{"product_id":"lewmar-559018-shear-pin-125tt-140tt-bow-thruster","title":"Lewmar 559018 Shear Pin for 125TT and 140TT Bow Thrusters","description":"\u003cp class=\"nvn-hero\"\u003eThe Lewmar 559018 is the genuine brass shear pin for the 125TT and 140TT bow thrusters. It's the small sacrificial part that breaks on purpose when your prop hits debris, so the shock never reaches your gearbox or motor. A cheap pin does its job so the expensive drivetrain doesn't have to. Keep a couple aboard.\u003c\/p\u003e\n\n\u003cdiv class=\"nvn-description\"\u003e\n\u003cp\u003eA shear pin is one of those parts nobody thinks about until it lets go. On the Lewmar 125TT and 140TT tunnel thrusters, the 559018 sits between the drive and the propeller. Under normal use it passes all the torque the motor makes straight through to the prop. But the moment that prop jams, on a stray dock line, a wad of kelp, or a log drifting through the tunnel, the pin shears clean instead of letting that shock load travel back into the gearbox. That's the whole point. A cheap pin breaks so a much costlier drivetrain doesn't.\u003c\/p\u003e\n\u003cp\u003eLewmar makes this one from brass, in the 4 by 20 mm size the 125TT and 140TT are built around. The material matters more than it looks. Brass shears at a predictable load, and that's exactly what you want in a sacrificial part. Fit an undersized or wrong-alloy pin and one of two things happens. Either it snaps under normal docking load and leaves you with no thruster right when you need it, or it's too strong and the shock passes straight through to the gears instead. Both are bad days. This is the genuine Lewmar part, cut to the spec the thruster was designed around.\u003c\/p\u003e\n\u003cp\u003eHow do you know a pin has gone? The motor still spins, and you'll hear it working, but there's little or no thrust at the bow. No push, or just a weak wobble of water at the tunnel mouth. That's the classic sheared-pin signature. Before you start suspecting the motor or the wiring, check the pin. Nine times out of ten on these units, a sudden loss of thrust with a healthy-sounding motor is the shear pin, not the expensive stuff behind it.\u003c\/p\u003e\n\u003cp\u003eYou'll find these thrusters on a lot of 35 to 45 foot cruising sailboats and midsize powerboats, the kind of boats where a bow thruster turns a nerve-wracking crosswind docking into a non-event. If you run coastal water with floating debris, or you single-hand and lean on the thruster a lot, you're a candidate for the occasional sheared pin. It isn't a defect. It's the system doing its job. The 559018 covers both the 125TT and the 140TT, so you don't have to sort out which unit you've got before you order. Same pin, same fit.\u003c\/p\u003e\n\u003cp\u003eReplacing one isn't complicated, but it does mean getting to the prop. On the 140TT that means pulling the propeller off the shaft, which usually happens with the boat hauled or, on some installs, from inside the tunnel. Slide the old pin out, line the new one up so it indexes with the drive, and reseat the prop. Orientation counts. If the pin isn't seated square to the shaft the drive won't engage cleanly, and you'll be back in the tunnel wondering why the thruster hums but won't push. A light film of waterproof grease helps fight the corrosion that seizes hardware in saltwater, just keep it off the gearbox internals.\u003c\/p\u003e\n\u003cp\u003eA word on the fix-it-forever temptation. Some owners try to fabricate their own pin or fit a harder one to stop the breakage for good. We don't recommend it. The pin is meant to fail at a set load, and that failure is what protects the drive. Defeat it and you're betting a cheap part against an expensive gearbox, and the gearbox loses.\u003c\/p\u003e\n\u003cp\u003eHere's the honest advice we give every thruster owner. Buy more than one. A single sheared pin can strand your bow control at the worst possible moment, and these are inexpensive. Two or three in the spares kit means a quick fix instead of a ruined docking. Keep them aboard alongside your spare impeller and fuses. The day you back into a slip in a stiff beam wind and feel the thruster go soft, you'll be glad the fix is already sitting in the locker.