Distributor Tach Drive

Hi everyone

I have a tach drive issue.

I have a 69 vert with a GMPP ZZ454, it has a Mallory model # 25711C distributor installed.

My question is what direction is the engine turning, and what direction should the distributor turn so that it turns the tach the proper way?

I am pretty sure this is the problem, as the cable works fine.

If I look at the cable while it is turning it turns clockwise while facing it from the drivers side of the car.

Is it possible to have a wrong rotation distribuor and the engine still run?

Crank/cam turn clockwise, like every other engine I ever heard of....looking that the harmonica balancer on front....

Mechanical tachs turn COUNTER clockwise as viewed from the BACK of the tach....obviously clockwise from viewing angle....they work like a speedo, so the cable has to spin counter clockwise.....

I have seen GM do dizzy's in both directions, the SBC turns clockwise looking from up top.....the olde tyme Pontiacs were CCW ....go figger....

I dunno about BBC, never owned one, 50 years of messing with cars....never owned a BBC.....

:bonkers::rofl:

All Chevy SB and BB distributors are the same (except the 409-series engines), and they all turn the same way. If you have a Chevy distributor in the engine, it's turning the tach the right way. Many aftermarket distributors require the use of an insert/adapter in the tach drive portion of the distributor in order for the cable to engage - if the insert is missing, the tach will be inoperative. If the tach cable is spinning at the tach with the engine running, the tach is defective.

Thank you guys for the help.

The tach will spin if I rotate the cable by hand, not when all is hooked up.

The tech rep @ Mallory stated that I may have the wrong rotation tach drive, he wants me to sent it in if I can not get this sorted out.

I'll check everything out once more, I'am getting good at this!

Before I go, thank you Lars, and welcome, I've enjoyed and learned alot from your papers, they have added greatly to my understanding of the issues you write about, keep them coming please!

Craig

I had a tach drive gear fail at 90,000 miles on a vette dist.

I had a tach drive gear fail after 200 miles on an aftermarket dist.

When they went, you could feel a little resistance when spinning the dist. by hand as opposed to spinning freely.

Lars is correct, to get the Chevy Tach Drive cable to operate you need a cable addaptor as the Mallory tach drive uses a shaft with a pin through it as opposed to the square drive of the Corvette Tach drive and drive cable,