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.

There is more than one way to skin a cat. I know the cause is still there but it fixes the problem so is that not good enough.
I guess a harmonic balancer and dowling would be the way to go but I'm beginning to think I should have went the cheaper CA18 way.
Olboy

The problem revolves around the fact that the holes in the flywheel are 'clearance' holes & the flywheel is prevented from moving through sheer brute force & ignorance. This is just fine in a stocker that rarely sees 5.000 rpm.

However,...... it would seem that at very high engine speeds, harmonic forces in the crankshaft can be great enough to cause the flywheel to move under the heads of the bolts. Basicly, it moves around the crank just a tiny little bit, within the constraints of the amount of clearance in the bolt holes. It doesn't take much of this to fret wherever the flywheel touches something, like the crank itself, as well as under the heads of the bolts. This quickly reduces the tension, or clamping force of the bolts & allows even more movement. If left to its own devices, the holes elongate, allowing the flywheel a good runup at the bolts untill they eventually shear off.

Using tightly fitting dowls removes the job of preventing flywheel rotation [around the crank] from these bolts in clearance holes.

It's a bit like birds & airplanes. Birds use wings for motive force as well as flight. Airplanes separate these functions & use wings for flight & engines for propulsion.
Dowels do the same job of separating tasks.
The bolts hold the flywheel on, while the dowels prevent any movement.

This method works, & works well, however it addresses the SYMPTOMS, & not the CAUSE. The harmonic balancer addresses the cause.

they break if you try to drive with it lose but this time I stopped it early enough and no damage was done. The biggest problem is that I'm flat changing and when you change up at 7500 rpm get nuetral and your foot is still on the floor who knows what revs it does
Olboy

Interesting thread.... I'm going to make sure I don't miss a gear!

When these flywheels come loose, do they shear all the bolts or do the bolts just loosen? Because if they are shearing, I can't see loctite helping. Also if you use loctite you can't use oil on the threads, and if the torque settings are given with oil as the lube, if you do they up with loctite you won't get the same tension in the bolt for a given torque setting. Overtightening is playing fire because you could reach the yield strength of the bolt- then you're in the ####e for sure.

Having the two fitted bolts like R-fast said sounds like a good idea, but I think if the bolts are shearing, extra dowels would be even better as they are sharing the shear load out a bit more, reducing the load on each bolt.

My flywheel is dowled in 2 places with 5-6mm dowles. As i said before I have never had any problems

b310gx,
a little misunderstanding here - I still use 6 bolts. 4 off have clearance holes at the flywheel like normal, but two (180deg apart) have holes with no tolerance so they locate the flywheel AND clamp along with the other four. Only reason I didn't dowell is the serious lack of room on the crank A larger face and therefore greater PCD for flywheel bolts would be a big improvement. Lets not forget though, when these motors were designed they were not really imagining 8 - 10000 rpm . Amazing little motors when you thing about the abuse we give them
Cheers

I will be using three dowels 120 degrees apart.




Benny

So just how big should the dowels be and how many should I use I thought I would just drill one or two 5mm holes between two bolts, maybe the bolt heads would even cover the dowel and keep it in.
olboy

ross balancers at blacktown here in sydney quoted be approximately $500 for a custom harmonic balancer to suit an a series.just one question,has your crank been knife-edged?this could be the cause of the original problem,but the end of the crank was probably damaged &
will keep throwing flywheels.have you tried other cranks in the engine?i also have never dropped a flywheel,with no harmonic balancer,
but i have a full weight crank.maybe someone can lend you a crank to see if it cures the problem.if i were going to dowel the crank,i'd try & get 6 small dowels & get the crank & flywheel drilled to suit.leaving two flywheel bolts out so you can add two dowels seems like a backwards step.