Vacuum Surprise and Then Some

[RAC68]

When taking a vacuum profile for the selection of a PCV, as a means of reducing crankcase pressure and rear slinger oil seepage, I was surprised to find a rapid flutter vacuum reading between 7 and 15 inches Hg at idle (900RPM). When increasing RPMs, the flutter diminished slightly, however, did not approach a steady reading. Since the engine preformed well and without any indication of any problems, I was very surprised to see this condition.

A friend suggested 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. While I’m waiting for a friend to return my compression gauge, I would appreciate any suggestions.

All the best,
Ray 64BJ8P1

 

[RAC68]

Forgot to add, plugs for cylinder 2 and 3 were black.

All the best,

Ray 64BJ8P1

 

[Johnny]

Hi Ray, sounds like cylinders 2 and 3 are getting oil in them either from the valve guides or cylinders and fouling the plugs. Doing a valve adjustment won't help this scenario. A compression check might reveal the culprit.

Good luck

 

[RAC68]

Thanks Johnny,

It seems odd that only these 2 cylinders have worn valve guides or rings but it fits. I was thinking blown head gasket, but if that were the case, why the black plugs? The kicker is that I have not experienced a miss fire or any difficulties pulling to past 5K RPMs. In fact, the engine seemed to be running very well. I should have followed my father’s saying “if the car runs good, don’t lift the hood”.

Thanks again and all the best,
Ray

 

[Johnny]

You will when the plugs foul completely.

 

[RAC68]

Hi Johnny,

You are probably right.

Yesterday, after re-adjusting the valves, I installed the plugs with the black exchanged with light brown ones. After a nice aggressive drive of about 2 hours, I extracted the plugs from the problem adjacent cylinders and found they had not turned black but maintained a nice light brown. Another vacuum reading showed the same vibrating needle between 7 and 14 Inches of Hg.

A friend will be helping me do a leak-down-test to determine the problem a few weeks from now. I will post the results.

All the best,
Ray

 

[RAC68]

 

[why]

your father was right, "a difference that makes no difference is no difference." I assume the point of the car is to take it for drives and if it does that just fine.......

 

[RAC68]

The picture above was only a test of placing an image in a post.

Ray

 

[Randy Forbes]

The picture above was only a test of placing an image in a post.

Ray

Please post larger pictures (640 x 480 pixels is an ideal web size), other wise, good job!

This is 640 x 480: