[Shotimes] Cancer with a twist

[Leigh Smith]

Mark;
One comment and one suggestion:
PLEASE READ BEFORE YOU START!!!
YOU CAN PERMANENTLY RUIN THE CRANK IF YOU ARE NOT VERY CAREFUL!!

>  Had a heck of a time breaking the crank bolt
> free.   Turns out the bolt
> sheared itself at the beginning of the threads. 

> The key had sheared directly
> between the pulley and timing sprocket.  The part under the dampener had
> about 1/3 of it's width worn away.  Did I mention that I could turn the
> dampener through ~1/4" without moving the crankshaft?


Possible scenario: Bolt was torqued too tight at some point, causing a 
stress fracture. This gave less holding torque on balancer, which caused 
wobble, etc... To confirm: look closely at crack in bolt and see if it 
looks like half of it is older and somewhat more oxidized.

I've had this happen on SS manifold studs frequently. They stress 
fracture real easy from the heat but torque can do it too.


> To do this I've decided on drilling out the bolt and
> re-tapping the hole.  With any luck I won't mess anything up... wish me
> luck!  I've decided against messing with easy-outs, since the risk of
> breaking it is just too great.



AGREED. Much safer in the long run. If you break off an easy out in 
there you may never get it out, and could ruin the crank. If you drill 
it crooked, you could ruin the crank. There is only one safe way to save 
the crank.

Use the best drill bits you can find, like zirconium coated (i think). 
Buy a whole set. Go slowly. MAKE SURE you have the first hole EXACTLY 
CENTERED. Use a centerpunch for this. Measure it three times before you 
punch it. Use a dremel tool to grind a flat spot if needed. It MUST be 
centered. You only get one chance. Start with the smallest drill bit. 
Figure out a way to measure the drill so it is PERPENDICULAR. Go up only 
ONE drill size at a time. Only use as a largest drill bit one that is 
the same or slightly smaller than the diameter at the bottom of the 
thread "valleys".

Then use a coreect size tap to clean out the hole. You might even be 
able to pick out some of the pieces with a machinists pick.

IF you centered it good, you should do almost no or minor damage to the 
original crank threads.

If you do thread damage, go up a bolt size, don't skimp. That is a lot 
of torque!!!

If you have any doubts, get a machinist to do the repair, not your 
typical mechanic!!! It's the worth your money to save the crank.

GOOD LUCK

Leigh
(5 years in a race engine machine shop)