I have a summit harmonic balancer that I'm putting on my new engine, however it does not fit. I measured both the crank snout and the ID of the harmonic balancer and they're almost exactly the same dimensions. I got the balancer a bout half way before I stopped because of extreme amount of force needed. I rented a h balancer puller and i stripped almost all the threads getting it off, I even heated up the balancer too. Besides sending it to a machinist, what can I do to hone out the balancer? I looked for a flap wheel for my drill but I couldnt find anything small enough.

 

make sure and use some oil on the threads of the installer, you are using something besides the crank bolt to install it right?

 

are you sure the woodruff key isnt comming out?

 

Yeah I used an OEM harmonic balancer installer. Regardless of what I used, if I stripped the threads off the puller then I know for sure something needs to be loosened up. Every balancer I ever pulled off and put back on did so pretty easily, this is far far too hard. I could boil the balancer to put it on, but that still won't help me any when I try to pull it off one day.
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Yes. The woodruff key has plenty of clearance for the h.b. to slide on, its just the snout of the crank. Both have the same ID and OD. I would think it would need at least .005 or so to slide on smoothly.

 

you could always use a brake cylinder hone

 

I wouldnt hone the hub of the balancer. If the interference fit isnt right, itll come off, bolt or no bolt. Heating and oil, or just oil alone should be enough to get the balancer on. If its giving you fits, Id try another balancer.

 

What is the correct clearance for the h.b. hub to crank snout gap?

 

The harmonic balancer and crank should have about a 1 to 1.5 thousands interferance fit. (.001 to .0015) .002 is ok. You need to accuratly measure using a micrometer and inside snap guage and a good eye. I recently went to install a new Profession products balancer cold and stripped the installer. Measured it and found the interferience fit was too tight.
(.003) Had to take the balancer to a machine shop. They honed out for me on the same machine they use to resize connecting rods. Took all of 5 minutes.
At that point its recomended you heat the balancer before installation.

If you hone it out to eliminate the interferience fit the crank vibrations will not be transfered to the balancer. the crank may crack or break as if you had no balancer at all.
Check the key also for burrs. Can clean it up with a flat file.
Did your Summit balancer come with install instructions?

 

I'm talked to Summit and I'm going to send it back as a defective part and they're going to ship me a new one. If that doesn't solve the problem then I'll take it to a machine shop to be honed. It came with install instructions (use an install tool and/or boil) however if it goes on and won't come off in the future then its still no good to me.

 

FWIW, a 0.001 press (interference fit) is going to require considerable force to install and remove on a 1-1/4" shaft. Most bearings that are "press fit" have .0001-.0005" (1-5 TENTHS) interference under 2" diameter. The measurements need to be expressed in tenths, not thousandths.

0.005" clearance would allow the balancer to wobble, hammer the joint, and probably eventually ruin both the balancer hub and crank snout. About +0.0003 to -0.0002" would be the limits. That gives the manufacturer almost a half thousandth to work with. If they cannot consistently produce within those tolerances, they have no business producing engine components.

That's probably why they're taking it back.

I'd be very careful about using a small expandable (brake) hone or bottle brush type hone, since the bore already has a keyway broached into it, which would tend to make a flexible hone produce an elliptical bore. A fixed hone (such as a Sunnen) sized up properly would do an acceptable job and not be influenced by the keyway.

 

When I measured both the h.b and crank I came up with 1.245 exactly on both parts. I'll wait to get my new h.b sometime next week to see if I have the same problem.

 

had the same problem with the summit balancer, I just wet sanded the balancer bore with 600 grit and used a sa flap wheel to polish it real smooth. Then put in the oven for 20 minutes on 200*(per instructions) and it went on pretty easy.

 

Here are the crank snout and balancer bore diameters tolerance from the instructions. The SBC crank snout is slightly tapered. measure it half way back.
crankshaft snout Diameter 1.2460/1.2470 "
Harmonic damper bore diameter 1.2441/1.2449 "

 

If they are the same size, it should go on with no problems. Are you using a pull stud to install it?

A full thousandth press? I'm sure you're right, but did the instructions mention if those specs are for the old, non-bolted balancer or "modern" SBC as well? I'm also guessing that is for a crude, raw machined surface finish like would have been produced in the '70s and '80s, and that the measured dimensions after once installing and removing the balancer (burnishing) would be slightly different.

 

If they are the same size, how will it fit on? I was using the tool that is a large threaded rod with a roller washer and a large nut. I had to use a 24" breaker bar and my jack handle on the end of it to even move the nut so I know something isn't right.

 

I'm not saying I'm right. I just gathered from the tolerences they are after a .001" to .002" pressfit. I have the old balancer but have not measured it.
At a .003" pressfit I got the new balancer about 1/2 or more the way on the crank when the installer nut gave up. (I did not use a 24" bar) I'm sure that since I reduced the press fit by honing to .0015" and will heat up the balancer this time it will go on like butter. Haven't had the chance to get back to it.

According to the instructions you also have to check the height of the crank key and height of the crank keyway in the balancer for proper fit.

 

Where did you buy a flap wheel that small? Also what grit was it?

 

600 grit paper and the flap wheel I got in a kit from summit that is usually used to port and polish heads

 

I'm currently running a Summit balancer, the first time I tried putting it on I was unsuccessful. I found a small burr on the edge of the keyway on the crank. I removed that with a file, smoothed the crank with emery cloth, and put the balancer in boiling water for about 20 minutes. After all that it went on with a balancer installation tool.

 

Well I got my replacement in from Summit today, its actually smaller! I called Summit tech dept and they said I could hone out the hub of the balancer. They said since my crank is new its on the high side of the tolerance and that they make the balancer for cranks that have the snout worn out???? I wouldn't think that a crank snout gets a lot of wear, especially since nothing spins against it. I might try boiling it to see where it comes out at. If I heated the balancer up enough to get it on, would the balancer "mold" to the diameter of the crankshaft snout? I don't think getting it on would be a big big problem if I heated it up, but getting it off is another problem. I don't want it stuck on my crank.

 

I took my nwe balancer to my local automotive machinist and had him hone out the hole to give it a thou and half press fit. (-.0015). It was too tight at 3 thou. (-.003) Took all of 5 minutes.
It's done on the same machine used to resize connecting rods.
Heated it up for 30 minutes in a pot of water on the stove. Went right on with a few wacks of a small sludge and a block of wood. Had a new install tool on hand but didn't need it. (take the smokin' boilin' hot pot, balancer and all out to the shop with mom's oven mitts)
The end snout of a SBC crank is actually tapered slightly. Measure it half way along its length using a accurate micrometer. take that measurement and your balancer in to see your local automotive machinist and he'll fix ya up.