View Full Version : Crank/Harmonic Balancer story...


dizzle
08-30-2011, 06:02:50 PM
Ok heres the long story...I finally got my car running the way i wanted it to. 77 camaro sbc 327. Headed up to Sac Raceway for a test and tune session, threw some 110 in the car and popped the hood to do a nuts and bolts check. Turns out my blower belt was riding on 2 of the 10 ribs (weiand 144). Anyways, I ran the car to see what the problem was and it appeard the harmonic balancer was moving slightly. So I let the car cool, grabbed my socket and started to loosed the crank pulley bolt and it broke off. Well after weaping to myself for a while my buddy helped load my car on his trailer (which is when the lower valence got smashed off).

The next day upon examining the crank and harmonic balancer it appeard that the balancer was loose previously to me buying the engine. The engine probably has less than 1,000 miles on it. There was no visible damage to the crank and the only damage to the harmonic balancer was on the keyway, where it looked as if it was the only thing holding it on.

So I measured the crank and it came out to 1.240 and the balancer was 1.245. I talked with ATI and they would have to make a custom balancer to fit this crank (over 500 the guy said and 6-8 weeks for delivery)...With the crank being so small was it machined when the engine was rebuilt? Does anybody know where I can get a balancer that size? And lastly how would you approach your mechanic who built this engine and did not catch this?:(

Cardinal
08-30-2011, 08:52:26 PM
And lastly how would you approach your mechanic who built this engine and did not catch this? I'd approach him with a BFH in my hands and give his melon a new dent!

How in the name of Zora Arkus-Duntov could anyone assembling an engine miss the fact that the harmonic balancer on a SBC is a PRESS FIT!

IMHO, your machinist should be replacing the crankshaft for FREE.

I googled the internet to find out what the crank shout should measure and the consensus of what I found is that it should measure 1.244" to 1.245".

Damon
08-30-2011, 08:53:16 PM
I've never heard of anyone machining a crank snout after the factory did their thing on it.

Part of me wants to think that the older cranks (like a 327) might have a smaller diameter snout than later stuff but....... nah, I don't think so.

Here's an idea.... many aftermarket performance/SFI-approved balancers are intentionally undersized and designed to be machined to fit. Without machining they are often too tight to install. But in your case that might be exactly what the doctor ordered. Now, I don't think they are 5-thou under, but they are tighter than a stock replacement. Might be worth a shot to see if works. Buy one local and see if it's tight enough to require a tool to isntall it. If so, you're probably good to go. If it just slides on by hand then it's definitely time to think more deeply about a solution.

Jim Mac
08-30-2011, 11:21:46 PM
I know your running a small blower but when I did some research putting a 6 71 on my camaro, I was told I needed a crank hub because the stock balancer would end up getting trashed because its cast. Could your balancer gotten loose or twisted on the crank spinning the blower?

dizzle
08-31-2011, 12:27:41 AM
thanks guys! i think i will try to pick up a high performance one tomorrow. i would hate to see my crank go to waste. not to mention all the work ahead of me...this engine doesnt even have 1000 miles on it yet. ugh first it was the blower problem and now this...i have some pretty bad karma built up

BondoSpecial
08-31-2011, 12:34:21 AM
I have run later style balancers on an early 327 (1966). It has the same size snout as the later SBC's. Actually the only thing holding the early balancers on WAS the press fit...the press fit alone should keep it on there without a bolt.

You could potentially use Loctite sleeve retainer products. They claim to fill up to .006" gaps and the stuff is really tough but that would in my eyes at least be a last resort, no-other-options fix.

dizzle
08-31-2011, 12:40:13 AM
I have run later style balancers on an early 327 (1966). It has the same size snout as the later SBC's. Actually the only thing holding the early balancers on WAS the press fit...the press fit alone should keep it on there without a bolt.

You could potentially use Loctite sleeve retainer products. They claim to fill up to .006" gaps and the stuff is really tough but that would in my eyes at least be a last resort, no-other-options fix.


I will grab this just incase it is a little to big...perhaps i can at least get one pass in friday. My first time at the track (ever) was with 3.42 gears, everyday tires, and no posi...13.4 @ 114. so if i can improve a second or so on that i will be satisfied....

BondoSpecial
08-31-2011, 12:42:11 AM
I have to buy it from industrial supply stores. I have never seen an auto parts store carry the loctite sleeve retainer products (they are quite different from the thread retainers)

dizzle
08-31-2011, 12:39:03 PM
I know your running a small blower but when I did some research putting a 6 71 on my camaro, I was told I needed a crank hub because the stock balancer would end up getting trashed because its cast. Could your balancer gotten loose or twisted on the crank spinning the blower?

