Crank to Flexplate bolts keep backing out

joefarmer

joefarmer

MR. Supreme Overlord
Joined
Jul 31, 2006
Messages
6,137
I'm chasing a harmonic issue with my latest 2006 CR build. Every 2nd burnout the flexplate to crank bolts come loose. Been using red loctite and tried both 95 & 105 ft/lb.

Specs:
  • 12v crank with 12lb shaved off. Came from a reputable shop that said it was straight and balanced.
  • ATI Superdamper, prototype that was run on my 12v too.
  • New BD flexplate, replaced older BD flexplate that was run in my daily without issues.
  • Balanced and matched CR rods.
  • Balanced and matched CR pistons.
  • Converter was run with the 12v and fully balanced.
  • Transmission internals were run with the 12v without issues.
  • New Suncoast 4x4 OD 2WD conversion housing and yoke support.
  • New 4" chromoly driveshaft fully balanced.
  • Custom pinion brake setup. Found zero-runout on it.
  • Ford 9" rearend setup exactly like it was in the 12v.

What's causing the flexplate to crank bolts to back out on every other burnout?
 
Last edited:
Not sure what could be causing it to keep happening but maybe you could try drilling holes in the heads and using security wire. Or try a thin plate with tabs to bend over the bolts.
 
Maybe try another flexplate. Is the centering ring a snug fit onto the crank?
 
I switched to an ATI this last year and it did the same thing on my flywheel bolts. After fixing it twice the bolts on the ATI sheared off. I switch back to my fluiddampner and not another issue. I would start with something easy like swapping the harmonic balancer.
 
Security wire is used on any of the heavy duty diesels with the Allison autos so that is a viable option. My only concern with security wire has been if the bolts even loosen just a little bit that cannot be good.
 
zstroken said:
Have you tried cross threading the bolts? :)
Click to expand...

You could also go a little larger on the bolts, and pound them in.

Before you do that, try the damper. Maybe even throw a stock one on to see.
 
Get rid of the ati damper... Theres something about them on a cummins, some harmonic issue for sure... My ati damper did the same thing... I switched to fluid damper... Truck is def more quiet.. Just leads me to believe its a better product for the cummins.:Cheer:
 
How flat and what RA are the mating surfaces? It sounds like not enough friction to me.
Are the bolts loosening or yielding first?
 
I am supposed to be receiving a fluidamper any day now for mine.. you want to borrow it for a week??
 
zfaylor said:
Security wire is used on any of the heavy duty diesels with the Allison autos so that is a viable option.
Click to expand...

I'm sure he'll invite you to come do it if you can wire 6 bolts through a 1.75" hole LOL
 
okie18 said:
I'm sure he'll invite you to come do it if you can wire 6 bolts through a 1.75" hole LOL
Click to expand...

Crank to flexplate bolts not flexplate to converter bolts....


Unless I am missing something here why would you make yourself work through a 1.75" hole? Move the tranny out of your way!
 
If the shop that removed the weight from the correct areas on the crank and spent the time to balance it correctly the crank won't be the issue. Also I have yet to have any issues with any ATI damper I have installed and used. One of my trucks also has weight removed from the crank and running a ati as well, I have swapped two different tranny set ups in it over last summer and never had an issue with anything coming loose or breaking due to a damper or weight reduction of the crank.
 
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