All Small Six Compression testing

[Invectivus]

So I have three engines I want to turn over to test the compression. I think the philosophy is turn it over and document the output. If pressure is low in some cylinders, squirt some oil in them and retry. If it improves-bad rings, if not-sticky/obstructed/burned valves.

first, these things have been sitting for years, I’m leery of not lubricating the cylinders before turning it over. But I don’t want to get false readings on the rings. Maybe oil, rotate the engines, then let them sit a week or three?
second, how much oil is a squirt? I know it’s silly, like a pinch of salt, but like a tablespoon?

 

[sixtseventwo4d]

A preferred oil to use when a used engine has been sitting for a length of time is of a light viscosity, such as any transmission fluid or Marvel Mystery oil. Some guys like using an oil-diesel mix. The point is you want it to easily migrate around the rings and respective lands. Allow the oil to do this for a few days. Have all the plugs removed and turn it by hand (ratchet or bar) before using the starter for your compression test. Stop if you incur any binding and try to reverse-rotate only an inch or so; you don't want to cause the oil pump to lose its prime. 2- tablespoons of oil per cylinder is sufficient to start with.

 

[pmuller9]

Often the compression is raised because the oil is sitting in the piston dish and decreasing the dish volume which raises the compression.
Be careful to keep the oil around the outside of the piston and not on the dish

 

[Invectivus]

Cool, thanks.

 

[powerband]

after build's been sitting for winter months, before firing I often insert 2tbls (1oz) (Marvel red) in cyl's which creates blue oil cloud until it cleans out.

a few too many projects...