VAC calibration way off

[Jack P.]

My L79's VAC died after about 30 or 40 years. It was a B20. Reading all the posts on VAC and timing (JohnZ , Duke W., etc.) a replacement number now would be B26. 16* full advance and rated at 16* @ 13 Hg.

I put it in, timed the car and what do you know?

19* to 20 * from VAC . Full in at 11-13 Hg . This was over the limit by 3* to 4* , for my aggressive timing map.

I put in a B1 and it only put out 13* at full vac 20* Rated for 16* @ 16-18 Hg.

What to do?

Put back the B26 and put a bushing on the rod. It fit just right and had a 1/4" OD. It held back the rod by 3 * bringing the VAC advance back to specs.

You can't trust today's replacement or reproduction parts to be on spec.

It only cost $.15 for a nylon sleeve or bushing: See photos

Jack

[Clem Z.]

Re: VAC calibration way off

My L79's VAC died after about 30 or 40 years. It was a B20. Reading all the posts on VAC and timing (JohnZ , Duke W., etc.) a replacement number now would be B26. 16* full advance and rated at 16* @ 13 Hg.

I put it in, timed the car and what do you know?

19* to 20 * from VAC . Full in at 11-13 Hg . This was over the limit by 3* to 4* , for my aggressive timing map.

I put in a B1 and it only put out 13* at full vac 20* Rated for 16* @ 16-18 Hg.

What to do?

Put back the B26 and put a bushing on the rod. It fit just right and had a 1/4" OD. It held back the rod by 3 * bringing the VAC advance back to specs.

You can't trust today's replacement or reproduction parts to be on spec.

It only cost $.15 for a nylon sleeve or bushing: See photos

Jack

this place has all kinds of ignition parts including vacuum advance stops. http://www.kendrick-auto.com/ignition.htm

[Jack P.]

Re: VAC calibration way off

Thanks for the great ignition source. I think most B26 replacement vacs, pull in too much . 2 to 4 degrees beyond the 16 has been reported by others. You just have to check your vac if you put a new one in. I chose this way, but I see from the site, there are other parts available.

Jack