302 Crankshaft Thread Problem

68Blue302Coupe · Nov 24, 2009

I was able to retap the threads on the crankshaft. I used lots of oil and cleaned the threads out every couple turns. Also made sure to run the tap back in again, now it threads in smoothly. I tracked down a new bolt, picking that up tomorrow and plan to reassemble this week.

As far as putting the balancer back on, since I have had to rethread, should I still use the balancer installation tool or tap the balancer on with a mallet? What about torquing the bolt down? I am going to use locktite on the bolt--should I torque to factory specs even with the recut threads? Any suggestions?

Thanks again, that advice on tapping worked great.

sparx · Nov 24, 2009

Best to use the installation tool, mallet not good idea.
I never heard of using lock tite, maybe others have an opinion.
I would be sure all is clean and try the new bolt by hand first. Looks like you are on the way to success.
I believe the torque spec on that bolt is 70 fp.
sparx

2+2GT · Nov 25, 2009

sparx said:
Best to use the installation tool, mallet not good idea.
I never heard of using lock tite, maybe others have an opinion.
I would be sure all is clean and try the new bolt by hand first. Looks like you are on the way to success.
I believe the torque spec on that bolt is 70 fp.
sparx

After this happened, I used Locktite on the replacement. I know it had been installed at the proper torque, because I installed it.

68Blue302Coupe · Nov 25, 2009

Success! I picked up the installer and had the balancer back on the engine by late this afternoon. Used locktite on the new bolt and was able to torque it back to spec. Looks like it worked! Thanks again for everyone's help, thought that crankshaft was a goner.

sparx · Nov 25, 2009

That's good news 68, be sure to use the correct puller next time.
sparx

1992MustangGT · Nov 26, 2009

Hey guys I have a similar problem with my crank shaft bolt and need some advise. I just rebuilt a 351 windsor and put it in my 67 Cougar XR7. When I was attempting to put on the damper and pulley, I noticed that the crankshaft bolt wouldn't even start to thread in the crankshaft. So I chased the threads with a tap and the bolt screwed in just fine after that. But the problem I have now is when I was using the crankshaft bolt to manually rotate the engine to find top dead center so I could install the distributor, I noticed that the threads on the bolt started stripping and the engine was not turning. So now I'm not sure what to do. Should I just take out the crankshaft bolt and put locktite on it and put it back in or is there a better option? Should I helicoil the threads (I think that's what it's called; putting in new threads) or just use the locktite and call it good? Now keep in mind that the engine is in the car and I don't want to pull it back out to fix this problem. How hard is it to helicoil new threads? I'm pretty good with mechanics, so I'm sure I could do this myself. I just don't know how to do it. If that's the route I should go, can someone tell me how to helicoil threads?

woodsnake · Nov 26, 2009

Heli coil in crank shaft bad.

Heli-Coil ( HeliCoil Inserts ) Helicoils Screw Thread Inserts | Emhart.com

Try and re tap the crank.
Get a new bolt, and try it again.
This is repairable, but be careful!

1992MustangGT · Nov 27, 2009

I assume that it's the threads in the crankshaft that's stripping, but if I rechase the threads won't I have the same problem? I'm guessing the reason it's stipping is because alot of the thread material was removed when I had to chase the threads the first time, therefore when I put some torque to it the threads probably weren't strong enough to hold and started stripping. I'm assuming if I chase them again, the same thing will happen......

So let me ask this....Is it possible to chase the threads with a size larger tap? Well of course it is, but I guess what I'm getting at is do they make crankshaft bolts in larger sizes or are they all the same size? If I can get a larger bolt, then my issues may be solved. All I would have to do is tap the crankshaft to a size larger then the new threads I made would be just as strong as the original; correct? Am I on the right track with my thought process?

68Blue302Coupe · Nov 27, 2009

Hey, I feel your pain! I think if you can retap and get a new bolt to torque to spec you should be OK, though I personally wouldn't use the bolt anymore to turn the engine. I used locktite, too, for a little added security.

Sounds like we had the same problem, I couldn't get the bolt to even start threading. I think it was either the balancer puller or the installer that damaged the threads.

The end of the puller has a cone-shaped tip that may have dug into and squashed the first coupe of threads.

I also suspected the installer. On the one I rented, I noticed that if you thread the tool into the crankshaft all the way (until it stops turning) part of the tool is pressing against the threads and could damage them. When I put the balancer on this last time, I was really careful to back the tool out about 1/2 turn, and made sure I held it steady with one wrench while using another wrench to turn the large nut that presses on the balancer.

68Blue302Coupe · Nov 27, 2009

As for using a larger bolt, I did some searching on this and seems like there are two theories. One, its fine; two, you could throw off the crankshaft balance. While I was able to fix this with the same size bolt, I considered using a larger bolt as a last resort if retapping failed.

I went to a local specialty bolt/fastener/hardware shop (not a mega home store or auto store) that had every size, grade, and type of bolt imagineable. They had grade 8 bolts that matched my crankshaft bolt by the 10 pack. If you have anything like this near you, I am sure you could find something that would be just a little larger than your current crank bolt (standard or otherwise). You'd also need a corresponding washer, or just drill out your existing washer.

woodsnake · Nov 27, 2009

It seems to me, (from memory here) that there are like 2 inches of threaded area inside the crank shaft, isn't there? I could see if you effed up a 1/4 inch or so the bolt might slip, but if you striped out two whole inches of threads, I think I'd look at pulling the crank, getting a couple boxes of bearings, and getting the crank properly repaired.

But that's me. I know it will be a pain, and, probably once you get it back together it won't ever come back out, but still. If it striped out two inches of threads, it needs major help.

1992MustangGT · Nov 28, 2009

woodsnake said:
Heli coil in crank shaft bad.

Heli-Coil ( HeliCoil Inserts ) Helicoils Screw Thread Inserts | Emhart.com

Try and re tap the crank.
Get a new bolt, and try it again.
This is repairable, but be careful!

Woodsnake, why do you say using Helicoils on a crankshaft is bad? What is the issue with doing so?

302 Crankshaft Thread Problem

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