Compression Test How To Help

[zul]

I've done loads of researched this topic and have found mixed answers. Just doesn't seem to be a good 'How To' out there for i/o sterndrive boats. Post up a link if you find one that I've missed.

If a compression test is done incorrectly, things can blow up. I've done several comp tests on my old 2-stroke but this seems to be a different beast with a sterndrive. I will do a leak down test later. Would like to get this done for a first round:

1. Do the compression test with a warm engine or cold?
2. Some say to disconnect the fuel supply, many do not. ??
3. Take all spark plugs out, number the wires, number the plugs. Or just take one plug out at a time?
4. Inspect each spark plug. Looking for build-up, corrosion, cracks, etc.
5. Open the throttle and choke. Details on this, anyone?
6. MOST IMPORTANT: Disengage the spark -- Take the coil wire off. Is this the main wire in the middle of the distributor cap?
7. Ground the distributor wire. Easy, fool proof method?
8. Double check that all of the steps above are done correctly.
9. Screw your compression gauge into #1, turn ignition key for 5-10 sec. Write down the result and proceed to each cylinder in order.

How often do you change distributor wires and distributor cap?
How often do you change plugs?

Thanks for the help, crew!

 

[Rick Stephens]

Warm engine. Since I pull all the plugs at once, I don't bother worrying about fuel supply, the engine isn't pulling any air without plugs. I don't number plugs, I suppose it would save on the ooops mis ordered wires if you number them. With a warm engine the choke is open. Set your throttle handle wide open. Use a mechanics starter switch with clip on leads connected to the starter solenoid - using one means you aren't powering the ignition anyway, so no key on. Crank for exactly 5 compression cycles when testing each cylinder.

 

[tpenfield]

I think you would have to be specially talented to 'blow up' an engine doing a compression test, but you never know. :noidea:

See my comments below . . .

1. Do the compression test with a warm engine or cold? Warm
2. Some say to disconnect the fuel supply, many do not. ?? No
3. Take all spark plugs out, number the wires, number the plugs. Or just take one plug out at a time? All out so the engine 'spins' faster.
4. Inspect each spark plug. Looking for build-up, corrosion, cracks, etc. Sure
5. Open the throttle and choke. Details on this, anyone? If the engine is warm, then the choke should not be a factor, Use the neutral lockout button and put the throttle all the way up in forward. (easier if you have separate throttle and shifter controls)
6. MOST IMPORTANT: Disengage the spark -- Take the coil wire off. Is this the main wire in the middle of the distributor cap? I just stick the coil lead off the distributor and stick onto a nearby bolt
7. Ground the distributor wire. Easy, fool proof method? See #6
8. Double check that all of the steps above are done correctly. What could possibly go wrong?
9. Screw your compression gauge into #1, turn ignition key for 5-10 sec. Write down the result and proceed to each cylinder in order. You want to notice how many revolutions of the engine it takes to reach most of the reading. I do it in terms of revolutions of the engine and not time. The pressure should go up most of the way within 3 revolutions of the engine. I spin the engine for 8-10 revolutions total.

How often do you change distributor wires and distributor cap? Every 10 years, whether it needs it or not.
How often do you change plugs? Every 10 years, whether they need it or not.

 

[zul]

Is this a good diagram to help me find the #1 cylinder and the correct order of the pistons? Boat and motor type listed below ....

 

[zul]

Checked the oil yesterday while the motor was cold -- right in the middle.

I spend today pulling plugs and putting them back in. Takes some patients and practice. But I've got it.

Then, I put the muffs on and warm everything up. Check the oil. It's super low. Way low. Not good .... Add a quart and check again. It's back where it's supposed to be. Hmm??

Now I remove all 6 plugs, disconnect the coil lead, ground it as suggested, place the throttle-neutral-full. Trying to screw the threads of the comp tester hose into the plug threads -- IS -- F&%$& -- IMPOSSIBLE. After working and working at it, I get the threads into #1. As far in as I can get it. Is it 100% in? I can't tell. Feels good, but ?? I twist, turn and twist and turn that black hose in there, best I can. Hit the ignition key, it hisses and goes up to 120, then hisses again and goes straight back to 0. After several attempts, this is what I've got from #1. Frustrated. I'm not even sure if the hose is not threaded properly (likely) or a stuck #1 piston (God, I hope not). The hose has black rubber gaskets, so I can rule that out.

Then I try the other plug holes and cannot even get the threads started. Over and over again. Cannot thread the tester hose. Are there different types of hoses? This model, I have to twist the hose to get 'er started. I'll bet there's a swivel-screw-head type fitting? If this hose were 10 inches shorter, I might have a fighting chance.

Any suggestions? Keep practicing -- Keep trying?? Get some different tools?? Exhausted and frustrated.

I've got all day tomorrow to bang my head on this one.

 

[tpenfield]

The hose that goes into the sparkplug hole should be as short as possible 6-8". Then you have the quick disconnect fitting of the compression test gauge, and connect the tester to the short hose that threaded into the spark plug hole. It sounds like you have a tool that it not right for the job.

If you are using a longer hose for the sparkplug hole, then yes, it will be impossible.

 

[zul]

SUCCESS People!! The correct tool does the job. I went through 3 sets of hoses and rods. The adapter rod was showing '0' :: Insert Panic Mode :: but only for a moment. I knew that rod wasn't holding air, the connector was lose when it was properly attached -- manufacturing error. This last hose went in nicely and check out these cold and dry readings:

#1 130
#2 129
#3 135
#4 135
#5 135
#6 120

I know it should've been warm and dry for this test, but with the troubles and struggles, a man can only take those plugs in and out so many times.

Wondering if I should warm up the boat and run this test again? Or if I should squirt some oil into #6 and test that one again??

My original problem is blow-by. I would like to think that these numbers are AWESOME!! and tells me that my engine will not need rebuild or rings ?? Where do I go from here? Guesses or suggestions?!! -- Damn blow-by.

zul

 

[tpenfield]

135 seems to be the predominant reading and the #6 cilinder is about 12% below the norm. Overall, a decent test, but a warm engine would be good to test.

 

[zul]

tpenfield - Don't make me go back in there!!

Ok, should I do the wet test and squirt some oil in there -- warm up boat and test again?

 

[Alumarine]

What makes you think you have blow by?

 

[zul]

Oil leaking from the breather tubes. A little last year, more this year.

My mechanic thinks that a valve job is in order ... does anyone agree with that? From the research, it seems like vale work opens a can-o-worms. Performance wise, this boat is working really well. Just leaking oil .... ??

 

[Bondo]

Oil leaking from the breather tubes. A little last year, more this year.

Ayuh,..... Carry a rag, 'n wipe it up when ya check the oil level each day,.....

135 psi ain't a new motor, but is a good runner,....
Down 'round 100 psi, 'n ya got problems,....

 

[zul]

I think the fuel pump is going bad. Places some gas into the oil ... right? That can cause blow-by with good compression test -- so far as my (lengthy) research tells me. I think my next step is a fuel pump, right?

 

[Bondo]

I think the fuel pump is going bad. Places some gas into the oil ... right? That can cause blow-by with good compression test -- so far as my (lengthy) research tells me. I think my next step is a fuel pump, right?

Ayuh,.... A '94 should have an electric fuel pump,....... so No,.....

 

[zul]

I had two (very minimal) power loses when throttling onto plane. Only happened twice on an 11-day boat trip... other than that, fine boat performance on that trip (just lotsa oil adding). Can I really rule out a $65 part causing my problems?!? Maybe I am too optimistic. Humph.

 

[Alumarine]

I think you're reading too much!!