The balancer was loose and that was why the blower belt was slipping off, the lower pulleys were moving slightly. I had a fluid dampr on it p/n 712615-003. I looked for that part number and it appears they dont have that one, but they do have a similar one just different p/n.

More to follow...ordered some of that loctite stuff and will order a balancer now.

When measuring the crank should you measure the inside or the "just the tip?"

mrvedit
08-31-2011, 01:12:05 PM
Sorry if this is obvious or insulting, but with something this strange, I would be sure to measure with a (2nd) micrometer and not just a digital caliper.

dizzle
08-31-2011, 01:22:06 PM
Im an idiot fluidampr 712615-003...not fluid dampr. found the balancer but talking to my mechanic doesnt think i should throw another balancer on it without checking the insides...it didnt run long after i found out the balancer was loose...thoughts?

Damon
08-31-2011, 03:14:18 PM
Forget tearing into the motor at this point. See if you can fix the balancer problem first. If not, you're probably going inside the motor anyway.

Short-stroke motors like a 327 don't tear themselves instantly to pieces just because the balancer gets loose. Probably things are fine inside unless you drove it that way for a considerable period of time.

John Wright
08-31-2011, 04:24:13 PM
I agree with Damon...I can't imagine that it hurt anything inside if it didn't run long. I've seen guys lose the balancer completely and drive it very easy back home from the track and not hurt it.(guy lived up the road from the track a couple miles)

crome dome
09-04-2011, 08:04:54 PM
Time to revive this.
How much smaller should the I.D. of the balancer measure compared to the crank.
I have a new Eagle crank and new balancer that i can almost push together by hand. I have to use the installer tool for the last quarter inch but it's easy. With a cheap set of calipers my balancer appears to be .002 smaller than crank. Does this sound right.

rustbucket79
09-04-2011, 09:59:19 PM
.0006" to .0015" depending on manufacturer. I've unpacked a couple three Eagle cranks where the snout was undersized, thankfully I checked this dimension before starting any machine work.

If you look at the inside bore of the balancer you'll see where it's counterbored (loose fit) and where the major area of interference is. It should be tight the entire distance. (needing an installer to pull on the balancer. If you can slip the balancer most of the way, That is a big problem.

crome dome
09-04-2011, 10:06:28 PM
Thats what I thought but didn't want to hear. My machinist bought the crank and Balancer and balanced my assy. You would think he would have caught this but it's right on par with the rest of the work he did for me.
Now I have to figure out a way to make this work. By the way this is a Big Block and the crank snout reads 1.600 while the balancer reads 1.598. Any idea wich one is the wrong size?

mrvedit
09-04-2011, 10:34:52 PM
Your measured .002 (2 thousands) sounded like a lot to me (it would be extremely tight) and RustBucket79 confirmed it - .0006 - the difference is only 6 to 15 ten-thousands. Therefore, you might need a more precise micrometer to determine exactly what you have.

crome dome
09-04-2011, 11:51:25 PM
Your measured .002 (2 thousands) sounded like a lot to me (it would be extremely tight) and RustBucket79 confirmed it - .0006 - the difference is only 6 to 15 ten-thousands. Therefore, you might need a more precise micrometer to determine exactly what you have.
You are probably right, but it is deff. not a tight fit. Does anyone happen to know what a Big Block crank snout should measure?

rustbucket79
09-05-2011, 02:23:55 PM
No spec off the top of my head, but the BBC's have one of the tightest fitting harmonics out there. (even right from the factory) .002 wouldn't be unrealistic.

crome dome
09-14-2011, 12:18:21 AM
I just wanted to post the conclusion in case someone else runs into this. My Eagle crank was undersized just like most of ya guessed it would be. I took a hundred dollar gamble and bought a balancer made by Professional Products. Just so happens that it has a tighter fit and solved this problem. It was tight enough that I had to use some force on the install tool but not so much that I worried about breaking it.

Damon
09-14-2011, 05:52:19 PM
Glad to hear it worked!

BondoSpecial
09-14-2011, 06:08:05 PM
lol you used manufacturing tolerances of that balancer to your advantage. Gotta love it. What luck that was

markw
09-14-2011, 08:09:12 PM
Good lesson there. Imagine buying that Professional Products balancer for a crank that had the correct size snout. Any aftermarket balancer should be measured for fit, just like any aftermarket crank should. http://www.atiracing.com/instructions/Super-Damper.pdf

CamaroMan79
09-15-2011, 03:04:48 AM
Anyone know if Dizzle got the problem fixed or not?