Exhaust stud removal gone awry...a little advice, please

[Konish]

Fellas,

In the quest to mount my Weber triples, I decided to deal with a broken exhaust stud (first one on cyl 1 closest to the thermostat housing).

The drilling was going pretty well but in the end I think it got cocked a bit.

 

As a result I think I may have clipped the actual head with my drill bit as a result. First clue was the different color metal chips that started coming out of the hole during the drilling operation (and the fact they don't stick to the magnet).

 

I'm pretty sure the hole is the correct depth as I compared the depth with the other exhaust stud holes.

 

Long story short, I was able to tap another set of threads in the head...albeit the stud isn't exactly parallel with the rest of the exhaust studs (sigh) and I have no idea how much of the original stud is left.

 

The bright side is that I can snug down the header flange to the head but the bolt head doesn't not sit flush all the way onto the flange.

 

Other than the risk of breaking that stud off again due to the asymmetric load on the bolt head, if the header can be snugged up properly, anything else I need to stress out about?? If I drilled it too deeply, what would I have screwed up? It looked awful close to water passage or timing chain housing just from what was bolted up to the head in that vicinity.

 

I need this to hold until such time I can pull the whole head and have it fixed properly...in about 3-4 years when I leave Japan. I guess if it becomes a regular problem, I'll have to deal with it sooner...here's to crossing my fingers

 

R/

Dustin

[Geking]

I assume this is a Datsun L series motor. The 1 and 6 studs do commonly break, I have even heard of people drilling them out to a bigger stud size and helicoling the hole. I don't think your fix will cause a problem. It is more likely to break due to the uneven stresses, but you did not mention any coolant leaking out so you did not penatrate into a water passage way or anything of the like. Heck, have a friend that is driving his 280z without a number 6 stud, has been doing that for 2.5 years, not that I would reccomed that though.

In short, from what you explained, you should be fine. I tend to use an easyout (the bigger screw type, not the reverse drill bit type.) instead of drilling out the hole to try and save the origional tap.