zz4 missing bolt hole in pass. head for serp sys.

[70zz4]

any advice on drilling new hole in head ,for proper loacation &trueness

[B. W.]

Use the accessory bracket as a guide.

[70zz4]

yes my thought also ,however iam concerned about holding true 90 degrees from the head , maybey iam just over thinking it.

[B. W.]

Spot drill the hole using the bracket. Remove the bracket & use a 90° jig to drill a pilot hole. You can buy a commercially made one (they don't cost a lot) or make one from a block of wood. use a drill press to drill the hole through the block so it is at a perfect 90°. Once the pilot hole is drilled square you can drill up to tap size by hand. (you could just drill the final tap size to start with & be done with it, I feel more comfortable drilling a pilot hole first.)

[chevy_mike]

I did this. Used the bracket to lay out the spacing.

[weq92f]

What about the depth? Surely have to be careful there eh?

-klb

[jjzepplin]

Done this twice. No bigge. Even if you drill too far you can use a stud and some RTV. Your water pump bolst go thru the block don't they. I used a stop on my bit but it slipped... HIt the water jacket and just RTV'd it and has never leaked yet. Happened on both engines as the castings for the head can be different. I used the bracket as the guide and a long bit.

[70zz4]

ok thanks for the info, & to any others who chimed in. hoefully have time this weekend.

[95 S_Trucker]

If you do drill into the water jacket, I would use thread sealant insted of RTV(Permatex 59235). It will make it easier if you need to remove the accessorie bolts. It wont leave dried chunks or RTV in your engine.