Engine Vibration

[Don W.]

Re: Engine Vibration

I understand that Ed. I believe the expensive part is the metal used. I think they use tungsten but I'd have to check.

Loooog time ago I had a 394 Olds which was also externally balanced. Both the flywheel and the damper had weights on them. I had it balanced by a guy in the Bay Area who did noting but balancing. Very smooth running, all the way to valve float anyway...:rotf:

 

[randy merritt]

Re: Engine Vibration

The front dampener is 'Neutral balanced' or at least I believe it should be. It may be worth checking that the outer ring hasn't slipped. Based on what others and myself have found, it will slip one day and you will either not be able to time it correctly, or even at all. I was in denial with mine, as checking it was one of the first things I did using a home made piston stop and it was spot on. However, it did slip eventually, by quite a bit, and when I removed the dampener, the outer ring didn't take much persuasion to come adrift from the elastomer ring. For what its worth, if its the original one, I would replace it anyway. $35 from Rockauto. If it has slipped, and it is timed wrong, it could be that the timing curve in the ecu at that rpm, with the 'basic' timing setting that you have set is making for an unhappy engine at that rpm range. If you disconnect the EST tan/black wire, although it will run rough, does it still vibrate? That may rule this out as the problem, but I would still replace it anyway if its the original.

I would chase this rabbit hole. Check the TDC against the dampener. Easy and free to do. Mine factory dampener had slipped when I checked it a few years ago, and I replaced it. I don't know if this would induce a vibration, but it did not in my truck.

Then again, I am running solid motor mounts, so I feel every vibration that the motor makes.

 

[Davemc1963]

Re: Engine Vibration

Regarding the balancing, although I realise the V6 is different from the sbc. When GM went to the one piece rear main seal in 86, they changed where they placed the rear counterweight, even though the earlier setup was classed as internally balanced (the 400 sbc wasn't). With the two piece, the counterweight was part of the rear crank flange. After that, with the one piece seal which had a round flange, they placed the weight on the flywheel or flexplate. Sort of a hybrid I suppose. The dampener was still neutral balanced, as was the older two piece seal crank (again, not on the 400) You mention that you have fitted or tried two different flexplates, one which was the original. Is this a V6 one.
I dont know the answer to this, but I'll throw it in. Is there a difference between the V6 and V8 flexplate, are they the same mounting pattern? Was the one fitted originally correct? I suppose someone could run the part numbers to check the applications.
The only other thing to check is if the crank is straight (snout or flange), is there any runout of either flexplate, or the balancer?

After reading the good info Don W. posted below, to try and not spread any misinformation, it appears from that information, the dampener (balancer) is 'neutral balanced' but 'trimmed' slightly if required to achieve the desired performance.

 

[Don W.]

Re: Engine Vibration

OK here the info I was trying to talk about:

Some balancers also compare the results of the left and right sides to see how the forces interact (3-plane balancing) before displaying the index location and amount of imbalance that needs to be corrected. Weight is then removed by drilling or machining the counterweights, or added by installing heavy metal tungsten (“mallory”) plugs into the counterweights to offset the indicated imbalance. The crank is then spun again to check the corrections that were made. This procedure is repeated as many times as it takes to achieve the desired degree of *balance.

From this site, an interesting read.

http://tinyurl.com/p652a68

 

[randy merritt]

Re: Engine Vibration

That is exactly what I had done to my motor on the last rebuild. The bob weight chart indicated a good result. I had mine balanced with the balancer and flex plate.

 

[Don W.]

Re: Engine Vibration

Finally found it.

From:

http://www.enginebuildermag.com/2000/04/rebuilding-the-new-chevy-262/

Which gives a good history of the GM V6,

"However, you should also be aware that all of these engines are externally balanced with various combinations of flywheels/flexplates and dampers for balance, and that they are "trimmed" at the factory after the hot-run test by pounding balance weights into the holes that are already drilled in the damper. So, if you build them right and still have a shaker, the customer will have to add or subtract weight from the damper and/or flywheel/flexplate in order to get it right."

What's kinda funny is where do you get the weights and which hole do you put them in?

 

[gstacky]

Re: Engine Vibration

Interesting information for sure, thanks guys. Both flexplates I have tried are from 4.3 engines, and have the big "batman" weight on them. There were differences between the 2 in smaller holes between the large holes in the flexplates, this is what lead me to change the flexplate, but it made no difference.
Another thought a friend had was a valve a little too tight, again another thing I need to check.
I plan on taking it for a drive this weekend to a truck show, I have only driven it 15 or so miles max so far, I guess I'll see if it needs a little break in.
On a side note, before this engine, I have had small blocks in the truck. A 327 (no weight on the flex plate) and a 400, with the weight, so I'm familiar with that part for sure.

 

[Damian]

Re: Engine Vibration

I think it's something electrical. Tune up, or the tune itself, or a sensor. Have you logged it yet?