Low Leak down on two cylinders

[liskinemail@gmail.com]

I have owned my car since 1997.  It currently has 62,000 completely documented miles.  I drive about 500 miles per year.  I just did an annual service with compression and leak down numbers of  Cyl# 1 130/6%, cyl #2  140/38%, cyl#  3 135/10% cyl#54 120/70% cyl#5 130/18% and cyl #6 135/12%.  We have tried a valve adjustment and there is no improvement.  The mechanic says the car runs really well but is probably down about 30 horsepower.  Options include doing nothing to a complete engine rebuild.  I am hesitant to rebuild the entire engine as I did not know there was a problem until I was told about it and the car is so perfect otherwise.  It is about a 95 point car with all matching numbers and no damage ever as verified by a bare metal respray.  Any recommendations appreciated.

[liskinemail@gmail.com]

Correction by author.   I meant a high leak down on two cylinders. 

[Benz Dr.]

Normally, these engines produce about 165 - 175 PSI when fresh. 130 PSI would be considered well within rebuild time but it can still run well for a while yet. The cylinders that show low compression and minimal leak down are simply worn out. The cylinders that are showing high leak down probably have leaking valves or possible broken rings.
 
At some point, the ring grooves wear to the point that the ring can no longer be properly supported and it will tend to break off about 20mm from the gap. This will produce high wear on the piston and cylinder wall in a very localized area. If it were my car, I would pull the head and do a rebuild. You can also inspect the cylinder walls for wear and scoring. I would also have the rad checked, IP calibrated, and have a new water pump installed if in doubt.

Rebuilding your engine will not devalue an original car. 

[liskinemail@gmail.com]

Thank you for your response.  I am less concerned with the value of my car than having the work done and having a problem afterwards because of poor work.  Several poster here cite post rebuild issues.  At least now I have a problem that can be diagnosed and has not caused major damage to the block.  Why would an engine with only 62,000 mile have "wear" issues.  The car was driven lightly throughout its entire life after the first 20,000 miles that were put on in the first three years of ownership.  Do you know of a great shop in the Santa Barbara area?  Also, would you rebuild the entire engine or just the top end if everything else looks "ok".

Have a nice evening.

[tel76]

If it was my car I would use it for several hundred miles (regularly) and then do the test again.

[Shvegel]

I am with Eric on driving it and testing again.  I have never seen anyone do compression and leakdown at the same time but I am stymied as to why the compression numbers are consistent and the leakdown are so disparate. I would tend to rule out valve issues based on the data but am concerned that all the sitting is effecting how the rings are sealing.  I am not a huge fan of chemical fixes but in your case you might also want to look into some sort of snake oil that claims to unstick stuck rings. 

[stickandrudderman]

Compression and leak down at the same time is common in aero engine testing, less common in cars.
I have seen engines that will happily pass a compression test and a leak down test but still give poor manifold vacuum. This is due to wear in the cylinders at the lower part of the bore; the piston is usually set at the top of the bore for leak-down tests and so this fault will not be apparent.
For this engine I would worry about the poor test results and want to know more.
If it were a customer's car I would NOT recommend that they drive it for fear of causing further damage. If it were my car I would probably chance a single "Italian tune-up" and then re-test.
If it then failed the second test I would do a complete strip-down; ovality in the bores being what I would expect to find.
This problem is fairly common in old but low mileage engines as the likelihood is that most of the journies are short and gentle which will mean that the oil never reaches correct operating temperature which in turn will mean high engine wear.

[tel76]

I would be very interested how these tests were carried out and what equipment was used?
How was the piston held in position when the leak down test was carried out (I assume it was held in position as one would do on a light aircraft engine)?
Just to digress a little, several years ago both Lycoming and Continental issued SBs (special bulletins)stating that engines should not be stripped down on the first set of mediocre results and should be flown a few more hours and then re-checked.
I cannot understand anyone advocating revving the goolies of an engine in the so called Italian Tune Up, regardless of who owns it. All you have to do is look at the previous posts regarding the engine failure to see what can happen.
My advice still stands, take the car for an extended run, make it work and then re-check the compression ratios, forget the leak down check it is not an air cooled aircraft engine.

[stickandrudderman]

A perfect example of why advice received on the internet should always be verified from other independent sources.