Compression check?

[bigdog]

Just FMI, how long do you think it would take to perform a compression check on a V4 outboard? 4 cylinders.....

Sounds like you would possible need two people to perform this test.
One person to turn the ignition key, and one person to read the compression gauge? Or do I have this all wrong?

Information is requested b/c I'll be bringing boat to a marine tech. and want to know how long this would take to perform this test, to guesstimate the cost at $100 an hour labor?

Thanks,
Bigdog

[HellRaZoR004]

That sounds reasonable to me.

You could also go to Sears and pick up the tool to do it...here's some instructions:
http://www.boatfix.com/merc/Bullet/97/97_25.pdf

Edit: just realized you mentioned outboard - same concept applies but different instructions.

[8gv]

I'd expect a pro to have a remote starter switch to make it a one tech job.

[Dave R]

Compression testers have check valves, you can check it alone. Just pull all the plugs, disconnect the fuel line, ground the spark plug leads (or if the motor will turn over with the kill switch activated, just do that), open the throttle fully, thread the compression tester into a plug hole, and crank the engine for 5 seconds. The gauge will record the highest reading. Release the pressure, move on to the next cylinder and repeat until all 4 are done. Should take 30 to 45 minutes, the plugs on those motors are shockingly simple to access.

You in Bridgton this weekend? I could bring my tester.

[4Fun]

Compression guages are also pretty cheap. You can probably pick one up at the auto parts store for <$50 and do it yourself. It's a pretty simple task. I would guess a shop would charge 1 hour labor.

It will probably take you longer ot drop off and pick up the boat than do the test at home.
Check out Youtube there are a bunch of videos showing the process.

Can I ask why you are checking it? It's a good first check on an engine but does not tell the whole story if you are chasing a problem. Is the OB a 2Stroke or 2 Stroke?

[NHBUOY]

If it is an outboard, make sure you have a water supply to the lower unit. Water pump impellers are easily destroyed without water flow. A V-4 should take all of 20 minutes to check compression.

[bigdog]

Thanks everyone for all the feedback, greatly appreciated !

4Fun... to answer your question, just wanted to check the overall condition of engine.. Bought last year from private party sale.
If engine shows low compression, in one or all cylinders, could have the potential for major repairs down the road.
FYI, its an v4- 2 stroke outboard.

Thanks again !
Bigdog

[SIKSUKR]

The standard tolerance between cylinders is 10%. If any cylinder is low, pour a little oil in it and test again. If the pressure comes up to near normal then your rings are worn. If it stays the same its probably your valves.

[4Fun]

It's a good idea to check it each spring and fall and track the differences. If you have the skills to take the cover off the engine you are half way there to testing the compression. It really is a DIY job.

It's a good idea to put new plugs in a 2 stroke each year as well. This is also a very easy DIY job and can be done at the same time. The compression check process probably adds 5 minutes to the plug change process....Just don't over tighten the spark plugs.

The spark plugs will also tell you a story when you take them out. Gummed up and messy you are rich and need an adjustment. If they are white you are in danger of burning a piston. Brownish black it just right...

Siksukr mentiones valves in his post but that only applies to a 4 stroke not your 2 stroke...