second hand engine hours

[Aussiesailor]

Good Evening,
I am in the market to buy a second hand boat and 2 of the options are ex pro boats with Yamaha four stroke engines. One has a 2013 250 four stroke with 2000 hours, the other has twin 115 2004 four strokes with 3000 hours on each.

My question is, is there an hour range that would be considered to much? Is there an hour range where it is recommended the motors be rebuilt? I don't have enough money to replace the engines on either of those boats in the near future and would like any feedback you may have please.

Regardless of motor I will have them compression tested etc in the pre-inspection purchase.

Thanks

[rodbolt17]

corrosion takes time.
not engine operating hours.
I would go with the newer one.

I would opt for a leak down test over a compression test.

[boscoe99]

If the motors are/were used in the salt then I second the "I would go for the newer one" comment. 11 years in the salt can take its toll. Internally if not externally.

Another negative for me is the F115's have 50% more time on them. And that model does not have a knock sensor and is known to be somewhat problematic. Yam added a knock sensor on later F115's but unfortunately yours does not have one.

I prefer the dynamic compression test over the static differential pressure test. If the compression test indicates anything amiss then do the differential to find out where the problem is.

[rodbolt17]

and I prefer the leakage test over the compression test cause I don't like to work twice.
the leakdown is so much faster than the compression test to perform and is much more accurate.
that compression test wont find small leaks or ring gaps that have lined up.
a leakdown will.

[boscoe99]

Both tests have their strengths and weaknesses.

A leak down test may indicate a cylinder with a score in it as perfectly good. A compression check may catch this defect.

Think about where the majority of the cylinder wear is? The area below the point where the piston ring resides when the piston is at top dead center. With the piston at TDC the ring is going to be sealing the best that it can possibly seal. This is the point where the leak down test is performed. Wear below the point where the rings reside at TDC is not going to be noted in a leak down test.

There may be a reason why Yamaha provides minimum compression reference values in their service manuals but makes no mention of minimum leak down reference values.

A ring and/or valve sealing at upwards of a thousand psi is one thing. How good can a ring and/or a valve be when sealing at but 80 psi?