\u003c\/p\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eKey Features\u003c\/h2\u003e\n\u003cul class=\"nvn-features\"\u003e\n  \u003cli\u003eGenuine Lewmar 559018 shear pin sized for the 125TT and 140TT bow thrusters\u003c\/li\u003e\n  \u003cli\u003eBrass construction shears at a predictable load to protect the thruster drivetrain\u003c\/li\u003e\n  \u003cli\u003e4 x 20 mm dimensions matched to the factory drive specification\u003c\/li\u003e\n  \u003cli\u003eSacrificial design: the pin fails before shock loads reach the gearbox or motor\u003c\/li\u003e\n  \u003cli\u003eFits both the 125TT and 140TT tunnel thrusters, one part covers both units\u003c\/li\u003e\n  \u003cli\u003eDirect drop-in replacement, no modification to the thruster required\u003c\/li\u003e\n  \u003cli\u003eInexpensive insurance for a far costlier bow thruster drive assembly\u003c\/li\u003e\n  \u003cli\u003eIdeal spare to keep aboard for coastal and debris-prone waters\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cdiv class=\"nvn-trust\"\u003e\n  \u003ch2\u003eWhy Buy from NVN Marine\u003c\/h2\u003e\n  \u003cul\u003e\n    \u003cli\u003eAuthorized Lewmar reseller, full manufacturer warranty\u003c\/li\u003e\n    \u003cli\u003eNMEA member and ABYC certified, advice from real boat techs\u003c\/li\u003e\n    \u003cli\u003eSame-day shipping before 3 PM ET on in-stock items\u003c\/li\u003e\n    \u003cli\u003eNY headquarters and Fort Lauderdale flagship retail store\u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003cdiv class=\"nvn-faq\"\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat does the Lewmar 559018 shear pin do?\u003c\/summary\u003e\n    \u003cp\u003eIt's a sacrificial part. Under normal use it transmits the motor's torque to the propeller, but if the prop jams on debris the pin shears cleanly. That protects the far more expensive thruster gearbox and motor from the shock load.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhich thrusters does the 559018 fit?\u003c\/summary\u003e\n    \u003cp\u003eIt fits the Lewmar 125TT and 140TT tunnel bow thrusters. One pin covers both units, so you don't have to sort out which model you have before ordering.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat is the pin made of and what size is it?\u003c\/summary\u003e\n    \u003cp\u003eIt's brass, in the 4 by 20 mm size the 125TT and 140TT are designed around. Brass shears at a predictable load, which is exactly what a sacrificial part needs to do.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhy did my shear pin break?\u003c\/summary\u003e\n    \u003cp\u003eThat's the pin doing its job. It shears when the propeller hits something it can't push through, like a line, kelp, or floating debris. A sudden loss of thrust while the motor still sounds healthy is the classic sign of a sheared pin.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eHow many spares should I keep aboard?\u003c\/summary\u003e\n    \u003cp\u003eWe recommend two or three. A single sheared pin can leave you without bow control at the worst moment, and they're inexpensive. Keep them in your spares kit alongside the impeller and fuses.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eIs it hard to replace?\u003c\/summary\u003e\n    \u003cp\u003eIt's not complicated, but you do have to get to the prop. On the 140TT that usually means pulling the propeller off the shaft, often with the boat hauled or from inside the tunnel. Slide the old pin out, index the new one with the drive, and reseat the prop.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eDoes orientation matter during install?\u003c\/summary\u003e\n    \u003cp\u003eYes. The pin has to seat square to the shaft so it indexes with the drive. If it's not aligned, the thruster motor will hum but the prop won't engage and you'll get no thrust.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eShould I grease the pin when I install it?\u003c\/summary\u003e\n    \u003cp\u003eA light film of waterproof grease helps fight the corrosion that seizes hardware in saltwater. Just keep it off the gearbox internals.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eCan I use a homemade or harder pin instead?\u003c\/summary\u003e\n    \u003cp\u003eWe don't recommend it. The pin is engineered to fail at a set load, and that failure is what saves the gearbox. Fit something stronger and the shock passes straight through to the gears instead, which is a much costlier repair.