Fuel flow and vibration

[Eric]

I have been battling a vibration on my port motor while under load all season, and will be having props pulled when the boat is hauled for winter lay-up to check balance. Both props were re-pitched last winter and supposedly balanced by a reputable shop, so Im skeptical that they may have missed balancing the port one.

Until i can get them checked, Im just trying to rule out other potential causes. I also notice my port motor has higher fuel consumption and higher engine load (both in neutral and in gear) and struggles to make full RPM, and is about 40-60 RPM short. Just wondering if there is possibly something else going on with my port motor.

I also plan to use an infrared thermometer to measure head, injector, and manifold temp on each cylinder to see if there is a noticeable temp difference. I’ll post findings when I can get a second hand to help run the boat.

Boat is a 2007 Sea Ray Sundancer with QSB425 engines. Both engines have about 1300 hours on them, and all coolers were serviced at the beginning of this season.

For now, attached are my sea trial numbers. Thank you for any thoughts or suggestions.

Topic

[Rob Schepis]

Was the vibration there since splash day or did it happen sometime during the season ?

[Tony Athens]

QSB 5.9 425's

ERic,

I kinda hesitate giving you this info, but it is what it is.. Plus, I really do not have an answer as to what the changes were to make a “measurable difference” in BSFC between the early & late versions other than maybe Cummins was still going thru a learning curve when they first “pumped up” the QSB 380 into a 420/425 and were in a hurry to compete in the HP race with the OEM demands put on them.

You have the early QSB420/425’s and both of yours came off the production line Aug 2006.. Not sure when your boat was actually put is service.

Anyway, the GPH per engine rarely matches the “test cell” curves other than at 100 % full load if you are making full RPM and loaded to 100%.. Running below 100% load but still making full WOT governor break-point RPM ( 3060-ish) is OK and maybe good in many applications……….

As to vibration, that is a different issue– Maybe the prop was not seated properly on the taper on that side ( it is riding on the key) — More common than many think.. If the prop checks good, then this is something that needs to looks at by a competent prop installer…………..Typical “boatyard monkeys” have no clue even though they may say they have installed 100’s of them..

Tony

..

[Eric]

Sorry about that.

Port SN: 46647462
Starboard SN: 46652475

[Tony Athens]

QSB 5.9 425's

Post the serial #’s or CPL –There a two different QSB 5.9 425’s..

Tony

1 user thanked author for this post.

Eric

[Author]

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