Hello, John Talley here with boats.net. Today I'm going to walk you through the process to
do a compression test on our Yamaha T60 engine. Now it's really simple to do. All we're going
to need is a compression tester, and that's really about it. But this is such a pivotal
way to check out the health of an engine, so if you're ready let's dive into it.
Okay guys, the one I've chosen is the compression tester made by Motion Pro,
but no matter which brand you go with you're going to use them in the same way. All right
guys, step number one-- if you can-- is going to start up your motor and let it warm up a bit.
What we're looking for from Yamaha is a minimum compression of 122 pounds. Now ours is going to
be cold, so it may be a little bit less than that 122. I'm hoping not, but what we're
really looking for is consistency across the board. You do not want to see more than a five
to ten percent deviation going from cylinder to cylinder. Now step number one we want to open up
the throttle bodies at least partially. That way it doesn't have to fight to pull air past the plates.
Now step number one, let's get the throttle plates held open at least
partially. That right there should do it. Next we want to remove all four of our spark plugs.
Now I'm working on a carbureted model here, so I'm not having to worry about fuel. But your, if yours
is fuel injected, you need to disable the fuel pump to where it doesn't drown the cylinders.
So that might mean you need to pull a fuse, or disconnecting a relay depending on your model.
The Motion Pro has three different hose attachments, and that's going to hit the majority
of the different spark plug sizes that you're going to run into. We've got our throttle plates
at least partially held open. We'll start up top with number one. So the way I do this is I turn it
over several times until the needle stabilizes at whatever maximum pressure it's going to come up to.
So we are at 210.
220.
Drop down to number two.
All right let's see what number two can
do.
All right, right at 210.
Number three.
215.
Now last but not least, number four. This one's a little bit tricky to get to. There she goes.
And away we go.
An aggressive one there 10, 20, 30. All right,
are they within the 10 percent? Yes, barely.
But considering we're doing this on a cold engine, I think she's fine.
All right guys, that's going to wrap this one up. I think she's ready to head on to the next boat.
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