P/C wear: causes and relate symptoms ?

[COL 911]

I'm currently 'under the knife', the car is at the local shop with top end disassembled. 1987 Carerra, stock, 118K miles or so. Existing service records show no major services performed by previous owners. 20-50 dino oil only. Oil consumption was 1 qt every 600-800 miles, some blue/white smoke on start up and no unusual leaks until recently when # six began to show seepage at cylinder head/case junction. Power seemed ok, with exception of miss on #6, where inspection of spark plug showed alot of sooty deposit. No track, no missed shifts, although it did 'sound' louder toward the end - hard to quantify.

I'll try to get pix of components posted soon showing wear patterns . All studs OK-none broken. Heads not disassembled yet, intakes look really clean, exhaust is black and built up with soot. Trusted technician suspects valve guide wear is going to be present, as per original diagnosis.

Upon disassembly and measurement, what surprised us is the amount of wear evident on the cylinders (Mahle Nik) at this mileage. All 6 reported outside reuse tolerances, no signs of scuffing (or cross hatching, for that matter) beyond spec. Only very light scuffing on the piston skirts, rings all seem OK. Rocker arm shafts showed unusual wear pattern and rocker arm wrist pins may be out of round - meaning we need to open the bottom end, as well.

Theories are that at some time it ran hot or low on oil , but confident that didn't happen since I've owned her. Wouldn't P/C wear severe enough to exceed tolerance specs have produced secondary symptoms, like excessive smoke, etc. earlier? Aside from the financial pain, I really just want to understand more - P/C wear doesn't seem to be a common issue with engine symptoms like I experienced with the mis-fire occurring rather suddenly. Thanks in advance, and will post pix and measurements ASAP.
Wayne

[kodioneill]

Were the cylinders out of round?

[Flieger]

How much zinc and phosphorous was in your oil?

[docrodg]

I would wonder if the piston squirters and/or other passages were clogged causing a reduction in oil at the cylinders and rods.

I think you mean the piston pins and small end rod bushings have unusual wear and need to pull the bottom end apart. Not the rockers.

What were the measurements for cylinders and pistons? which spec compared to - production or wear?

It is possible that the wear is related to at least a minor degree to the oil consumption. And worn valve guides could result in a plug that is fouled enough to not fire consistently. The blue tinted smoke means oil burn occurred in the cylinder at startup.

Clarify please the "seepage" on #6 - was this cylinder/head interface and oil? If there was a leak at that point and it was from the cylinder head leaking then you would possibly have lost compression on that cylinder, thus the miss.

[COL 911]

Sorry for the delay: pix attached. No oil sample sent-filter is still on the car and probably will be cut open to inspect, but no metal filing/shaving of any kind evident so far in tear down.

Pistons: no unusual wear evident eye on piston/skirts

Cylinder: Cylinder bore as measured: .007" -.0045", spec is
.0009" - .002" ( I have to double check Bentley), no cross-hatching evident, smooth surface with exception that you can feel where an 'edge' is worn with your fingernail, around the top edge to about 3/8" down, at the farthest limit of the piston stroke

Rocker arms and rocker arm shafts: uneven wear pattern on both shafts and bushings

Connecting rod end bushings, uneven wear

What could cause 'severe' P/C wear while the other components show 'normal' wear for 118K miles?

[Ray_G]

By looking at your cylinders I would say that they are Alusils, not Nikasils. As to why they wore like that I don't know. But with Alusils the cross hatching does not stand out like it does on Nikasils.

[COL 911]

Ray, I'm pretty sure 1987 OEM was Mahle nikasil cylinders, and there's no evidence of PO having any P/C rework in service records.

Two more photos of cylinder, one from top showing carbon ring and 'lip edge' worn just below, another from bottom showing wear pattern in bore more clearly.

Any thoughts on the causes for extent and wear patterns on the rocker arm shafts or non-concentric wear of connecting rod lower busings?

[docrodg]

It is not uncommon for con rod bushings to wear unevenly as the forces on them are greatest at the outer and inner ends. Rocker arm shafts also can wear unevenly as the forces on them are on the side towards the engine (the "outside" of the bushing is pushed away from the shaft by the springs and cam lobes). Consider that these components do not rotate fully and have forces placed on them in specific directions by either the piston firing and pushing in or the springs and lobes pushing out from the engine center.

From looking at the photos I would venture that this engine was run low on oil. The wear would not necessarily cause symptoms earlier if it is not severe at key components. The rings could retain a good seal keeping compression up (really burnished in), and valve seals keeping oil out of the chambers.

The cylinders are probably the key here. With that wear the engine likely had a period of low oil to the pistons (and thus con rod bushings). This is either low oil pressure or low oil flow (clogged oil system) or both. While a low oil level could be the culprit for this there is also the possibility that the pressure was a factor as well. Idling of the engine, especially when cold, for any length of time is bad as the pressure is very low. If this was always "warmed up" in the driveway by the PO then it would accelerate wear if it already had low idle pressure and flow.

The miss was probably not directly related to this wear, but to the loosening of the head and thus improper burn and charge leakage.

[Tom F2]

I think that those are alusils. The few 87 US market cars I've seen apart all had alusils. Wouldn't be surprised not to see cross hatching. What are the measurements? You might get some more info if you posted your photos on the engine rebuild board.

[Ray_G]

this is what nikasil cylinders look like, they look like, well chrome. I think if you look at your pictures and compare you will see a difference in the appearance. And Mahle did make both types of cylinders.



OH that picture was shamelessly lifted from a pelican post from years gone by.