\u003c\/p\u003e\n  \u003c\/details\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003ctable class=\"nvn-specs\"\u003e\n  \u003ctbody\u003e\n    \u003ctr\u003e\n\u003cth\u003eTitle\u003c\/th\u003e\n\u003ctd\u003eLewmar 559018 Shear Pin for 125TT and 140TT\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eBrand\u003c\/th\u003e\n\u003ctd\u003eLewmar\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eManufacturer Part Number\u003c\/th\u003e\n\u003ctd\u003e559018\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eUPC\u003c\/th\u003e\n\u003ctd\u003e743683010705\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003ePart Type\u003c\/th\u003e\n\u003ctd\u003eShear Pin (Drive Pin)\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eMaterial\u003c\/th\u003e\n\u003ctd\u003eBrass\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003ePin Size\u003c\/th\u003e\n\u003ctd\u003e4 x 20 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eCompatible Thrusters\u003c\/th\u003e\n\u003ctd\u003eLewmar 125TT and 140TT\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eThruster Type\u003c\/th\u003e\n\u003ctd\u003eTunnel Bow Thruster\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eFunction\u003c\/th\u003e\n\u003ctd\u003eSacrificial drivetrain protection\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eApplication\u003c\/th\u003e\n\u003ctd\u003eBow Thruster Drive\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eProduct Type\u003c\/th\u003e\n\u003ctd\u003eBow Thruster Parts\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003cscript type=\"application\/ld+json\"\u003e\n{\n    \"@context\": \"https:\/\/schema.org\",\n    \"@type\": \"FAQPage\",\n    \"mainEntity\": [\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What does the Lewmar 559018 shear pin do?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"It's a sacrificial part. Under normal use it transmits the motor's torque to the propeller, but if the prop jams on debris the pin shears cleanly. That protects the far more expensive thruster gearbox and motor from the shock load.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Which thrusters does the 559018 fit?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"It fits the Lewmar 125TT and 140TT tunnel bow thrusters. One pin covers both units, so you don't have to sort out which model you have before ordering.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What is the pin made of and what size is it?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"It's brass, in the 4 by 20 mm size the 125TT and 140TT are designed around. Brass shears at a predictable load, which is exactly what a sacrificial part needs to do.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Why did my shear pin break?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"That's the pin doing its job. It shears when the propeller hits something it can't push through, like a line, kelp, or floating debris. A sudden loss of thrust while the motor still sounds healthy is the classic sign of a sheared pin.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"How many spares should I keep aboard?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"We recommend two or three. A single sheared pin can leave you without bow control at the worst moment, and they're inexpensive. Keep them in your spares kit alongside the impeller and fuses.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Is it hard to replace?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"It's not complicated, but you do have to get to the prop. On the 140TT that usually means pulling the propeller off the shaft, often with the boat hauled or from inside the tunnel. Slide the old pin out, index the new one with the drive, and reseat the prop.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Does orientation matter during install?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Yes. The pin has to seat square to the shaft so it indexes with the drive. If it's not aligned, the thruster motor will hum but the prop won't engage and you'll get no thrust.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Should I grease the pin when I install it?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"A light film of waterproof grease helps fight the corrosion that seizes hardware in saltwater. Just keep it off the gearbox internals.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Can I use a homemade or harder pin instead?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"We don't recommend it. The pin is engineered to fail at a set load, and that failure is what saves the gearbox. Fit something stronger and the shock passes straight through to the gears instead, which is a much costlier repair.\"\n            }\n        }\n    ]\n}\n\u003c\/script\u003e\n","brand":"Lewmar","offers":[{"title":"Default Title","offer_id":44785933254749,"sku":"1004633","price":17.79,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0299\/7266\/0317\/files\/LEW559018_001.jpg?v=1784943421","url":"https:\/\/nvnmarine.com\/products\/lewmar-559018-shear-pin-125tt-140tt-bow-thruster","provider":"NVN Marine","version":"1.0","type":"link"}