Compression Test - Doing it the Wrong Way

CBGale2 · Apr 22, 2010

Alright dont beat me up about this.

Ive got a 62' 40hp that I have pulled off my boat, my boat is flipped upside down in the paint process right now. I bought a compression tester to check the motor before I get too involved in it. The situation is this. I have the motor pulled off the boat and it is hanging on my work bench. Issue I have is I cant really get at the front of this thing to pull on it and the electric starting option is not operational at this time. Messing around I hooked up the tester and did my best to operate the pull start from the back end of the motor. Got it to turn about one full cycle and it was just enough that the top and bottom would hit 30-32 psi, held at 30 for a couple seconds and then went down. Can I tell anything by this? And yes...... I know, I know not the proper way. Just wondering.

You can see my perdicament in the background

. Maybe I could cut a hole in the back of the garage wall. LOL

restornator · Apr 22, 2010

Re: Compression Test - Doing it the Wrong Way

make a motor stand with wheels that you can effortlessly manuever around in that garage. 5-6 quick pull starts will usually max out the compression.

How did you flip that boat?

ab1 · Apr 22, 2010

Re: Compression Test - Doing it the Wrong Way

You didn't get a max pressure reading with only one cycle.

You didn't get a good test at all and the results prob don't mean much but,...if you did the same procedure on each cylinder and got the same reading, then maybe you can feel ok for a while. Why not just re-mount the thing where you can get access and start working on it? You already have the boat flipped upside down and everything...

Lookin good by the way...I like the red on that boat!

moonfish · Apr 22, 2010

Re: Compression Test - Doing it the Wrong Way

Yeah the paint looks good. I've hung my motors from a board in a vise. Yours is heavier, you might need a leg down to the ground to hold it up but you don't have to build anything permanent. You've gotta pull full speed and a full stroke to get the compression reading maxed out.

CBGale2 · Apr 22, 2010

Re: Compression Test - Doing it the Wrong Way

restornator said:
How did you flip that boat?

Its not really heavy to start with and gutted out, but I have a system that I figured out and actually flipped a 15ft tincan by myself last year. This one I had someone help me since it has the windshield I was worried about. I wouldnt try it with a heavy boat.

What I do is take a tie down strap (the tension kind, not the ratchet type), hook one end on the rafter of the garage and the other end I tie it really good into the front eye hook with a rope (rope so it wont bind up). Using the strap I lift the front off the boat up off the trailer so its hovering. Lift the back end up by hand and set it on a saw horse or something. Pull the trailer out. Get a buddy, both get on the back end and turn the boat over, front end pivots on the strap. Picture a boat on a rotisserie.

CBGale2 · Apr 22, 2010

Re: Compression Test - Doing it the Wrong Way

Yeah I need to come up with something else to put it on, space is limited in the garage..... way too much stuff. I can get to everything on the motor to work on it, but just not enough room to pull on it, and its not exactly the easiest thing to pull start......

Just had an idea, pully on the wall stud infront of it, tie a rope to the pull start handle, through the pully and pull the other way.

Rick. · Apr 22, 2010

Re: Compression Test - Doing it the Wrong Way

Your test was inadequate. What I've heard and it is best with the engine warm but not critical. Both plugs out, Put the gauge on one hole and briskly pull until the gauge stops climbing counting the number of pulls. Write down the cylinder and number. Move to the other hole and briskly pull the same number of pulls and then write down that number. Best of luck. Rick.

F_R · Apr 23, 2010

Re: Compression Test - Doing it the Wrong Way

CBGale2 said:
Just had an idea, pully on the wall stud infront of it, tie a rope to the pull start handle, through the pully and pull the other way.

Love it!! You related to Rube Goldberg by any chance?

cougar1985 · Apr 23, 2010

Re: Compression Test - Doing it the Wrong Way

space is limited in my garage also so i bought a folding engine stand and bolted a 2 x 10 piece of hemlock to it.i have a 90 evinrude on it at the moment and you can work on it anywheres as it will wheel all over and with the motor bolted on you can tilt the motor upsiide down if you really wanted to!sideways, backways, frontways ,lol.in theory with a strong enough mounting board you could mount 4 90,s on it and it wouldnt even break a sweat.would make a good movable motor storage area also,and their cheap to boot!

jonesg · Apr 23, 2010

Re: Compression Test - Doing it the Wrong Way

I bought an engine stand too, $25 from craigslist, stored my 150hp on it all winter, its a no brainer unless you a lot of lumber laying around to make one.

CBGale2 · Apr 23, 2010

Re: Compression Test - Doing it the Wrong Way

F_R said:
Love it!! You related to Rube Goldberg by any chance?

Yeah, hes my cousin.

Well my idea didnt work out to well, think the motor was a little too close to the wall and my pulley I had from the 1800's wasnt working out too well. I did however get the compression to 60 top and 61 bottom using this method. So now I feel twice as good about it.

Doing a proper test.... what would I expect to see for numbers? Or is it more important that they are close to being the same?

Rick. · Apr 23, 2010

Re: Compression Test - Doing it the Wrong Way

With in 10% of each other is important. Sounds like your comp. is going to be good enough but let us know once you get the motor moved. Rick.

jonesg · Apr 23, 2010

Re: Compression Test - Doing it the Wrong Way

Hand pulling it you will be hard pressed to get 70 psi.
I'd say you're ok.

Have to find something else to fret over now.
What about the crankshaft?

CBGale2 · Apr 23, 2010

Re: Compression Test - Doing it the Wrong Way

:

jonesg said:
Hand pulling it you will be hard pressed to get 70 psi.
I'd say you're ok.

Have to find something else to fret over now.
What about the crankshaft?

My crankshaft???? What about the crankshaft? Is it broken? What am I going to do? How do I fix it? Is there a topic in top secret area?

Compression Test - Doing it the Wrong Way

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