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HELP and ADVICE needed on bad Crank Shaft\Flywheel threads

HELP and ADVICE needed on bad Crank Shaft\Flywheel threads
project74

project74

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Location
Upstate SC
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1974 CJ5, 304v8... purchased 8/8/11
Hi all,
Imagine my joy when I was torqing down the flywheel bolts to my new crank in my newly rebuilt engine and had hand tightened first, then was torqing first time around to only 50 ft.lbs and was on the six'th bolt when it just happend to jump threads and loosen up.....:censored:
Upon removing the flywheel I see that the threads in that one hole are now flat...must have been bad threads from the factory.....bolts ALL still look great.
NEED ADVICE......will I be successful in tapping a slightly larger thread and useing a bolt to match?
Can I run with only 5 bolts with the one bad one missing?
Should I eat the cost and time of a new crank shaft and replace the :censored: thing entirely?
Anyone else run into this and have a solution...?
thanks for any help, Ed:chug:
 
Just put a helicoil in it, some will argue that the weight difference will throw off the engine balance but I say that since the slight weight gain is so close to the center mass of the crank rotation you will never know you stripped any threads.

This has come up before. -->> http://www.jeep-cj.com/forums/f2/flywheel-bolt-stripped-9652/
 
I've run them with a bolt missing. I'm betting it might have a small vibration, tho.
another option is taking the crank to a machine shop and let them deal with it...
 
CJ said:
Just put a helicoil in it, some will argue that the weight difference will throw off the engine balance but I say that since the slight weight gain is so close to the center mass of the crank rotation you will never know you stripped any threads.

This has come up before. -->> http://www.jeep-cj.com/forums/f2/flywheel-bolt-stripped-9652/
Click to expand...

I agree, a helicoil would be your best bet.
Or if the crank is new why not take it back and make them give you a new one.
 
Old Dog said:
I agree, a helicoil would be your best bet.
Or if the crank is new why not take it back and make them give you a new one.
Click to expand...
X2 a larger bolt or none at all will make it out of balance and that can cause bigger problems down the road. do it right pull the crank and replace or that it to a shop and have it fixed right. IMO
 
I would have no problem with the Helicoil but I would have a machine shop drill and tap for it. Way to easy to get the hole crooked hand drilling it and I can see no way to set it up on my drill press.:cool:
 
IOPort51 said:
I would have no problem with the Helicoil but I would have a machine shop drill and tap for it. Way to easy to get the hole crooked hand drilling it and I can see no way to set it up on my drill press.:cool:
Click to expand...
A horizontal mill would come in handy right about now.:)
 
That sucks man. It would be a cold day in hell before I pulled the crank to do that.

Might look into tapping and then running a helicoil in the current hole and then running a smaller bolt. Not sure if you had the engine balanced but a few grams aren't going to kill you.
 
Pull it. Get crank repaired or warranty exchanged. Send them some pics. show pics of the bolts, too.

Helicoils aren't designed for variable shear loads. The coil is a different hardness than the crank, to boot.

It will work lose. Worst-case scenario is Flywheel grenades with the clutch. even in a low-end loving jeep, this is bad news and potentially deadly stuff.

If you don't fix it now, you'll have to fix it someday. Who knows? You may not achieve a proper break-in with an improper crank repair.
 
I would vote for the heli-coil. Actually it will distribute the load quite well, preventing it from coming out. If you are handy with a hand drill you could make it work, I would advise a locking heli-coil and step ream it instead of drill.
 
A ream could work. I would think the torqued bolt was more of a friction joint than a shear but I would not argue that point for long. This whole thing just plain blows chunks!:eek:
 
Sometimes you can substitute and tap a Metric sized bolt into a stripped hole without re-drilling.
The 1/2 gram change in weight that close to the crank center line will not make a difference as most cranks are overbalanced anyway.
 
IMHO you need to get the old threads out not just try to put new ones over the top of old ones.
I still say take it back and get a new crank. If that hole was oversized (dull drillbit) the others maybe too, you just haven't stripped them yet.:eek:
 
I normally would just say helicoil it and move on, but in this case - you had ALL threads in 1 hole gone at <50ft/lbs.

Makes me wonder about the quality of the steel...??? :confused:

I wonder if you should continue tightening the remaining 5 to the correct torque to see if you see more issues before you dump any time or money in the 6th.

My guess is if you helicoil one hole, you'll void your warranty on the crank...
 
Update, Contacted the machine shop that provided the master kit when I had them do the machine work on the block and heads...was told the crank supplier said they inspect every crank before ship and have no control over how it is put in and will NOT swap it, machine shop didnt offer any assistance to help either so I guess that tells me what I need to know about them...huh!
I will pull the P.O.S. crank and replace it to be on safe side...My block was bored .030 over but the crank was stock...anyone have a good crank they want to suggest for me...?
thanks, Ed
 
IMHO, since they won't work with you - helicoil it. The 390 in my CJ has had a helicoil in the crank for 20 + years and it has been abused. I ran 100 yard sand drags every weekend, sludged through the mud and traveled from state to state. 60k later still going strong.

Drill it out, put some red loctite on it and helicoil it. Then drive it!

My 2 cents again - take it or leave it,
 
:agree:

Give it a shot. Im not surprised at all with the company's response. For all they know, you cross threaded it.

In my experience, heli coils are stronger than the steel that they are in.
 
Checked in with a couple of machine shops and they all believe the hellicoil will work loose, hard to redrill and retap due to the clode distance to outside edge of the flywheel. I have a new re-maned crank on the way, will also use new bolts....too bad I have to practically tear the whole bottom end and the timing area out and redo all the bearings and gaskets...oh well.
Thanks for the replies and opinions.
Ed
 
Man that really sucks. Feel bad for you.

Perseverance always prevails; you'll win eventually.
 
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