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No Shear Pin on 2009 Merc 9.9 4-stroke?

T

troutguy

New member
I have never before owned a small fishing motor that didn't have a shear pin for the propeller, but I cant find one under the parts listing for this 2009 9.9 Merc 4-stroke. How does that work, and are there any things I should know about for check if I hit some submerged object?
 
Hmmm - you must have had some old small outboards :)

Since at least the mid-1980's the major mfgs (Merc, OMC, Yami etc) have been using a "splined" hub on the prop and a nut/washer to keep it fastened to the splines.

On these (new) models they have a clutch dog that is designed to "slip" if you ground the prop where the shear pin would sacrifice on their predecessors in an attempt to save the gears from damage..
 
You"re right, I've owned several old (probably 1970s) outboards, 4 hp and less, could be called "second hand Bob". But thanks for the info, this solves the problem of having to get out of the boat and position it so I can reach the propeller from the bank. And sometimes there's no bank to get out onto.
 
galamb said:
Hmmm - you must have had some old small outboards :)

Since at least the mid-1980's the major mfgs (Merc, OMC, Yami etc) have been using a "splined" hub on the prop and a nut/washer to keep it fastened to the splines.

On these (new) models they have a clutch dog that is designed to "slip" if you ground the prop where the shear pin would sacrifice on their predecessors in an attempt to save the gears from damage..
Click to expand...

Curious about the "clutch dog designed to slip" comment. The only clutch dog I am aware of is spring loaded, locked to the prop shaft internally and is used for shifting. It contains an overrun clutch for F gear (ratchet if you will) which allows the engine speed to be less than the prop speed, primarily used when decelerating, just like the over run clutches used on farm tractors with transmission driven PTOs and implements like a brush hog mower.

I know now-a-days props have removable insert props with plastic and brass and a lot of talk about how they operate, but I grew up with the rubber hub that would slip upon impact and once clear, with the engine reduced to idle, possible shifting to N, the rubber would reunite with the prop hub and you had your power back just as if nothing happened. The shear pin on older units was just as you said replaced with a spline that doesn't snap and leave you helpless like the pin did......windward side of rip rap, wind blowing you onto the rocks, need to get out of harm's way and oh !@##$$% the pin shears. Never again for me. One reason I left OMC and went with Merc.

Mark
 
Yes, the clutch dog is pinned to propshaft. When you shift gears the propshaft itself moves laterally and it's the (ears) of the clutch dog that engages your forward or reverse gears (which are both simultaneously turned by the pinion gear) to turn the propshaft.

Those ears will sacrifice somewhat quicker than will the fwd/rev gears themselves (usually a gear issue on an older motor that has never hit bottom will be a worn clutch dog from "granny shifting").

So yes, agree that it's primarily the prop hub (in whatever configuration - rubber sleeve, torsion bars etc) that provide protection to the gears (which I failed to mention above), but the clutch dog is the second line of defense before your gears bite the bullet. You will round off/destroy the ears on the dog and she will slip (and a 30'ish dollar dog beats a 300'ish dollar set of matched pinion/fwd gears) :)
 
galamb said:
Yes, the clutch dog is pinned to propshaft. When you shift gears the propshaft itself moves laterally and it's the (ears) of the clutch dog that engages your forward or reverse gears (which are both simultaneously turned by the pinion gear) to turn the propshaft.

Those ears will sacrifice somewhat quicker than will the fwd/rev gears themselves (usually a gear issue on an older motor that has never hit bottom will be a worn clutch dog from "granny shifting").

So yes, agree that it's primarily the prop hub (in whatever configuration - rubber sleeve, torsion bars etc) that provide protection to the gears (which I failed to mention above), but the clutch dog is the second line of defense before your gears bite the bullet. You will round off/destroy the ears on the dog and she will slip (and a 30'ish dollar dog beats a 300'ish dollar set of matched pinion/fwd gears) :)
Click to expand...

Hear you on the back up protection.

Years ago I was restoring a badly deteriorated Starcraft 18' Holiday I/O, 110 Mercruiser 4 banger, tilt, no trim, 1965 model and this was the late 80's. It had spent a good deal of it's life in Lake Dallas and probably half of that semi-submerged. It's what happens when you get your mindset on something and common sense flies out the window. Won't do it again I assure you.

"Anyhew" when I was working over the lower unit the interface of the dog and the rear of both the F and R gears had really rounded edges from shifting over the years. I was raising 4 kids at the time, trying to completely restore this sucker, down to the bare hull, engine and outdrive, the whole shebang on a shoe string budget.
So I take the gears to a machine shop thinking I could get them to square off the corners rather than having to buy new gears which I didn't know where I'd find them if I could afford them.

I made my proposition to the shop foreman as to what I wanted to do and he laughed in my face. Ha he said, I'd have to de-temper those gears before I had any chance of milling on them and then I wouldn't be sure I could get them back to their correct number when finished. I went with what I had and lived with the sloppy shifting.

Course probably the weak link in the dog would be the SS pin that moves the dog back and forth. That would probably be what would shear first. But I don't know.

Nice chatting,

Mark
 
I completely understand what you are saying there. I find myself, quite often, diving far too deep into a problem. I wonder if I have rebuilt a carb that could have been "fixed" with simple replacement gasket.

Like the issue of this thread - totally stepped over the prop hub (because that's just common sense, right?) and thought immediately of the "downstream" parts.

Have to remember that sometimes a crappy running motor really is because the sparkplugs are 3 years old - don't need to crack the shop manual and grab the tool box :)
 
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