350 small block with m12 crank bolt?!

[Bruce Wingate]

And Ace is closed on Saturdays.

I did my best to clean out hole in the crank and managed to get the new bolt in but not far enough. I can get the old bolt in until I think it bottoms outs. I have to double check, but I think now the problem is that the new bolt is too long. I'm going to clean out the hole a few more times to be sure, but I should be able to sort this out.

 

[BillK]

Bruce,
I just checked a couple of cranks I have here and the stock bolt threads in just about 3/4" into both of them. Do you have the big washer that goes on the bolt ? It is almost 1/4" thick.

 

[Bruce Wingate]

I have the big washer and I put the whole assembly together and the new bolt's base sticks out about 1/2 an inch (this is not torqued down, dry without antisieze). I'll do the math later and try to figure out how much of the new bolts threads are captured, but it is at least 1/2".

 

[MikeB]

Maybe someone stripped the crank threads trying to suck up the balancer with the bolt, then tapped it for 12 mm.

Yes, that's the only thing I can think of.

It would strange, but using a new 12mm bolt may be the way to go. I don't know what else can be done other than replacing (or possibly repairing) the crank.

 

[Raider L]

@Bruce Wingate,

Since everything that used to be Standard, 7/16" - 20, is now metric! Find you a metric scale and measure that bolt and I'll bet you it's metric! It being so big my scales don't go that high or I'd tell you what it is.

Don't think that just because it's a Chevy part that means it's standard. Not any more. And they won't tell you that fasteners are all now metric either. I guess they leave that up to the customer to either know, or find out. If it won't go in but part of a thread, it's metric.

Bruce, don't retap the crank, that would be terrible if you ever wanted to use that crank for something else in the future. Just go get the right length 7/16" bolt and put that in. It's no wonder if it had been someone else they would have had a 3 foot breaker bar on that sucker cranking down on it by standing on the end of the bar and bouncing on it to get it to go in, ha, ha.

 

[BillK]

dry without antisieze)

Bruce,
The torque spec is for oil only. If you use anti-seize you can actually overtighten the bolt and risk stripping the threads. Just keep that in mind when you tighten it. I have never used anything but a little oil on those bolts.

 

[Bruce Wingate]

@Bill K thanks for your help, after a couple of false starts, I got the right chasing tap and cleaned the threads up. A little oil on the threads and I got the bolt all the way in and torqued down.