2/27 update w/ NEW PICTURES. Scroll down to post #9 or click here



This piston came out of a D16y8 with 75,000 miles that was burning a quart of oil every 500-1000 miles, depending on how it was driven. Oil consumption was greater the harder it was driven.

Compression was 190 across all 4 cylinders, so I knew compression rings were good and the cylinder walls weren't badly scored or out of round. It was just too much oil to be getting past the valve seals. All other mechanical and vacuum systems were known to be good.

I removed the #2 piston this morning. Compression rings were free, but the oil rings and separator would not spin on the land and were really "gunked up" with carbonized oil. Skirt shows wear, but not excessive and there is no scoring. Measures 74.870mm across the skirt.



Piston sides show a lot of carbon build up.



So much oil residue on the top of the piston, there was valve-to-carbon deposit contact. You can see the imprint of the valve in one of the large deposits stuck in the relief. The flakes coming off the top of the piston are 1/2 mil thick, easy.



It had been suggested by a machinist that the motor may have been badly overheated and the oil rings had failed. They do seem to be an issue, but I don't see a tell tale sign that they are the culprit, unless them being "stuck" in the ring land is an indicator. Does anyone know?

I'm also wondering if these piston can be re-used with a new set of rings and a hone. Thoughts?

 

get some new rings, gap them, clean the pistons really good so there is nothing that will cause the rings to bind up, rehone the block, throw it together, and most importantly....


change your oil more often. are you sure the PCV system is working correctly?

i think the problem originated from contaminants in the oil building up in the land for the oil rings.

 

looks like lack of oil changes or poor quality oil used causing the oil rings to stick.

 

Previous owners inflicted the damage and they did disclose the oil consumption before sale. I got it a price where it wasn't an issue for me and didn't really expect to stick with the D series, long term, anyway.

There were plenty of indications that the car wasn't being serviced and/or cared for properly. I could definitely believe there were long intervals between oil changes. The PCV valve was functional, but I haven't opened up the vapor separator yet.

I understand what you're saying about the oil ring just being bound up in the land due to the junk that's collected there. Sounds like a reasonable explanation. I'm going to clean up the piston and see how those lands look. Thanks for your input!

 

That doesnt look too good at all!! haha

 

if you clean those ring lands up and install new rings you will be good to go....

 

This is a classic case of "A compression test will tell you nothing about your oil control rings or your oil consumption problem". Why do people keep spreading this myth?! Oil control rings do not seal compression and compression rings do not seal oil. Your stuck oil control rings are exactly why you are consuming oil, your compression rings don't have anything to do with it. Assuming you pistons are salvageable and your cylinders are straight and round you should be able to install new rings, clean up the walls with a bottle brush hone and reassemble it and your oil consumption problem should be solved. Of course, this is assuming there is nothing wrong with your stem-to-guide clearance or your valve stem seals.

 

Seems to be a VERY common issue with higher mileage d series motors.

 

Finally finished getting the motor apart and I'm looking for more input on whether or not some of these parts can be salvaged or are worth salvaging.

#1 and #4 pistons did show a bit of scuffing on one side of each skirt. You can't feel it when you run your finger over it, but it looks like this:



A couple of the connecting rod bearing halves are worn through to the copper layer:




Here's where it starts to get ugly.

Valve faces are encrusted with carbonized oil deposits.



You can see how they're layered.



A big chip of crust came off the face of this exhaust valve at some point.



I CANNOT chip the deposits off with my fingers. Will they come off if they're hot tanked, or are these junk?

Ports also thick with residue. Exhaust:



Intake:



Even the intake runners are caked...



Through the TB...



Seems as if the PCV system was non-functional for a long time. The PCV valve does work though, and the vapor separator box is much cleaner than the intake runners and ports.

__

I've found a complete rebuild kit at a good price. It includes everything, including pistons, but not valves. The potential need to have to buy valves is probably the budget breaker on this project. Thoughts?

 

I believe all of your parts are "salvageable" but you have to ask yourself how much you are willing to invest in your Y8. New rings, bearings and gaskets a long with a bit of work from the machine shop and you will will be good for another 75k

 

I think you can salvage most of the parts, they are just dirty. A good machine shop can clean all those properly. The valves should be salvageable unless there is something wrong with them that you can't see in the pictures. They need to be inspected after cleaning.

Based on the fact that the oil consumption was occurring on all cylinders I suspect the oil was not change enough, the pcv system was not working, or a poor quality oil was used.

 

wire brush and drill

 

some varsol and scotch brite pad would work to clean the pistons and the valves.