Flywheel Bolts Shearing In Half

[TimG]

Ever so recently I've dropped in a AWD 6-puck ACT clutch kit. It's unsprung so it's very harsh with engagement. Anyway, here's the story. About a month ago, I was a kilometer away from home when my clutch decided it didn't want to work anymore.

I pushed it home with a couple guys and took the transmission off. Low and behold 3 out of 6 flywheel bolts were SHEARED off right at the heads.

I took them out, replaced them torquing them down in a star pattern progressively all the way up to the torque spec 10Xlbs-ft from what I remember and threw everything back together.

Fast forward to this past Wednesday night at Cayuga. I'm blasting down the track, tuning the car just right, doing a forth gear pull. When all of a sudden I feel my engine and my transmission disengaging. I pull of to the side of the slip booth and get it towed home.

After about 18 beers between 2 guys, we take the whole motor out, take off the transmission and clutch assembly. DAMN FLYWHEEL BOLT! One of the bolts is sheared right off AGAIN. It caused my clutch disk to ram itself into the TOB sleeve and cause damage there too.

Can anyone suggest ANYTHING to help me out here.
I'm going to start by buying 6 BRAND new bolts. Any other suggestions. I might even pick up a street disk rather then this puck chatter. Pictures are coming.

 

[Defiant]

Sounds like it'd be happier with a sprung disc.
Or, if you want it to break somewhere else, you might try allen-head capscrews.

 

[Nanan]

I am guessing that you have a 2600 lb PP with that ACT disk so that bad boy is going to grab rather fiercly. With you using an unsprung disk that is going to translate to a hell of alot of shock force on the bolts, what amazes me is that you have not sheared all of the bolts off in one good launch.

You could try grade 10 Aircraft bolts but it is likely that you will break your input shaft.

 

[MNGSX]

1. Sprung hub..
2. Look at the ARP catalog and see if they have a bolt that size... I think they do.

 

[gsx951]

If the bolts are tight, they can't shear because the torque is transmitted through the clamped flywheel/crank hub. They'd have to first loosen before they could shear.
Post a pic of the bolts with a good clear macro in the break.
Remember to use Loctite!

 

[MNGSX]

That little alignment dowel cant hold crap for TQ its all on the flywheel bolts.

A grade 10 is probably more likely to shear....

Flywheel bolts are a different grade. You dont want grade 10 in that application..

http://www.arp-bolts.com/pages/products/pages/drive/dr_flyflx.html

 

[gsx951]

I believe in a bolted joint such as this that the fasteners do not work in shear. All of the shear load is being handled by the clamped union of the flywheel and crank flange with the bolts being in tension. The only way for the bolts to see a shear load would be for them to loosen and allow the flywheel to move.
Dowels are not used as retainers. The dowel is a locator and is further evidence that there is not a shear load on the fastener because the dowel would break. I'm guessing that this is some kind of fatigue failure but pics will really tell.

Tim, what flywheel are you using?

 

[MNGSX]

Either way the bolts take up all the work of clamping...

One of the metric ARP flywheel bolts will work on a DSM...
You just have 2 left over bolts.


ARP 203-2801 Flywheel bolts.. M12x1.25

You get 8 bolts because its for a supra 3SGTE engine...

http://www.dsmtuners.com/forums/showthread.php?t=170841&page=2&pp=25&highlight=Flywheel+bolt+size

 

[TimG]

Stock AWD flywheel. ACT 2100PP and 6-puck ACT disk which is unsprung. Pics are being taken as we speak.

 

[MNGSX]

Consider a better flywheel...

Ever see what happens when a stk one comes apart?

 

[TimG]

First occurrence. Two of the bolts looked like the ones where the head was sheared right off. Two of the bolts looked like the ones where some thread is still there. One of the bolts was tight and another was loose. It is possible the torque wrench I used for this torque down was faulty.

Second occurrence. Snap-on brand new torque wrench used. Only one bolt sheared. Looked like the one where the thread was still 1/2 there. There is the possibility that one of the bolts I originally used (the loose one in the first occurrence) was the one that sheared here. I might have re-used it without knowing (obviously the one still intact).

This time, I think I'm going to get the longer Supra bolts from ARP and Loctite. A thread on NABR shows that this has happened in the past and these Supra bolts were longer and helped out.

