Stripped Harmonic Balancer Bolt

Rat Rods Rule

Help Support Rat Rods Rule:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

jmlcolorado

Well-known member
Joined
Jul 23, 2010
Messages
1,839
Location
The flat plains of Elbert County, CO
Need some advice folks

I bought my SB350 off Craigslist. I did a compression test and it tests out okay. I went to turn the engine by hand the other day and found the center bolt on the harmonic balancer is stripped. I pulled the bolt out to find the threads on the bolt are gawled. I can't tell if the threads inside are or not.
Does this bolt serve any other purpose other then turning the engine by hand? Should I repair this?
Thanks!


Edit:
Upon further inspection, this bolt look okay though it looks like just an off the shelve hardware store bolt. What is the length, thread and pitch this is supposed to be?

I cleaned the threads on the bolt and they seem okay. I'm thinking the PO lost the original and replaced it with the wrong one.
f1eed194.jpg


bcda2f17.jpg
 
Last edited:
That bolt keeps the balancer from coming off. The bolt looks like it is galled to me in the pictures. Thread size is 7/16 x 20, and I would use that tap size to run into the crank hole to clean up the threads. The bolt and washer are readily available, here is a Mr Gasket version. Use lots of antiseize on the bolt when installing it.

http://performanceparts.com/part/Mr-Gasket/945G

Don
 
Like Don said, run a 7/16-20 tap into the hole.
Use a bottom tap if you have one.
Measure the hole depth and buy as long a 7/16-20 grade 8 bolt that will not bottom out in the crank and you should be good to go.
No need to pull the engine apart, if all else fails you can tap it out to 1/2-20 and get a grade 8 bolt and washer.
The three other bolts just holds the pulley on and are 3/8-24 fine not coarse!!
 
Like Don said, run a 7/16-20 tap into the hole.
Use a bottom tap if you have one.
Measure the hole depth and buy as long a 7/16-20 grade 8 bolt that will not bottom out in the crank and you should be good to go.
No need to pull the engine apart, if all else fails you can tap it out to 1/2-20 and get a grade 8 bolt and washer.
The three other bolts just holds the pulley on and are 3/8-24 fine not coarse!!

Great info guys! Thanks!
Now ingot a good reason to buy dedicated standard and metric tap and die sets to replace the small one I have. [cl dang, I hate it when that happens :D
 
Some, if not all, of the old 307 small blocks didn't even have a bolt. The balancer was a press fit. I ran across one, years back, that the balancer actually came off going down the road. The easy fix: I cleaned the crank and inside the balancer up with carb cleaner, let dry and brushed some battery acid on both and slapped it together. Next morning, it was tight. I never tried to get it apart after that. I'm guessing it went to the big junkyard like that. Either that or some mechanic somewhere had a problem.:D
 
Man, I turned wrenchs in a GM dealerships

Some, if not all, of the old 307 small blocks didn't even have a bolt. The balancer was a press fit. I ran across one, years back, that the balancer actually came off going down the road. The easy fix: I cleaned the crank and inside the balancer up with carb cleaner, let dry and brushed some battery acid on both and slapped it together. Next morning, it was tight. I never tried to get it apart after that. I'm guessing it went to the big junkyard like that. Either that or some mechanic somewhere had a problem.:D

for a lot of years, Chevy/Buick and Olds / Pontiac, including when they came out with the 307 chevy motor....never did I see one with out a crank/damper bolt....not to dispute....just in my experience....was the crank threaded for it? If not, I would bet it was a mistake.....like wasn't drilled and tapped for it.... the guys on the line wouldn't care, they'd knock one on and walk away without a care....JMHO.....
 
I had a 61 Vette 283 and yes they never had one and weren't tapped either.
I was on I44 runnin around 80 and the balancer came off hit the highway bounce up hit the brake line cut it in too and v walla no brakes :(
It's not a common occurrence but, it does happen.
Short story, I wouldn't advise not having the bolt :)
 
I had a 61 Vette 283 and yes they never had one and weren't tapped either.

I still have an old 283, 1958 to be exact. It's not drilled and doesn't have a balancer, just a pressed on hub. It's a skinny little thing and maybe 5'' dia.

The early Small blocks didn't have bolts or threads, [283-327] small journel stuff. Not till about '68 when they came out with the 350 the put them on all small blocks.

Some, if not all, of the old 307 small blocks didn't even have a bolt. The balancer was a press fit.

for a lot of years, Chevy/Buick and Olds / Pontiac, including when they came out with the 307 chevy motor....never did I see one with out a crank/damper bolt....not to dispute....just in my experience....was the crank threaded for it? If not, I would bet it was a mistake.....like wasn't drilled and tapped for it.... the guys on the line wouldn't care, they'd knock one on and walk away without a care....JMHO.....

Who knew the venerable SBC could be so mystical? They're all the same aren't they? :D

I'll offer a theory about the undrilled 307. It was introduced in 1968, the same year the 327 became a large journal. Since a 307 is essentially a 283 with a 327 crank, the 307 could be made from old small journal inventory. Of course my theory goes out the window if GM never made small journal 327 cranks with a pressed-on balancer. Stranger things have happened, however.

Check this bulletin from the horse's mouth...

Cast_crank_big_1.jpg



Cast_crank_big_2.jpg
 
Make sure you have the correct balancer!!!! they are not all the same. The 327 and 350 are internally balanced and the 400 is externally balanced. I have known some one to confuse the issue and the damn engine would come unbolted everywhere all the time.

gold03
 
That bolt that was in there looks to be quite a bit longer than what it should have in it....if that wasn't right what else might be done incorrectly? You should probably inspect it even further.
 

Latest posts

Back
Top