C1 283 Harmonic Balancer and Pulley bolt fit

[Daniel S.]

I bought a rebuilt 283 (mid 1959 date code) a couple of years ago and finally getting ready to start it up. I trying to put on the harmonic balancer pulley and the bolt for the harmonic balancer is 7/16-20, The bolts will not fit through the holes of the harmonic balancer fully which I have two - one with a 15/16 off set which I saw from Paragon. I looked at Paragon and they say that the bolt size is 3/8-24 which would fit through the hole. Can anyone shed some light on what I am dealing with - I do not want to modify the pulley.

Any help would be appreciated

mechanic in training

Thanks

[Joe L.]

Re: C1 283 Harmonic Balancer and Pulley bolt fit

I bought a rebuilt 283 (mid 1959 date code) a couple of years ago and finally getting ready to start it up. I trying to put on the harmonic balancer pulley and the bolt for the harmonic balancer is 7/16-20, The bolts will not fit through the holes of the harmonic balancer fully which I have two - one with a 15/16 off set which I saw from Paragon. I looked at Paragon and they say that the bolt size is 3/8-24 which would fit through the hole. Can anyone shed some light on what I am dealing with - I do not want to modify the pulley.

Any help would be appreciated

mechanic in training

Thanks

Daniel------

Are you saying that the 3 holes in the balancer intended for pulley attachment are tapped for 7/16"-20? If so, they have been drilled and tapped oversize. They should be 3/8"-24.

[Daniel S.]

Re: C1 283 Harmonic Balancer and Pulley bolt fit

Daniel------

Are you saying that the 3 holes in the balancer intended for pulley attachment are tapped for 7/16"-20? If so, they have been drilled and tapped oversize. They should be 3/8"-24.

I guess they have been drilled then - I guess I should buy a harmonic balancer with the right threaded holes.

Does the spacer for the harmonic balancer always go on the car or just when the pulleys don't align?

Thanks

Dan

[Joe L.]

Re: C1 283 Harmonic Balancer and Pulley bolt fit

I guess they have been drilled then - I guess I should buy a harmonic balancer with the right threaded holes.

Does the spacer for the harmonic balancer always go on the car or just when the pulleys don't align?

Thanks

Dan

Dan------

Harmonic balancers, especially the original kind, can be difficult and expensive to find. You could probably restore the original thread size with heli-coils. Otherwise, you could enlarge the holes in the pulley for the 7/16" bolts. That should not cause any problem other than possible judging penalty (assuming any judge would ever notice it).

I believe the spacer was used for all 1957-62 Corvette applications. However, there might be specific engine applications. Someone else more familiar than I with C-1's will have to confirm on this.

[Jim L.]

Re: C1 283 Harmonic Balancer and Pulley bolt fit

I believe the spacer was used for all 1957-62 Corvette applications. However, there might be specific engine applications. Someone else more familiar than I with C-1's will have to confirm on this.

The spacer compensates for the thickness of the front motor mount which pushes the water pump and hence the water pump pulley forward. So, yes, it should be included on all V8 C1s.

[Daniel S.]

Re: C1 283 Harmonic Balancer and Pulley bolt fit

Thanks to both of you I will try the heli coil great suggestion and put the spacer on
Dan

[Richard G.]

Re: C1 283 Harmonic Balancer and Pulley bolt fit

Daniel;
The 3/8 NF tap drill for a Helicoil is 25/64 (.3906)
7/16-20 drill size range is .3830 to 0.3916

It appears that you will have two threads on top of each other as the tap drill for each is very close to the same size.
I don't see any reason this wouldn't work but getting the insert started in the correct thread may be an issue.
I would sure give it a try.

Another option is what is called E-Z Lok that requires a larger hole and no specialized tap. The OD is a standard thread.

It may be an option.
Rick

[Daniel S.]

Re: C1 283 Harmonic Balancer and Pulley bolt fit

Hi Rick,


Thanks for this suggestion but I must say I am a little concerned after I thought about it because I have never drilled and tapped holes and I am sure you have to make sure they are true and not on an angle. I will probably do more research on how to do this before I attempt it.

Thanks
Dan

[Richard G.]

Re: C1 283 Harmonic Balancer and Pulley bolt fit

No need to drill for the helicoil, if you go that route, as the hole is already the correct size. Just tap it as is. You will know right away after inserting the helicoil if its going to work.
A good method of getting the hole and tap started straight is to use a drill press. Sometimes they will have a large enough center hole for the crank snout to go through. If not some 2x4 for spacers, around the preripheral, will work. Put the tap in the chuck and turn the drill by hand. Get it in as far as you can get it by hand then release the tap from the chuck and finish tapping it by hand. A two handled tap wrench is best but a crescent wrench will do the job.