Compression #s 2005 Yamaha F150

[SteveSC]

I'm looking at a Yamaha F150 - might buy it but I need a little help. This motor looks good - runs good. The compression #s are from 145 - 154. The spread looks good, well within 10% of each other but I need to know what they were supposed to be when the motor was new. I've heard around 185 but that might not be right - seems high to me.

Any help with this is appreciated.

 

[seahorse5]

Re: Compression #s 2005 Yamaha F150

That low a reading could be from an inaccurate compression gauge or that the throttle was not advanced all the way open. Most F150's will be around 170-180 or so depending on gauge and temperature of the engine.

A leak-down test is more informative on a 4-stroke outboard and that is what Yamaha recommends for checking condition.

 

[robert graham]

Re: Compression #s 2005 Yamaha F150

Those numbers sound fine to me, within 10% between cylinders is the rule of thumb. Readings may vary from check to check. The best proof is in the running, on the water, at all speeds from idle to wide open/maximum RPM, throttle response, cold starting, cooling,etc. When was water pump impeller replaced last? Any reason to suspect problems with this motor? Any major work/repairs been done? How many hours on motor? Fresh or saltwater useage? Good Luck!

 

[SteveSC]

Re: Compression #s 2005 Yamaha F150

New water pump - no major work done on the motor - low rpm saltwater usage. Would you believe 7000 hrs...! The hrs. are the reason to suspect problems but all indications show no problems. This motor would go on a low usage boat - maybe 100 hrs. a yr.. I know 7000 hrs. is almost unheard of but if all looks good and the sea trial turns out good I might go with it... What do y'all think..? Try not to think about the 7000 hrs...LOL...before you reply.

 

[99yam40]

Re: Compression #s 2005 Yamaha F150

Like seahorse said the leakdown test will give you info on rings and valves conditions.
I would have it done

 

[robert graham]

Re: Compression #s 2005 Yamaha F150

It has a hobbs/hour meter showing 7000 hours? That's a good bit, must have been a commercial fisherman, crabber, or other? If the motor has 7000 hours of actual saltwater useage, then I'd worry about internal corrosion, unless the price is so attractive that you could justify some repairs later. Just my thoughts on this. Good Luck!

 

[SteveSC]

Re: Compression #s 2005 Yamaha F150

Not sure about the type of hr. meter - just going by what the current owner has told me... It is a commercially used motor as you figured. It there a way to diagnose any internal corrosion without a partial tear down..? I'll have a leak test done on the motor but since all the compression #s ( per owner ) are so close I'd suspect what Seahorse5 suggested - faulty gauge or engine issue. I just can't see all cylinders being down to 145 - 154 from around 180+\- ( specs. ) and all cylinders still within a 10% spread. You'd think there would be more spread between #s - at least one cylinder would stand out. That just doesn't sound right.

 

[robert graham]

Re: Compression #s 2005 Yamaha F150

Any 7000 hour saltwater motor would be suspect and subject to major corrosion issues, in my fair opinion. Why is this commercially used motor(work boat?) for sale and how much are they asking for it?$$$ It sounds like there are no problems with compression on this motor. It would cost time and money to tear it down for an internal inspection and you still might not catch a problem. If the price ain't real attractive, I'd keep looking, preferably for a freshwater motor. Good Luck!

 

[SparkieBoat]

Re: Compression #s 2005 Yamaha F150

I would pass on that motor unless it was dirt cheap..you can pick up a fairly new one with 300-500 hours for a reasonable price if you are patient