• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Vacuum Surprise and Then Some

Share this page

RAC68

RAC68

Darth Vader
Offline
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
 
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
 
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
 
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
 
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 said:
The picture above was only a test of placing an image in a post.

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

This is 640 x 480:

IMG_0763.sized.jpg
 
Back
Top