Compression test not good

[rainman99]

I just got a chance to do a compression test on my 1973 115hp. #1 Cylinder 0 2,3,4, psi . Started it up it would only do about 2ooo rpm. Hooked to compression gage started engine was jumping up to 120psi when I shut it down was reading 20psi. What am I looking at as far as repair rings ,valve piston or run as a 3 cylinder ?

 

[itsaboattime]

Re: Compression test not good

I'm not clear on how you did your test. What type of tester are you using?? I use the screw in type. It threads right into the sparkplug hole. I pull all the plugs and number the wires with masking tape and a sharpie. Then I connect the tester and turn the engine over. Let it turn over about 5 times per cylinder. All the cylinders should be within 10% of each other. Try testing it like this and post back the results.

Out of cuiosity, why were you testing the compression anyway? Whats the ailment with the motor??

 

[kenmyfam]

Re: Compression test not good

Need to know exactly how you did the test. Is the motor in the water ??? if not and are on muffs you should not be over revving it or you get a runaway motor.

 

[rainman99]

Re: Compression test not good

I used a screw in type of type gage.With muffs on initially only cranked the motor(not starting it) to get a reading. I just bought this boat and engine last weekend and Finlay got a chance to do a compression test, Everything else on th motor is working fine charging,water pump, fuel pump,etc. only the the # 1 cylinder problem . Runs with a slight miss and hardly any smoke. Thinking its a valve problem ?

 

[kenmyfam]

Re: Compression test not good

No valves in a 2 stroke.
You should never test the compression by running the motor. Always without starting it. Is the gauge sealing properly on the #1 cylinder ?? Test it with a little dishsoap solution around it when you turn it over. If you get some bubbles it is not sealing. Just make sure the dishsoap spolution does not get into the cylinder after testing though and rise it off afterward. Most dishsoaps contain some salt.

 

[Robj]

Re: Compression test not good

Hate to say it, but with compression numbers that low, you probably have a holed piston. Time to start investigating, and you may probably end up doing an overhaul.

Good luck and have a great day,

Rob.

 

[rainman99]

Re: Compression test not good

Kenny thanks for the help. The gage was well seated I allso did the finger test wihile cranking felt weak puffing some compression but verry weak On #1 .

 

[rainman99]

Re: Compression test not good

Hate to say it, but with compression numbers that low, you probably have a holed piston. Time to start investigating, and you may probably end up doing an overhaul.

Good luck and have a great day,

Rob.

Overhaul WOW My next stept was going to be a decarb because all the cylinders when I looked into them were very nasty looking and plugs were black . If you are correct can run this motor as 3 cylinder with creatining more damge?

 

[itsaboattime]

Re: Compression test not good

Did you run the test again?? pull all the plugs out and then do the test again and post the results please.

 

[HybridMX6]

Re: Compression test not good

Agreed with itsaboattime, redo the test. It jumping up to 120psi then dropping back to zero is very odd, more like a blown gasket than a shot cylinder. Worst case, pull the head off that side and take a look. Head gasket is relatively cheap compared to a complete overhaul.

 

[kenmyfam]

Re: Compression test not good

Need to get 1 thing clear here. Maybe I am missing something ??
Post the compression results for each cylinder.
#1 = ???
#2 = ???
#3 = ???
#4 = ???

Let's go from there before we start ripping the heads off.

 

[jbjennings]

Re: Compression test not good

I just got a chance to do a compression test on my 1973 115hp. #1 Cylinder 0 2,3,4, psi . Started it up it would only do about 2ooo rpm. Hooked to compression gage started engine was jumping up to 120psi when I shut it down was reading 20psi. What am I looking at as far as repair rings ,valve piston or run as a 3 cylinder ?

I'm anxious to see these compression readings in terms I can understand also.

Just looking though, I would say if the gauge was jumping up to 120 and then went to 20 psi, the obvious problem is that the valve in your compression gauge is shot, releasing the pressure every time the piston gets past the exhaust holes instead of keeping it in the gauge.
Just my thoughts from what you posted,
JBJ

 

[freddyray21]

Re: Compression test not good

agreed. redo the test. if it gets to 120 then back to zero does sound like valve in the guage is sticking.

 

[rainman99]

Re: Compression test not good

I see there is a typeo in my first post that caused some confusion. cylinder #1=0psi
#2=124psi
#3=124psi
#4=126
This was done buy cranking the motor 5-7 times . #1 I put my finger in the plug hole and felt a light puffing with very little preasure. Then I ran the motor with the gage on #1 and seen the bounce from 20-120 turned off motor and preasure was 20psi.

 

[JB]

Re: Compression test not good

http://forums.iboats.com/showthread.php?t=299680

 

[Robj]

Re: Compression test not good

Like I said before sounds like a hole in the piston. That is the only reason you are going to see a "0" psi. When running of course there is going to be some pressure, because the engine is turning so fast and not all the air has a chance to excape through the hole. Time to start taking apart.

Have a great day,

Rob.

 

[HybridMX6]

Re: Compression test not good

Agreed with itsaboattime, redo the test. It jumping up to 120psi then dropping back to zero is very odd, more like a blown gasket than a shot cylinder. Worst case, pull the head off that side and take a look. Head gasket is relatively cheap compared to a complete overhaul.

I still don't know, that's awfully odd, but it sounds like a dead cylinder. As I said above, pull the head off and take a look.

 

[rainman99]

Re: Compression test not good

I still don't know, that's awfully odd, but it sounds like a dead cylinder. As I said above, pull the head off and take a look.

Thanks for the advice all . Going to pull head tonight to see whats going on in there.

 

[rainman99]

Re: Compression test not good

If I have to replace the pistion what is the best manual to use for my 1973 115hp Evinrude ?

 

[iwombat]

Re: Compression test not good

The OEM manual for a 1973 115hp.

Seriously.