I have a question about my harmonic balancer install.

I bought a Romac balancer off this board for sbc. I go to install it on my 383 crank and it just easily slips over and i can push it all the way on. Surprised at this i go get my stock balancer and try it on my crank and it doesnt fit on easily at all...i would have to hammer it on and possibly heat it up first.

I go put the Romac on the stock L98 crank and it doesnt slip on this crank. I'd have to hammer it on and heat it up to fit over the keyway

SO i go to measure things. Stock crank and the eagle forged 383 crank have same diameter snout at 1.246 inchs but the key way on the 383 is .186-.187 while the L98 stock keyway is .190.

Is there anything to worry about here if i can just slip the balancer on? it fits good and doesnt move once on, but its just easy to get on and off.

 

I believe the balancer should have at least a "snug" fit to transfer the vibrations from the crankshaft to the balancer. Maybe the manufacturer of the balancer could give you some tolerances on the I.D. vs. O.D. fitment...?
-Bill

 

I don't want to make you mad, but I would return it or throw it away. If it was new then it's out of spec. If it's used then someone probably honed it so it wouldn't be so hard to get on and off.
This part must be a press fit. The key takes the rotational load like when an alternator locks up and the belt screams. The press fit takes the oscillating torsional load that would cause the balancer to chatter the key to bits.
The best thing to do is think of it as if it had no bolt holding it on the crank (the older engines didn't).
I've dealt with this before and the balancer will wear the snout of the crank smaller so it won't even take a balancer that is correct. Guess what happens next? (no you can't weld it on).
$63 for a balancer, or have to pull the engine later, tear it down and replace the crank. Your call.
EDIT: also, hammering on a balancer will destroy it. You have to crank-'em on and off.

 

It should take some force to install. If its not tight to the crank, image what will happen when you get you accessory pulleys on it? I'll bet someone honed it out to fit on a problem crank.

Sorry to hear of your situation, but I wouldn't run it.

 

You'd think it would still be with the crank then, huh?
Unfortunately, I don't the balancer was the only thing that got reamed here...

 

well the key way differences are the problem. there is a difference from my 383 crank to the old L98 crank

like i said, the Romac balance DOESNT fit easily on my old small block crank. I dont think it was honed

From my calipers, both cranks are same diameter, but the keyway is abit thinner on the forged 383 crank. Both balancers measure about the same in inside diameter and keyway diameter, with maybe a .001-.002 difference for the stock keyway on the stock balancer.

I dont understand this situation at all. similar dimensions yet one slips on fairly easily and one doesnt, and the old factory crank doesnt allow the romac to go on easily either

I dont wanna order another one and run into the same problem, new balancer that doesnt fit my engine crank...

 

Do you have a caliper? Maybe between the two measurments, it could be sorted out?

 

yeah i have one and i posted above that they are similar in size, from the measurements i'm taking.

i cant figure i out. ONLY differenceis the keyway on my new crank is alittle smaller like .002-.003 from the stock L98 crank, YET the Romac balancer will not fit on easily on the stock L98 crank

Neither does the stock balancer which appears to me to have similar dimensions to the Romac one

So situation summary is this. Stock balancer is a press fit for both cranks. romac is a pressfit for stock L98 crank, yet slips easily onto 383 crank.
L98 and 383 crank measure the same diameter but 383 crank has slightly thinner keyway. Romac appears to possibly have .001 or so wider keyway than the stock balancer.

This is probly the reason why the romac slides over the 383 yet is a press fit on the stock crank.

 

It probably will if you take the key out. The interference fit is in ten-thousanths of an inch.
If you're bound and determined to use it, at least give it a fighting chance. Coat the bore of the balancer and the crank snout with red loctite and put the center bolt in with a torque wrench to spec or an impact wrench.
It might just last...

 

i mean i bought this thing to use and i like it, and if i was camming my old L98, it would fit fine as it would be press fit over the stock crank and keyway. If i have to sell it i will and get a different balancer, but i'm not sure its the balancer thats the problem, it may be the keyway

Could i possibly swap keyways from crank to crank?

 

Let's try a little logic.
If the key on the L98 is .002 wider, then the keyway in the stock balancer should be .002 wider also.
If the snout on the 383 was "small" the stock balancer would slide on the 383 crank easily because it has a keyway that is .002 wider than the key on the 383 crank, right?
But it doesn't.
If the stock balancer takes considerable force to press onto the 383 crank (with or without key) then:
it
ain't
the
383
cranks
fault.

 

Thats what i'm saying, its not the snouts thats the problem as i measured them both to be the same diameter, its the Keyway thats the problem. Can i swap keyways? Are they press fit into the crank or something?

 

oh and the keyway on the 383 crank sits .006 shorter than stock crank/keyway setup. I think that also isnt allowing a snug fit on the crank. The stock balancer keyway slot may be abit thinner than the romac balancer so thats why it doesnt fit on each crank, but the new balancer will work if the keyway was larger like the L98 one

 

I also had a problem like this. I'm using an Eagle 1pc rms for 383 crank. The guy at the machine shop was as confused as I was. I had tried several different dampers that would fit the stock L98 crank but not my new one. Also confusing, was the stock damper would fit snugly on the new crankshaft. I don't think that changing the key is going to solve the problem of the snout not being tight enough to the damper hub. I ended up using a Professional Products damper which fit just fine. Go figure. Hope this helps

 

Thank you for typing that. I would have, but for some reason I had to go get my keyboard which had been thrown across the room...

 

If the key way isnt the problem then explain to me how it wont fit the larger keyway crank when BOTH CRANKS are the same diameter and the balancers feature the same inside diameter???

 

The bores in the dampers (I like that word better) are different. By a few ten-thousanths of an inch (as I stated earlier). Not a few thousandths of an inch.
The key is not what makes it a press-fit.

 

ok i just checked the stock balancer again and it appears that the stock balancer crank bore features a step up that i didnt see, and it sits about a 1/4 inch inside the bore

inside diameter to that point is the same on both balancers, within .001-.015 it appears by the calipers. However at that point, it necks down another .003 so that has to help with the tight snug fit on both cranks

Sorry i didnt notice this before but i do feel the keyway influences the fit alittle else the new balancer would fit the stock crank with ease but it doesnt.

Talked to the owner of the balancer i bought it from and he says his other romac he installed on another car with a eagle crank slipped on with only alittle press fit as well. Seems to be a problem with the cranks from eagle, do they install the keyway prior to shipping cranks out?

 

I have 2 eagle cast steel cranks. Both of them are .002 smaller than gm or scat cranks. I have a 383 crank at the machinists shop now for a balance job, and he don't want to use it. I just built a 406 and it spung the 3 center mains, when I pulled the balancer off I noticed it had a gaulled spot on the crank snout. I'm calling eagle tomorrow to find out what measurement their crank snouts are supposed to be. The stock ones we measured were 1.2475 and the eagles measured 1.2452. .002 press fit is quite a bit.

 

I just got a new one from Romac and on their site it says eagle cranks are commonly ground .001 under factory sizes, so i needed a .001 smaller bore balancer. thats why the other balancer didnt work