ARP Crank bolts coming loose

[oldhead]

All of my street cars have been blown, mostly 671 & 871 but even my YSI Vortech crank bolts come loose...SBC-400...After I got tired of retightening 7/16 bolts I went to 1/2-20 ARP(120# of torque using there lube) but same thing. It seems that a new bolt lasts longer. I sent one used bolt back to ARP they said its ok and sent me a new one that lasted longer. OLDHEAD

[DaveMcLain]

All of my street cars have been blown, mostly 671 & 871 but even my YSI Vortech crank bolts come loose...SBC-400...After I got tired of retightening 7/16 bolts I went to 1/2-20 ARP(120# of torque using there lube) but same thing. It seems that a new bolt lasts longer. I sent one used bolt back to ARP they said its ok and sent me a new one that lasted longer. OLDHEAD

Why are they coming loose? Is your crank hub working on the timing gear and getting shorter causing the bolt to come loose?

[mark_follweiler]

yea, something is causing this. never had a crank bolt come loose....

[oldhead]

I want to add....The balancer is ATI and fit VERY VERY tight on the crank. The six 3/8 X 16 that hold the V belts and cog pulley on have never been found loose Oldhead

[oldhead]

I use a grade 8 bolt to pull the balancer, it takes much more then 120# to pull it on, then I install the APR bolt(120#) Maybe the balancer needs to be fit looser?????Oldhead

[DaveMcLain]

I want to add....The balancer is ATI and fit VERY VERY tight on the crank. The six 3/8 X 16 that hold the V belts and cog pulley on have never been found loose Oldhead

I have a friend who always had to tighten the balancer bolt on his big Ford when he ran an ATI damper. After he switched it to a Romac elastometer type its has stayed tight.

[pamotorman]

are the bolts bottoming out ?? are you using washers under the bolt heads that are not hardened ??

[modok]

Maybe the ATI damper is not the best one for YOUR application.

[swampbuggy]

Oldhead---on my last engine it was necessary to hone the ATI balancer for PROPER interference fit, high end Crower crank. Just thought i would throw this information out there. When you said very very tight i thought about this ???? Mark

[MadBill]

Still, unless the damper is more fully seating with time, too tight a fit won't loosen a bolt. You could mark its position and see if it actually unwinds or just gets looser where it sits (i.e. damper wasn't fully seated.)

[ProPower engines]

Oldhead---on my last engine it was necessary to hone the ATI balancer for PROPER interference fit, high end Crower crank. Just thought i would throw this information out there. When you said very very tight i thought about this ???? Mark

I have never found a new balancer and new crank combo that did not require the balancer needing to be honed to fit properly. Any of the durabond stock replacement balancers new to be fit never mind an aftermarket HP style of balancer.

Most of the time I use the .0012 per inch of shaft size for press fitting balancers. They are good and tight installing and neversize type of lube is needed to get them to slide on smoothly using an installer tool.

That said using the threads to pull a non fitted balancer may have stretched the threads some allowing the bolt to loosen .

[fdicrasto]

swampbuggy and propower are right on with the fit issue. I use ATI on 90% of my stuff and in almost every case need to hone the balancer for proper fit. Check that crank snout, pretty sure you will have some galling from too tight on balancer.

[superpursuit]

[/quote]

I want to add....The balancer is ATI and fit VERY VERY tight on the crank. The six 3/8 X 16 that hold the V belts and cog pulley on have never been found loose Oldhead

This sounds like it may be the problem. Are you using anti seize on the crank snout and inside the harmonic bore? If no or if the interference fit is too tight then the harmonic may be seizing / welding itself onto the crank and not bottoming out properly. With some use the harmonic may move slightly on the crank, causing your bolt to be loose. This is assuming your washer is still flat.

I would try removing the harmonic and check to see if it is seizing or welding itself to the crank. I would also do a quick check on the interference fit and if all is well then reinstall it with anti seize using a proper harmonic installation tool. Using a bolt to pull a tight harmonic on is VERY hard on the crank threads and may be hard to tell when the harmonic has gone all the way home. I hope this helps. Good luck!

[Jeff Lee]

All of the above with emphasis on making sure you are not bottoming out the dampener bolt and using the proper thick washer. I’ve seen that before, especially those using aftermarket cranks.
And the last “professional shop” I used honed the ATI balancer to a nice and loose .0125” clearance to make it easy on them to R&R the balancer. Then you get real ugly bearing texture...
I suggest only using a balancer R&R tool which has the large plate.

[modok]

Still, unless the damper is more fully seating with time, too tight a fit won't loosen a bolt. You could mark its position and see if it actually unwinds or just gets looser where it sits (i.e. damper wasn't fully seated.)

huh, I think you are right.
Even if it was shifting slightly on the crank, it would not necessarily loosen the bolt.

I would use some 150 grit to rough up the inside surface of the pulley bore a little bit (if it's smooth) and apply ARP lube, but anti-seize may be a good choice also. Does wonders for steel on steel press fits.
If nonferous material, then I go with the anti-seize.