broken piston

[Salmonid]

I have had two different 150 four strokes blow a piston/rod. Both motors were under warranty but I would like to know the cause before the warranty expires. Does anyone have any ideas or is this just really bad luck?

Thanks

[rodbolt17]

were the rods bent?

[madharchod]

you would have used shit fuel which caused this ,better get your warranty done before they refuse the repair as your negligence

[Salmonid]

Yes the rod was bent, and the piston was jammed sideways.

These motors are the f150/105 jet drives. I have heard of rumors that if at speed the motor is turned off that it is possible for water to enter the number 4 cylinder through the exhaust valve causing really high hydrostatic pressure upon start up. Has anyone heard or have first hand experience with this in the f150 model?

The other theory is that the stock impeller is pitched to high. From the factory these motors only get up to 4800 rpm WOT, causing premature ware and tare.

Any thoughts?

[rodbolt17]

yes, high speed shut downs can and will lead to water injestion, happens on ALL outboards.
happens on sterndrives as well.
on jet drives,incorrect muffler tube fit can force water up the exhaust.
on jet drives,incorrect CDI module can lead to low RPM.
you simply cant slap a jet on the bottom and go play.

[Salmonid]

Rodbolt,

Thanks for your input. I think we ruled out the CDI, initially we tried two different impellers and was able to get to 6k at wot. However both didn't work. One the pitch was to low, causing slow speeds, the other at WOT got to 5200 but hole shot was terrible, since it was only a 3 blade alum/zinc composite. We are currently looking into using a specialized impeller made for a Honda 150 inline. Currently Yamaha is using a four bladed stainless steel impeller which was designed for the older v6 outboards. I'm assuming the torque and hp are significantly different throughout the rpms bands between a v6 and i4. Thus possibly causing the lower rpms, even though both are rated at 150hp.


As far as water ingestion, I have not received feedback from the boat operators on the conditions the last motor threw a rod. The first one happened while cruising. I would assume the catastrophic failure would be instantaneous upon start up directly following the high speed shutdown?

Thanks again for your insight.

[rodbolt17]

not nessesarily so.
I did a powerhead on an F250 last year,grady 36 with triple F250,
port engine had had water forced up the ex into #6 cyl.
on start up it bent the rod into an S shape.
the only thing the operator noticed was a light ticking sound.
I found it while checking for a loose wristpn or piston slap.
I noticed #6 piston at TDC did not come up as high as the rest.
the ticking was the crank counter weight knocking on the wristpin area under the piston at BDC.

I saw another that had NO symptoms other than off about 250 RPM at WOT.

had either been run much more both would have suffered a catastrophic pisto/rod failure.