Crankshaft pulley bolt broken

Hopefully this goes well and you can re-thread it after you clean it out a bit. Take your time and make sure your pilot hole is legit so your larger drill bit doesn't slip.

 

The method that has worked for me for many years is to make a cavity into the end of the broken with a Dermel tool with a carbide cutter and then drill it with a HSS cobalt drill bit with lots of tapping libricant. After that, it can be removed with a screw extractor.

 

Very unfortunate as this is one of the worst places for a broken bolt. Many people are straggling to remove perfectly fine crankshaft pulley bolts so I am afraid that the remaining bolt is so tight that a drill and a bolt extractor will not work easily.

I know most in this forum we are determined to work on out Prius DIY but maybe this is a specific case where an experienced mechanic that does similar staff daily might have a better chance of extracting it. Extracting this bolt is now becoming more art than straight forward procedure. Just an idea.

 

The method that I prescribe has been used in the aircraft industry for many years and generally wotks very well, since the cobalt bit will easily drill out the ISO 10.9 J.I.S. bolt that holds on the crank pulley.

The last resort is to drill the bolt out to the root diameter of the threads, If done carefully, the threads can be peeled of the treads of the hole and chased with a rethreading tool.

 

Understanding how a bolt works, with NO head on the bolt, there should be no tension on the remaining portion of the threads that are inside the crankshaft.

If the broken portion of the bolt is bottomed out in the threaded hole, then there may be pressure on the threads, making it hard to turn.

As long as the threads are clean, and the broken portion isn't bottomed out in the hole, there should be no significant sources of resistance to it turning. Damaged threads, corrosion, lock-tite, etc will change that.

Being broken 3/4" down inside will make dremel work difficult, but a drill should be ok, especially if you have a sleeve or something similar you can insert into the threaded hole to help keep the drill bit from going off center. Think of something similar to drilling a slightly oversize hole down the center of the broken piece of bolt that has the bolt head. Then insert that into the crank and use it as a guide for your bit to drill into the piece remaining in the crank.

Even easier if you have reverse twist bits.

These situations are often a one-shot deal, so it's fairly important to do it right the first time. After that, it gets really messy

 

One of my most essential tools is a Master re-threading kit a purchased nearly 20 years ago at Sears in the Craftsman brand. The taps actually reform the threads instead of recutting them. In the case of bolts like that on the crank pulley, I first hand threaded them to check for smoothness. If not, I chase them with a rethreading tap first,

 

Remove a sparkplug and push a bunch of 1/4" (or so) nylon rope (or similar soft rope) down into the cylinder. Keep the loose end of rope sticking out. When the crank rotates, it will compress the rope and then lock down.
When done, just rotate crank opposite way to release pressure on the rope and pull it out.

 

What will happen if you fit a long breaker bar on the bolt extractor, somehow use some leverage to make sure it doesn’t move and allow the hybrid engine to crank for half a second?

 

You need to make or buy a crankshaft pulley holding tool.

I've done it before with a 12x5 inch piece of 1/2 inch thick plywood. On one end, with a hole saw, cut a 1-1/2 inch hole for the crankshaft bolt and two 3/8' holes to match the spacing of the two M8x1.25 threaded holes on the crank pulley. Thread two M8x1.25 bolts into these holes and mount the assembly onto the crankshaft. This will keeep the crank from moving as you remove the broken bolt.

It will also help when replacing the assembly with the new bolt.

 

Wow, that's some impressive old timer technique right there!

 

I've tried this in my younger days with a standard starter motor ice, and would be scared to death to try it with a Prius.

As for what would happen? Worst case? Broken extractor, broken breaker bar, broken engine components, broken bones, breaker bar through an eyeball, who knows. I just see devastation, since I see no way to control how long it would spin the engine, lol.

If anyone ever has the gonads to try it, please set up a few go-pros. I bet the slow motion would be awesome!!

 

Now, I use this tool with two M8x1.25 bolts.

OTC 6613 Variable Pin Spanner Wrench

 

Yes they also make a tool that fits in the spark plug hole that has a bolt in it you turn down you put the crank you put the Piston top up against that the bolt has a flat on it so it doesn't stick a hole in the top of the Piston crown I think it's called positive stop

 

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