Vibration when idling in gear?

[Weekiman]

0T932349
2004 Mercury 225 EFI two stroke
Mirage 48-19838 15P
5700
Idle water pressure 4.3 psi and WOT water pressure reading
I forget to get WOT reading but 5010 rpm was 12.2 psi
Analog gauges with Vessel View Mobile

I'm relatively new to boating and working on boat engines. One of my local Merc dealers said this may be normal. I noticed a vibration right after a prop change. The dealer said the engine may behave differently after the prop change. He didn't seem to concerned but I only spoke with him over the phone. He hasn't seen the boat. Same Mercury Mirage prop part # 48-18275 17P except I changed from a 17P to a 15P. My current prop is a Mirage 48-19838 15P. The prop may be relevant or not. It's just about the time I noticed the vibration. I plan on putting the old prop back on for testing. When idling in gear I feel what I describe as an out of balance condition in the deck or maybe a miss. I changed the lower unit lube and it was very clean. I also replaced the prop hub which I thought might have fixed the problem because the old one was very sloppy but no change. Boat idles normal, cruises normal, WOT as normal. Vibration is strong but gone after slight increase in speed.

Is this just the nature of the prop or should I pursue it further. I'll no more when I put the 17P prop back on.

[EuropeanAM]

What part number hub kit did you use (important- must be torqued correctly)?

If it does NOT do this in NEUTRAL, spin the prop and observe the dimple in the end of the propshaft. It should NOT be moving around (visibly)- if you can see it moving around, the shaft is bent.

[Weekiman]

What part number hub kit did you use (important- must be torqued correctly)?

If it does NOT do this in NEUTRAL, spin the prop and observe the dimple in the end of the propshaft. It should NOT be moving around (visibly)- if you can see it moving around, the shaft is bent.

Oh shoot I may have thrown the box out. What is the difference? A couple other things to add. The new hub had no effect. Same vibration before and after. Also there is no rhythm to the vibration. It's random. I checked and the shaft looks straight to me. I suppose there is a runout spec. I could always put an indicator on it. I'm going to swap back to the older prop first and see if the problem goes away. I'm thinking it all started with this new/used prop I bought on <Edit- See Announcements>. I'm still not sure I have a problem, but I haven't been around boats long enough to know any better.

Searching around I found this. I guess there is something called "prop rattle"

https://www.mercurymarine.com/en/us/.../?article_type[]=be-inspired

Mercury has also updated materials to address the issue of prop rattle, which can occur in some low-speed situations. Flo-Torq SSR is the quietest hub system ever offered by Mercury – up to 23% quieter than Flo-Torq II. Boat owners can install the new Flo-Torq SSR system in most Mercury prop models and enjoy an instant reduction in noise when shifting, as well as some peace of mind on shallow waters.

[EuropeanAM]

Yes- that would be why the question as to which hub kit you purchased.

I would switch back to the other one and confirm that you do (or do not) still have this vibration concern.

BTW... just a reminder that we do not support the "bay"- or any items purchased from the "bay" here in the forums.

[Weekiman]

Yes- that would be why the question as to which hub kit you purchased.

I would switch back to the other one and confirm that you do (or do not) still have this vibration concern.

BTW... just a reminder that we do not support the "bay"- or any items purchased from the "bay" here in the forums.

Understand on the rules. Thanks for the help!

[EuropeanAM]

Be sure to report back after you try the previous prop.

[Weekiman]

Be sure to report back after you try the previous prop.

I will, I'm planning on taking the boat out this coming Monday.

[Weekiman]

Be sure to report back after you try the previous prop.

Took the boat out two days ago after swapping back to the previous prop. The knock or vibration that I felt while idling in gear went away. I think it might just be inherent to the prop, and nothing is wrong with it. I'm not sure. It may still exist but at a much lesser degree, as in barely noticeable. It's a random knock so I don't believe it's an out of balance condition. I don't know what could be wrong with it? I'm new to boats and two strokes. Maybe it's the nature of the prop?

[JOE54]

when ideling in gear bump trim up just a touch see if it changes feel and sound

[Weekiman]

when ideling in gear bump trim up just a touch see if it changes feel and sound

Thanks I'll give it a shot. Maybe it's play in the drive knocking back and forth caused by the rough nature of the two stroke idle.

[JOE54]

some of the more solid composite transomes will transfer more vibs to the boat also , and some off brand props magnify clutch rattle also

[Weekiman]

some of the more solid composite transomes will transfer more vibs to the boat also , and some off brand props magnify clutch rattle also

It may just be rattle. I read that a Mercury SSR hub 8m0150151 might help, but Mercury notes say not for two stroke for some reason.

[EuropeanAM]

Won't hurt to use the CORRECT SSR Hub kit on your engine (though this has been a "debated" topic).

[Weekiman]

some of the more solid composite transomes will transfer more vibs to the boat also , and some off brand props magnify clutch rattle also

The transom on this boat is extremely solid all Composite construction with a Stainless Marine brand full length Aluminum engine bracket. The prop is aft approximately three feet from the transom. So maybe?

[Weekiman]

Won't hurt to use the CORRECT SSR Hub kit on your engine (though this has been a "debated" topic).

I'll have to do a search. I'm curious what the debate is.

[EuropeanAM]

Good luck- it's more of an engineering-level (calibration program) thing. Has to do with the shift interrupt strategies, and how the PCM reacts to reduce shift effort.

IMHO... unless you're running a very low pitch prop (19 pitch or below), it's very unlikely that you would ever have anything negative to report.

[Weekiman]

Good luck- it's more of an engineering-level (calibration program) thing. Has to do with the shift interrupt strategies, and how the PCM reacts to reduce shift effort.

IMHO... unless you're running a very low pitch prop (19 pitch or below), it's very unlikely that you would ever have anything negative to report.

Well I am running a 15 pitch. Negative it what sense?

[EuropeanAM]

The switch and slide geometry permit some lateral movement that trigger the switch "early in movement" where extra effort is being required.

A lower-pitch prop could reduce the amount of load and potentially cause some unusual shifting, since the hub is absorbing some of the forces involved.

That being said- it probably wouldn't keep me from using one on my own rig.

[Weekiman]

The switch and slide geometry permit some lateral movement that trigger the switch "early in movement" where extra effort is being required.

A lower-pitch prop could reduce the amount of load and potentially cause some unusual shifting, since the hub is absorbing some of the forces involved.

That being said- it probably wouldn't keep me from using one on my own rig.

Yea that's over my head, but I get the gist of it. Thanks as always for sharing your expertise.