Stripped crank: Helicoil? Tap?

I bought a 350 chevy off of a guy about a year ago and finally started to prepare it for my 51 chevy truck. To my demise I found some oddball bolt holding the harmonic balancer on. Went to autozone and bought the correct bolt and of course the crank is stripped. Now the question is do I drill and tap the hole to 1/2" and use a bigger bolt or helicoil it. Wondering which would be stronger and or easier. Any advice would help. Im pretty sure it is a cast crank.

 

I would take the crank out..have it drilled and tapped for the next size up, than tap it.

Taking the crank out and having it drilled square and straight is your best bet..dont try to do it in the engine.

 

Use a Time-sert, much better then a heli-coil. Do a search, there's been much discussion here. They use a STI tap like a heli-coil, but they are a solid insert.

 

For many hears Chevy didnt bolt on the balancers. Just relied on the press fit. After adding the bolt to the snout they still have the press fit. In all the years of running the pressed on balancers I only had one develope a crack in the keyway and come off going down the road. Wasnt a happy sound. You can always take a chance and do like we used to and press it on and hope for the best. Other than that the crank need to be taken out and chucked up in a big lathe in order to drill and tap it true.

 

Make sure you got the correct fastener.
The later sbc had a slightly larger metric fastener.
I freaked when putting a brand new balancer bolt on a new engine and it stripped.
Went and talked to my parts counter person and got the correct fastener.
Fit fine and torqued to the correct value.
I have had two more just like it since then.

 

Drill the crank, in the block, make up a sleeve that sits square on the crank and the helicoil bit just fits thru. Weld a handle on the sleeve so you don't hurt yourself and drill it straight. The old hole will actually help you keep it straight. Then install the helicoil with some loctite, don't forget to break the little tab out of it when finished. Done it with great success numerous times, which would lead you to think, why doesn't he check the crank before he puts it in??.......

 

the person turning the crank usually has a jig to fix this kind of problem. if you have ever had a balancer come off at 4000 rpm you will know why they decided to start bolting them on.

 

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........what he said.

First, of course I wonder what's wrong with the 'oddball' bolt that was in there? Did it work?

I've drilled a lot of holes for helicoil, and actually, even if you try the drill it crooked it'll tend to go straighe. Don't waste time removing the crank.

OF COURSE, if you haven't done helicoils before, get some help by a mechanic...
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helicoils suck, keyed inserts are the way to go if its that bad, helicoils suck. this is the type on insert you should use, http://www.carrlane.com/Catalog/ind...006280B1713050245221E0107070F1A3C3B285356445A

 

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Helicoils are the choice of aircraft engine manufacturers, Pratt Whitney, Avco Lycoming, Teledyne Continental, Franklin, etc., and many production automobile motor builders, VW, Porsch, etc, installed in New production alloy crankcases and assessory cases as the primary threads. I'm sure there are more.

If you can't get a helicoil to work, call a mechanic...........
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there only ment to be used once, then there screwed. junk

 

Man, you shouldn't say stuff you don't know about. Some people read here and believe it.
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I think this is the best solution.

 

BTT for more reading!

 

I stripped the bolt in my 55, went to the parts store bought the right drill bit tap and helicore for the correct bolt. I also had a drill bit 1 size smaller. since the hole was already oversized from being stripped I drilled it twice, 1st with the smaller drill bit and then with the correct drill bit. It worked fine and stayed straight. I tapped the hole, installed the helicoil and was good to go. By the way I did have to change the helicoil every time I took the bolt out.

 

In the 33 years I worked at United Air Lines I put in a lot of Helicoils and Keenserts. They are both good. For what you are doing I would put in a Helicoil or go to the next size bolt. Either way will work great. The idea that a Helicoil can only be used once is something I have never heard before and is completly untrue. I wpuld never consider removing the cranl for a repair like this. Which I did in a neighbors truck.

