351W Harmonic balance

Kens67cobra · #1 (**permalink**) 02-06-2007, 06:30 PM

I have a vibration at at about 2100 rpm in all gears. Someone sugussested the balancer might need need replacement. I need to replace the water pump this spring, so I guess this would be a good time to do both. What balance is used in early 351W motors, 28 or 50 oz.
Any suggestions

Rick Parker · #2 (**permalink**) 02-06-2007, 06:36 PM

Early engines took 28 oz balancer.

olddog · #3 (**permalink**) 02-07-2007, 05:35 PM

The only thing that matters is, how was your engine ballanced when assembled? In honesty it could be either or internally ballanced. It just depends on how it was built.

I would recommend having someone, who knows how, to verify what the damper that comes off is.

Some purrests say if you change the damper the engine should be pulled apart and all components ballance together.

I wouldn't change it unless I was certain that it was the problem.

Could be a clutch, as well.

jeffko · #4 (**permalink**) 02-09-2007, 11:53 AM

Ken, be very sure of what you are doing here, but the "olddog" has it right.

1bad66 · #5 (**permalink**) 02-09-2007, 12:01 PM

It also matters what tranny you are running. My 69 351w has a 28oz balance, but when I put a t-5 behind it, I had to go with a 50oz. Had the same problem you did at 2100rpm, put a 50oz on the front and everything is smooth now.

olddog · #6 (**permalink**) 02-09-2007, 03:39 PM

Quote:

Originally Posted by 1bad66

It also matters what tranny you are running. My 69 351w has a 28oz balance, but when I put a t-5 behind it, I had to go with a 50oz. Had the same problem you did at 2100rpm, put a 50oz on the front and everything is smooth now.

I'm not trying to through rocks here, but this makes no sense to me at all. The 28 oz or 50 oz ballance is how much the engine lacks being internally ballanced, so the wieght is added externally to finish getting the internals of the engine ballanced out. This has everything to do with the components the engine is built with. The transmission is nutral ballanced and should not matter.

To go to the T-5, did you change the flywheel to a 50 oz and then get the vibration? Then change the damper to the 50 oz to get rid of the vibration?

I am afraid your engine is not properly ballanced and at high rpm the damper may come unglued or worse the flywheel.

1bad66 · #7 (**permalink**) 02-09-2007, 03:47 PM

Yep, when I put the t-5 in with the 50oz wheel I got a bad vibration. The motor was "sitting around" for about 10 years and I did not run it before putting the t-5 in. Do you think my old balancer was bad to begin with? All I know is the vibration quit when I put the 50 oz on. I do notice some vibration at about 4500rpm.

olddog · #8 (**permalink**) 02-09-2007, 04:04 PM

Do you know what the flywheel and ballancer that came off the engine were?

If they were the 28 oz, I am very concerned.

1bad66 · #9 (**permalink**) 02-09-2007, 04:14 PM

When I built the engine about 15 years ago, I had it balanced and printed, the tranny was a 69 FMX auto (the motor and tranny came out of a Mach 1). When I had it in my 66 f-100, I could take it to 6000rpm no problem. I am not sure though if the balancer that was on the motor at the time I put it in the Corba was the same one that I had the motor balanced with. (I am not the best of keeping track of stuff). So it should not matter what is behind the engine for a tranny and flywheel?

olddog · #10 (**permalink**) 02-09-2007, 04:39 PM

The tranny should not matter, but the flywheel does. The flywheel is out of ballance (not nuetral) to compensate for the crank shaft not being completely ballanced. Same is true for the ballancer on the front.

For high performance engines they try to get the ballance to +/- 1 gram (there are 454 grams in a pound). If you have 50 oz flywheel and ballancer on an engine that should have 28 oz, the engine is out of ballance by 22 oz or a 1-3/8 pounds. That would be huge!

I have no experiance with this, but I would expect the motor vibration to be worse than you described. A nieghbor put a SB chevy 350 damper on 400, when the 400 first came out. He didn't notice the vibration, but the damper went through the radiator, when it came off. It took the keyway out of the crankshaft on its way off. Seems to me the bolt head snapped off, but I'm not sure anymore. So if he didn't notice the vibration, maybe what you have at the upper rpm is all the warning you will get.

To sum it up I am concerned for you.

They do make flywheels and dampers for both 28 & 50 oz, so what you need is available. The question is how do we get you some help to sort out what you need for sure.

Not to high jack this thread, so back to the origonal poster. Since 1bad66 may have had the wrong weighted flywheel and he had the same vibration at the same rpm as kens67cobra original post. I have to ask, are you sure you have the right flywheel on your engine? I think this is a common mystake.

1bad66 · #11 (**permalink**) 02-09-2007, 04:45 PM

I think you are right old wise one...I have been on the web looking at this, and every body who has swapped out a 302 for a 351w (with a t-5 behind it) said you must get a new flywheel to compisate for the balance. They say the part number is m-6375-a302. I would almost guarantee this is my problem and that I just put a bandaid on it by putting a 50oz on the front. I sure am glad that I am a memeber of this site, you guys always have the answers. Thanks man!!!!!!!!!!!!!!

coosawjack · #12 (**permalink**) 02-10-2007, 06:11 AM

I have a slight vibration in my CR at 1200 RPM that returns at about 2400 RPM with a fully balanced engine that I doubted was the culprit??

I found that the side pipes are causing it since they are attached to the frame just in front of the back wheels!!

Unbolt them and take a short spin to see if that is your vibration (harmonic) source??

I made some heavy rubber "Donuts" to help isolate the side pipes from the frame and they helped quite a bit!!

I can send you a couple to try if you like!!

Coosawjack