Harmonic balance bolt

[itsbrian707]

Hi all, So i was looking through my engine bay and noticed the Harmonic balancer bolt was stripped a little bit and it came off, there is also a spring type thing coming out... Do i need to replace the harmonic balancer bolt of the actual thing?

 

[achris]

Spring thing? Could that be the threads that have been pulled out of the end of the crank?

Has anyone recently tried to turn the engine using that bolt?

 

[itsbrian707]

possible not sure it almost looks like a helicoil

 

[nola mike]

Sounds like those are the remains of the threads from your crank. What are you working on?

 

[itsbrian707]

I was fixing a cooling problem with the engine, Is there any way to fix that?

 

[achris]

I was fixing a cooling problem with the engine, Is there any way to fix that?

Usually, replace the crankshaft... What engine are you working on?

 

[itsbrian707]

its a 87 mercruiser 5.7 I dont want to replace the crankshaft

 

[achris]

You've pulled the threads out of the front end of the crankshaft. Your harmonic balance is staying there with just a little friction, and it's going to come off without a high tensile bolt holding it in. Unless you have access to the front of the engine to get a VERY straight drill and tap in there, you will need to get that engine out. Some cranks have a hardened 'nose', so drilling and tapping is completely out of the question. Start removing the drive and unhooking the engine, ready for it to be lifted.

And don't even thing about running the engine without the bolt. When that balancer comes off, spinning at 3,000+ rpm, it's going to do a LOT of damage, possibly even hole the boat....

Chris......

 

[Scott Danforth]

its a 87 mercruiser 5.7 I dont want to replace the crankshaft

You tried turning the motor over with the crank bolt, didnt you?

Only two choices, pull the motor, pull the crank and replace it

Or

Pull the motor, pull the crank, take it to a machine shop, have them drill and tap the crank with a helicoil, polish the journals

A new crank is cheaper

 

[nola mike]

achris Scott Danforth Is it possible to get a longer bolt? It looks like on my crank that the threads go significantly deeper than the bolt, maybe an inch or so anyway (didn't measure, but certainly a good bit deeper than the bolt). Service manual calls for 1/2" of thread engagement...
I might measure it on the junked 4.3.

 

[itsbrian707]

The bolt it’s self stripped

 

[Grub54891]

Can you post a pic of the bolt and end of the crankshaft? I've personally accidently cross threaded that bolt, just a bit but the bolt is a harder material than the crank. Hard to believe the bolt itself is damaged. Either way, it needs to be fixed properly or all the bad things will happen that others have listed.
A buddy was driving along a gravel road once with a used car he bought cheap. Suddenly started running rough, stopped and opens the hood, belts off, pully missing, radiator leaking, and a big hole in the gravel where the pully hit the ground and proceeded to never be found again.
In my case I was able to save it, but it was just two threads that got damaged. Still made me nervous.

 

[Scott Danforth]

The bolt it’s self stripped

you will need to post a pic of that.

it would be the only grade 8 bolt in history to have its threads stripped out in a crank application on an cast crank SBC

not even forged cranks should strip the threads from a bolt its always been the threads come out the crank snout.

and in 99 times out of 100, its from someone putting a breaker bar on the crank bolt to turn the motor. that other 1 time is when someone tries to pull the damper in with the bolt

you may be able to get a longer bolt as Mike mentioned, the threads are usually about 1/4-1" longer than the bolt you would have to measure prior, however you will need to clean up the threads that are in there to begin with prior. that means getting the proper tap to begin with.

sbc damper bolt is 7/16-20 thread

stock length is 2.470" under the head.

you will need to measure with a caliper or depth gauge the depth of the existing pilot hole and threads prior to determining if you can simply run a longer bolt.

 

[itsbrian707]

I will post a picture when I get back from work I put a socket on it and twisted it just a bit and it started to slip and then I stopped it was no breaker bar

 

[Bt Doctur]

If you put anything on a crankbolt to turn an engine you just screwed the pooch

 

[Bt Doctur]

This is the tool you must use click to enlarge

 

[itsbrian707]

Wym screwed the pooch

 

[76SeaRay]

Before doing anything else, it might be helpful to take some measurements in case the bolt was way too short. Guessing the damper is on all the way since it sounds like it has been running but if it wasn't that would shorten the amount of thread engagement. Get a set of calipers and measure the depth of the bolt hole (to the bottom) from the surface of the balancer. Then, measure from the end of the crank to the surface of the balancer and note the difference. Now check the length of the bolt that came out and how much thread was stripped. This will tell you how far into the end of the crank the threads are stripped. With that info, a machine shop can give you guidance on what to do... I am at work but when I get home tonight, I can measure mine and get you some info to compare as I am assembling my new engine, just put the damper on last night but have't put the damper bolt in yet.. I need to do that anyway since I need to make sure I have the correct length bolt myself as I am scratch building my engine... Mine is a 1996 5.7L... I will post later tonight o

 

[Bt Doctur]

also known as FUBAR

 

[Scott Danforth]

SBC damper bolts are 2.470" from under the head to the end of the threads

if you tried turning the motor over with the damper bolt, you stripped the threads out of the end of the crank. as indicated prior, 99 times out of 100 stripped crank bolts is from someone trying to turn the motor over by the crank bolt. the other 1 time is when people try to pull the damper on with the bolt and not use a damper installation tool

the only way to turn a chevrolet based motor over by the crank is with the tool that is in post #16. this is every chevrolet 4 cylinder, 6 cylinder and 8 cylinder. the torque required to turn your motor over with the plugs out is almost twice the torque needed to strip the threads out of the crank (about 90 lb-ft), and about 3x the torque required to torque the bolt (60 lb-ft max)

the only engines you can potentially turn over with the crank bolt are the old pontiacs where the bolt has a torque spec of 160 lb-ft