And just use regular 20W oil?

Won't it read higher anyway if you put oil in there? (reduced displacement)

So if the reading remains the same, the rings are rooted? (oil just gets pushed out beside the piston) And if it reads higher everything is all good?

And how can you avoid damaging your compression tester and how do you clean all the oil out of it after all this?

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I just used what spare engine oil I had around the place. I used a syringe and long tube to remove whatever was left over (in the instance of the cylinder that I over filled).

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We’re talking compression readings, not really compression ratio (hence volume). As many gauges or comp testers will vary in their readings, it is important to take more notice of the difference between the pressures rather than the actual pressure readings themselves.

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If the rings have cracks or sealing problem the oil will temporarily seal those minute gaps and stop air from passing by, what you will see is a rise in your compression readings meaning that the oil has sealed off the blow-by leaks and therefore raised the compression reading and confirming that you do in fact have an issue with the piston rings in that they do not seal properly.

The difference between the readings will determine exactly how severe the problem is, generally if there is more than a 15% improvement of the original reading you should begin to consider rectifying the issue. Any more than 15% and you should almost certainly rectify the issue. (You might want to confirm that 15% figure, that's only from memory).

In the instance you have the piston slapping about in the bores and the rings completely disintegrated, yes the reading will not change and you can confirm that your rings are rooted. The gap is simply too large for the oil to breach and seal (viscosity).

The other way a compression reading can be affected is via the valves or head gasket. When you turn your engine over manually, that hissing you hear (sometimes) is air escaping the compression stroke via the valves and ports. You can either replace the head with one that you know has properly sealing/seated valves and then conduct your compression test. Or remove the head, do a leak-down test on the head, confirm the valves are sealing/seated properly and then re-install it and conduct a compression test.

If the head gasket has been breached between two pistons (more commonly between the front and rear pairs of cylinders as they are located closer to one another) you will find the compression ratio is low on the two cylinders that are side by side each other. I’m not sure how you would confirm this issue without actually removing the head entirely and doing a visual inspection. Perhaps it is providing just enough info to confirm your suspicions and decide on whether you replace the head gasket or not.

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Well it depends how yours is built and how much oil you have put it in there. If it gets oil in the tube then remove it and clean it. You’re combustion chambers are 29cc or 31cc (stock), you also have some dish in the pistons (8,9,10cc?) so unless you put something like 50cc’s of oil in their you shouldn’t have to worry about the oil going where it shouldn’t. I don’t know exactly how much you should put in because I do not know the dish etc perhaps when they say ‘squirt’ some in there, do just that. Squirt it in there with a syringe or oil can so the oil hits the side of the bore and leaks down to seal the piston rings as opposed to you pouring some in there and having to fill the piston dish before any oil actually overflows to saturate the rings.

Give it a go, if you don’t get it right, start the engine, burn off the excess oil and try again.

Have you tried to Google how to use a compression tester? Otherwise the local library always has a good collection of mechanics books. There are also some online workshops that can be useful.

GL with it all.

A good engine will have 0 difference between wet and dry tests. On the dry test, cylinders should be within 10% of each other or it's time to repair. Gasket or valve damage is indicated by compression way down, e.g. 50 psi and doesn't improve on the wet test.

After you put a squirt of oil in each cylinder, spin the engine a couple of seconds. This will remove excess oil and spread it evenly on the rings. Then use the compression tester. There won't be enough to damage anything.

This is called a wet compression test and is standard procedure. The oil only affects the rings, so is compression improves indicates the rings are worn.

The compression tester/kit I got cost $90 so is fairly good quality. Not sure if the hose is removable though.

I pulled all the plugs out when I tested it, so if I got a nil reading on 2 cylinders or heard hissing out the plug hole next door, I'd know the head gasket was rooted.

Thanks again fellas