604 balancing?

[PolakMotorSports]

Have 604 crate, with 7.25 quater master clucth, am i supposed to have external balancing plate on crank. Can anyone tell me or help me? Motor has vibration at about 2000 RPM.

[FF21]

Pretty sure those motors are externally ballanced.

[ptodd]

yes you do. quarter master makes the flywheel for a 604.

[dynoman14]

Polak,
If you need to balance your assembly and cant find anybody to do it, I can either make a plate or modify your clutch/flywheel combo to get rid of the harmonics. I have an older hines that works realy good on the larger diameters of flywheel balancing.

[fast55]

You'll need the QM balanced crate motor button flywheel. Just make sure, if you're using the big flex plate starter ring, that it's not balanced too.

[dynoman14]

Since you can't balance the crank and it is externally balanced, you might want to check your crank with the QM or any other unit you get. I have found them to be pretty far off like 10-15* and 10-15 in.oz. In most cases that will run fine, but the bearing look like hammered dog $hit when you pull the engine down.

New pistons -v- old pistons ( +/- 20g. ea. ) as well as 3 styles of PM rods ( +/- 30g. ea. ).

Vibrations will be readily present on the engine dyno around 2700 and 5400 if you look for them. Lots of folks think it is the timing shaking around when it is vibrational transmitting from the crank thru the timing chain to the camshaft to the dizzy gear to the dizzy.

That is why folks break timing chains on engines with many laps or freshens without checking the crank balance???

Rules say you can't balance the crank, they don't say you can't match up all of the rotating assembly and equalize bob wt. with parts matching, and then when you get the final bob wt. you use the flywheel to final balance the assembly. In 50+ engines I have seen final bob wt vary +/- 100g, over 8 cylinders that is almost 2# misbalance. 100g mis-balance at 2500rpms in my Hines machine the crank will almost jump out of the v-blocks.

Understand it is not so much the amount of weight as it is the degrees that it is off balance that compounds the problem.