Vibration - Wrong balancer?

If it were a regular balancer it wouldn't vibrate at all, it would have a very noticeable shake to it at all times. Not sure what it would be with a fluid type.

assuming he put on a standard balancer, you should be able to look at it and tell which one is on. Compare it to pics of the proper balancer or see if you can read the part number

When you have either the wrong harmonic balancer or the wrong flexplate (flywheel), you will have a "shake" or a "shutter" from about 1,800 RPM to about 3,000 RPM. It'll begin to smooth-out above that. Well, actually it doesn't really smooth out in reality, it just oscillates so fast, you don't notice it as much.

When an engine is out of balance, or you have something like 1 rod cap on backwards, it will usually cause a vibration. What I mean between a shake and a vibration is the speed or "frequency" of how it presents.

A shake or shutter is like an off balance washing machine on the spin cycle. It actually makes the entire engine "wobble", which you can feel through the whole vehicle. A vibration, such as an engine out of balance" is more like, well.... a vibrator.

Most machine shops (and rightfully so) don't balance rotating asemblies. Neither did any factory. No engine ever came "balanced" from the factory. They would take a typical crank, a typical rod and a typical piston, do a rough balance on them and set all of the machines to make all of the parts the same. They never took into account for rod changes, batch changes, piston upgrades, etc. In other words, it was very "vague" on the balance numbers.

Now, when a machine shop does a balance job, we take everything into consideration, including the weight of the oil that is on the parts, and balance that to within 1/4 gram. Factory engines weren't even close to that kind of accuracy, in fact, they were usually pretty far off... by "ounces", not by grams.

If you have a "shake" or a shutter, you probably have a mismatched balancer or flywheel. It could even be a bent crank or a bent crank snout causing that shutter. I have seen this on a few engines over my years and have bent a few crank and snouts on small block Fords in the early days of supercharging.

If you have a "vibration", then it is probably a component within the rotating assembly. Not all engnies use the same components. In other words, if you had one bad rod, a machine shop might replace that rod. Well... that replacement rod is most definately a different weight from the other 7, thus potentially causing a vibration.

The only time you REALLY need to balance an engine is when you use after market components, such as a crank, rods or pistons, or any combination of the 3. After market components do NOT have the same weights as factory components, so you can't just go throw a set of after market pistons in, or a new set of rods, or a new steel crank and run with it (them). You HAVE to balance the assembly or you're asking for a vibration problem which will eat-up bearings.

Some people get very anal about balancing and when it comes time to "freshen-up" their engine, they may keep everything but swap out the pistons for forged types. Well, those are much heavier pistons (if you use something like Sealed Power's compared to a stock cast piston), so there went the balance job right out the window. This also rings true if you bore your block and go with a .030" over piston. You now have pistns with .030" more material on them, so naturally they are now heavier than your last set, so in theory, your engine needs to be re-balanced. The reality of it is though, you don't really need to balance it all again. There ARE tolerance areas where being a little off here or there won't make an effect on how "smooth" teh engine runs. Again, ALL facory engines fall into this category, except for maybe the very rare, special performance engines that came in limited edition cars.

Hope that helped

Well if it were a balancer believe me you would know, my buddy had a retarded mechanic do his and put the wrong balancer in, the ending felt like it was going to vibrate itself apart.

to make it short,
-make sure your wires are ok
-check your cap and rotor also
-try new plugs and gap them if everything is ok, stick with motorcraft, i had bad luck with bosch and one other brand.

To elaborate on the plug issue, I would make sure you have motorcraft spark plugs and decent wires, as in good condition, dont need high end stuff. I went through 2 sets of plugs that didnt run right with my 302 before going to motorcraft, although my compression is on the higher side at 10.8:1 I assume thats why the plugs were more sensitive. But through in some new plugs and try it out, my problem only happened at part throttle underload and carry on at times to higher rpm.

hope that helps

Yah, good point! Don't rule out that it ain't a miss in one cylinder at certain RPM's. I was just assuming it was running good. A "dead hole" will most certainly feel like you have the harmonic balancer on there.

Good call

Arron Johnson said:

Yah, good point! Don't rule out that it ain't a miss in one cylinder at certain RPM's. I was just assuming it was running good. A "dead hole" will most certainly feel like you have the harmonic balancer on there.

Good call

Click to expand...

Thanks dude, its just a team effort in here thats all

Match balancing flywheel and flexplate

I've been having a similar problem with my '68 302 ever since I swapped a T5 in place of the C4. Seems to peak around 1500 rpm and clears up by 2000 rpm.

I've messed with the ignition (new wires, plugs, advance changes) with no real effect. If I hang the vibration damper on tail shaft that I used to have on the C4, it seems to knock the amplitude down a bit, but the shaking is still there.

I'm to the point that I am going to pull the flywheel and have a machine shop compare the balance to the old flexplate.

My question is this: should the flexplate be measured with the converter on or not? It seems to me that the hole in the flexplate for the converter drain plug would throw the balance off a bit. If it is spun with the converter on , should it be dry or full of fluid, or it won't matter because any fluid will uniformly be flung to the O.D. of the converter?

The converter should be a neutral balance so as not to interfere with the engine's balancing. So you only need the flexplate to be matched to the new flywheel. This is the way the guy who has done all my balancing work does it. He "match balances" flywheels to flexplates and vice-versa all the time.

You will also want to bring him the pressure plate and clutch disc you're using on the flywheel to insure they don't throw off the balance. These parts should be neutral balanced just as a torque converter should be to a flexplate.