I am having a vibration issue in my 406 small block. I am running eagle crank, rods, and keith black pistons that were all professionally balanced. I am running a jegs externaly balanced flex plate. What should I be useing for a dampner. Where are these bad vibes comming from?

Thanks,

Tim

Depends on what crank you have, with A/M cranks I think it is possible to balance a 400 internally. Your balancer should have been balanced with the rotating assembly, along with the flexplate. Please post some part numbers from your parts and someone like BillK can tell you what you need to do.

A stock 400 is externally balanced and uses a specific balancer and flywheel/flexplate. The balancing should be done with both pieces attached. Is it possible that you didn't get the flexplate located correctly? The flexplate should be marked as well as the crank so they are lined up correctly.

Good Luck
Marty

Tim,
How about a bit more detail on the "vibration". Low rpm ?, High rpm ? could it possibly be a missfire or just a rough running radical camshaft ? The damper you should be running should be the one they used when they balanced the assembly.

The cam is a Comp Cams XE-284H cam with about .510 lift not sure of the duration. Talked to the guy that did the balance work and was sure that it was ballanced correctly. The vibration is most noticeable between 2000-3000rpm. It gives a chattering feeling through the car. At this point I am thinking it must be an ignition problem. I am running a mallory HEI with summit wires and champion plugs. All ignition parts are new. What should I got about looking at first?


Tim

Tim,
Does it get better as the rpms go higher ? if so, it is probably just a harmonic of some sort, probably from the cam. My 67 Camaro race Car used to really rattle at about 2500 rpms coming down the return road, the cam just did not like that rpm. Used to spin 7800 no problem though. Hard to tell without having the car here.

Thought I would bring this back up. In addition to all my other problems, I might have found something that is causing them. I'm not sure, but by looking at the crank pulley, it looks like there is a little vibration happening. I thought I noticed the balancer vibrating back when I first put the engine together, but then I came to the conclusion that it wasn't. The problems i'm facing are loping/fluctuating idle that won't calm down until the mechanical advance is in, and an engine that doesn't sound smooth with the rpm steady. When I hold the rpm up, the pulley looks smooth. Engine also revs up easy and smooth. Engine is a 383, rotating assembly came from StrokerMotor in Dallas, cam is a 292H. The rotating assembly came as a balanced kit, but when I sent the block off to the machine shop to get machined, I sent the kit with, and the machine shop said it was way off balance so they rebalanced it. Is it my cam that is making the engine seem imbalanced?

They shouldn't balance a balancer but rather just the crank with an untouched balancer attached! Same way with a f/w or f/p...

AND I would double check to see if the flexplate, (IF you are using a flexplate?), is located where the dowl should be too to make sure it is right. That is if the dowl is gone??

Or maybe you were given wrongly a 454 flexplate by mistake instead of your 400 f/p??

I will say that my old, throwed together out of unbalanced stuff, junk 301 had about 3 harmonic vibration points going up through the gears to above 7,000 rpm!! I could tell my rpm by the way it vibrated b/c I hammered it so much and got use to the way it ran..

pdq67

LOL That poor old 301! LOL

Is their any way to check the location of the dowl with the torque converter and flexplate hooked up? No way to really confirm anything without taking it apart, the business that sold the parts seemed to be a deadbeat business. Trying to sell me pistons that worked on a different rod. Sent the pistons in a piston box that was for pistons with 5.565 rods. Hard to believe the crank would have to be balanced twice, isn't it?

BTW, we're going to tear into that grain truck engine pretty soon with the bent forged crank. I have to find a crank first.

Not that I know of??

Have to pull her down and look...

pdq67

Yeah, figured so. Anything simpler to cancel out first before pulling the trans? :)