Harmonic balancer bolt and other sources of frustration

[Terry S]

So here's the deal.

I was moving my 72 swb around in the driveway several months ago when I started noticing white smoke coming from both sides of the dual exhaust. So I say to myself; "Self old pal, what you've got here is antifreeze from a loose intake manifold. Not a problem, we'll just fix that right up when it gets a little warmer." The truck is undergoing major body work so it's not like I have to have it fixed in time for work on Monday.

Anyway, after several weeks I dig into this thing and, by using my Columbo-like powers of observation, I quickly eliminate all of the easy to fix (cheap) potential causes. When I got the heads off, I found a huge vertical scratch in the number 4 cylinder bore where it ate God-only-knows-what. So I say to myself (slightly less optimistically) "Not a problem, you were planning to freshen up the motor some day anyway, this summer will be a good time to take it .030 over and maybe even go with a hotter cam...hey, what's this little .040 that's stamped in the top of each piston?#$!!!." Oh, by the way, the white smoke was coming from not one but two cracked heads

So anyway, I used this engine along with a virgin bore that needed to be sleeved (that one had 305 heads on it when I got it???) for a core on a rebuilt .030 over 350 with a nice cam.

That brings me to the reason for this this thread. I got my new engine back from the shop last week, so after my wife and kids went to bed last night I snuck out to the garage and spent until the wee hours painting it up pretty and hanging accessories. About 3:00 a.m. I was installing the harmonic balancer with a long bolt and managed to pull out a heli-coil insert right out of the end of the crank (suprize!)

I'm going to call the local shop that did the rebuild and see what they want to do, but I would like some input from you guys as well; What are the chances that they can put another heli-coil in it? Should I push to have the crank replaced. I really don't want to have to take everything apart again, but better now than later if it comes to that.

All input is appreciated

[jef5150]

i work in a machine shop,<not-automotive> anyway as long as the threads on the crank are NOT stripped they can run a "heli-coil tap"back through the threads,to clean them up,and re-install another "same size heli-coil",,there are 2 types of inserts,[locking] &[non-locking].Obviously whoever put the old heli-coil in used the WRONG type .You need to put in "LOCKING-TYPE"......I do not know if useing a heli-coil is a common fix for cranks,,but you can replace the heli-coil,,,,,,see if they can fix it but, its no big deal to replace one yourself,,,,,

[Terry S]

Thanks for the info, but I think that I need to clarify a little. The threads in the crank are appear to be pretty much shot, lots of filings and so forth. Also, the heli-coil came out in pieces, not all at once, like it was the non locking type.

I'm no machinist, but I'm pretty sure that the threads on the crank will have to be taken up from 7/16 x 20 to the next larger size, whatever that is (1/2 x 20?).

Is there a heli-coil insert that can do that and still keep the i.d. the same size so that a standard crank bolt will fit?

Otherwise, can anyone think of a down side to going with an oversized bolt to hold the balancer on?

[jef5150]

ok,well,since the threads are trashed,your gonna hafta re-drill & re-tap,to the next size up....However,I would "STRONGLY" ADVISE" that you dont even think about doing this with a hand drill!!!!!!!More than likely you'll end up bellmouthing the hole & you wont get an even % of thread down the hole....I know you dont want to hear this,but your probably gonna have to pull it and have it done by a shop,,,,,if it can be done at all,,,

[hanssolo]

My crank snout threads are a little chewed but I always get the balancer on by smoothing it out with my die grinder and a tootsie roll so it goes on smoothly. But yours is a different matter altogether. If its already so chewed up that next size tap will rethread it w/o much hassle you might go for it. But what rpm or horsepower you have will be dependant on this. I can't say what levels it'll take or for how long. If its stock or mild it should be OK for a while IMO. The balancer will still be true and thats the first important thing. Can you weld up a snout and re-drill it at the machine shop? Sounds like you're close to a re-build maybe with all those problems. You probably want to ask will your engine overheat at .060 next.

[cdowns]

man that really sucks!!! but it just sort of reenforces the opinion that in the long run a new crate engine is the way to go

[Terry S]

Hey guys, it's a new rebuild from a reputable shop, so I'm sure that they'll make it right. worst case scenario, I'll just buy a new crank (ouch) but in all honesty, I still think that it's cheaper in the long run than a crate engine, especially for a daily driver.

I guess that I just wanted to vent a little frustration with this thread, but mostly I was just hoping that someone could tell me if it was commonplace to oversize the crank bolt so that if the build shop suggests that, I could have some idea of whether or not I should go along with it.

[Fred T]

I'd be calling or visiting the shop and asking what they will do to fix the problem. Personally, I would not have used a Heli-coil, but would have drilled and threaded for a larger bolt. These holes can be drilled by hand, but you have to be good at it. A job best left for the experts, like jef5150 said.

[73stepside]

i've seen heli-coils in aluminum housings with way more torque on them than a h-damper that have lasted wel over 30 years. if the machinist did the job right then you would not have had this problem. take it back and have them fix it or give you a good crank. heli-coils done right will hold and last for a good long time. just think of all the military guys changing aircraft parts alot and have them last 30 years with that type of abuse.

[71GMC_3/4T]

I would suggest NOT using the "Locking" helicoils! At least not the ones I'm used to calling "locking". They have a deformed thread and are designed to retain the bolt. Experience tells me that they wreck the threads on the bolt with one use.
Maybe you are referring to "keenserts"? These are the ones where you tap a hole the next bolt size up and screw in the keensert. After it's in, you drive the pins down which locks it in place. They work very well and you use standard sized taps to install them.
I wouldn't worry too much about getting the hole perfectly true. The balancer is centered by the slip fit on the crankshaft. The bolt pulls it up and holds it in place.