Oil System

[Tim]

I am currently rebuilding an A4 purchased from ebay. I see from disassembling the engine and from reading the manual how the oil flows around the main bearings, rod bearings, cam bearings, reversing gear and valves. How does the oil get to the piston rings and wrist pin bushings?

[67c&ccorv]

I am currently rebuilding an A4 purchased from ebay. I see from disassembling the engine and from reading the manual how the oil flows around the main bearings, rod bearings, cam bearings, reversing gear and valves. How does the oil get to the piston rings and wrist pin bushings?

Early model A4's used a "valve chamber oiler" (which can be seen as the small diameter pipe on the carburator side of the engine);

...late model engines relied upon "oil vapor and spray emanating up from the crankcase through four 3/4" holes in the base of the valve chamber which connect directly to the crankcase".

[Tim]

Ok, so how does the oil in my late model A4 get from the valve chamber to the rings and wrist pins?

[67c&ccorv]

Ok, so how does the oil in my late model A4 get from the valve chamber to the rings and wrist pins?

By the action of the rods as they reciprocate through the oil bath at the bottom of the crank.

Oil and oil vapour is getting thrown around the bottom of the cylinder liners and bathes the reciprocating parts.

The bottom piston ring is an "oil control" ring which scrapes oil off of the cylinder walls leaving just enough to coat the walls for the next ring...the top two rings seal the combustion chamber gasses within the cylinder head.

The rest is magic.

[ILikeRust]

Some small horizontal-shaft air-cooled engines (typical Briggs & Stratton engines) have an oil flinger - a little metal extension attached to the bottom cap of the connecting rod - that dips down into the oil with each revolution to fling the oil all over the inside of the crankcase to make sure the oil gets up into the piston.

[Tim]

So oil is sprayed and splashed into the bottom of the cylinders and then the oil ring distributes the oil around the cylinder, piston and wrist pin. Is there any trick to installing the oil ring to make sure the oil is properly distributed?

[ILikeRust]

The installation instructions should come with the rings themselves. On the set that I bought, the instructions were printed on the paper that the rings were wrapped in.

As I recall, the bottom ring (the oil scraper) has a springy spacer behind it, and a couple of the rings have a "top" side and a "bottom" side, so you have to make sure you put them on the piston right-side-up. The other thing is to offset the gaps in each ring so they're not lined up.