Hi all,

I'm mounting my flexplate onto my crank, and I'm using new ARP bolts. All the online references I can find say to torque them to 55 ft. lbs., but the ARP instructions say 75 ft. lbs. Which is correct? ARP included some lube to put under the bolt heads, not sure if that changes the torque spec or not. Any advice would be appreciated.

Roger

55 is for OE bolts, go with the ARP specs (with their lube) with ARP bolts.

Hmm, the maker of the bolts said one thing some internet site says another.

It's like the pool hall routine in my Cousin Vinny.

I'm going with option A.

See the chart, notice how higher grade bolts get torqued to higher specifications?

Thanks, guys. Just took them down to 75 - nothing snapped off.

Also got a laugh out of the Cousin Vinny reference - one of my favorite movies.

The bolt strength is one thing, looking at that chart adding oil to the 7/16x20 lowers the torque a bunch, doesn't it
My point is the threads in the crankshaft flange need to be thought of also when making decisions like this How thick is your flange?
I use the FSM when it comes to flywheels and flex plate torque specs

I usually follow the FSM in all things. But when I deviate from it I have a good reason that I understand fully and concur with. ARP's recommendation falls into that category. They have proven, to my satisfaction, that they know what they are doing.

I went with 55ft. pounds for the flexplate bolts on the 440 in my wife's Challenger because that was the factory spec. I found on the internet. I also used new ARP bolts.

After putting about 50 miles on the car I started it one day and heard a terrible knocking noise from the bottom of the engine, sounded like a rod knocking
After a stressful hour of trying to locate the source of the noise I determined the noise went away when the RPMs increased so I hoped something was just loose. I got it up on my lift and after checking everything I discovered the converter was moving around because the flexplate to crank bolts had come loose.
After doing some research I found the correct 75ft. pound torque spec. for the ARP bolts and replaced the bolts and flexplate.
No problems since.

Just so we all know, the reason the ARP bolts specify a higher torque spec is because it is a higher grade bolt. Bolts maintain their hold by stretching enough to essentially act as a clamp. Not enough clamping force and it will loosen, too much and it breaks. Higher grade bolts are harder to stretch and require more torque to properly clamp. There are fancy bolt stretch gauges to more accurate set that clamp, you may have seen them for rod bolts. The torque to yield bolts are essentially doing that more accurately as well.

The chart I posted above shows that change in specs. As someone noted, the dry vs lubed specs are different, some substantially so. Unless otherwise specified the spec lube is 30wt oil. ARP has their own lube and you should always use their specs when using their stuff.

Great info, everyone. Thanks!

the FSM calls for 55 Ft. Lbs. with the 7/16x20 flexplate and flywheel bolts for all the motors that use those size bolts. The 1/2x20 Hemi bolts call for 75 Ft/Lbs, does your wifes car have a hemi motor in it?
ARP specs show different torque if you DON'T use their lube, I try to always use locktite on all the flexplate and flywheel bolts , all of them

The wife's car has a 440 Six Pack engine in it.
The first flexplate was the factory type used with an 11" HP 764 converter with 5/16 lug bolts. The second flexplate was a solid SFI one from 440 Source. I used Loctite red both times.

I have not used red locktite since breaking off a 7/16 cam bolt off in one of my motors years ago removing it to degree the cam
The first 425 street Hemi motor I raced in NHRA stock was in a 1970 Baracuda, not a original car, in A/S. I misread the FSM on the flywheel bolts and torque them to 55 Ft.Lbs. for the 7/16 bolts Four of them came out and was rattling around caught between the clutch disc and the crankshaft flange, luckily I caught it before hurting myself or the car
Once I used the proper torques specs. there was no more issues on them coming loose

ARP calls for 90 ft.lbs. of torque for the 1/2” flex plate bolts.

with their lube ?

Yes.