My wife’s car had flex plate to crank bolts loosen last year at the bracket finals, about 175 runs since we put the engine together. Installed a new flex plate and new ARP 12 point bolts with loctite then.

Checked them a couple times since then and they were tight but this weekend they loosened up again, about 65 runs later. I got under there with my long 3/4” wrench and stood on each bolt to tighten them and a couple loosened after one run.

This weekend I’m going to slide the trans back and install new bolts and flex plate if necessary. Anyone run into this before? What should I be looking for? Nothing else seems to loosen up on the car and neither of us feel a vibration driving it. It’s an internally balanced big block Chevy going 7.50s in a dragster.

Fine thread?
Whoops I was thinking torque converter

This message has been edited. Last edited by: Bucky,

ARP bolts, red loctite, torque to 85 ftlbs. If they still come loose you have a hell of a vibration somewhere

the threads in the crank could be oversized, either by a production error, or by using the incorrect tap during later tear down clean ups. The only way to know for sure is with a correct go-no go gauge. If you find them to be oversized, then correcting the threads might be possible with threaded steel inserts, and a competent machine shop. Another option might be drilled ARP fastners, torque with Loctite and safety wire.

Bolts possibly bottoming out in the threads? I would spin a bolt in without flexplate installed to see how far they will spin in.

A common problem. If you look very closely at the underside of the head of the bolt. It appears rolled ever so slightly. I normally take a die grinder or a file and put a taper in the holes of the flywheel. You will see the exact issue when say, you have the flywheel out of the car. Put a bolt through the hole. You will see it resting on the underside of the bolt taper. Just had one last month. They loosened up on a 598. He never tapered the holes in the flywheel. With the good red also.

Even happened with the JW's i was using.

This message has been edited. Last edited by: TD3550,

also, it is important to grind off any plating or coating on the flexplate where it touched the crankshaft flange and where the bolts touch the flexplate. Any type of coating or plating will eventually deteriorate, causing the bolts to lose torque.

I never had this happen with an ATI flexplate and never tapered holes either. I believe ATI doesn’t paint around the holes.

I know on the JW's the bolt holes are a little on the smaller side. That's all i ran before.I guess it's always better to due the visual. Some older guy. lol told me about the underside issues long time ago.

quote:

Originally posted by Big Steve:
ARP bolts, red loctite, torque to 85 ftlbs. If they still come loose you have a hell of a vibration somewhere

I'm glad you decided to go with another set.

I use the star washers all the time. But I do not have the HP you do.

FWIW
When I ran a automatic I would have that happen.
I had a habit of doing "chirpies". This would result in elongated holes.
The 2 part cure was to
1: TIG tack some head bolt washers to the plate making it thicker.
2: Cut back on the chirpies.

Betcha no dowel pin in the crank.
Nobody seems to think that it is needed or sold with the crank anymore.
Dowel pin is a precise fit, stops movement of the flexy plate for a few years.

quote:

Originally posted by Bad News:
Betcha no dowel pin in the crank.
Nobody seems to think that it is needed or sold with the crank anymore.
Dowel pin is a precise fit, stops movement of the flexy plate for a few years.

It can't be that easy can it?

i have run with a dowel and with out,the powder coat seems to be the bigger issue for me.i now sand it off where the crank runs.

This message has been edited. Last edited by: rusty,

lol i took a crank in to be worked ,the machinist said dont yall believe in dowels.i said if you will put them back in when you are done i will use it.

This message has been edited. Last edited by: rusty,

I just bought a Winberg billet crank, came with no dowel, never gave it much thought till now. every crank I have used had a dowel...

Indexing master locator to use during initial machining of the crankshaft.Dowel hole purpose. Also locator.As far as i can remember all my internal balanced engines never had the pin. Back in the day when i was running an external balanced
BBC running a clutch flight trans, yes it had the pin.The old boys would know what a clutch flight trans was. Torqflite/727 with a clutch.

This message has been edited. Last edited by: TD3550,

quote:

Originally posted by TD3550:
Indexing master locator to use during initial machining of the crankshaft.Dowel hole purpose. Also locator.As far as i can remember all my internal balanced engines never had the pin. Back in the day when i was running an external balanced
BBC running a clutch flight trans, yes it had the pin.The old boys would know what a clutch flight trans was. Torqflite/727 with a clutch.

The first fast car I ever drove (1974) a clutch flight !! What a blast!!

I will never forget that darn clutch i had in it. Was a button clutch. Took 2 men and a boy to work it. Darn left leg was a shakin. lol I'll bet ya it was a 3500 PP at least.