spun hub?

[guywhofishes]

so it was as my first time out with the 2005 big white johnson last week

I’m crusing along at 30mph and I see my RPMs are 6500 rather than 5500. What???
I have had it propped so WOT was 5800 (33 MPH)

Do tachs ever “over report” RPMs? After 10 years of listening to that engine it didn’t seem higher than normal.

My only guess is a spun hub. Guess I’ll have to stamp the prop/hub and look for spin.

Any other thoughts/ideas?

 

[SLE]

If it's a standard old analog tach, then I'd say there could be a good chance the tach reading is off. There may be an adjustment dial on the back of the tach that will switch between 4/6/8 cylinder engines. If your's has that dial/adjuster, take and turn it back and forth a dozen times or so. This will help clean up the contact point, just make sure you set it to it's original position when you done. This trick may work for a while but this is usually and indication that the tach is on it's way out and it may be time for a new one.

 

[sweeney]

i have had mine read high on my boat when running before, I gave the tach itself a quick love tap and the rpm jumped back down 800, guessing a bad connection somewhere along the line.

 

[Captain Ahab]

That stallion just wants to run again! Seriously, if you didn't notice it by ear after all these years it's probably the tach or a trip to the Miracle Ear center

 

[Davy Crockett]

Tachs lie and need to be kept honest with calibration. If you remember what RPM it used to idle with the muffs you could try that and see if it's changed . My old boat seemed like it idled rough and it would sometimes die when I put it in gear if I wasn't quick to give it throttle so I hooked up the tach from my tool box and the dash tach was reading 600 when actual RPMs were around 400. Turned the screw on the back for calibration.

 

[Allen]

I could be wrong, but I think once you "spin" your hub, you'll pretty much be left stranded as your boat revs like she's in neutral.

So tachometer it is.

 

[guywhofishes]

upon researching I’ve read a lot of threads where spin behavior was “partial” believe it or not, you have to stamp hub and prop and see if it moves to confirm slippage

seems goofy to me too but prop stores have videos on stamping/diagnosing

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[Allen]

Damn, I would have thought for sure that once spun she's done.

 

[JayKay]

I could be wrong, but I think once you "spin" your hub, you'll pretty much be left stranded as your boat revs like she's in neutral.

So tachometer it is.

Agreed. Sometimes with a spun hub, the prop is gone. All that's left is the hub.

Okay, 30 seconds later, I stand corrected.

 

[guywhofishes]

ha ha - I know right? strange

 

[Davy Crockett]

This is good to know , I'm surprised manufactures don't put line up marks on them at the factory.

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On second thought I suppose if you nicked a stump that didn't cause damage it would throw the marks off.

 

[eyexer]

I think you'd easily hear 1000 rpm difference. I would bet your tach took a shit.

 

[ccarver80]

My tach is doing something similar... Only I know it's the tach cuz when ideling it will randomly jump between 1000-3000 rpms... It's like it flickers in and out....

 

[guywhofishes]

mine was following smoothly up/down - just off quite high by a factor of some percentage

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I wiped the pole selector so we’ll see what happens

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thanks guys

 

[eyexer]

mine was following smoothly up/down - just off quite high by a factor of some percentage

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I wiped the pole selector so we’ll see what happens

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thanks guys

"wiped the pole selector" LOL. easy now

 

[guywhofishes]

gol dangit - I paused and analyzed that comment and thought "nobody can twist that against me"

I was wrong