Trace of Oil in Cylinders 3 and 4

[david.g.chapman]

Hi again!
I am in the process of doing my occasional engine re-sealing/valve grinding preventative maintenance job. On taking the head off I see a trace of oil in cylinders 3 and 4. There is a similar trace around the edge of the piston crowns on 3 and 4 as well. As you may be able to see, the spark plugs are free of oil.

Now this could be because I still feed back the crankcase gasses to the engine from the air intake. I am running Stromberg carbs. Is this usual, or is there a case for popping the pistons up for further investigation?

Dave Chapman.

[nmauduit]

a leak down test would have needed to be performed before taking the head off, to give an idea of segment seal...

but on the head side, you can check for play in the valve stem/guides, which can become an oil path when wear gets the clearance out of specs.

[david.g.chapman]

Looking through the exhaust ports, the valve stems are dry. The oil trace in the pics above look to be more around the inlet valve seat, perhaps.
Dave Chapman.

[Quart Meg Miles]

The fact that both 3 and 4 show oil suggests it is the common Stromberg path providing it (from the crankcase). If the two cylinders show a marked difference in the oil, especially if 4 is much oilier, then it may well be valve stems due to the notorious oil pooling at the back of the head.

[david.g.chapman]

Thanks for your responses. I will take the trouble to get the pistons out and measure up the ring gaps and groove clearances. I have had broken rings in the past so that's another reason.

Before I started compressions were just above 160 on all cylinders. Ok for my low compression head but still worth having a look IMHO.

Then it's time to measure up the head, guide clearances etc. and get out my Dad's old grinding paste again!

Dave Chapman.