302 Crankshaft Thread Problem

[68Blue302Coupe]

So today I was removing and reinstalling my harmonic balancer (had to take it off to fix something else) and I used a harmonic balancer puller to remove it, rented the tool from a near by auto parts store. When I went to reinstall the balancer it appears that I damaged my first thread on the crankshaft. I don't know how it happened, but maybe I used the tool incorrectly--it occurred to me that maybe I should have some kind of washer or spacer between the end of the puller and the crankshaft.

But anyhow, now I can't thread the large crankshaft bolt in, the one that holds the balancer to the shaft. I can't get it started on the crank, though I can see plenty of good threads left.

I don't want to make this any worse. I thought about getting the correct tap for the threads and just cleaning up the first thread or two on the crankshaft. Would this work? I just need it cleaned up so I can thread the bolt in straight--the crankshaft does not need all the threads recut.

Anything else I should do? I know this is the death blow to an engine, I don't want to do more damage. I also saw a tool called a "thread restorer" at Sears, sortof a more mild version of a tap. Should I use this isntead?

Oh, last, the threads on a 302 harmonic balancer bolt are 5/8" 18, right?

 

[sparx]

I think the only thing you can do is chase the threads. If you have a machine shop nearby you might want to drop in and ask them for advice.

I assume the engine is in the car so those threads cannot be closely examined.

I am not sure what bolts you are asking about but the pulley to balancer bolts are 5/16".

 

[D.Hearne]

Get a tap with the correct thread count and run it into the hole. But make sure it's not a "Bottom tap". A standard tap will be tapered so it'll first contact the threads past the damaged portion, that way it'll be be correctly started so that when it does contact the damaged threads in the end of the hole, it will already be indexed to the rest. What happened here is the stud that went up against the crank snount was small enough in diameter to go into the bolt hole and damage the threads, instead of seating itself against the end of the crank.

 

[68Blue302Coupe]

Ok, so kinda big problem today. I found the tap, cleaned up the first few threads (or so I thought) and threaded in the crank balancer bolt to test the threads. I got it started but about half way in the bolt stopped, was stuck. I tried to back it out, and stuck that way too. It took my impact wrench a while to get the bolt out, and the threads on the bolt are toast. I assume the crank threads, probably most or half of them, are toast too.

Ideas!? Am I looking at a new engine now? I have never replaced pistons or a crankshaft, and am not sure how hard this is. I've had quite a few set backs with this car as it is.

Since I have the tap, should I try to just recut all the threads? At this point could it be any worse? Any way to save this? Heli-coil, recut threads + locktite, welding, etc.?

 

[sparx]

Did you run the tap all the way down?

 

[68Blue302Coupe]

Hey,

No, just enough to get it turning smoothly. Ironically, I didn't want to cause any damage to the threads!

I guess another option is a scrap metal buyer. Must be easily a few thousand pounds of iron and steel there....

 

[sparx]

Well I would have run it in as far as possible.
How much resistance was there when tapping?
Oh, forgot to ask but what is the tap thread pitch and size?

 

[68Blue302Coupe]

I was using a 5/8"-18 tap--seemed to match the bolt exactly. So, what do you think? Should I go back and try retapping--would that work if some thread are already damaged?

 

[sparx]

How does the bolt look was it stripped, how much resistance was there when tapping?
Did you use oil?

 

[68Blue302Coupe]

Hey,

There was little resistance when I was tapping. Some, but not much. I only ran it in a few turns, what I thought was enough to clean up the threads. The crank bolt itslelf has piecse of thread near the tip of the bolt missing. It's hard to get a good look inside the crank. I can try to get a picture in there.

 

[sparx]

You didn't chase enough.
I would not put that same bolt back in.
I would try to chase the threads again, slow and careful with cutting oil on the tap.
Do you have tapping experience besides today?

 

[D.Hearne]

Did you use the impact to screw the bolt in ? If you did, that was your second mistake.

 

[2+2GT]

Did you use the impact to screw the bolt in ? If you did, that was your second mistake.

Yep. NEVER use an impact on this bolt.

 

[68Blue302Coupe]

Hey all,

Thanks for the replys, appreciate the help. I screwed the tap in first by hand and then using a small wrench, very slowly, and (what I thought) was checking to make sure it went in straight. I only broke out the impact to get the bolt out after the socket wouldn't work. I have run a few taps but not many, really just a few and nothing this size, just smaller ones.

 

[D.Hearne]

I use one to loosen it, but never to run it in the hole.

 

[68Blue302Coupe]

Yeah, on the tap I used a small wrench after threading it in by hand, and on the actual bolt I used a socket wrench, slowly, until it got stuck, and then I tried to back it out with a socket, got stuck on the way out, so I used an impact.

 

[sparx]

Well when you tap, lube the tap.
Turn the tap a small amount then back it up. In and out and keep it lubed. You also may need to back it all the way out and clean up and go in again.
Also clean out all the chips before you try a NEW bolt.

 

[68Blue302Coupe]

Thanks, I'll give it a try tomorrow evening and let you know how it goes. If I can run the tap do you think there will be enough material left with a re-thread to hold the balance in place? Should use locktie or anything on the bolt?

 

[2+2GT]

Should use Locktite or anything on the bolt?

I would. You don't want to see what happens if this bolt loosens, even a little. Ask me how I know.

 

[sparx]

Big problem if it loosens.