Crank bolt coming loose

Anybody have any idea why the crank bolt keeps coming loose on a hemi ? I know detonation will cause this but we have no sign of it and it runs fine but we torque it to 250lbs with red locktite and it comes loose almost every pass ? Any ideas

 

Crankshaft flex will cause this. imo.

 

we torque ours to 350 for that reason

 

Do you use the Automan Bolt/Washer? We had the same problem and after switching to that, problem = gone. You'll need a torque multiplier because the bolt torques to 400#.

Brandon Booher
NHRA TAD #34

 

Ditto to Brandon's post

The Automan bolt will also take stress off your keyways on the hub.

 

now your talkin over my head what is a automan bolt ?

 

Just a grade 9 bolt

Torque it to 400 pounds or like us we torque it to 275 then put a big pipe on there and let it have it! no more ti hubs either the steel one comes on and off just fine now.

JR at RBS has them. www.rbssuperchargers.com

Mark

 

I believe the supplied washer is just as critical as the grade 9 bolt Automan/RBS sells. I wouldn't go and buy a grade 9 bolt somewhere else to shortcut the cure. There is also a torqing arm he sells to help hold the rotating assembly still while you're torqing the bolt to 400#. the "kit" (bolt and washer) come with instructions on lubricant to use as well.

 

bolt torque

We use the blower drive ratio to multiply the torque wrench, figure your ratio, the torque wrench will be in left hand or loosen mode, put a long braker bar/socket on the crank bolt and torque

 

Make sure you're using good hardened keystock, otherwise it will rattle, also.

 

I've wondered this and did some hardness checking but with little luck, how hard are you talking, C50?

 

you still need to replace it once in awhile. We had one of those high grade bolts ( not sure if it was an automan ) doing that so I went to napa and got a new grade 8 and it stayed tight. Also make sure you are getting the hub pulled all the way up tight you can hear it when it bottoms out. I torque it as tight as I can with a 3/4 impact.

 

That bolt is a cat bolt that is were it comes from

 

loose bolt

Also check the washer for flatness, I have seen a few that are bowed, thus only making contact on a very small portion of the face.

I have made a replacement washer out of hardened 4340 that does not bow.

 

Torque

Check the thread on the bolt we had one that would bottom out on the thread and not really torque on the washer so you would think it was torqued but it was not