harmonic balancer

[mcditalia]

It all started with the thermostat housing needing replacement!
It all snowballed from there, found out radiator is shot, so while I'm at it pulling everyhing out it's a great time to change the pulleys to correct setup. Now I realize that my harmonic balancer is the 6" base 300hpmotor kind that is pressed into the crankshaft.? I knew when I bought my car it consisted of many different year parts slapped together. My block is supposedly the original L79. I say supposedly because it has the HT stamp with with my vin number on the engine pad. I took the engine pad paint off years ago and showed horizontal broach marks which looked convincingly factory.

So my point is will the 6" balancer work on this motor? If its pressed into the crankshaft, will the bolt on 8" finned correct one fit too? And how do I make the swap? I'm assuming that the correct double grove/belt pulley setup will not fit into my 6" balancer? With many years into digging into this car with limited mechanical abilities this is new territory for me.

 

[JohnZ]

The tab on the timing cover will determine what you can use without further disassembly - L79's originally had an 8" balancer, and the 300hp had a 6" balancer; if your timing cover is from a 300hp, the timing tab will interfere with an 8" balancer. If the timing cover is from an L79, it will accept either balancer.

The front face of either balancer (where the pulley bolts on) is in the same fore-aft location, so that's not an issue.

I wouldn't recommend using the 6" balancer on an L79; the 8" balancer is tuned specifically to the torsional frequency of the L79 rotating assembly. If your innards are indeed L79, the nose of the crank will have a 7/16"-20 threaded hole in it for the balancer bolt; if there's no threaded hole, it's a 300hp crank.

If you have the threaded hole, you'll need to rent a proper balancer remover/installer tool to pull the existing balancer and install the 8" balancer. Do NOT try and install the 8" balancer using the balancer bolt instead - you'll probably strip the threads in the crank, and you'll have more problems than you can deal with. Use some Permatex #2 on the crank keys when you install the balancer, or you'll have an oil leak through the key groove in the balancer hub.

 

[maxphunn]

Use some Permatex #2 on the crank keys when you install the balancer, or you'll have an oil leak through the key groove in the balancer hub.

John, I think you just made my day! I have been chasing a tiny oil leak from the front of my L79 for a very long time and that may be the answer. I will try it when the '66 gets put away for the winter. Thank you.

 

[mcditalia]

Thanks John. I wont be able to get a good look at the end of the crank until i pull the balancer off, but took this pic. Looks like it was drilled, but can't really see any thread marks in there. So besides the drilled end, is there any difference between a 300hp crank and a 350hp?

The timing cover has an aftermarket timing tab bolted on to the side. Either way it doesn't look like an 8" balancer would fit with this set up unless i change the tab.

 

[JohnZ]

That's a 300hp crank - only drilled for the machining center locator, not drilled/tapped for a balancer bolt. The two (forged) cranks are the same, except the L-79 (350hp) crank was drilled/tapped for the bolt and was Tufftrided (a wear-resistant chemical hardening process that gave the crank an overall light gray appearance).

Bolt-on timing tabs are available for both 6" and 8" balancers - Summit and Jeg's have them.