vacuum guage, is it shot?

[Doc Dave]

Back when I was in high school in the late 60's (grad in '71), I assembled a few tools, including a vacuum guage (made by RAC).
I got it out the other day from a box in my garage and I see that the needle sits at 11 inches of vacuum at rest, not down at 0 which is what I would expect. When I hook it up to t he intake manifold, it pegs out at 30.
I took the back off to see if there was an adjustment and I did not see one.
Is this guage shot? Could I pull the needle loose and reattach it at 0? Should I just get a new one and be happy?

[Hawk]

seeing as the internals of these are picky and you want it to be on a dime, not off the scale. I would just go buy a new one. They range from $10 to $100 pending on the MFG.

From Craftsman.com
Actron Vacuum Gauge, Fuel Tester
Sears item #00902179000 Mfr. model #2179
$19.99

[MoparNorm]

Hawks right, not expensive, but FYI that "19" lbs is right on if you're under 1,000 ft. elevation,,,ha!ha!
I have a Vacumn Guage readings section at the DTA Album "Parts and Schematics"
I find a timing light arbitrary and in accurate for most applications and I always time my motors and adjust carbs by vacumn.
MN

[Gordon Maney]

Hawks right, not expensive, but FYI that "19" lbs is right on if you're under 1,000 ft. elevation,,,ha!ha!
I have a Vacumn Guage readings section at the DTA Album "Parts and Schematics"
I find a timing light arbitrary and in accurate for most applications and I always time my motors and adjust carbs by vacumn.
MN

Actually, the only thing that could cause a timing light to be inaccurate [in use] is if the marks on the engine were not calibrated correctly. You could verify the marks by using a dial indicator on top of your number 1 piston to verify TDC.

The worst possibilities involved some engines that had vibration dampers that could experience relative rotation between two parts, thus moving the mark.

I am 55. I think only you really old guys use vacuum gauges for timing.

[MoparNorm]

Actually youngster...ha!ha!
If you CHANGE the cam or the carb or advance the cam, add headers, valve work etc, the factory timing specs for a light are worthless.
An engine will run much more efficiently and get better power and fuel economy if timed with a gauge rather than a light.
MN

[Gordon Maney]

Actually youngster...ha!ha!
If you CHANGE the cam or the carb or advance the cam, add headers, valve work etc, the factory timing specs for a light are worthless.
An engine will run much more efficiently and get better power and fuel economy if timed with a gauge rather than a light.
MN

OK, I can go with the idea that the best timing specification may have changed from the original. I can find credibility with the idea that a vacuum gauge can be used to set timing. My approach, ignoring how we arrived at the best, new setting, would be that once it is established, we measure it with the light, and then set it at that new setting during future work with the light.

Because we toss out the original specification because it is no longer correct does not mean we toss out the measuring device as no longer being accurate. Consider that not all people will have the confidence you have with a vacuum gauge, and consider that once a new setting is derived, the average person will be much more easily able to reliably set the timing at the new setting with a light.

[MoparNorm]

OK, I can go with the idea that the best timing specification may have changed from the original. I can find credibility with the idea that a vacuum gauge can be used to set timing. My approach, ignoring how we arrived at the best, new setting, would be that once it is established, we measure it with the light, and then set it at that new setting during future work with the light.

That would certainly be a possibility. I've always adjusted the carb with a vacumm guage and then, leaving it attached, proceeded to set the timing also. One insturment for two tasks, and I feel more confidence in the settings arrived at.
But if I could adjust a carb with the timing light, I might give serious thought to changing my technique...= )
MN

[Hawk]

man timing is best done by feel, if went with factory settings on the mods, you would be screwed in the long run.

But then again that comes with exp. on doing this over many of years. OH hold on I am one of those young ones too :) opps LOL

[MoparNorm]

man timing is best done by feel, if went with factory settings on the mods, you would be screwed in the long run.

That's pretty much what I said in my post above, I do agree that "feel" or "ear", works good, once you have experience, but you still need a baseline to start from, that's where the vacumn gauge comes in to play. It verifies that "ear" after your hearing starts to go........= )
MN

[Hawk]

but you still need a baseline to start from, that's where the vacumn gauge comes in to play. It verifies that "ear" after your hearing starts to go........= )
MN

Um, I hate to say this, but mine Hearing is already gone :P

So feel is the best way. Gages can be wrong and/or off. And if your are dealing with something very sensitive to the valve/piston clearance, you can not take that chance to have it opps and CRUNCH.......BOOM..... BANG....

[MoparNorm]

Vacuum is a by product of the valves, the only way you can hurt an engine using a vacuum gauge, is on purpose. A vacuum gauge is the best diagnostic tool you can use also, if you don't have $40,000 worth of electronic equipment.
"feel" is close, vacuum is exact.
MN

[JimmieD]

Got to agree with the vacuum gauge based on the principles of its operation. As Gordon said, dampers and elastometric inserts can change for various reasons. With a vacuum gauge you're taking direct readings of the actual real world timing relationships of valves, ignition and air delivery. It's almost like an X-ray of the innards of the engine while it's running. Not only that but the vacuum gauge can diagnose a whole world of other relationships all at once, as shown in Norm's Image Event pics.

I also agree that the timing light, once a baseline is determined, is a good quick way to check the timing. Only problem I see with that is how to know for sure that the damper's rubber/elasto hasn't spun since the last baseline check? I usually leave a vacuum gauge permanently installed under the hood so it's a simple matter to pop her open, have a peek and know it's good, bad or ugly. Even the best vacuum gauges will fail after a couple of years of continuous duty like that due to the crankcase blowby.

JimmieD