Z250 hpdi question

[35marlin]

Hello to all,
Just bought a new to me boat and it has the z250 motors (2003) on it. I know these motors were not yamaha best. I have 2 questions:
1. Does anyone know why there were many failures with this motor ( especially on #2 cylinder).
2. What can I do to help these motors last?

More info: they currently run great and only have 250 hrs on them. Pushing a Marlin 35' SF

New member,
Lee

[boscoe99]

I have seen a number of big block HPDI's with cylinder damage, mostly with the number two cylinder but from time to time other cylinders are damaged in a similar manner.

The damage that I saw appeared to me to be detonation related.

Only things that I know to prevent detonation damage in an HPDI is to make sure the motors are propped so that they run at the upper end of the WOT RPM range when the boat is loaded and to run clean fresh fuel of a higher octane rating. Maybe 91 if not 93 octane.

Also, make sure that the motor is run on Ring Free or decarboned from time to time to prevent a carbon build up issue which can cause increased combustion chamber pressures and temperatures. Finally, make sure the cooling system is working correctly. Keep a check on the thermostats to make sure they are in good working order.

Good luck.

[rodbolt17]

there were multiple updates on the B model Z250.
3 for the oiling system and one for the charging system.
you may wish to find out if they were done.
its old enough now Yamaha probably wont help.