Re: harmonic balancer for 5.7 whats the difference between the 6 3/4 and 8 inch
i basically want to make sure i can swap out the timing tab that came with new longblock with the 8 inch tab and then everything else will fit from old motor. or should i get a 6 3/4 balancer and use smaller flywheel and buy another starter that will fit that flywheel. i dont know if the new starter i have will work on both flywheels. its for the bigger flywheel. or does none of this matter and the flywheels and balancers are interchangable. i keep getting mixed info from different mechanics and forums. a lot say it dont matter. and some say it does.
Again, it depends. the 2 basic issues are :
1. Location and actual marking for the timing tab in relation to the timing mark on the harmonic ballancer (vibration damper).
2. The actual ballancing of the harmonic ballancer in relation to what is contained inside the block.
For those 2 reasons, no one on here can absolutely answer your question with any degree of certainty.
The 1st can easily be worked around when installing by using a degree wheel to be sure everything is as it should be.
The second is the most critical. GM used a large variety of ballancers for the way the engines were ballanced. Internally or externally ballanced configuration, forged or cast crank, small or large beam rods, flat dome or relief cut pistons. Sooooo many variables. That is why I suggested going to the builder to find out, especially since the builder seems to have placed a flywheel on there (large one) that doesn't seem to jive with the small ballancer front cover. Only he will know why and how the engine is ballanced. The specific type of crankshaft / rods / piston assy dictates the type of ballancer / flywheel combination that needs to be used to ensure proper engine ballance. After a rebuild, the info garnered from the SN: may or may not apply any longer, depending on what the builder did.
I believe this is critical on marine engines, as they tend to spend most of thier lives in RPM ranges that automotive engines don't see very often. If it was me, I would have the entire rotating assy, consisting of the crank (with the timing gear on it) / rods (with bearings) / pistons (with rings) / flywheel and harmonic ballancer, all ballanced as an assy to ensure it is correct. You NEVER know what was replaced or substituded during a build. Builder could have thrown in a set of pistons or a re-built / recut and polished crank, not checking the ballance AND they could be for an engine with a different ballance scheme. They all bolt in the same but have different characteristics. Not saying he did, but have seen it before.
Have seen way too much wierd stuff done when I was building pro racing stuff for customers in the 70's and the years following. I don't take anyone's claims of everything "being correct" when doing a build.
