My apologies for the longer than expected delay to part 2. Had been really busy with work recently, and still am, but I'll try to update this blog regularly.
In our last post, we stopped after we removed the plugs. The next thing we want to do is to apply some anti-seize on the threaded end of our compression tester hose.
The two rows are for recording two runs of this test, one for a dry test, one for a wet test. First we'll do the dry test, and we'll talk about the wet test later.
Flick the Run button to "OFF" and then hit the starter. This turns the engine over, but the coils won't fire.
EDITED TO ADD: I made a mistake in my initial test. I forgot one very important step, and that is the open the throttle all the way. It will make a huge difference to the PSI readings, so make sure you fully open the throttle before cranking the engine over.
I generally hold the starter for 5-8 cranks, but no more than 8 cranks. There's a lot of current passing through the cable to the starter when you do this, so you don't want to hold it too long as the heat will fry the cables. After each cycle, wait awhile to let the cables cool down, before you repeat.
When you press the starter button, you'll hear the engine cranking over. Maybe something like this, "eeee........eeee.....eeee....eeee..."
You can tell I'm not to good at sounds, but you get the idea. I listen for 8 of those "eeee" sounds, while watching the needle on the gauge reading. Sometimes, you need to repeat this two or three cycles for the needle to hit its maximum reading. Now do you see why we need that battery charger?
Once the needle doesn't go up anymore, write down the reading in the table I told you about earlier. This goes under the "Dry run" row. The reading for cylinder #1 is 105 PSI.
After you're done, use the air-release valve on the hose to release the compressed air in the system before unplugging the hose.
The purpose of doing this is so that the oil will help seal the piston rings against the cylinder walls. What we're trying to do is to find out where our loss of compression is coming from, either we're losing compression through gases escaping through the piston rings, or gases escaping through the valves because they're not sealing properly.
By squirting the oil into the cylinder, we're trying to eliminate one variable in the equation: gas escaping through the rings. If the readings increase significantly after we add oil, we know the piston rings are not sealing properly. If the readings stay about the same, most probably we're losing compression through the valves.
There are exceptions to this however, and it's important to realize this is not fool-proof. One example is if the gaps in the rings align and allow the gasses to pass through. I've seen this happen in a car engine once, so it's possible.
A more accurate way to troubleshoot where the leak is coming from is to do a leakdown test, but you'll need an air compressor for that.
Back to our wet test. If you have an oil can, squirt 2-3 squirts of oil into the cylinder. Otherwise do what I did. Just use a straw to draw up some engine oil from a bottle...
After this, just repeat this for all the cylinders. I'm only going to show the pictures and readings for the dry test.
Next up is cylinder #3:
Finally, cylinder #4.
The readings of the wet test didn't really increase compression by much, except in cylinder #2, which went up about 10 PSI, which isn't really that significant I think. However, they're all below the minimum specification. The allowable range is 142 - 199 PSI, so if these readings are accurate, that means this engine needs a rebuild
Frankly, I'd want to run this test on a bike with a known good engine and see what kind of readings it gives me, just to confirm that the gauge is reading correctly.
Well, that completes our compression test. All that's left to do now is to put all the plugs back and button up everything else.
The use of a torque wrench is highly recommended for this, because the cylinder head is a critical component and it's aluminum, so you don't want to overtighten anything in there.
Mine's a Craftsman. This model is the microtork, and it has worked fine for me so far (about 10 years of occassional use), and has a very nice action. However, avoid their "digitork" range, that one crapped out on me in weeks. It's a complete waste of money.
I torque down each of the plugs to their specified torque setting, and then I'm done.
So give it a try, and see how your engine's doing. Happy wrenching!