If you sit in your car while starionary and rev it up to say 4k revs should the engine seem smooth and the car not shake much. I'm finding that at 2k revs the engine is v. rough and the car shakes and above 2k its not very comfortable but not as bad.

My harmonic balancer is in a bad way, the rubber is comeing out and the outer steel part is tight up against the lower pulley which I think it should not be.
I have done some searching and a 6 3/4 internally balanced replacment is what I need right?

Thanks

Simon

88 350 iroc

 

Well your motor mounts could be going out, but logically it is going to be a little more harsh at 2000 then at say 4000 or 5000. But if you take a look at them, you might learn something. If they are dry rotted then they are going to make the whole car shake a little like that and if they are oil soaked or like ripped in half then, they are basically not going to be doing anything at all anyways. Like my TRANNY MOUNT WAS!!!

 

i also have a bad vibration only at 2000 rpms. its almost unpleasant to be driving and have the RPMS at 2000. maybe its just somethign with these engines?

 

Yes the motor mounts could be bad but I think they are Ok. I'm reluctant to change them as it looks like a PITA job
I'd be interested to know how significant the harmonic balancer is to the smooth running of the engine. Anyone replaced one and found the engine was much smoother?

Thanks

Simon

88 350 iroc

 

If the balancer is failing, you'd better replace it. It's there for a reason.

 

I also notice quite heavy shaking which occurs mainly at two points across the rpm range, and between the points the engine is smooth.
I think this is just the result of having two opposing banks of cylinders, the block just finds its natural frequency and resonates as a result. Its probably just natural.

I also thought that balancers just eliminate high frequency vibrations that can open up fractures, I have seen this explained as having the same effect of a high pitch tone on a wine glass.
I would not say that a faulty balancer would have as profound an effect as shaking the car about.

 

my camaro revs smoothly to 4500. at idle it vibrates a little. my truck on the other hand vibrates like crazy at about 1600 and again at 3200. it started doing it after i put the a/c belt back in. if your harmonic balancer is got rubber sticking out replace it. another thing could be the flexplate cracked/broken. that would cause vibrations.

 

so how do we know if this is our balancer going out or if its normal?

 

Ever since I've replaced my tranny mount with Spohn's (prothane) version, I've noticed the vibration at 2000 and again around 3800 or 4k.

 

if it's not obvious then there really is no way of knowing unless you change it and the vibration goes away

 

It's not terribly unusual for the engine to shimmy or shake just a little at idle, and doesn't necessarily indicate that anything is wrong if the engine is computer controlled.

Vibrations at any other RPM are bad news. Mine steadies out by about 900rpm and is smooth as glass from there till redline.

 

Do a search for "harmonics" and you may discover that the SBC (with 5.7" rods and 3.48" stroke) is inherently harmonic around 1780 RPM os so (and all multiples of that). It's just the nature of the beast with those pistons, rods, and stroke. Many truck engines use a large diameter balancer to help mask that tendency, since they are frequently operated closer to those ranges under heavier loads. Change the stroke, rods, lighten the rods and pistons (like the LT1) and alter the dynamic balance of the rotating assembly, and all that will change.

Either way, you still need to change your bad balancer.

 

around 2k my car vibrates a bit too, im thinkin this is normal for these things if u guys are havin the same deal. puttin in a heavier fly wheel helped my car out, its a 5spd

 

Thanks again. I think I need to replace my balancer because it is visibly broke but in doing so its unlikely to make the engine much smoother as it smooths out high frequency harmonics. Nobody seems to have fitted a new balancer even expensive 'fluidamp' silicon balancers and noticed any difference.

Simon

 

wait, you can see that the harmonic balancer is cracked just by looking at it with your eyes, and you're still wondering why its running rough? i think it should be clear what your problem is.

 

wait oh contrair, i had mine replaced today, it was wobbling around on the metal inside and it idles rougher now with evena heavier balancer installed, but i'vew obviously got worse prolbems, goptta continue my darn searh.

 

Mines the opposite of what alot of you guys are experiencing... Mines got a little 'rock n roll' at idle, but it smooths out at 1000 revs and its silky smooth after that.

 

Interesting this topic is brought up. I had a ballancer go out TCI POS! It vibrated above 1000 RPM. You need to make sure replacment ballancers are correct for your application. I know people who have purchased new ballancers and were given ballancers for 400's some with 400's were given ballacers for 350's.

Ive got a wierd vibration in one if my trucks engines. It's is off and on at 3k+. Sometimes it will be silky smooth other times it will shake the truck real bad. Gotta look into it one of these days.

 

My understanding is, the h-balancer is to dampen problems caused by distortion of the crankshaft under heavy load.
Comments?

 

This is exactly how mine is, stock bottom end LB9 for now...

 

Mine's also that way. But I just love how when you rev it hard the entire car rocks a bit.