ARP Crank bolts coming loose

[Newold1]

MY thought is that if you changed the size bolts and thread size on your existing crankshaft you had to tap out the bolt holes on the crankshaft flywheel hub. Crankshaft hubs and cranks are usually induction hardened and that steel is hard and tough and one must be careful with taping out the holes to a larger size especially when taping out a 7/16" threaded hole to a 1/2" as the amount of material available in an existing 7/16" thread to a 1/2" thread is only about .030" per side and that does not leave a good amount of material to get the new threads of the 1/2" tap size to cut into and make a good well placed thread depth in the holes. When a crankshaft is re-tapped like this I have seen the new threads not in the best shape for tightening and re-torquing new flywheel bolts to a good hold value. If this is your case you should use some thread locker and maybe a set of serrated under head washers on the new bolts.

The other thing that can cause engine and driveline bolts to loosen is an out of balance condition and if your engine balance is out or something in the flywheel or clutch assembly is likewise out of balance this can sometimes loosen up bolts.

[amcenthusiast]

Aw Man! Since that's an externally balanced engine, this really does sound like a 'harmonic balancer' problem.

Only recently I learned that a 'harmonic dampener' is more accurately described as a 'torsional absorber':

http://www.epi-eng.com/piston_engine_te ... orbers.htm

Not sure but maybe the blower pulley is affecting the external balance factor of the engine whereas this adds a certain weight onto the end of the crank.

As I understand it, the 'torsional absorber' bolt needs to be 'freaky tight' in order to make it like one piece with the crank snout = needs no movement whatsoever... but the inertia ring on the 'torsional absorber' acts like a hammer, hitting back on those torsional forces that cause them to happen. (like the weight of a punching bag opposes the force of a boxer's punch)

It could be that the stock level of torsional resistance of the externally balanced crank is getting overwhelmed by the increased strain of the blower drive; eg: if the engine is re-externally balanced with heavier pistons this adds more 'unseen' flex in the crank cheeks, main and rod journals etc -combined with the strain of the blower assembly, the engine even if it is more accurately re-balanced (including the weight of the blower pulley) it may still need more 'torsional absorbing' than the current absorber is able to apply; eg this may be a case for running a new and improved fluid damper type?

[pamotorman]

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

i did not understand he was refering to flywheel bolts not main crankshaft bolts

[oldhead]

The balancer bolt has more then 3/8" before bottoming.I use the 1/4" thick ARP washer under the bolt with ARP lube under the head of the bolt.As to the redrilling the crank and retapping it, I drilled a .453 hole and tapped it to 1/2"X20. It was HARD metal....................................... I just called ATI, they agreed with to tight of a fit and not going on far enough......Oldhead.

[Jeff Lee]

Should be .001”-.0015” clearance. Yours is tighter? I’ve never done it but I know at least one guy that makes for a tighter fit and freezes the balancer to install. And I’m curious as to how you determine the balancer is fully installed?

[SupStk]

Should be .001”-.0015” clearance. Yours is tighter? I’ve never done it but I know at least one guy that makes for a tighter fit and freezes the balancer to install. And I’m curious as to how you determine the balancer is fully installed?

Now freezing the hub seems to be the opposite way you'd want to go.
Too tight of fit, small snout crank, external balance and running a blower drive off it. Don't seem strange to me there is a problem.
Check the damper hub for a crack. If there is, most likely in the keyway.

[ProPower engines]

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.

had to ask but you did mean .00125 not .0125 right

[DaveMcLain]

Should be .001”-.0015” clearance. Yours is tighter? I’ve never done it but I know at least one guy that makes for a tighter fit and freezes the balancer to install. And I’m curious as to how you determine the balancer is fully installed?

I don't think it should have any clearance but instead it should fit with .0005-.001 interference. Any more than that and it can become REALLY tough to take off and put on.

[Steve.k]

Im with Dave on the damper fit. Sounds like harmonics to me and you may not be able to fix. I had a engine that would spin the oil pan bolts out continually. Did it on dyno from day one. Asked dyno guy and he said he seen it and he said yes quite abit. I asked if he thought balance or what. He said no its a frequency in crank and asssemblies that resonates at certain rpm. Could be at hp peak or at cruise speed in your case. Damper may pick it up but its basically a crap shoot.He figured its came on since the flood of aftermarket cranks and different materials used? I have no idea if this is the case but i had to loctite most of fastners in. Even changed damper no change. Motor pulls and works great i pulled down for inspection and no abnormal wear.

