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broke off the flywheel.
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Broke off two flywheels in 4 days. 1st one was with standard bolts. 2nd was with ARP bolts and steel dowel.

Both happened while launching at 5500rpm revving to 8000rpm every change to third where disaster happens.

Cars runs 4.8:1 diff, sticky 195/50/15 tyres. Its an A15, ported head, twin webers, electromotive 300 degree 12.3 camshaft.

Flywheels were supposedly balanced,lightened cast items.

What am I doing wrong?

Posted on: 2016/8/27 22:53
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Re: broke off the flywheel.
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A-series flywheels don't need balancing because they are round and symmetrical to begin with -- unlike some engines that are "externally balanced" with a specially weighted flywheel and/or crank pulley

Did the flywheel bolts get loose or did the flywheel bolt heads break off?

Posted on: 2016/8/28 4:31
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Re: broke off the flywheel.
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Here's a quick video showing how to install the flywheel bolts on an A12 with a semi-precious aluminum alloy flywheel. Note the "torque the bolts down first to seat the flywheel, then remove the bolts, THEN install the threadlocker inside the crank threads, then reinstall and re-torque the flywheel bolts" procedure.
https://www.youtube.com/watch?v=Yxv9xeBB0L0
Hope this helps!

Posted on: 2016/8/28 5:03
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Re: broke off the flywheel.
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Great point about the flywheel preparation (don't get any liquid or oil between the flywheel and crank)

If using a single flywheel dowel, it will make the flywheel unbalanced (maybe that's why they had to balance it?) Normally two or three dowels are use evenly spaced on the flange so they the balance each other

Here is some information we've compiled over the years:
Quote:
Nissan flywheel bolts are very strong. Just clean the threads and use a torque wrench to install. ARP does not make A-series flywheel bolts (though some use non-A-series ARP bolts on the A-series). In any case the stock bolts are plenty strong.

Best practices:
* Reusing the flywheel bolts is acceptable. Even new bolts will come loose due to shaking. Even ARP bolts will snap!
* To reduce vibrations, always re-balance the engine after changing rods or pistons or crank
* For 7000+ rpm use have the flywheel doweled. Loctite is not needed.
* Do not get the flywheel bolt "good and tight", as overtightening weakens them. Always use a torque wrench.
* Use stock Datsun flywheel bolts. If using aftermarket bolt, ensure they are 1) not too long and bottoming out 2) ensure the head face shoulder design is compatible 3) Use high strength steel like the factory bolts

If using high RPM, look at getting the crank flange dowelled. The flywheel is actually clamped on the head of the bolt not on the shank of the bolt (there is side-to-side play), so three dowels 120 apart should do the job. The end of the crank is soft unlike the journals and easy to drill.

Posted on: 2016/8/28 21:57
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Re: broke off the flywheel.
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I'd get the flywheel and clutch balanced again and be very careful when putting the flywheel back on as mentioned above.

If it does it again I would next pull the whole bottom end out and have the crank pulley, crank, flywheel and clutch all balanced.

4 cylinder motors have inherent harmonics that shake stuff loose. Fairly well known to shake the oil filter loose in a racing A series. If your bottom is even slightly out, 8k rpm and no harmonic dampener will definitely shake a flywheel loose.

Posted on: 2016/8/29 1:07
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Re: broke off the flywheel.
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Whenever we tried to re-use a flywheel where the bolts broke or the flywheel got loose, (in racing applications) the flywheel would always come off again. The flywheel would never index correctly on the crank if it was ever rotated loose. I hate to say it, but you should look for a new flywheel. Peter

Posted on: 2016/8/29 5:58
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Re: broke off the flywheel.
No life (a.k.a. DattoMaster)
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balanced improperly? I remember this happening to my fiat 124
and when I went to get it balanced it was found to be warped
ever so slightly enough to be dangerous.

Your rear main seal is fine? no leaks?

Posted on: 2016/8/29 6:38
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Re: broke off the flywheel.
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The flywheel or the Fiat was unbalanced Dave? They were death traps too ;)

Posted on: 2016/8/29 8:16
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Re: broke off the flywheel.
No life (a.k.a. DattoMaster)
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If you dont get electrocuted by a Mafioso made car
then you could cut a vein open with the rust

Posted on: 2016/8/29 9:45
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Re: broke off the flywheel.
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I would strongly advise putting the flywheel in a lathe and giving the mating face a quick lick to make it true again. Having them fret about doesn't improve their seating any.

Posted on: 2016/9/2 8:30
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