The problem is as Chris stated, that the standard bolts have side clearance and rely on the bolt stretch to clamp the flywheel to the crank. The clamp friction between the crank and flywheel provides the drive.

In a competition engine rotational loads are a higher order than standard engines, load direction is constantly reversed (especially during down shifting or during incorrect gear selection -buzzing).
The standard flywheel bolt clamping force can not provide sufficient friction between crank and flywheel in this circumstance, so the flywheel starts to move. The bolts limit travel movement while they are being bent around the holes in the crank. The problem gets progressively worse until the flywheel is moving so much the bolts can no longer take the side loadings on them. Eventually they fail through a combination of shear and bending forces.

To fix the problem first clean the flywheel mounting face ensuring it is flat. Re-thread the crank bolt holes to fit larger ARP flywheel bolts. Thoroughly clean the holes and blow any particles out. Larger bolts increase the clamp load and also the friction required to make the crank move.

Secondly, fit three X 4mm diameter dowels at 120 degree intervals to totally remove shear loads from the bolts and who's shear force is added to the clamp force before any flywheel movement can take place.

Zero balance the crank, crank pulley, flywheel and pressure plate individually. Then balance the components as an assembly and you will not have a problem.

I always clean all components with parts cleaner wash then thinners in a spray gun.. Parts are then placed in a metho bath till removal and air dried with a compresssed air nozzle. This primes the part for best quality bonding of loctite

Use 601 loctite on the bolt threads and no lube. Torque to bolt makers specifications in one step.

Thanks mate I was heading along those lines anyway. What size bolts do you think I should use. the last time I used 10mm arp flywheel bolts ( suit a 4AGE )and some of the washer heads almost touched. I guess if I went bigger I could just grind them down till they fitted.
Thanks Olboy

3/8 Arp bolts are fine.

Um..... my factory bolts are 10x1.25
If I was to use 3/8 bolts these would actually be smaller than what I have now

I'm going to stick with my metrics I think

Ok looks like this is what we are going to do ( I think ). Its a bit risky going to a bigger bolt as the side of the bolts are only about 2mm from the edge of the cranksharft now so a bigger bolt may be a bit close. looks like we are going to make a sleeve to fit tight over the bolts and a neat fit in the flywheel holes. Aswell we are going to use 3 dowels. Thats the latest anyway. The other solution is to change my driving habits.
Olboy

This is the crank in my A14
For some reason i thought it had 2 dowles
I had to do a rearmain seal so i thought i would take a photo to show you. But you have probably fixed it now
Sorry about the photo its abit blurey but you can see what i mean

I taped the holes to 7/16 unf which has the same turns per inch as the late cranks

then i ran unf cap screws high tensile

I also ran the tread heaps deeper an extra 10mm

then I lock tighted them in with super stud lock and did them up with the rattle gun

I knew I wasnt going to break them

has worked a treat and that engine sees 8000 on the track

Here's what I've done. We worked out that the holes have almost 1mm clearence so we made some sleaves to fit tight in the holes and a neat fit on the arp bolts. Then we used 3 3/16 dowels. we used locktite on the threads and the dowels. havent used the car yet so I'll have to wait and see but its only insurance anyway. I have to learn how to change gear. Thanks for everyones interest and help.
Olboy

A question for dowlers, Isn't the crankshaft as hard as hell? How do you drill it?
I opened up the oil galleries in my crank as per the nissan rally prep specs, and it was farkin hard.
Plain hss drills wouldn't even get a look in. I used three carbide tip drills by the time I was finished

I expected it to be hard but it was no problem. Just like mild steel. Maybe the jurnals are hardened.