low compresion

[riflipping]

I have a 2001 OX66 225 and the odd cylinders are all running approx. 80 PSI while the even cylinders are 105 PSI. The head gasket on the odd cylinders needs to be replaced. Could a bad head gasket cause the low compression?

 

[racerone]

Take the head off and inspect those cylinder wall.----Your best option in the path forward.

 

[99yam40]

if the head gasket is letting some compression to leak out, then it would lower it.
but the odds of all of them doing it equally is reaching

 

[Sea Rider]

Could retorque odd cylinder head to factory specs and make a new compression test to check if compression upped a bit. When head gaskets become dried, hardened with use, the perfect seal between both mating surfaces is lost and engine will begin to miss when at higher revs. How much compression was lost will depend entirely on the head gasket shot condition.

If going for new cylinder gasket, better replace both sides, take advantage to clean both mating surfaces, water paths, thermostat and decarbonize internal head and piston heads to look as when engine was new.

Happy Boating

 

[99yam40]

both of the 2 motors I have found with blown head gaskets bad enough to let the hot compressed gases out actually cut a grove in the head and block where it was leaking out.
these were not my motors, so I have no idea how long or bad they had been run like that tho

 

[James R]

The compression's on the Yamaha are usually much higher than this so it would not hurt to remove both heads to inspect the bores for scoring.