2007 Yamaha 70hp 2 stroke compression

[grandpamike]

Need help, I'm looking at a stratos 176 xt/bs with a 70hp 2 stroke Yamaha.
The compression reading was 110 120 115. Does this seem O.K. for a 2 - 3 year old outboard? I'm not familiar with compression tests except that I read
there should not be more than a 15# difference between cylinders - some say 6# - 10#. I would appreciate any info you guys have.

Thanks.

 

[rodbolt]

Re: 2007 Yamaha 70hp 2 stroke compression

its blown up.
ill give ya 100 dollars for it.



now that I have your attention.
its designed that way.
if your concerned have a leak down test run on it.
had a big hoo hoo a few days ago about compression on the boards.
quite a few of the 3 cyl yamaha motors have a 15 PSI spread designed in. should have the spread from top,highest, to bottom lowest.
its not in any service manual either.

 

[robert graham]

Re: 2007 Yamaha 70hp 2 stroke compression

Probably the best way to tell is take the boat/motor out to the lake/river and run it for an hour or 2, all RPM's, idle, wide open, listen to the motor, look it over carefully,check the spark plugs, if it runs good, sounds good and looks good, then it's most likely in good shape, especially for a later(2007) model. Has it been maintained well, run in salt water or fresh? I've had great luck over the years with the Yamaha 3 cylinder 2 strokes. It's all about clean, fresh, stabilized fuel and good preventive maintenance. If you buy the motor, order a manual to study up on it. Good Luck!

 

[kaferhaus]

Re: 2007 Yamaha 70hp 2 stroke compression

The compression on MY 2006 model (bought new in 2005) is 135, 135, 128 from top to bottom. This engine had 386hrs on it when those readings were taken a couple months ago. They were within 2psi of the readings that were taken right after the 10hr break in period.

No one knows if your readings are accurate or when if ever your gauge has been calibrated.

If the engine performs well under load it's probably in decent health.

Personally I rarely buy a used outboard that I cannot water test first. The alternative is to have a leak down test performed on it. If it's running good on a stand, has good compression and passes a leak down test it MAY perform well under load. I've seen plenty that passed both those tests and ended up needing fuel system and or gearbox repairs... which can be expensive if you cannot do them yourself.

The only exception for me is when the price is so cheap that I'm not hurt even if it needs those repairs.