Crank pulley bolt keeps coming loose

[MerloZ]

This is the third time my crank pulley bolt has come loose i torque it to spec every time and i use loctite?? Im at a loss never had this happen on anything before.

[Chickenman]

1: What are you using for Spec Torque? FSM says 87 to 116 Ft Lbs. 87 ft/lbs is NOT enough.  Use a new bolt and go to Maximum Torque. Or even a Tad Over. Threads inside and out MUST be cleaned and lubricated with either oil or Loctite.  Dirty threads will result in bolt being under torqued and it will not reach it's Stretch  or " Plastic " specification. 

 

2: Do you have the correct length Factory bolt with factory thick washer? Washer is very important. Threads will bottom out in crank if you use the wrong washer.  

 

3: Buy a new  Factory Nissan bolt. Bolt may have stretched beyond it's " Plastic " state. Once that happens they will not maintain torque. 

 

4: Is the Harmonic balancer stock? Some of the aftermarket hubs have a thicker hub and require a longer crank bolt. Found that out the hard way on a Tilton damper. Damper loosened and bent the crank snout. It was a Tilton crank... so BIG $$$$$

 

5: What type of Loctite are you using> Medium strength ( Blue ) is not good enough. You need the Red high Strength Loctite 462. Just a couple of drops. Make sure threads are clean. Inside of crank and on bolt. Use Brake Clean.

 

Really, on a street engine, the Loctite should not be necessary. I would suspect that the Bolt is " Stretchy " , threads may be worn or  you are using the wrong bolt and washer.  These things should not back out... unless you are constantly twisting over 8,000 RPM.

 

One other thing I just thought of. If the damper came loose onec... you may have bent the snout of the crank. Check the radial runout with a dial indicator. I'll have to double check.. but I think the limit is .002" . If snout is bent it will setup vibrations that will keep loosening the damper  

[seattlejester]

There was some discussion on here about this although I recall it not coming to a consensus.

[Tony D]

"2: Do you have the correct length Factory bolt with factory thick washer? Washer is very important. Threads will bottom out in crank if you use the wrong washer. "

^^^^^This all day long! JeffP machined a Volvo Washer down - it was thick enough that it didn't "Bell out' when you torqued it. The crank pulley should be slightly proud of the crank snout, if you have pulled out the oil slinger...it will be closer! If that washer bells AT ALL it will contact the end of the crank and it's the same as it was bottoming on the threads: you are torquing something bound and the strain goes up without actually clamping anything.

My comments on the above: Clean the threads with brake cleaner and use Locquic Primer N for the threadlocker. Loctite Blue 242/243 Schnell should be fine in this application, and you should also be using RC608 Cyndrical Parts Locker on the snout and key to hold the pulley from working back and forth and loosening the bolt. Loctite Red should be considered permanent, and heating the bolt with a torch should be required to remove it...if it comes out with red without torching the head to break down the bonding, your threads were oily in the first place. Used on clean threads and with Primer N no more than 4 drops (8cc's) of 242 should be MORE than enough to have you cursing and reaching for the torch to relax the 'removable' locker's bond to get it off! A Note here on "Cleaning the Threads" - use a BOTTOMING TAP and MAKE SURE all the threads in the crank are full depth as far into the snout as they can go to ease use of the longer bolts.

I agree that buying a new bolt and proper washer is not expensive and is probably the best bet if you are having issues. I have a car where the guy got upset and put in this HUGE SPS Bolt into the nose of the crank. It's extreme, but it doesn't come loose. Thing is, he had a thin washer (guess what the problem ended up being!!!) Torque the bolt to the 75% Tensile Region Specification, no more than 85% tensile...this should keep you away from plastic elongation and allow re-use at least a couple of times (remember if using threadlocker properly, you will likely be torching the head of the bolt which isn't good for longevity!) I ESPECIALLY agree with another bolt (Use the KA24 bolt and washer if nothing else, and have it cut down to your needed length) if you have an ARA A/C Pulley added. The one they used in their kits WILL BOTTOM.

If you have the crank out EVER...consider having the machine shop cut the woodruff keys into a single large key, and use standard key stock the FULL LENGTH of the crank snout. Seal it in with loctite, and a little RTV at the back to prevent oil leakage. I've seen guys with that slotted nose also fill the area under the washer with Loctite 598/Permatex Ultrablack as a leak stop as well. I haven't had issues if I seal the key. That full length key will SAVE your crank by greatly increasing the area that secures the pulley/damper should it come loose. This is common in the JDM since the 70's and I don't know why more in the USA don't do it.

 

[tioga]

I have been running a Ka bolt and I believe three washers. This gives more bolt shank not engaged in the threads to stretch and holds well. I turn over 7k on a daily basis with no problems.  

[HowlerMonkey]

Remember that once a balancer has been run loose, it could beat the key and keyway grooves up.