stripped crankshaft harmonic balancer bolt - Chevelle Tech
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  #1  
Old Jan 5th, 08, 6:43 PM
dsy1 dsy1 is online now
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Default stripped crankshaft harmonic balancer bolt

When trying to turn the engine to adjust the valves using a socket on the crankshaft harmonic balancer bolt, I found that it is stripped. The treads hold enough to not get loose when driving, but they don't grip enough to turn the engine, the bolt just turns instead. I was able to get the valves adjusted by turning the engine using a pry-bar on the flywheel teeth, but that is a pain.

Any experience here, or ideas to repair this correctly? This is a '69 with 396.
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  #2  
Old Jan 5th, 08, 7:03 PM
Dave427 Dave427 is offline
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Default Re: stripped crankshaft harmonic balancer bolt

Is it the bolt of the crank?

Dave
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  #3  
Old Jan 5th, 08, 7:07 PM
dsy1 dsy1 is online now
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Default Re: stripped crankshaft harmonic balancer bolt

Yes, this is the large bolt into the front of the crankshaft. Also...I already tried some mix-together hardening thread repair product I had on hand, but it didn't hold up to the torque needed to turn the engine. I think the threads are 1/2"-13, but I don't recall exactly.
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  #4  
Old Jan 5th, 08, 7:12 PM
Dave427 Dave427 is offline
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Default Re: stripped crankshaft harmonic balancer bolt

This is not a great repair, I used red loctite and loctited a stud in the end of the crank let it dry overnight then just put a nut, lockwasher, and the big flatwasher back on.

Dave
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  #5  
Old Jan 5th, 08, 7:14 PM
trmnatr trmnatr is offline
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Default Re: stripped crankshaft harmonic balancer bolt

You can heli coil it but you should not turn the engine over by the bolt, you should bump it with a starter button or the flywheel
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  #6  
Old Jan 5th, 08, 7:16 PM
Tom Mobley Tom Mobley is offline
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Default Re: stripped crankshaft harmonic balancer bolt

up front, the balancer is a press fit on the crank, the bolt is a safety device. Early SBs weren't even drilled for a bolt. BBs are famous for having a really tight press fit on the balancer. Often normal pullers break before moving them, etc.

Now, unless you are a highly skilled and tooled up guy or you know somebody who is the chances of getting that properly repaired with crank in the engine are about zero, zip, nada and all that. I'm not saying it can't be done, but there's a good chance of ending up worse off that you are now. The hole need to be drilled oversize and a long heli-coil installed or just drilled to the next size and tapped. Either way the drilling must be dead straight in all respects and the chances of doing this in the car with a hand held drill are slim, IMO. Best way would be to pull the crank and do it in a lathe.

One thing you could do is investigate whether the existing bolt is too short and pulled the first few threads. In that case there might enough threads left in the bottom of the hole for a longer bolt to grab. Have to be careful not to get one too long and bottom it out in the hole.
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  #7  
Old Jan 5th, 08, 7:17 PM
dmg1029 dmg1029 is offline
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Default Re: stripped crankshaft harmonic balancer bolt

That would be one large helicoil
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  #8  
Old Jan 5th, 08, 7:22 PM
JimM JimM is offline
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Default Re: stripped crankshaft harmonic balancer bolt

I agree with Tom, but... Brian Lewis on the camaro site did it, and posted a nice writeup on how. It involved running the drill thru a block clamped to the balancer (with a known straight hole all ready in it) to guide the bit.

Search that user name over there, posts started by... it was last summer.
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  #9  
Old Jan 5th, 08, 7:30 PM
trmnatr trmnatr is offline
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Default Re: stripped crankshaft harmonic balancer bolt

I have done two of them in the car but you have to remove the radiator and use a 90* drill, for some this may be an issue but i think you can buy a right angle drill at sears, mine is makita
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  #10  
Old Jan 5th, 08, 7:31 PM
frankf72malibu frankf72malibu is offline
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Default Re: stripped crankshaft harmonic balancer bolt

You can also see if the bolt will thread all the way in without the thick washer. If so, then use a thinner washer. As Tom said above, the bolt is a safety device and as long as the washer is not too thin you should be OK.
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  #11  
Old Jan 5th, 08, 7:32 PM
trmnatr trmnatr is offline
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Default Re: stripped crankshaft harmonic balancer bolt

Also, as tom said you must be straight, i have drilled out many cooler line fittings in 727 chrysler transmissions in the car but it must be done with a right angle drill.

I can drill out bolts or brass fittings broke off and you dont even have to tap them, the key is start off small and work your way up, if you start drilling start with 7/16" and work your way up to the drill bit needed for the thread insert
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  #12  
Old Jan 5th, 08, 7:48 PM
BillsCamino BillsCamino is offline
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Default Re: stripped crankshaft harmonic balancer bolt

Will the bolt come out? If so, 'ya got it made.

Helicoils work fine but this is simplier...

The original crank bolt is 1/2"-20 thread.
So, REAM the hole to 33/64 (.516") and then tap the hole 9/16"-18.
The reamer (unlike a drill bit) will follow the original hole.
Then, just install a 9/16"-18 bolt. Done.

I've done this a few times...motor in the car...it work's fine. Trust me.
I've also stepped up SBC crank holes to 1/2"-20 using the same method.

If you have any trouble locating the correct tooling, drop me a line and I'll send you a "First Aid" kit.
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  #13  
Old Jan 5th, 08, 8:24 PM
oktunes oktunes is offline
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Default Re: stripped crankshaft harmonic balancer bolt

Just went thru this same deal on my 396. The bolt had been loctited in and I couldn't get enough good threads for a longer bolt to hold.
I was lucky and the local machine shop I frequent is a little hometown operation. One of the machinists had a tap for a metric bolt that is just slightly larger then the stock sae bolt. I was able to tap the oversize metric without drilling out the old threads with the motor in the car. Bought a new metric bolt that used every bit of thread depth in the crank and loctited it in. No torque wrench, but probably got it to 50-60 lbs or better. It is tight and firm.
I didn't try to turn the engine with the new bolt.
Summit/Jegs make a front crank turner that mounts with the three pulley bolts and has a nut you turn. Cheap and you can turn it all day without stressing the threads on the crank.
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  #14  
Old Jan 5th, 08, 8:41 PM
Tom Mobley Tom Mobley is offline
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Default Re: stripped crankshaft harmonic balancer bolt

good info here.

the reaming deal I never thought of. Excellent idea.

the slightly larger metric bolt deal sounds like a winner too. Just realize with any of these that a quality tap will be needed. These taps are not sold in $10 kits at a chain store. minimum quality level might be a Craftsman.

making a drill guide is a good idea, depends on the skills of the guy working on it and making the guide.

is this a great site or what?
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  #15  
Old Jan 5th, 08, 10:00 PM
BillyGman BillyGman is offline
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Default Re: stripped crankshaft harmonic balancer bolt

Yep, I agree that there were some good suggestions here alright. I'm just curious though.....did you have the spark plugs out when you were trying to turn the engine over by hand? I usually bump the starter over myself with a jumper switch as it was previously mentioned. But the few times that I have turned engines over by hand with a breaker bar and a socket, I've removed the spark plugs first. It's still takes some torque to turn it since you're fighting the valve springs, but it's considerably easier than trying to do that with the spark plugs still threaded in since you're also having to fight the compressed air inside the cylinders.
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