OMC Cobra 4.3 Low Compression #1/6

[I/O New Guy]

I know very little about I/O engines and am no mechanic, but I'm looking to gain some knowledge. The above engine is 19 years old, and the compression readings are 80/150/150/150/150/95. What are the most likely causes of low compression on cylinders 1 and 6? I'm assuming there is one source to this reading on both cylinders, but not sure what it is. Any info is appreciated.

 

[achris]

Re: OMC Cobra 4.3 Low Compression #1/6

How was the test done, and how are you numbering the cylinders?

 

[Bondo]

Re: OMC Cobra 4.3 Low Compression #1/6

I'm assuming there is one source to this reading on both cylinders, but not sure what it is.

Ayuh,... I doubt it's a problem Common to both cylinders, they're on opposite corners of the motor...
Unless Worn Out can be called Common...

 

[Haut Medoc]

Re: OMC Cobra 4.3 Low Compression #1/6

You will need to do a proper compression test, add a couple squirts of oil to the suspect cylinders & see if the compression comes up.....
If it does, most likely worn rings....
If not, then it is time to look at the valves.....
Welcome to iboats, BTW.......​

 

[I/O New Guy]

Re: OMC Cobra 4.3 Low Compression #1/6

I'm unable to get details on the testing - boat not in my possession. I'm trying to support a local charity (and maybe get a good deal) by buying a donated boat. They do good work, but aren't as thorough as a certified marine mechanic. The boat did run and cool well in the shop for 30 minutes, but the compression variance leaves a pretty big unknown. I also know boats are normally donated instead of performing a pricey repair, so I'm walking away from this one.

I really appreciate the quick responses and depth of knowledge! I'll definitely ask more questions with better detail in the future. Thanks again.

 

[Bondo]

Re: OMC Cobra 4.3 Low Compression #1/6

I really appreciate the quick responses and depth of knowledge! I'll definitely ask more questions with better detail in the future. Thanks again.

Ayuh,... Just another Tip for a boat Shopper,....

Don't even Look at any barge that's OMC powered,... The company is Dead,+ Gone,.. Years ago...
And,...
Don't buy a 470 Mercruiser.....

 

[achris]

Re: OMC Cobra 4.3 Low Compression #1/6

...Don't even Look at any barge that's OMC powered,... ...Don't buy a 470 Mercruiser.....

You take all the fun out of life!

 

[I/O New Guy]

Re: OMC Cobra 4.3 Low Compression #1/6

Last post on this thread - thanks so much for the advice! I did find a boat I am very happy with - mechanically very sound, and a bit of a cosmetic fixer-upper, which I can handle. Found out there is a big difference between my old 90 hp Johnson and an I/O! I really appreciate the info - thanks again.