Sheared off supercharger pulley bolts on whipple
 

I recently installed a 2.3 whipple blower (ford racing kit) on my 2013 coyote. I was shredding belts and eventually figured out I had to space out the blower pulley. I successfully spaced the pulley with some homemade spacers (drilled bolt holes in some zinc washers to fit inside pulley lip area) and it fixed the ripping issue. I had to shim it so much that the lip on the pulley didn't overlap onto the snout anymore. Am I able to space it this much without breaking something? I started thinking that the pulley overlap may absorb/share some of the shear force on the bolts.

Anyway, I drove it for a few days and put about 200km on it driving it hard.... no issues... but out of nowhere cruising @30mph my pulley flew off and all four bolts sheared off inside the snout. I used longer 12.9 grade bolts (non stainless). The blower did not lock up I can still spin it freely with my hand. What I came up with:

1. Overtorqued or under torqued bolts.
2. One of the spacers shifted at some point causing bolts to loosen then shear.
3. Spaced so much that all shear force was put on the four bolts instead of sharing load with the overlapped section of pulley on the hub of blower.

Any help would be great. What's the strongest bolt you can buy? A 12.9 grade but can you buy a stronger metal? After I get these sheared bolts out I don't want to run the same washer set up and have it happen all over again. Also, any advice on how to get these sheared off bolts out? Research tells me a carbide tipped drill bit then a bolt extractor?

Thanks!!

no no no....figure out why you need to space the pulley so far out and fix that. By spacing like you describe you add an enormous shearing load to the bolt shank without having the bolt placed so it can take it. There is no bolt made that can take this. The pulley needs to sit flush on the snout with the stud protruding in the centre bore of the pulley.

If you absolutely cannot do this without a spacer, have a solid one cut and drilled.

the remains of the bolts should unwind fairly easily the load is off. Good luck drilling a 12.9, it's harder than your drill bit OR bolt extractor and if you bust off one of those in the remains of the bolt, you're in a world of hurt.

That lip must somehow sit on the hub. I'm glad that's finally settled, thank you.

Haha if I bust off a bit in there I'll never mod a car again

Don't be that upset about it, everyone starts somewhere and mistakes are made by pros every day!

This is a chincy trick, but if those bolts are going into aluminum, you may try to remove it. It's a serious cobbled together abortion. I've tried this same thing, just not in a vehicle...I just did it with some scrap, way back in a class I took years ago. It's slow, but you won't have to worry about dealing with center punching, step drilling and all that good stuff.

There are ways of getting that stuff out; no need to give up because of a hiccup! Worst case, if you don't want to deal with removing those sheared bolts, you can remove the part and take it to a machine shop for, in my experience, a very reasonable fee.