Camshaft bearing failure 4.2

[nefematic]

What could have caused the bearings to look like this?








I have aquired this xj6 engine „with minor valve issue“, this is what we found after taking the head of yesterday (2hrs!).

I‘m fixing this one as a interim engine for my E-type 1970 OTS. The original engine needs RR.

Thank you for your opinions. What I noticed on disassembly was silicone used on the cam covers had lost some parts of itself to the cam valleys. Might that be the cause and would that render the engine toast? Underneath the #2 bottom cam bearing the hole is clogged. I‘ll try to pull that up and find out what is is. The cam itself seem to my novice eye to be OK. The reason we pulled the head (thanks davidsxj6!) was #5 exhaust valve seems to bee stuck and or bent.

[politeperson]

These bearings almost never fail as they should run in a bath of engine oil.

In the case of lack of oil, everything else will have failed first (or should have).

The head may have been starved of oil if the feed was blocked. This is pretty unlikely and I have only seen it once after DIY tampering.

If the head is warped due to overheating, the cam could cause uneven pressure on the end cam bearing, leading to rapidly accelerated wear and overheating as shown.

Check both sides of the the head for straightness.

Some warped heads have had the mating surface milled flat, but the cam bearings may still be out of alignment.

[Durango2k]

I would think it possibly stood still for a LONG time on old oil. This contains acids, which then eat holes in the soft metal.

Carsten

[Moeregaard]

I'm inclined to go with Carsten's theory, as this appears more corrosion-related than a case of accelerated wear due to lack of oil. From the photos, it appears to be from an engine that was laid up after many miles.

As James mentions, premature bearing wear can often be attributed to the cam bearings being out of alignment, usually due to having the head skimmed and without checking the align bore prior to reinstallation, but I'm not seeing this here.

[Durango2k]

There are no marks in line - shape like ————-.

What we see is dots, singular, roundish.

This means it was a local damage, nothing to do with rotation. This leaves.... acid.

Carsten

[nefematic]

Thank you for the replies. The crater does look more like corrosion. I‘ll have alignment checked and order new bearings. Also check oil feed lines. I‘ve taken out the inlet camshaft, no funny marks on that side. Once the bottom is open the main bearings will have to checked as well.

Martin