Team Chevelle banner
1 - 18 of 18 Posts

·
Registered
Joined
·
13,473 Posts
Discussion Starter · #1 ·
I'm getting ready to swap the fresh 383 into my 51 Chevy and when I went to move the 56 Vette last night to make room for the 51 engine swap, I heard a clanking noise toward the front of the Vette engine. To make a long story short, I've diagnosed it as a broken crank at the front of the crank (apparently just behind the front main). The balancer/pulley rotate back and forth WITHOUT the rest of the engine turning. No telling how long it's been broke.
So, once the new 383 is in the 51, I then get to pull and tear down the 400 in the Vette! When it rains, it pours! :(

I have a couple of 400 cranks, but the one in the Vette is internally balanced with heavy metal and I bet it's going to be impossible for my machine shop to match the balance on another crank.
 

·
Premium Member
Joined
·
11,205 Posts
Sorry to hear this.....
I've not heard of any breaking
 

·
Registered
Joined
·
2,384 Posts
I've never heard of a 400 chevy breaking, but I've witnessed a ford 5.0 truck motor snap the crank between the 2nd and 3rd main caps. Sorry about your luck though.
 

·
In Memoriam
66 El Camino 57 Chevy pickup 2004 Tahoe
Joined
·
29,419 Posts
I had the second rod journal fall off a 400 crank, but it was on the front straight at
Manzanita Speedway in Phx where a cast crank has no business in the first place. They're nodular iron, pretty tough.

I saw another where the middle main cap broke, more or less the whole part between the bolts fell off. Never know whether the crank or the block broke first.

dirt track racing in Phx in the summer is pretty hard on engines.
 

·
In Memoriam
66 El Camino 57 Chevy pickup 2004 Tahoe
Joined
·
29,419 Posts
Was that crank ground down to 350 mains? have a look at the radiuss (radii?) on the main journals.
 

·
Registered
Joined
·
13,473 Posts
Discussion Starter · #8 ·
Was that crank ground down to 350 mains? have a look at the radiuss (radii?) on the main journals.
Tom,
When I built that engine, it was a virgin 72 400 (4bolt block) and as I remember, the crank went .010-.010. I put it together with stock bolts and the factory Chevy stud bolts for a windage tray and a hi-volume oil pump. The FRONT of the crank is internally balanced so that I could use the hi-perf 327 finned balancer (didn't want the obvious 400 balancer). The rear of the crank has an external balance flywheel.
I built the 400 for the 56 Vette to be a serious "hotrod", and I do kick it in the @zz from time to time. Funny, things like a broke engine doesn't really bother me. I'll just build another one. But if someone puts a little nick in the paint, they need to have life insurance paid up! :D
 

·
In Memoriam
66 El Camino 57 Chevy pickup 2004 Tahoe
Joined
·
29,419 Posts
I understand completely. I can build an engine anytime, but dents and chips, no good.
 

·
Registered
Joined
·
13,473 Posts
Discussion Starter · #10 ·
Externally balanced correctly? Correct damper/flexplate or flywheel?
What the heck is a flexplate?????????????????? :D
 

·
Premium Member
Joined
·
1,499 Posts
Hey DZ,
A friend who use to own a 409 64 Impala must of over revved the motor because when the motor was idling it was making a ticking noise. He pulled the 409 out removed the oil pan and found nothing. He looked in the oil pan a found no metal shaving. It was clean.
Then he removed all the main and rod bearing caps and the journals were smooth as glass. He pulled the crank out to our surprise a piece of the crank at the rear from 7 and 8 fell off. There was hair line fracture we did not see. It was so perfect you could not see the line. The line was angle in such a way it interlock in the crank. Nothing else was damaged, so he found another 409 crank put it in and the motor ran perfectly normal. :D
 

·
Registered
Joined
·
13,473 Posts
Discussion Starter · #13 ·
Well, I did sort of get lucky.
First, the crank isn't broke.
Somehow, someway, the balancer apparently loosened up which apparently is the result of the crank bolt becoming slightly loose.
So, my nice chrome plated finned balancer is junk! :(
After continuous slipping back and forth on the crank snout, the key was severely worn, a big notch was worn inside the balancer keyway and the ID of the balancer hub has become enlarged due to the balancer moving back and forth on the snout.



The outer outer edge of the keyway in the crank snout is worn some, but a test fit of a new key in the keyway is nice and snug in the bottom of the keyway.

Tomorrow I'm going to take two balancers and the finned balancer to my machine shop and have them match the balance of the two balancers to the chrome balancer. The chrome balancer is SUPPOSED to be neutral, but I want it checked, as well as the other two balancers, anyway.
A test fit of the two replacement balancers was very tight.
Once I have a replacement balancer ready to go, I'll put it all back together (with my fingers crossed) and go from there. :D
 

·
Registered
Joined
·
1,477 Posts
You should have the crank magnafluxed, and for that matter measured for size, as there is no way a neutral balanced harmonic should have rotated on the snout of the crank, they (the factory parts) have a good .0015 interference fit. (same as a wrist pin in the con rod)

FWIW I internally balanced a factory 400 crank that had seen no previous carnage, took 3 slugs per end to accomplish that feat. (my personal engine) I ran it exactly 1 season at the drag strip, and pulled it apart for a freshen. Mag'd the crank, cracks in the rod fillets on all 4 pins. What a waste of time and money. FWIW the external GM 400 crank it replaced, with SFI pieces so full external balance, along with a CAT fluid dampner, ran the previous season, same RPM, was fine. Go figure. Crank is still on the rack. :D
 

·
Registered
Joined
·
13,473 Posts
Discussion Starter · #15 ·
Just got back from the machine shop and I have a 350 balancer ready to go.
I also had a little talk with my machinist. The next time I have a crank worked on, I'm going to have the keyway cut full length and and use a one piece full length key. :thumbsup:
 

·
In Memoriam
66 El Camino 57 Chevy pickup 2004 Tahoe
Joined
·
29,419 Posts
you gonna have the keyway in the crank fixed? I don't think it'll live the way it is.
 

·
Premium Member
Joined
·
486 Posts
Yeah DZ,I was looking at the pic where you can see the indent of the key and was wondering why its not all the way down the ballancer.I guess you answered your own question about running a full key.Good Luck.
 
1 - 18 of 18 Posts
Top