 

Thanks for all of the advice. It sounds like the bolt is just there for reassurance, so I think I am leaning toward helicoil but I also pondering putting in a stud after helicoiling so I would never have to take a bolt out

 

I've got one that is stripped too. I tried several things short of drilling and retapping it with a larger size. I ended up with using RTV on the bolt threads. It has held fine for over 7 years. Of course if I ever rebuild it again, I'll let the machine shop do it's thing to it.

 

yeah, if you cant drill and tap down a pre-existing hole, and make a heli-coil work for the duration then take up macrame. brake off the tang in the end, and make sure there are no heli threads hanging out the end of the crank. it'll be fine.

 

i had a 305 that was stripped & i just put in a longer bolt, held up fine,used loctite.The "balance" isn't too critical that close to the center of the rotating mass.
I think its not as big of a deal that your woried about, hole is kinda deep so a slightly longer bolt should work fine.Run the correct tap into it first & blow it out.
The "stud" idea sounds good.
JimV
PS make sure you don't use the bolt to "press on" the damper

 

The longer bolt trick often works, I did that on a diesel engine head bolt and it's still running 6 years later. Never heard the story about Helicoils not working the second time, I've reused them many times in iron and aluminum. A trick is to back up on the installation tool and tighten the coil in the hole before you break the drive tang off. I do this in aluminum, never saw a need to do it in cast iron. I've installed literally hundreds of them in the last 40 years, only had one fail and that was because the casting was cracked through the bolt hole.

 

drilled a cast big block crank in a 56 chevy .used a helicoil never had a problem.

 

If you are going to re-drill it and then tap it for a helicoil why not just go with a 5/8 18 tap and use a good grd 8 fastener. Problem solved. Yes you can drill it yourself. And if your not a retard you can also tap it yourself and get it straight. I have done it in the car and no it did not blow up catch on fire or make Godzilla come out of the ocean. It will be ok just drill and tap it. Take it slow on the tap.

 

That's exactly what I did with the snout on my 283 crank. I hand drilled it. It works fine.

 

Drill,tap,larger BBC bolt.

 

Your 350 should have originally been drilled and tapped for a 7/16 fine thread, the cool thing about it is if you strip those thread out, you can get the appropriate drill size for 1/2 inch fine thread, run the drill through (which is real easy as it just barely cuts out the 7/16th threard and leave just enough to retap), tap to 1/2inch fine, and you're done.

Much easier than doing an insert.

 

I'd first run the correct size tap all the way down, use a bottoming tap (you might have to grind it yourself). If there is at least 6 good threads, go with the original bolt and loctite threadlocker.

The next best thing is a helicoil. Make up a guide as others have suggested, drill it for the helicoil. Go with a 1.5 or 2.0 diameter insert, install the insert as prescribed, use thread locker on that as well.

Keenserts or Twinserts are a last ditch effort for thread repairing, from there you have to go with an oversize bolt.

I like the idea of installing a stud, that could work very nicely.

But you don't have to remove the crank to do a decent job on it. Ever try chuckin a crank in a lathe? First of all it has to be a pretty big lathe and you'd need to have a steady rest on it to hold the snout. Seems too much like work to me.

Bob

 

after I looked a little closer the threaded hole in the crank is in worse shape than i thought. the bottom of the hole i can see stripped threads but at the top it looks like the hole tapers bigger like someone really messed it up. I think I will try to tap in out to 1/2 fine thread, but i hope there will be enough theads in the bottom to hold it. The thought crossed my mind to somehow put in JB weld before i tapped it to give me more threads?

 

Go for the 1/2-20. If that dosn't work try a 1/2-20 Helicoil. The idea is to get something that will excert pressure on thr dampner to hold it in place. Not to glue a bolt in to plug the hole.

 

I had a METRIC bolt in mine, made it fun when it stripped out and i lost the pulley comming home from work one time, i drilled and tapped it oversized and ran it