Inliners International Forums General Discussion Engines Harmonic Balancer Install, Can I Do It This Way?

Hi all again,

Getting closer to getting the 250 back together. I have read everywhere that I should drill and tap the crank but I am not sure I want to risk it and screw something up.

I know using a mallet is not great on the thrust bearing but I had an idea to help prevent damage.

If I put a block of wood between the engine stand and the back of the crank, wedging it forward, then using a mallet to install it. This would keep the the load off the thrust bearing.

Would this work?

Heat the balancer around the center hole to make the hole bigger, you get an easier fit that way. Use a handheld propane torch or something but don't heat too much or you may compromise the bond of the rubber membrane in between the hub and the pulley (unless you have a solid metal balancer, I dunno). By getting it just hot enough that you don't want to touch it with bare hands, would help a lot.

Your trick would also work but it still sends shocks through the length of the crank. Maybe try both these tricks together and be gentle. I'm facing the same challenge again soon with mine, and I also need a new balancer... just noticed a crack on mine where the keyway is. Didn't see it when I took it off. Didn't look for one either.

If you drill and tap, you need to get the drill hole perfectly straight with the crank. If you screw it up, well, you are no worse off than what you started with - no tapped hole at the end of the crank

Spend the time and drill/ tap the crank. You will be glad you did.

The crank drills and taps easily. Drill it at least 1.5" and tap about 1-1.25. You never know how long the bolt might be.

Yeah, that's what I really want to do but I am not sure I can get it square in the crank and I am running out of time to get this engine back together and I don't want to create a new problem.

Create a new problem?
Like a bent crankshaft, damaged balancer or wiped thrust bearing?

Make a jig. Use a socket that fits tight to crank snout with a 3/8 shaft size. The crank is already centered for the bit. Allign and drill with correct bit for 7/16 fine thread.

Okay, I think you got me doing the drill and tap method.

Once you drill it you can use the right tool to install your dampener. And Not hammer on to the crank.

Report back with your experiences, I'll probably be doing that later this summer too.

Taking a break for lunch so I figured I would update this.

I was able to drill the crank. I found the center had a 1/4" step that allowed a drill bit to snugly center and square up. I started with that and drilled about 1 3/4" deep. Stepped up a few sizes and finished drilling to 2". Then a couple more steps up in size until I got to the final tap size needed. Got my 7/16-20 tap and it is going in nice. Have about another 1/2" to go and should be done.

Overall it's not hard and getting the first pilot hole is the hardest but after that, it goes easy. Thanks to everyone who kept saying I can do this. It will definitely make installing the balancer much easier.

A follow up to this. Used a balancer installer and was able to put the new balancer on without any problems. Definitely worth the time to drill and tap the crank.

Thanks to all again.

Glad it worked out.

Where there any pictures to go along with this i am hoing to be doing thos very soon.

Maybe pictures of the jig and such would e awesome for the record books

Also in leos book he says to go to a 1/2 by 20 is that too much?

The snout on the crank is the same size as a SBC, and they are tapped with a 7/16 x 20. These balancers don't fall off without a bolt, a 7/16" bolt is plenty.

The snout is also the same as an older GMC six which has a 5/8-18 thread. I have made custom washers as the originals often crack when torqued to factory specifications.



Use a new grade 8 fastener and lock washer too!

That's true Ken, but they're also steel, while the lions share of the 3rd generation crankshafts are only cast iron, and not very good cast iron either. If you could find one of the rare steel 292 cranks, then I would say that 1/2" would be safe, but not for a cast crank.

Cool mine has already been drilled

For a turbo car would i need to drill any on the reverse side of the crsnk for the fkywheel?

You could drill the flywheel bolts to 1/2" if their not already. Just make sure the flange doesn't get too thin around the bolt holes. You can also drill and tap the camshaft snout for a bolt also.