shear pin keeps breaking

[chrisbitz]

I have a 3.3 mariner, and the shear pin on the prop has broken twice in 3 weekends.

is it really likely that i've hit something submerged in the medway, or is there another reason why a shearpin would shear?

How often do they break, an what else could cause it to break?

 

[sailorman]

I have a 3.3 mariner, and the shear pin on the prop has broken twice in 3 weekends.

is it really likely that i've hit something submerged in the medway, or is there another reason why a shearpin would shear?

How often do they break, an what else could cause it to break?

You must be hitting some thing, have you inspected the plastic prop for damage

 

[Norman_E]

Generally they will only break if the prop hits something, but if the prop is a very loose fit on the shaft you may break them because of that. Do not be tempted to drill things out and fit a bigger pin, or change the pin to a stronger one. It is a deliberate weak link to prevent much more expensive damage to the prop or the gears.

 

[Rigger Mortice]

I had the same problem with my engine (also a 3.3 mariner) when I first got it. The OEM pin was far too delicate and even a bit of weed would break it. I replaced it with a stainless steel pin and have had no problems since I did so about 8 years ago.

 

[jdc]

they just do!

I have a 3.3 mariner, and the shear pin on the prop has broken twice in 3 weekends.

is it really likely that i've hit something submerged in the medway, or is there another reason why a shearpin would shear?

How often do they break, an what else could cause it to break?

They just do: if you put it into forward gear it will shear the pin unless you're completely at idle. Solution is to replace the shear pin - which as supplied is a bronze colour - with a new one from a chandler's unbranded stand (the one which has sundry overpriced stuff in small packs, eg 4 self tappers in a pack for £2.50, on a whirlygig).

These unbranded ones are stainless colour, not that I'm sure what they're made of, and don't shear so pathetically easily. I broke several genuine parts without striking anything when I first had the engine, but since I put in the non-genuine part 7 years ago I never broke it again - nor damaged the prop.

EDIT: Rigger Mortice just beat me to it!

 

[toad]

Buy a length of brass rod from a model shop and make your own or buy stainless pins from a chandler. The problem is mainly on the 3.3hp with forward gears with the tick over speed to high or putting it into gear before the revs have slowed down.

 

[chrisbitz]

I think you guys are right - I may have put it in gear without waiting for the revs... thank goodness I had a bundle of spare shear pins onboard too! And they're the stainless colour..

 

[rob2]

IIRC the brass pins are for use with the plastic prop and the stainless with the metal one so that the prop is always stronger than the shear pin. One of my friends at the sailing club breaks pins regularly (cuts his own from brass now) and the prop hub is a right mess! It's quite possible that wear or deformation of the prop allows movement before the pin takes up the drive, so it gets some momentum up and breaks the pin. Mind you, I'm as guilty as anyone of yanking it into gear at fast tickover when the engine hasn't yet warmed up! I suspect the real cure would involve a new prop unless you're willing to go to the stainless pin.

Rob.

 

[Skylark]

True story. I have a Tohatsu 2.5. Spent a pleasant evening ashore near the Gazelle in the Menai. I get in the dinghy alongside a pontoon and start the engine. My pal gets in and his weight pushes the prop to the seabed and the pins shears. No tools, no spares, 23h00 at night. Menai running like a train, it would be madness to row to the mooring. We decided to walk to Beaumaris, a good few miles, in the hope of finding a B&B for the night. Both of us dressed in sea boots and foul weather gear (it is Wales, afterall). Car stops, offers us a lift. We tell our plight so he takes us to his home, lets us rummage in his garage to make a pin and take a few tools, then he even drives us back to the slip way and trusts us to return the tools the following day. He wasn't a sailor, by the way.

What a great gesture, well worthy of a few bob contribution to RNLI, 'cos that's all he wanted.