Here's the Eng Compress. results from earlier video

[bimerguycw]

I thought I would start a continuation thread from my previous to update those so helpful in the past thread please read and comment for help needed.

After getting time to perform the compression and vacuum testing here's the results and I appreciate your addition advice on locating actual problem for repairs:

Vacuum:

At idle 650 rpm = 8.5 inHG steady
At 1000 rpm = 10 inHG and steady
I held the RPM's at several levels and the vacuum increased with rpm's and held steady in each case with no fluctuations at each rpm.

Compression:
1 cyl failed...
Tested each cyl 2 times to verify repeatability and values after 4-5 strokes.

7 cylinders = 175-180 psi
1 cylinder = 88 psi (Cylinders on pass side at front of head where noise the loudest.

Any and all advice appreciated now that we have some real numbers to work with, right?

Can we determine if this 1 year old bottom rebuild is okay and it's in the top-end only or what?

Thanks.

[bimerguycw]

the compression number look like the other 7 cylinders. I understand this means the cylinder is the leak...either piston ring or cyl wall...crap!

I wonder what caused this 1 cyl to go bad if the btm-end was rebuilt about 1 year ago?

Any ideas out there and how much repair I'm looking at? Can I have the head pulled and ring replaced on this 1 cyl from the top if thats all that was failing or should I suspect more problems and do more repairs to avoid another similar problem?

[aston_jag_tech]

Wow! a piston ring fail, ver would have guessed that was the problem....

Good for you in tracking it down...

As you mentioned, go an investigate why it failed and then expand on what else could fail and could cause the fail...

[BillionPa]

slick 50 oil treatment would have caused a ring failure.

[bimerguycw]

20-50W oil at startup according to the Prev Owner that rebuilt it. Then I waited until 1500 miles or so and put 0-40 Mobil syn in it.

Is it possible the prev owner's rebuild could have been faulty and that is just now showing up?

What about the sound on my video, does that add up with this type of failure?

[bill g]

I had this happen on a Jag XJ6 engine years ago - recent rebuild including re-sleeved cylinders - piston slap due to excessive wear in 1 cylinder after only a few thousand miles.
Compression leakage can be caused by excessive wear (abrasive particles in the cylinder), scored bore, rings installed incorrectly, for example upside down or with incorrect end gaps or end gaps next to each other instead of staggered.

Bill G

[BillionPa]

i would suspect a problem with the rebuild rather than wear due to operating conditions.

[bimerguycw]

I think I've read that a piston/ring can be repaired without an entire engine removal and dis-assembly. Is this possible since I appear to have only 1 cyl with compression issues.

[bimerguycw]

So what did you do to repair and did your car have a similar sound and symptom with this problem?

[bimerguycw]

When I first got the car I did a compression test 1st thing and all 8 where in spec with readings of 180 psi +/-5 psi.

But over the year I've had it I have noticed the plugs burning with what appears to be oil. The 2 rears with the most and the other 6 with slight brown/black coloration. I expect the 2 rear were the known valve cover seepage due to the fact that the plug chamber had small puddles above the plug holes each time but suprised about this since it was rebuilt and had new valve cover gaskets. I will take picture of the plugs for comments.

With the year long plug burning with this brownish/blackish coloration I switched to NGK and same issue, so I wondered what was causing the oil into the chamber and thought the PCV plate as it was not replaced with the btm-end rebuild.