Rear Shock Bolt Sheered off -- Advice needed.

[drwhosc]

I was driving pretty hard yesterday, and my left rear shock bolt sheered off. I was able to remove the shock and continue to drive, and made it home without any obvious issues. Now I am left with the task of repairing the bolt. I did the measurements, and about an inch of the bolt remains in the training arm.

I have a 71E and I replaced the training larks with Aluminum ones. I did not do the mods to correct the geometry on my 71, but I am not getting the hitting problems on the heat exchangers. Obviously I am getting some excess force, enough to sheer the bolt.

So the advice is Do I just drill out, and re-tap (M14 1.5), or do I need to use a hell coil kit? Also the best I can tell, I can get away with a 0.5in drill as the tap chart is calling for a 0.4999 drill

[Frank Beck]

Obviously I am getting some excess force, enough to sheer the bolt.

So the advice is Do I just drill out, and re-tap (M14 1.5), or do I need to use a hell coil kit? Also the best I can tell, I can get away with a 0.5in drill as the tap chart is calling for a 0.4999 drill

No "excess force" here. You just had a rusty or loose bolt.

Step drill up to 1/2" making sure your hole is completely centered. Gotta be Dead Eye Dick.

Too soon to worry about a Heli-Coil. Hopefully the remainder of the broken bolt comes out. Use left hand drill bits if possible.



BTW: .4999"? That was a joke, right?

[drwhosc]

Thanks on the advice of a left hand drill bit, that is good advice. I know I have to be dead center, not sure how to do that just yet, I would like to make or use some type of guide, but I do not want to remove the arm...

[Frank Beck]

First the .4999, now nonsense about a guide for center punching?

You have to be an engineer.


Like my Vo-Tech welding instructor Mr. Nolan used to bark:

"Eyeball it!"

[Olivier]

Engineer's advice:

Use someting harder than your screw to mark it (obviou...)
Use a sharp punch to make a Frank mark on it. Dont be shy, make a real mark on it.
When you'll start to drill use a small bit, but not too small, if you break it in, its going to be a whole less fun story I d say 5mm. And turn slow on the first, untill you bit correctly in.
Than, make several steps.
If it doesn t want to unscrew you can hit it a bit more, as it loosen a bit seized screws. Use plenty of wd40. Ask Frank about the benefits of a good quality lubrication (you should visit the off-topic section for more "insight" about it)
If it really doesnt want to unscrew, than try to screw in a bit.

Once its done and when you replace your bolt, use the right grade, right washers and torque it correctly.
Frank is all right, it must have been a crap screw or a loose one.
How is the rupture face looking? Shiny? Or blurry?

Good luck!

[boxster03]

A new bolt ?

[Frank Beck]

ooooooh...

You're not an engineer; you're a doctor?

And you own a 928.

That helps explain some things.


Just curious: If you need a guide to center punch accurately what are you going to use as a guide to prevent you from striking your hand with the hammer?

[Olivier]

A new bolt ?

Sorry! I am french and I sometimes make mistakes. The actual technical term should probably be "an effing german quality new expensive screw"

If you don't buy it from yr porsche dealer, and if you still have it, there should be some markings on its head, like 8.8 or 10.9 or even 12.9 souse the same, and torque it accordingly.

Oliviet

[304065]

Shock Mount Bolts- M14 x 1.5 x 80 (900 082 054 02)

[drwhosc]

Thanks for the replies. The face was shiny, and very straight. I was able to get the bolts from Jim Ellis porsche. My local dealer was kind of scary when I told him it was from a 70s car. Unfortunately I can use the PET better then they can.

To drill the hole, I went by loses and bought a 1/2 inch nylon spaced that was about an inch long. I wrapped some tape around the outside, and hit it in the hole so it was tight. Then I was able to use a 3/16 drill bit, and the hole was nicely centered using that guide. (so yes I am 928 owning doctor, but I play an engineer on TV).

I then tried to use a larger left handed bit with an extractor. that did not work at all. the bit barely cut into the bolt. I had the drill on the reverse setting, but it just did not make any progress. I think my chuck kept losing up.

After my arm was dead, I switched out to the 1/2 inch drill bit, and was able to get to the bottom of the hole, and remove the bolt. I then tapped it with new threads. Seems Ok, but Have not gotten my bolt yet. I also discovered that my tap was fluted, so I ordered a bottoming tap to try to get the threads to get a bit more deeper.

So seems to have worked, but I go a helicoil kit just incase.