buy them Canadian Tire, Harbour Freight. It is a coil that you put on the bolt head and it breaks the rust completely free. I have used this tool on a multitude of frozen, rusted and red antilock compound and it has never let me down. Now that you have broken them of iff you were to drill a hole for a easyout, and before cranking on it use the infared heater to break the rust it should just come out no sweat. Once out I think I would agree and drill out the original and use a helicoil steel insert to replace the thread and upgrade to bolt to a grade 8 or 10. Should have no problems in the future.

 

[loxley007]

I would agree that when you initially had a problem with the bolts coming free you should have stopped before breaking the bolt. One thing that has worked wonders for me is a infared heater coil, you can buy them Canadian Tire, Harbour Freight. It is a coil that you put on the bolt head and it breaks the rust completely free. I have used this tool on a multitude of frozen, rusted and red antilock compound and it has never let me down. Now that you have broken them of iff you were to drill a hole for a easyout, and before cranking on it use the infared heater to break the rust it should just come out no sweat. Once out I think I would agree and drill out the original and use a helicoil steel insert to replace the thread and upgrade to bolt to a grade 8 or 10. Should have no problems in the future.

Cheers for advice. I’ll have a look for that item.