Is it safe?

Fellas,

Is it safe to do a compression check on an engine with the lower unit off? I cant see there being any issues but its better to ask now than to regret it later!

Re: Is it safe?

I see zero problem...

Re: Is it safe?

It's fine,remove all plugs

Re: Is it safe?

Now just to verify I know how to do this right... Here is what my plans are, yall tell me if its correct

I have removed all the plugs and even the wires... I just put the compression tool into the top spark plug hole and crank it a few times and check the reading... hopefully in the 100's.

I then put it in the second hole and crank it a few times... check the reading... hopefully it is close to the last one.

I then put it in the bottom hole and try and crank it.... check the reading and if they are all within 10% of each other and over 100... it should be fine correct?

It is a 1986 70hp Evinrude.

Re: Is it safe?

That sounds right, Neal.

Do at least 5 revs on each cylinder, and the same number on each.

Many recommend that the throttle be full open while doing this.

Re: Is it safe?

Crank it however many turns it takes to get the maximum reading. Some gages come up faster than others. Contrary to popular belief, it is not necessary to block the throttle open on a two stroke like you do on a four stroke. That's because the ports are wide open at the bottom of each stroke.

Re: Is it safe?

Okay, did the compression check today. I didnt write the exact numbers down but here is what I remember...

The first(top) was 118'ish
The 2nd(middle) was 110'ish
The 3rd(lower) was around 100'ish

I was kinda suprised at how spread out they were. Does it look like I may be in for some suprises or is everything looking okay? I didn't check it multiple times, only once then moved onto the next cylinder so it may be off a little.

Re: Is it safe?

Spray some fogging oil through the plug holes and test it again, starting from the bottom. Tell us what you find.

Re: Is it safe?

Ezeke, it will be a while I actually started dis-assembling things within the boat. I have a mess of wires everywhere. Someone really did a number on the wiring job. Once I get all that straightened up I will give it a go

Out of curiosity, what is fogging oil? I have sea-foam and 2stroke oil at home.

Re: Is it safe?

Fogging oil is a spray lubricant that you use to winterize the engine with. It sticks to the innerds of the engine when sprayed into the intake when running and keeps it from rusting and protects it from moisture during lay-up...

Re: Is it safe?

Your the man Rick! Thanks bud!

Re: Is it safe?

When the engine has indications of rusted cylinders as yours does, it usually is at least suspect of poor maintenance.

Any time an engine sits for very long without a source of oil, condensation alone can put enough water in the cylinders to start oxidation.

If the cylinders rust, you get poor compression.

If the rings rust, you get poor compression.

If condensation or other water source is a factor, gravity usually carries it downward.

Running compression tests without oil does not help; rather, it makes it worse.

Fogging oil is cheap, universally available, and designed to help prevent rust in the moving parts of the engine.

Since it is sold in aerosol form, it is easy to use and will provide enough lubrication for a compression test. It will also help to prevent further damage.