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Old 08-16-2010, 05:46 PM
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Vacuum Gauge Surprise

Yesterday, on the spur of the moment, I decided to test the engine with a vacuum gauge�something I hadn�t used in a very long time. Since the engine was running quite good, I was not expecting anything but a steady reading at around 20�of Hg at a fast 900RPM idle (a mild cam). I tapped into the manifold by disconnecting the brake servo line and was surprised to see the needle fluttering at a high rate between 7�Hg and 15�Hg. Increasing RPMs did increase vacuum but only modestly diminished the needle vibration. Since it�s been a while, I would appreciate any interpretations of vacuum test results before I get into the hassle of further testing.

Thanks
Ray (Healey64)

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Old 08-16-2010, 05:51 PM
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Quote:
Originally Posted by Healey64
Yesterday, on the spur of the moment, I decided to test the engine with a vacuum gauge�something I hadn�t used in a very long time. Since the engine was running quite good, I was not expecting anything but a steady reading at around 20�of Hg at a fast 900RPM idle (a mild cam). I tapped into the manifold by disconnecting the brake servo line and was surprised to see the needle fluttering at a high rate between 7�Hg and 15�Hg. Increasing RPMs did increase vacuum but only modestly diminished the needle vibration. Since it�s been a while, I would appreciate any interpretations of vacuum test results before I get into the hassle of further testing.

Thanks
Ray (Healey64)
Fluttering needle usually is a sign of bad or tight valves.
Was it good in the past?
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Old 08-16-2010, 06:08 PM
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HERE is a vacuum gage reading guide, of sorts.

THIS is another one.
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Old 08-16-2010, 06:12 PM
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Hi Chet,

Wow!!

It did provide a much steadier needle in the past but that was before I re-bushed the rockers and set the valve train. All seemed to be running well so it never occurred to me to recheck the engine, and not with the vacuum gauge. Thanks Chet, now I know what I will be doing next.

All the best,

Ray (Healey64)
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Old 08-16-2010, 06:38 PM
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Thanks Cobalt327

Good charts.

When reviewing the charts and explanations of vacuum gauge responses I have a problem matching my gauge response to those presented. Although my gauge needle does waver rapidly at idle, it reads lower (between 7 and 15 inches) than any condition presented. Also, the swings start to settle down (but nowhere near steady) as RPMs and Vacuum climes.

Thanks again and all the best,

Ray (Healey64)
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Old 08-19-2010, 09:59 AM
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Vacuum Gauge Supprise and Then Some...Help

To recap, when taking a vacuum profile for the selection of a PCV (car did not come with a PCV) as a means of reducing crankcase pressure and rear slinger oil seepage, I was surprised to find a fluttering vacuum reading between 4 and 14 inches Hg at idle (900RPM). Since the engine preformed without an indication of any problems, I was very surprised to see this condition.

Upon suggestion that the condition could be the result of tight valves, and since I had re-bushed and adjusted the rockers 3 months earlier, this seemed to have a high possibility. When extracting the plugs in preparation for the adjustment, I found all plugs but cylinders 2 and 3 to be a perfect color. Since this is a straight 6, 2 and 3 are adjacent cylinders. While Iím waiting for a friend to return my compression gauge, I would appreciate any suggestions.

All the best,

Ray (Healey64)
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