Yamaha sx230 compression issue

[kkocher13]

I'm looking at purchasing a 2006 yamaha sx230 with roughly 450 hours on each motor. The boat runs well. Compression on the first engine is 177-171-170-180. The second engine is 175-160-130-175. Do you think engine 2 is an issue? Just don't want to buy a problem.

 

[David Martin]

Great compression for a 18 year old boat except on 130 cyl is bothersome. You can rent or purchase a boor scope Amazon has them for $20 to $40 dollars and I would like to see the plug..............if you look at the cyl wall you could determine if she has a broken compression ring..............you would see scratches on the cylinder that move up and down on the wall you will see wear scratches anyway but you are looking for a deep scratch the stands out...............................I would first look at one of the 170 or 180 cyl to see what good looks like.

Its possable a valve is leaking and could be just a little carbon build up that a cleaner would solve or a tweek adjustment on the valve spring.....just giving you info. Also if you tested 5 boats that old you might get even worst numbers. How well taken care is the rest of the boat.........that's also a big factor for me.

 

[kkocher13]

Great compression for a 18 year old boat except on 130 cyl is bothersome. You can rent or purchase a boor scope Amazon has them for $20 to $40 dollars and I would like to see the plug..............if you look at the cyl wall you could determine if she has a broken compression ring..............you would see scratches on the cylinder that move up and down on the wall you will see wear scratches anyway but you are looking for a deep scratch the stands out...............................I would first look at one of the 170 or 180 cyl to see what good looks like.

Its possable a valve is leaking and could be just a little carbon build up that a cleaner would solve or a tweek adjustment on the valve spring.....just giving you info. Also if you tested 5 boats that old you might get even worst numbers. How well taken care is the rest of the boat.........that's also a big factor for me.

The boat itself is in good shape. A couple of scratches here and there, but otherwise pretty good. I like the idea of looking at the cylinder. I'm just worried that the compression issue gets worse and then I'd be looking at a rebuild. You mentioned the spark plug...what would you be looking for?

 

[buckbuck]

Is this a salt water boat or fresh water boat?

 

[kkocher13]

Fresh water boat

 

[buckbuck]

About 700 hours on my fresh water 2008 boat and it still runs great. If you can get some resolution on that one cylinder I think you will be pleased. Does it have the HO MR-1 engines?

 

[kkocher13]

Just the standard 140 horse motors. I'm hoping the issue is just carbon build up. Otherwise I might be looking at a rebuild.

 

[David Martin]

The boat itself is in good shape. A couple of scratches here and there, but otherwise pretty good. I like the idea of looking at the cylinder. I'm just worried that the compression issue gets worse and then I'd be looking at a rebuild. You mentioned the spark plug...what would you be looking for?

Vary black plug with lots of carbon build up is over rich...over rich could carbon up valve seat causing poor seal and loss of compression.....cleaner in gas could clean her up but you still need to find cause of rich fuel mixture like Injector corrosion/weak spark as in the coil.

Now you could add a small amount of oil to the cyl right before the compression if ring is broken or lots of were blow by she will shot up to a much higher number say 160 is she only goes up a small amount say 135 or 140 its will lean it towards leaking valve seat because oil does not seal valves as well as it does for the rings.............Now if plug shows lean burn....look up lean burn and rich on YouTube for examples. Lean burn heats up cylinder stripping oil off walls causing low compression test....... adding oil for the test on lean will cause a sharp increase in compression.....IT THE PLUG READ THAT WILL STEER YOU IN THE RIGHT DIRECTION. The great thing is you have a good motor to compare and 7 cyl that look good.

Now last clue the OIL......... broken ring and scored cyl will have a lot of compression blow by into the block IT SHOULD cause oil to be vary black or darker than the good engine. If Thay changed the oil and plugs not much you can do but scope or have a mechanic do a leak down test.

Hope this helps not trying to scare you.