How Good is your Diagnosis

[RAC68]

In preparation for taking an initial vacuum profile in preparation for the installation of an oil catch can and PCV, I was surprised to find a vibrating needle with low readings (7” to 14”of Hg) at a 900RPM idle. When preparing to adjust the valves, in concert with recommendations, I found cylinders 2 & 3 with black plugs and a nice brown on all others. Following the valve adjustment and after exchanging black plugs their light brown counterparts, I took the car for an hour’s aggressive ride and then reexamined all plugs. Expecting to find cylinders 2 & 3 turned black, I was surprised to that all plugs were a nice brown. However, the vacuum gauge still displayed a low reading with a vibrating needle.

Now phase 2. Early this morning, after an aggressive run (it is common for me to shift between 4K & 5K RPMs), I ran a compression test. The reading were as follows:

Cylinder 1 2 3 4 5 6
Dry 170 162 165 171 171 172
Wet 210 200 210 183 183 183

As you will note, reading are within 10% of a selected Base reading,
BASE % Difference from Base
Dry 171 -0.58% -5.26% -3.51% 0.00% 0.00% 0.58%
Wet 200 5.00% 0.00% 5.00% -8.50% -8.50% -8.50%
However, Cylinders 1,2,3 jump substantially to a high pressure where Cylinders 4,5,6 move moderately higher.

Based upon the above information, what is your diagnosis?

By the way, the engine is running strong and without any obvious problems.

All the best,
Ray (64BJ8P1)

 

[why]

My diagnosis, OCD, forget you own any of these measurement gauges and continue to enjoy a car that is doing exactly what cars, especially Healeys are supposed to do, give you a great thrill driving them. It is running fine and the plugs suggest has nothing wrong.
Jay,
65 3000

 

[Keoke]

------:Keoke

My diagnosis, OCD, forget you own any of these measurement gauges and continue to enjoy a car that is doing exactly what cars, especially Healeys are supposed to do, give you a great thrill driving them. It is running fine and the plugs suggest has nothing wrong.
Jay,
65 3000

 

[Randy Forbes]

OCD, LOL!

I wasn't going to say that, but it is pretty funny.

Two (2) things come to mind for me, the first and most obvious is that the wet readings indicate leakage past the valve seats (the oil has sealed the area around the rings. <span style="text-decoration: underline">Or</span>, the oil from cylinders 1, 2 & 3 has now contaminated your gauge, giving eroneous readings on #'s 4, 5 & 6.

Wasn't a leakdown test prescribed in the last thread you started on this subject? That's where they come onto their own, in discriminating between intake, exhaust valve & ring seal leaking.

However, I do applaud your driving style; I wind out every gear I get the chance to (no matter which car I'm driving). Only time I shift below 3000 RPM, is in stop & go traffic!

 

[RAC68]

Hi All,

Jay, I will only address the issues when the Healey’s performance is no longer a source of enjoyment. This threat is meant to help me stage for that time.

Randy, a leak-down-test will be performed within the next 3 weeks, however, until then I thought it would be interesting to see what the diagnosis would be with the available information. I stand corrected, however, in that I thought high readings obtained from a wet compression test would indicate warn rings as the oil would have no effect on valves or guides. By the way, for all its worth, I did not test the cylinders in order but followed the sequence 1,4,2,5,3,6 to deminish any possibility of cross comtaminated readings.

Thanks for the input.
Ray (64BJ8P1)

 

[Deleted member 8987]

Oil in the cylinders won't have any effect on valves...unless you put enough oil in.
The oil is squirted down through the sparking plug hole, the valves are ABOVE that.

Now, on a flathead, if you're not careful, it can make a difference, but I don't think flathead engines were an option on your vehicle.

What he's saying is the low readings (or slow to pick up) on oiled cylinders tends to indicate valve issues.

I used to do two squirts of oil, roll the engine over a couple of turns to distibute the oily substances properly, then do the wet test.

 

[Roger]

Off the cuff - I make no sense of your wet tests and discard them.
The dry tests coincide with your slight oiling of plugs 2 and 3, so I'd say you have slightly more bore wear on 2 and 3 than the other cylinders.
In any case, you have nothing to worry about, unless you want to, of course!