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Stripped thread. - metal fatigue?

Don Gitzel

Aluminum
Joined
Jul 25, 2017
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I stripped out a thread on the flange of my crankshaft during installation of flywheel at only 70 lbs. I could not find new bolts even at a clutch and brake shop. The old ones I am using have plane shoulder which I imagine is a shear point. Could be the reason for stripping. Less threads engaged in flange or metal fatigue. I am going to insert a heli coil and use grade 8 bolts the proper size. I wii use blue locktite and torque to 90 ft lbs. what ya think ��? I may be posting this in the wrong place or wrong forum but you guys so knowledgeable. Thanks
 
Interesting info off of the web


“assembly technique. it involves using a speed handle to tighten down the flywheel bolts in proper sequence and then hitting the top of each bolt with a hammer ( like driving a nail) to seat the bolts andthen bringing up to proper torque
 
Show us a magnified, head-on view of the crack. That way we can look for signs of fatigue. I am skeptical of a fatigue theory, because there should not be much cyclic loading in a flywheel bolt. Unless the crack was pre-existing, if the bolt broke while being torqued, that is not a fatigue failure. (Or it's a single-cycle fatigue failure ;-) )
 
practice, practice, practice with the torque wrench, especially if its of the type that click. calibrate it yourself.
 
what is the exact torque specified for your vehicle, and do you have an old style beam torque wrench? the clicker type will go out, a beam will never go out of calibration unless it has been damaged. 90LBs seems excessive should like 60LBs be look it up or ask.
the bolt appears was incorrect bolt or was over torqued causing it to fail. look up on the internet for the year, and model of the vehicle for whole new set
of bolts, get the correct torque values. use the correct pattern of torqueing. a Heli coil will require a special tap drill & tap buy a kit.
use the medium strength Loctite or equivalent don't use ultra strength Loctite or it will be a PITA to remove next time.
I do recommend Loctite to prevent from vibrating loose.
the Heli coil thread I would back off slightly because it has been compromised.
 
Can you oversize the hole enough to press in a top hat with ID threads from the backside? Helicoils suck at a job like this. As far as loctite goes I use high strength red everywhere I feel I need Loctite, never had a problem getting anything apart and nothing falls apart either.
 
Interesting info off of the web


“assembly technique. it involves using a speed handle to tighten down the flywheel bolts in proper sequence and then hitting the top of each bolt with a hammer ( like driving a nail) to seat the bolts andthen bringing up to proper torque

I will bite, who is the manufacturer of this engine?
 
View attachment 296073

I stripped out a thread on the flange of my crankshaft during installation of flywheel at only 70 lbs. I could not find new bolts even at a clutch and brake shop. The old ones I am using have plane shoulder which I imagine is a shear point. Could be the reason for stripping. Less threads engaged in flange or metal fatigue. I am going to insert a heli coil and use grade 8 bolts the proper size. I wii use blue locktite and torque to 90 ft lbs. what ya think ��? I may be posting this in the wrong place or wrong forum but you guys so knowledgeable. Thanks


You are talking torque numbers but we don't know what size the screw is ( it's not a bolt until it has a nut on it). There are 10 blue Loctite thread locking products. USE THE NUMBER!! What is a "plane shoulder" and how does it affect the threads?
 
Be careful here. Stressed cap screws like this are generally torqued to put the fastener in its elastic range.
The torque is wildly affected by the medium applied to the threads and contact face.
Up to 60% of the torque is from the face of the cap screw rotating against the part.(contact face)
Loctite can affect this value greatly and change the applied stretch on the fastener at factory specs. (over torque)

I never use Loctite on cap screws that are tightened to their elastic range (stretch) Flywheel, connecting rods,main bearing caps,cylinder head etc..
If stretched within their elastic range they do not need nor want a thread locker....
After market connecting rods (ex Carrillo, Panki etc.) are very specific...require use of anti scuff paste on the bolts (threads and face) ...Definitely no thread locker!
Torque should be derived by test assembly using the appropriate lube and measured for stretch to proof the assembly torque....

Cheers Ross
 
Thread locker is applied as a sealant- thread bore passes through crank flange.

OEMs recommend replacing every fastener, it seems- because of this disco TTY claim.

TTY headbolts was a point of contention. I NEVER saw a stretched one after the OEM changed from M10 to M11 in 1985.

similarly, I've never seen nor heard of a flywheel bolt failure on that specific domestic application. I FREQUENTLY sold used long crank bolts, as late models used a 'modular' flywheel (read ATX flexplate) and people converted to a conventional flywheel.

Here's some used ones that went out Friday:
(you can b a r e l y see Blue thread lock/sealant patch)
20200523_083135~2.jpg

Now rod bolts; well, there I become scaart. I go to the friendly dealership.
 
Only marginally related but when I did my clutch my spidey senses were tingling while tightening the flywheel bolts and I stopped and double checked the torque figures. Turns out I looked at the wrong engine variant of my truck, and that particular engine had torque to yield bolts, whereas my engine doesn't (or at least isn't supposed to).
 
I have done a few fly wheel installations, old school, thus 1953 chev , had a 383 stoker, now has 350 SB with A R heads
in the process, never had an issue so far, I put Loctite on every thing, to bolts and screws getting lose even if torqued correctly, sure could of used other means, but gets expensive. only exception, any bolts on exhaust system, I use anti seize
especially on aluminum threaded any thing, it never fails it will strip out on removal the next time, really careful with
aluminum heads and spark plugs, heat zone, look at it and fart it will strip out.
I have been doing this since I could pick up a wrench.
 
I picked up some ARP bolts for high performance applications. They include a lubricant to go between the chamfered washer (included) and the head of the bolt. Seems this would increase the torque put on the thread. Makes me nervous ��.
 
I picked up some ARP bolts for high performance applications. They include a lubricant to go between the chamfered washer (included) and the head of the bolt. Seems this would increase the torque put on the thread. Makes me nervous ��.
are you testing me lol :D
actually ARP goes by preload and are measured differently, and I am having a brain fart but go to their web page, to much trash in my head
they have the specific procedure on the tightening the arp bolts, it's actually more precise technique. they don't use torque values.

if I remember correctly or may be an other mfg, they washers that change color. I done but it's being a while. correct me because right now to busy to look up for the correct answer.
 
I inserted a heli coil in the stripped out thread and ran a bottoming tap through the rest. I tried my new ARP bolts in the other holes and found I could get slight movement side to side on the bolts. I would have rather found no movement. What ya think?26170A4A-6387-4BED-8AE4-ABE322BFF594.jpg
 








 
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