[Newold1]

I think I at least need some clarification here. It appears this is a GM SBC 400 engine and as such most 400 cranksahft and rotating assemblies are external balance which means the ATI damper he is using needs an external counterweight to bring the rotating assembly on a stock 400 GM crankshaft into balance. He is apparently using a belt drive front mount Vortec centrifugal supercharger and he has a supercharger belt drive pulley bolted to the front of the ATI damper with standard size 3/8" bolts which are not coming loose. Apparently as this thread lengthens it appears the OP is talking about the front centered damper crankshaft retaining bolt working itself loose. The OP apparently drilled and tapped the snout of the crankshaft for a 1/2"x20 ARP thread high strength bolt and washer. The Op is not sure or indicated what the damper crank hub to crankshaft snout clearance was on installation and with his statement of 120lbs required to pull the damper onto the crank snout his interference fit may be way to tight on the crankshaft snout and the damper might not be fully pulled on into seating against the crankshaft lower timing gear face as it should be.

My questions to clarify and hopefully help find his issue are:
1. Is the ATI damper truly an external balance type with counterweight matched to a 400 SBC engine.
2. Was the entire engine rotating assembly balanced including with the ATI damper and extra supercharger pulley?
3. Was a flywheel or flexplate used that was also for an external balanced 400 engine with appropriate counterweights?
4. What is the final lb/ft. torque the crankshaft bolt is being torqued to?
5. Is the engine having any vibration issues or problems at any rpms?
6. Was the engine possibly put together with aftermarket crankshaft and assembly for an internal balanced assembly and an external balance damper installed with an incorrect external balance damper.

Some of these items improperly mismatched can cause serious vibrations, harmonics and torsional movements that can easily cause things to give up set and tightening and work themselves loose.

Know this seems like a lot of questions for clarification but it is sometimes an improper set of component parts that create an issue like this and the earlier posts here seem to be addressing possible multiple issues without proper understanding at least on my part for what this total assembly really is and how it is not working.

Would OP please answer these questions for further clariification.

[Keith Morganstein]

From previous posts, the OP has an all aftermarket, Dart block 400 making 1200HP with a YSI supercharger.

[Jeff Lee]

My bad on the zero’s behind the decimal point!

[mark_follweiler]

I think I at least need some clarification here. It appears this is a GM SBC 400 engine and as such most 400 cranksahft and rotating assemblies are external balance which means the ATI damper he is using needs an external counterweight to bring the rotating assembly on a stock 400 GM crankshaft into balance. He is apparently using a belt drive front mount Vortec centrifugal supercharger and he has a supercharger belt drive pulley bolted to the front of the ATI damper with standard size 3/8" bolts which are not coming loose. Apparently as this thread lengthens it appears the OP is talking about the front centered damper crankshaft retaining bolt working itself loose. The OP apparently drilled and tapped the snout of the crankshaft for a 1/2"x20 ARP thread high strength bolt and washer. The Op is not sure or indicated what the damper crank hub to crankshaft snout clearance was on installation and with his statement of 120lbs required to pull the damper onto the crank snout his interference fit may be way to tight on the crankshaft snout and the damper might not be fully pulled on into seating against the crankshaft lower timing gear face as it should be.

My questions to clarify and hopefully help find his issue are:
1. Is the ATI damper truly an external balance type with counterweight matched to a 400 SBC engine.
2. Was the entire engine rotating assembly balanced including with the ATI damper and extra supercharger pulley?
3. Was a flywheel or flexplate used that was also for an external balanced 400 engine with appropriate counterweights?
4. What is the final lb/ft. torque the crankshaft bolt is being torqued to?
5. Is the engine having any vibration issues or problems at any rpms?
6. Was the engine possibly put together with aftermarket crankshaft and assembly for an internal balanced assembly and an external balance damper installed with an incorrect external balance damper.

Some of these items improperly mismatched can cause serious vibrations, harmonics and torsional movements that can easily cause things to give up set and tightening and work themselves loose.

Know this seems like a lot of questions for clarification but it is sometimes an improper set of component parts that create an issue like this and the earlier posts here seem to be addressing possible multiple issues without proper understanding at least on my part for what this total assembly really is and how it is not working.

Would OP please answer these questions for further clariification.

WOW! glad he figured it out already...

[BOOT]

Sry kinda skimmed if someone already mentioned it but if you don't wanna use threadlocker maybe try a Nordlock washer you can get them at McMaster carr. If it still comes loose then I'd think the large thick washer is moving.

https://www.youtube.com/watch?v=IKwWu2w1gGk

[Geoff2]

ARP need stop trying to make their products a 'one size fits all' deal. Myself & a few other people wasted a ton of time [ plus a few skinned knuckles...] trying to figure out my the gears were crunching, trying to select gears on a manual trans Pontiac V8. Engine was rebuilt & new ARP f/wheel bolts were used. Factory f/wheel. It turns out the thicker than stock head on the ARP bolt, along with the supplied washer, stuck out too far & fouled the cushion springs on the clutch plate.