 

[bigjdog84]

Did you check to make sure the flywheel bolts threads didn't stretch?
I would keep the stock flywheel if the step height is within spec. Make sure to chase those threads on the crank, you may be suprised to find alot of old loctite in there. Proceed to clean with some brake cleaner and blow it out with some compressed air.
Then use new factory bolts w/red loctite @ 100 ft. lbs.

ARP's are a nice upgrade from 100k+ flywheel bolts, but for 15 bucks you can't lose with new factory bolts.
That clutch combo is very strange, I don't see any benefit of using a puck disk with a 2100 pp. You may want to up it to a 2600.

There are probably two reasons why this problem happened; user error or a warped flywheel. Have everything checked out and take your time.
Good luck.
Later/joe

 

[bigjdog84]

This is a good example of why you should not re-use old flywheel bolts. Also, was that crank dowel alignment pin there in the first place? There have been many issues in the past with flywheel bolts backing off w/out this alignment pin.

 

[MNGSX]

ALOT of service manuals for normal non gearhead repairs say to use NEW flywheel bolts always...

The locating dowel is absent too..

 

[TimG]

The locating dowel is in the flywheel actually. I will take it out and install it in the crank first before I install the wheel next week. New bolts for the flywheel are on the way from Chrysler. Can't beat $5 for new ones.

 

[MNGSX]

Cant beat not having to worry or drop the trans again because you have ARPs holding on a SFI approved flywheel..

 

[gsx951]

The photos show that those are fatigue failures.
Measure the surviving old bolts with a digital caliper or mic and they'll be a bit longer.
Most likely, they were over torqued at one time and stretched beyond their elastic limit.
Here's a link to some good info on bolted joints: http://www.boltscience.com/pages/basics1.htm
In a nut shell, the bolt stretches beyond the limit where it can snap back. Lacking this elastiscity, the bolt just can't hold and loosens. When it loosens it dies.

As mentioned already, clean the crank thoughly and install new bolts with red loctite.

Listen when these guys talk to you about your flywheel. The 6 puck makes much more heat than a organic disc and the O.E. cast flywheel can't deal with heat. It will crack.

 

[TimG]

I understand that it is possible the bolts COULD have exceeded the Yong's modulus of the bolts from a prior torque down. Stretching basically to the point where they don't return to their original state.

Now that I think about it, when I was torquing down the bolts after the first occurrence, one of the bolts snapped in half exactly like the half threaded bolt shown in the picture above @ 90ish lbs-ft. I figure a few of the bolts I used have exceeded their elastic region and were on the verge of their rupture point.

I have new ones on the way from Chrysler.

[(Young's)]

 

[MNGSX]

Listen when these guys talk to you about your flywheel. The 6 puck makes much more heat than a organic disc and the O.E. cast flywheel can't deal with heat. It will crack.

This guys killed more than a bellhousing.. Look at MR turbo..

You must be logged in to view this image or video.

http://www.dsmtuners.com/forums/showthread.php?t=132528&highlight=Flywheel+Explosion



http://www.mightymouseracer.com/gallant.html

Click on the video link...

At the end of last season I was unfortunate enough to have the flywheel on this car explode! The spilling of coolant and oil was enough to tug the car into hitting the wall at over 100 mph! The car ran 13.2 at 88 mph on that run going through the traps in reverse after hitting the wall twice! I walked away without a scratch and not even sore. I was not sure what I was going to do with the Galant – as it was pretty smashed up. The engine – transmission – transfer case - & turbo were trashed. But I did decide to rebuild it. I am very glad I did! I really have fun with this car.

An exploding flywheel will take out anything in its path.. They have gone thru hoods and cleared the roof of cars on drag runs...

Now you know why I went SSG.. better alloy than fidanza... and with ARP fly bolts.. then capped it off with a scatter sheild.

 

[gsx951]

It slices , it dices...

 

[MNGSX]

http://store.titanmotorsports.com/arpflbo.html

ARP 203-2801 Regular price: $35.57Sale price: $23.95

Cheap insurance

 

[TimG]

Hey guys, update. I'm a moron.

The motor originally came from an automatic. You can see in the picture that I left the torque plate spacer in place and the flywheel was resting against it. Basically I'm a fool and pulled my transmission twice because... I'm an idiot.