Harmonic balancer bolt

[E R.]

I am restoring a 64 300 hp vette. removed the harmonic balancer and noticed there was no bolt, I thought they all had bolts to hold them on but after checking the old posts I see that wasn't the case. My question is do I need to get the crankshaft drilled and threaded or can you reinstall the old harmonic balancer I don't want this to come off later? How much of a job is it to drill and thread, what is the best way to solve this, I can't believe GM would not have installed a bolt to hold the balancer on.
Thanks for any help
EV

[Mike M.]

Re: Harmonic balancer bolt

the 250 and 300 hp hydraulic lifter 870's didn't have bolts securing the harmonic balancer to the crank snout. (the solid lifter 870's did). I've never had, seen or heard of a harmonic balancer flying off the cranks(as long as the engine were stock). I usually drill and tap the cranks on the hydraulic lifter engines and remove the bolt when having the car judged. probably not necessary tho. drill and tap a job for a machine shop with crank out of case. mike

[Loren L.]

Re: Harmonic balancer bolt

"probably not necessary" but you are referring to a potentially 55 year old "press fit".....I'll supply the bolt and washers....

[Duke W.]

Re: Harmonic balancer bolt

These "no bolt" balancers are a tight interference fit - fairly easy to remove, but somewhat tricky to reinstall. Also it's possible that one or more R&Is can weaken the interference fit, which reduces the balancer's grip on the crank, so many have the crank drilled and tapped for a center bolt when the crank is removed for inspection/rework during major engine overhauls. Then it's easy to pull the balancer on to the crank with the bolt, and the joint is more secure.

If detected during judging, it's a small deduction, but like Mike said, if you remove the bolt before judging...

Duke

[Joe L.]

Re: Harmonic balancer bolt

All-----

Starting in 1969, possibly 1968, all small blocks got the balancer retaining bolt. Mark IV big blocks always had the balancer bolt, right from the start.

As has been mentioned, the biggest problem with the non-bolt cranks is installing the balancers without damage. The factory used a large, special press to do this. NOBODY in the SERVICE environment has such a press. That results in folks having to use "other methods", none of which are the least bit ideal.

[Jim T.]

Re: Harmonic balancer bolt

MY first Corvette a 1964 327/300 4-speed factory air convertible engine was rebuilt by me in 1969. I installed a new harmonic balancer. It came off. I took the 64 to the Chevrolet dealer in Cornado, CA. My new balancer I had installed was replaced with a new one by the Chevrolet garage mechanic and never came off when I drove my 1964 from the west coast to the east coast and to Dallas and the balancer remained on.

[Michael M.]

Re: Harmonic balancer bolt

I would drill and tap the nose of the crank if you had a choice. To me it's like buying insurance since I saw a harmonic balancer from a stock original engine go through a hood.

[Steven B.]

Re: Harmonic balancer bolt

Does the 300HP 327 carry a forged or cast crank? Is the hardness such that it requires special equipment to drill and tap?

Steve

[Joe L.]

Re: Harmonic balancer bolt

Does the 300HP 327 carry a forged or cast crank? Is the hardness such that it requires special equipment to drill and tap?

Steve

Steve------

If you're talking about 1962-67 300 hp 327, it's a forged crank. If you're talking about 1968 300 hp 327, it's nodular cast iron.

[Mike M.]

Re: Harmonic balancer bolt

i've drilled and tapped them without any special bits/taps. i THINK all the small journal abc cranks were forged but not sure. mike

[Domenic T.]

Re: Harmonic balancer bolt

Mike,
If I remember right, (way back then) the pass automatic cars had a cast crank and the stick shift had the forged. We used to thump the counter weight to hear the difference. Ringing sound with forged and thump with cast. w We also saw the clean up grinding (about 1/2") at each journal.
Watched them at Allis Chalmers bend the cranks for tractors. All journals were straight up after casting. Then they bent each 90 and ground them.

Dom

[Steven B.]

Re: Harmonic balancer bolt

'67 was what I was interested in primarily, but just out of curiosity, were the 250hp cranks cast?

Steve

[Joe L.]

Re: Harmonic balancer bolt

'67 was what I was interested in primarily, but just out of curiosity, were the 250hp cranks cast?

Steve

Steve-----

No. They were also forged. All 1962-67 Corvette small block cranks were forged steel.

[Duke W.]

Re: Harmonic balancer bolt

It's my understanding that all 283/327 cranks through '67 are forged (probably 265, to, but I'm not sure). 327 SHP/FI cranks are a different forging than 250/300 HP forging due to a slightly different balance weight configuration because the forged SHP/FI pistons are heavier than the 250/300 HP cast pistons.

Of course, all are heat treated to a specified hardness, and SHP/FI cranks got a special surface hardening treatment called "Tufftriding", generically known at nitriding, which makes the crank more durable. This is why these cranks should never be turned unless absolutely necessary because even a .010" cut will remove the hardened material at the surface.

When I rebuilt my SWC's 340 HP engine at 115K miles all the crank journals were right in the middle of the factory tolerance range and it passed Magnaflux inspection. I ordered the machine shop to measure runnout (it was within limits) and polish the journals, and that was it.

The trouble is that most machine shops will just turn the crank without measuring anything, so a lot of cranks get turned that don't need it. If you have your engine rebuilt, don't let this happen.

There's an easy way to ID a forged crank by looking at the width of the parting line. If memory serves, the parting line on forged cranks is wider than on cast cranks.

Duke

[Domenic T.]

Re: Harmonic balancer bolt

Steve-----

No. They were also forged. All 1962-67 Corvette small block cranks were forged steel.

Joe,
I have a 64 283 with a cast iron crank. Came out of a powerglide car. My understanding was that the cranks were steel or cast iron. Maybe I am mis-understanding the cast vs forged. I thought the forged were all steel, and the cast were iron.

Dom