darkesp

Hi all - I am the recent buyer of an '86 951 and am trying to bring it back to life - I wouldn't have gotten far at all without this forum, so thanks to all for your contributions.

I have a unique twist on a common problem. I'm in the middle of a water pump job, and found a nasty surprise left by the PO - the lower left pump bolt was broken off, and they had not bothered to repair it, just had put the pump back on with one less bolt. It seemed to seal ok, no leaks when I bought the car, but obviously I want to make it right. I went out and got some left hand drill bits, M6 helicoils, and even a right angle drill to follow in the footsteps of many others before me. Had to pull the radiator fans to get even the right angle drill in (which required removal of the lower rad hose and the oil cooler bracket - this car is so cool, but it sure does baffle me sometimes...)

Here's the tricky part. The bolt broke with a jagged edge right underneath the edge of the hole, and I can't figure out how to get a bit centered in the hole before I go deeper. Any small pilot bit just wants to walk to the edge and bite into the softer surrounding aluminum. A center punch is mostly the same, it wants to slide off center and I don't really have room to give it a solid whack anyway. I even cleared some debris from the hole edges and tried starting with the full diameter 1/4" bit for the helicoil, in the hopes that it would use the surrounding material to guide it in, but that doesn't seem perfect either and I don't want to back myself into a corner.

So... for you folks that have done this before, is there any "best" method for getting a centered hole? Buy/make a drill bushing that uses my old waterpump as a guide? Use a grinding bit on a dremel or something that can take a side load and smooth out the remains of the bolt before trying to drill on center? Call a professional?

A tiny part of me is even worried that there's a broken screw extractor in there, which is why it never got replaced. I can't see well enough in the hole to get a lot of info. Is there a way to tell? Should I be shopping for small block crate motors? I'm committed to seeing this thing through but this has been a long and frustrating job. Any advice would be really appreciated!

PorscheDoc

First i would probably take an air grinder bit and see if you can grind the old bolt down more evenly in the hole using the tip of a good metal grinding bit. If that didn't work, I would probably bolt the old waterpump back on, then use that hole as a guide and use a bit slightly smaller than the 6m hole to try and cut the jagged edge down until it has a good flat surface. There are a million ways to skin a cat, broken bolts are sometimes trial and errror. Obviously when you helicoil (or preferably time sert) it, you will drill a larger hole anyway, so you do have a little room for error, just take it slow.

V2Rocket

using the old waterpump as a drill guide is a good idea.

MAGK944

Tom M'Guinn

Don't take it to a "professional" -- or at least not the one I used. I got it back with a big ugly weld-blob where they damaged the block getting it out.

You need to make a drill jig of some kind. An old water pump is better than nothing, but the holes in the bump are actually bigger than you want and will allow the bit to center itself. Get a piece of metal, and drill a hole the exact diameter of the bit you'll be using (and I'd start small like 1/8"), then drill larger holes (maybe 3/8") to line up with the closest pump mounting holes. The larger holes give you wiggle room so you can bolt the jig to the block as needed to line up the smaller guide hole exactly over the center of your broken bolt. I'd remove the radiator (sorry) to give yourself a clear view and room to work. I'd also use standard heli-coils personally (if needed) so that you are removing the least amount of material possible. A heli-coil will hold all the torque ever needed there, be stronger than the original threads, and should last forever.

Tom M'Guinn

Extractors are the worst -- at least the kind you reverse drill into the bolt. They just snap off 99% of the time and make it significantly harder to get the bolt out.

p.s., despite my jig suggestion, I once helped Crazy Eddy drill out a broken water pump stud by hand just as you describe. He had the radiator out, and made a little support to steady/support his hand. He started with a tiny drill bit -- like maybe 1/16" -- in case it went off center, but to his credit he nailed it and was then able to keep stepping up the drill bit size. If memory serves we also but a collar or tape on the bit to avoid going to deep! Pretty sure his never "came out" and we ended up heli-coiling it...

tinkerbill

I have a rasp i use for ceramic tile that is about 3/16" in diameter and about 1-1/2" long that is diamond coated including the tip(home depot). I have then carefully etched the center of the bolt to make a half ***'ed center punch style divot. Then, using a cobalt drill I tried to drill down the center of the broken bolt with as large a drill as possible before using a ez out to back out the broken piece of the bolt. I also have one of those little butane torches you use for cream brulle(sp) to heat down the drilled hole if necessary to break free any loctite that may have been used. If there is part of a hardened HSS extractor broken in there that will be a different issue in which case you may try tapping the broken extractor with a center punch a few times to break it loose. They only usually grab in one direction, Again with a dremel tool or something similar I have also used an abrasive cutoff wheel (1" dia or less?) to cut a groove across the bolt and then use a flat blade screwdriver to back it out, You will probably also cut into the material around the bolt if that is a show stopper.
good luck
Bill

944crazy

There's another option...I've never tried it myself, but it looks quite interesting.

snb13

Try a spring loaded center punch.

steven74

audisport

darkesp

Wow, thanks everyone - I didn't have notifications setup properly and had only seen PorscheDoc's post until I checked this evening. These are all awesome responses.

I have success to report! I actually bought drill bushings from McMaster to make a template using the old pump - was planning on punching the hole locations into aluminum plate so I could press a proper bushing into it. However, before they arrived, I wanted to see if there was anything else I could do. The die grinder approach made a lot of sense, so I replicated it with my Dremel and kept attacking it - first with a burr bit, and then with a stone grinding bit, which was actually more effective (may have been due to some poor quality tool steel, not sure). I was able to flatten the surface a bit, then tried a punch again and was able to push the broken object further into the hole. It was still stuck, but that gave me enough room to drill the hole to a larger diameter (since I would do so for the helicoil anyway), and with the extra room it freed up. I was finally able to run a left hand drill bit and drag the fragments out. It had broken into some smaller pieces at that point, but based on what I saw at various stages, I'm pretty convinced it was a broken drill bit. Thanks, lazy PO. Some pictures for posterity:


What I uncovered after initial drilling - this is where I had to regroup since any further attempts were just walking the hole sideways.


Finished repair with helicoil inserted. I think timeserts are a good option, but I had these on hand and had found enough people saying that they work adequately to be comfortable with putting in the helicoil. It also leaves room for one more "adventure" if, god forbid, it ever needs to be drilled again.

Anyway, I'm a happy man and now have a hole with fresh threads and some new experience in my arsenal. Now onto getting it buttoned up and running once more. Thanks again!

Tom M'Guinn

Awesome work, congrats! Better than new (literally)!

Is it my imagination, or is there an insert in the hole to the right too?

I'd suggest a nylon brush and a bottle of simple green to clean up the oily stuff...

audisport

Nice job. Yeah, looks like there's an insert there already. And if he's saying he drilled out a broken bit, that seems about right.

gruhsy

Nice work, glad to hear it worked out.

Not sure what process you used to clean out the hole but at work we have refillable plastic spray bottles with your typical adjustable spray nozzle. I use Isopropyl alcohol, Naptha or degreasers with water to clean out thread holes all the time. This is when installing new hardware or inserts or painting parts. It works very well and I have found when it comes to painting it does a better job than compressed air alone. Hundreds of threads on the stuff I work on....it's just become habit with any of this type of thing. It always surprises me just when you think threads are cleaned out.....spray in more liquid and out comes more crud.