No sheer pin on Johnsons?

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Phil
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No sheer pin on Johnsons?

Post by Phil » 04 Jul 2018, 17:53

I’ve been meaning to buy some replacement sheer pins for my outboard to have on the F-RIB. My understanding was that was that OB motors sheer a pin if the prop hits something to protect the impact damaging the engine’s innards, but that this could leave you stranded with a prop that won’t spin.

I was thinking that the sheer pin was the same as the split pin labelled D in the below pic (called a cotter pin in the manual), however, I’ve realised that this part doesn’t work that way. Sheer pins lock the propeller in from the inside and it doesn’t seem that my Johnson has one.

Am I right in saying that Johnson OBs therefore don’t have anything that will sheer that I should keep a spare of onboard for if the prop knocks in to something? Any help would be very much appreciated.

Cheers,

Phil
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chris moody
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Re: No sheer pin on Johnsons?

Post by chris moody » 04 Jul 2018, 19:22

No shear pin. The props usually have a rubber bush internally that will break on a really hard strike, but usually the prop blades just bend or snap. If you hit something it's bye bye prop. You could carry a spare prop but not many people do.
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Phil (04 Jul 2018, 20:03)
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Phil
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Re: No sheer pin on Johnsons?

Post by Phil » 04 Jul 2018, 20:06

chris moody wrote:
04 Jul 2018, 19:22
No shear pin. The props usually have a rubber bush internally that will break on a really hard strike, but usually the prop blades just bend or snap. If you hit something it's bye bye prop. You could carry a spare prop but not many people do.
Nice one, thanks Chris. I was mainly worried that there might be a weak link pin that could shear on a light knock and leave me stranded on the water.

Good to know the set-up is a more robust on my outboard. Many thanks :thumbsup
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Re: No sheer pin on Johnsons?

Post by James » 04 Jul 2018, 22:34

Your good mate, thats how it's suppose to be.
I've taken my prop off enough times to remember.

This is why I won't get a stainless prop. Hit that, bye bye gear box.
James

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Re: No sheer pin on Johnsons?

Post by PeterM » 05 Jul 2018, 18:39

Usually only the small ob... without the through prop exhaust will have a pin that shears. Did one on my 3.5 Johnson and Suzuki..... a tiny fink and they went

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Re: No sheer pin on Johnsons?

Post by nala » 07 Jul 2018, 12:33

Shear pins are mainly fitted on smaller O/B as to machine a splined shaft wouldnt be practical.
Also your most likely to use a smaller O/B in shallower depths where it would cost you a prop every time.
So the sacrificial pin does its job , so it's good to have spares and split pins.
The larger O/B 's have more torque so a splined bigger diameter shaft is required to deal with it.
As the prop's have a rubber mounting built in to the hub, which act like a transmission noise silencer .
When this impacts the seabed it causes the rubber shear from its bonding to avoid engine,gearbox and shaft damage.
And limits further damage to prop as there's a good chance it could be repaired ?
A lot of the modern props have a separate hub which is torqued via the locking shaft castleated nut.
This compresses the rubber hub mounting forcing it onto there inner gripping it as if it were glue bonded .
These are a separate item to the prop £££ .
To avoid dinking your prop get to know the vessels draught , the seabed via sounder and paper chart.
If you venture where you can see the seaweed floating just on the surface, stop engine and use paddles to go
in. If you don't you may have enough draught, but the prop will pick up the weed along with the rock it's attached to :O !
This'll wedge into the prop and jam up against the cav plate and stop the engine.
Just hope and pray that nothing else is damaged.
Unusual vibration from engine after accelerating could mean the prop may have a bent blade(s)
Very much like an imbalanced wheel/tyre on your car.
Hope this shine's some light and helps in avoiding damaging your engine as well as the prop.
Stay Safe on the water :)
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Phil (27 Jul 2018, 13:54)

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Phil
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Posts: 222
Joined: 30 Apr 2017, 14:54
Boat Make: F-RIB 360
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Re: No sheer pin on Johnsons?

Post by Phil » 27 Jul 2018, 13:55

nala wrote:
07 Jul 2018, 12:33
Shear pins are mainly fitted on smaller O/B as to machine a splined shaft wouldnt be practical.
Also your most likely to use a smaller O/B in shallower depths where it would cost you a prop every time.
So the sacrificial pin does its job , so it's good to have spares and split pins.
The larger O/B 's have more torque so a splined bigger diameter shaft is required to deal with it.
As the prop's have a rubber mounting built in to the hub, which act like a transmission noise silencer .
When this impacts the seabed it causes the rubber shear from its bonding to avoid engine,gearbox and shaft damage.
And limits further damage to prop as there's a good chance it could be repaired ?
A lot of the modern props have a separate hub which is torqued via the locking shaft castleated nut.
This compresses the rubber hub mounting forcing it onto there inner gripping it as if it were glue bonded .
These are a separate item to the prop £££ .
To avoid dinking your prop get to know the vessels draught , the seabed via sounder and paper chart.
If you venture where you can see the seaweed floating just on the surface, stop engine and use paddles to go
in. If you don't you may have enough draught, but the prop will pick up the weed along with the rock it's attached to :O !
This'll wedge into the prop and jam up against the cav plate and stop the engine.
Just hope and pray that nothing else is damaged.
Unusual vibration from engine after accelerating could mean the prop may have a bent blade(s)
Very much like an imbalanced wheel/tyre on your car.
Hope this shine's some light and helps in avoiding damaging your engine as well as the prop.
Stay Safe on the water :)
Many thanks for the detailed info Nala :thumbsup. And sorry for my delay in reply!

Cheers,

Phil
F-RIB 360 with F-RIB wheels, seat cushions and bag and Scotty rod rests
15hp 1992 Johnson GT 10 2-stroke

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Re: No sheer pin on Johnsons?

Post by Alan » 31 Jul 2018, 19:37

Back in the early 80's I had a 6hp Chrysler outboard with the rubber bushing and a stainless steal prop on a small boat. I hit a rock and had the pleasure of replacing every gear in Lower Unit and the drive shaft that winter. While not the end of the world but not an experience I would like to repeat.

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