low compression number 5 cylinder

[alpumpdup]

I have dual 2000 ox66 yamaha 225 on 27 sailfish....sent to shop to have the engines looked at prior to season and received a call that i have low compression reading number 5 cylinder and they want to do a rebuild with new lower end either with yamaha or jasper....also that it will cost about 6k ...i need some feedback on this as the motors have only 450 hours and the engine ran perfectly prior to pullout his year....did some research and compression 10% less than other cylinders is no big deal....also would ringfree help or any other remedies other than a rebuild.....am confused at this point and need some guidance....thanks in advance
steve

 

[seasick]

What were the readings?
Why would they recommend a new lower unit for low compression? Perhaps they said Upper unit?

 

[alpumpdup]

they reccommended a rebuilt powerhead........sorry

 

[Grog]

10% is the allowable difference. Be careful, some motors don't have the same compression on all the cylinders the 225 OX may be one of those.

(Jasper makes the rebuilt motors for Yamaha)

 

[Gman25]

Why did you want the engines looked at if everything seemed fine? Was there something that didnt seem right?What kind of rpms did you get last time you ran them? Do you use ring free? Did the spark plug look beat up indicating a broken ring? Not sure I would jump right into a new powerhead until I was convinced the wall is scored and clear evidence of piston/ring damage.

 

[RAINMAKER]

Why did you want the engines looked at if everything seemed fine? Was there something that didnt seem right?What kind of rpms did you get last time you ran them? Do you use ring free? Did the spark plug look beat up indicating a broken ring? Not sure I would jump right into a new powerhead until I was convinced the wall is scored and clear evidence of piston/ring damage.

X2 Also shine a pen light into the spark plug hole and look at the top of the piston. It shouldn't have "pecker" tracks on it . You might have to turn the engine by hand to get a good look at the piston . If you possibly have a cracked ring and a scored cylinder wall that will not show on top of the piston.
Also ask the mech how he performed the comp. check. This is how I do it ... warm up the engine to operating temp. Pull all the plugs out , open throttle wide open , put in comp checker in ,spin the engine until max reading on gauge . usually about three or four compression strokes. write down # on paper
then do the rest of the cyl. the same way. A good comp checker will run you about 30.00 to 35.00 bucks.....

Heres what I use
http://www.lislecorp.com/tool_detail.cfm?detail=206

 

[ahill]

That piston may have "coked" causing the bottom ring to seize thereby losing compression. It causes a lean running condition and will eventually show up on top of piston but not initially. Been there b4.

 

[3rd Day]

I'm thinking second opinion. 450 hours is not many to have a ring issue. Just my .02 cents.

 

[seasick]

I'm thinking second opinion. 450 hours is not many to have a ring issue. Just my .02 cents.

It's plenty if Ring Free wasn't added and/or lower quality oil was used.

 

[alpumpdup]

ring free has never been used...only stabile....compression figure on one cylinder was 20psi all the other read around 100...engine ran fine and rpms were equivalent with the stbd engine...the mechanic showed me bottle of oil removed from tank and it had small amt of h2o in the bottom...i was having the engines gone over for the beginning of the season.....i had no concerns cuz when put away all ran good last time out...took to taylor marine for another opinion and they will pull the head and get a look at the cylinder but basically i'm told that it will either need to be rebuilt or maybe i should look for another used engine with no compression problems...so proactively i'm going to look for used engine while prognosis is being made......never used ringfree is that somethine that everyone uses?....

 

[Grog]

Ringfree - yes

You might be able to get by without it if you de-carbon the motor often but it's cheap insurance. The shot cylinder is probably from the water more than the lack of ringfree.

 

[georgemjr]

I posted this once before: I had one cylinder go down on my '90 250 HP OX66. My mechanic, a trusted friend and Yamaha certified tech, inspected the cylinder and determined it was not scored too bad. He removed just that piston, by going in through the intake port (behind the carbeurator) and removing the connecting rod. He replaced just that piston and the head, since the head was damaged when the piston let go. Put it all back together and the engine ran fine for 10 more years and was running fine when I sold it at that time. The compression for that cylinder was well within limits. I do not know the extent of the damage to your cylinder, but if not bad, a solution such as this was very cheap and reliable. Always ring-free, only Yamalube.