Harmonic balance bolt

[Rick Stephens]

I always pull the pulley off the balancer and use three longer bolts and a bar to push a motor around. Only risk there is to the harmonic balancer. I too once damaged the threads in a SBC trying to pull a balancer on with the nose bolt. The threads in the crank are not very hard and strip pretty easily. Lesson learned. So don't feel like you are the first this happened to.

 

[itsbrian707]

It looks like there might be enough room for drill and tap would I use the same size bolt or bigger

 

[Rick Stephens]

Next step is to measure how deep the threads are and if there is an inch or so undamaged, run a tap in and then try an inch longer bolt. I've not had to drill and tap. Suppose it could be done a size bigger. Not something I've ever done.

 

[76SeaRay]

If you drill and tap, you probably should use a "bottom tap" so that you get threads all the way to the bottom of the bolt hole.

 

[itsbrian707]

[No message]

 

[Rick Stephens]

That looks like a 7/16 14 thread bolt. I think the nose is threaded fine at 20 threads per inch. Someone swap out that bolt on you before you bought it?

 

[itsbrian707]

Not sure I know the motor was rebuilt but that is the bolt stripped correct

 

[Rick Stephens]

Almost certain supposed to be fine thread. Might hold a tape up to it and count the threads per inch.

 

[itsbrian707]

You are right it’s 14 threads per inch, I found a 20 thread bolt near me I’m gonna try it tomorrow do you think the inside it stripped?

 

[Scott Danforth]

wrong bolt in the front of the crank. as I posted, a 7/16-20 is the correct bolt (fine thread). that pic is a coarse thread

since the pilot drills are different, someone forced the wrong bolt into the crank and FUBAR'd the threads in both the crank and the bolt

 

[itsbrian707]

So I am picking up the right bolt tomorrow... should I just tap the thread to the right one?

 

[Grub54891]

So I am picking up the right bolt tomorrow... should I just tap the thread to the right one?

Without seeing the crank itself, I can't judge how well simply re-tapping would work.
The motor was rebuilt by who? Someone may be responsible for messing that up.

 

[nola mike]

Wow, so I went back to rechecking the torque specs on the bolt. I had stripped out the first couple of threads on my crank bolt when I went to torque it to 74 lbft per the Merc manual. When Scott Danforth mentioned 60 as the max, I double checked the manual. Anyone care to chime in on these screenshots? Also Scott, my bolt was 2.23" below the head (actually that was the measurement on both engines). If the true torque value should be 40, then a) it's no wonder I stripped it out, and b) this is the second time the manual has screwed me in short order with inconsistent values. We're approaching Clymer time here.
i was able to tap out my threads, but they weren't in terrible shape and were only the first few threads. I'd be worried about getting a tap in there straight if the threads are stripped all the way. If your tap was off, you might get a ton of wobble when it runs and the bolt wasn't parallel to the crank, but maybe not.

 

[Rick Stephens]

I have never heard of it done, but can it be drilled and tapped to 1/2 fine thread?

 

[itsbrian707]

So i was just checking it out, and its a helicoil where the bolt that was on there went. I went to see the threads and there looks to be threads

 

[Rick Stephens]

Helicoils are all coarse threads...Seems stupid place for a Helicoil to me. Already drilling and tapping it to a bigger size. Might as well just install a bigger and stronger bolt.

I don't know what you do next. Certainly don't try a 7/16 x 20 bolt in there.

RIck

​​​​​​​

 

[achris]

So i was just checking it out, and its a helicoil where the bolt that was on there went. I went to see the threads and there looks to be threads

Sounds like you weren't first to try to use that bolt as an engine turning point. If it is a helicoil that has pulled out, then you are royally screwed. To try to put another, bigger helicoil in will likely push the whole thing off centre (if it isn't already). If it were me, I'd be taking the engine out and either stripping it down for a replacement crank, or just finding an old 350 and building it up as a 'new' engine, or taking the opportunity to make it up as a 6.2 litre engine.

Chris......

 

[itsbrian707]

Tomorrow I am going to see what i can do the Orginal threads for the OG bolt dont seem Messed up, so I dont know what is going on.

 

[Rick Stephens]

I would have to say that doing a quickie rebuild with a new crank and bearings plus gaskets would be fast, relatively inexpensive and quite satisfying as far as the results. Crankshaft for a SBC just doesn't cost much. ANd the fresh rebuilt motor will need a minimum of attention.

Of note, when I bought a donor boat with a freshly rebuilt 0 hour motor, unbeknownst to me the motor had been left with the flame arrestor off the carb and a tarp over the motor. That brand new motor was full of water. I spent all told less than $600 reboring and replacing brand new shiny pistons rings and gaskets with new shinier gaskets pistons and rings. So I know just what this feels like.

 

[tank1949]

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?

I learned the hard way decades ago on an Chevy Truck. Do not turn motor using balancer bolt. I seems like I had to rethread it and of course I had to pull radiator and other "hangons" to access it.