At idle, the salvage 350 the prev owner installed runs rough, vibrating like a large cammed motor (doop-doop, doop-doop) and then at 1200rpm, all the loose panels in the car rattle like crazy, I think due to the engine vibes because if I punch it to 1500rpm, the rattles go away and the engine sounds smooth and good. Is this my external vibration damper (balancer)? Do I need to invest in a Fluidamper? Thanks in advance!

 

Anybody? Anybody at all? Maybe the vibes I'm gettin' are just typical of all thirdgens? I have a friend who rode in a two year old 92 (that'd be back in 94) and he said the car rattled like crazy even when it was that new, so I guess my 87 is bound to rattle. However, the engine's pretty new, and new car engines sound smoother than mine which is carbed. Would multipoint fuel injection solve that?

 

It could be something as simple as a vacuum leak or a shorting plug wire causing a low RPM miss in one or more cylinders. Running on less than all 8 will cause a vibration.

If you find that you get the vibration recurring at several different RPMs then you might have something out of balance inside the motor- or outside if someone installed a 400 style balancer or flexplate/flywheel on your 350.

A bad harmonic dampener you won't get the kind of vibration you are referring to. You'll get one around 2700-2900 if you get one at all. Usually the outter ring of the balancer slips and you can't get the timing mark to line up. Or it could just start to "eat" timing chains every few thousand miles. That's more what you get with a bad balancer.

 

I've had the same problem any luck? It is still there with the TC backed off and I'm still running the stock balancer (150k Miles). Issue occus at identical RPM's. I do have a new fluid dampener that I am ready to install. Any Luck?

 

I can't figger it out! I'm gonna get SFCs semi-soon, and hopefully, that'll help (it certainly can't hurt), but this seems to be an engine-associated vibration.
It really sucks b/c I spend a lot of time cruising at exactly 1200 rpm and all the loose/cracked interior panels in the car just buzz like crazy! It's really annoying!
I'm also planning to try a torque strap on the engine, but I don't think that's supposed to help low rpms since the engine can't torque over at low speeds. (Again, can't hurt.)
It seems like the engine's running too smooth to be a miss, but I guess new plug wires and a new MSD coil might help...
To sum it up, I'm gonna try a lot of things, but as of now, I don't know what it is... just shots in the dark, basically.

 

If this helps I have changed the torque converter and flex plate w/o any luck. I have also installed a new torque arm, trans mount, and balanced the drive shaft which seemed to make the issue worse (explainable - more ridgidity). I also think that I have an internal engine problem but the balancer swap is more practicle.

 

What does your vacume gauge read? If the needle bounces around...poss vacume/intake leak. spray some carb cleaner to find the leak. Are the wires in the right firing order? And are any of the wires burnned and grounding out? And what condition is the coil in? Basic stuff, just wanted to make sure you checked it because it can be overlooked.

 

Thanks for the info, guys.
I think I might agree that the ignition stuff is pretty old, but if it was a "miss" how would I pass emissions like I did? Anyway, I want to replace the wires and coil like you said just to be sure. (Also, I probably/definitely wouldn't have passed smog with a wrong firing order.) More likely, my carburetor's sick... I'd like to rebuild it sometime; I need to check for a vacuum leak like you said, craiger.
Brock, how can it be an internal engine problem? From your sig, it looks like a new and custom mill. Are you thinking you or your builder messed up on something in the assembly?
My solution is to basically live with the problem (if what stated above doesn't help, which it probably will, actually), and after getting the SFCs to replace the cracked interior panels. Thus, the vibration that causes rattles will still be there, but un-cracked panels can't vibrate, and so it won't be as annoying.

 

Chris - This is a long story... When I put the new engine into my car I had a bent rim in the back as well as a bad tire. I lived with it for a while then I changed the transmission. While finishing the trany I was lowering the car down on a jack stand that broke. When it broke the jack which was under the front engine cross member crashed into the oil pan. The dent was large enough that I could hear the crank banging on the pan. I pulled the dent out patched it with some JB weld and it worked. I then bought new rims and tires and I still had a vibration. I could never determine if the rims were masking the engine vibe before or after the dent. After a few other mods with the drive train I am now under the hood again.

I also heard throught he grapevine that the person who built my engine "could have put a 400 crank in, either accidently or on purpose." Even if I would think the vibe would be worse. like you said it's liveable. I still hope to change the balancer and perhaps check for vacume leaks. I might change the coil and wires but the wires are in good shape. I'll try to check for vacume leaks but I don't know how to tell the condition of a coil.

I keep a positive attitude by remembering if I run out of opitions I'll just have to pull the engine out and build it bigger, darn!