Sierra NEW 18-2959 Cylinder Head Gasket Replaces: 306048 V4 75-115 HP 60-72 0810

Sierra Marine Cylinder Head Gasket — Part Number 18-2959

Brand: Sierra | Condition: New Old Stock (NOS)

Genuine Sierra Marine part number 18-2959, a cylinder head gasket for the Johnson and Evinrude V4 outboards of the 1960s and early 1970s — the 75, 80, 90, 100 and 115 horsepower cross-flow V4s. It replaces OMC part number 306048. This is new old stock from long-term inventory, a genuine Sierra component carrying Sierra's Limited Lifetime Warranty.

Important: a V4 takes two of these. The engine has two cylinder heads, and the correct order quantity is two per motor. If you are doing a top-end job on one of these V4s, you need a pair.

The head gasket is the part everything else on a powerhead rebuild depends on. It seals combustion pressure in the cylinders and cooling water out of them, at the same joint, through every heat cycle the motor will ever see. On these older OMC V4s the classic failure is a breach between cylinder and water jacket — compression bleeding into the cooling passages, water finding its way into the cylinder, and a motor that runs hot and won't make power on one bank. A head gasket is also unambiguously single-use: once torqued it has crushed to its final thickness and cannot be reused, which is why a new one is the only correct way to put a head back on.

Condition Details

New old stock. The gasket is unused and has never been installed or torqued. As with all warehouse-stored inventory, the packaging may show shelf wear, dust, fading, price stickers, scuffs or minor crushing from stacking. The gasket itself is flat, uncreased and undamaged, with clean sealing faces, intact fire rings and water passage openings, and no tearing, delamination or compression set from storage. Please review all photos, as what is pictured is what you will receive.

Specifications

• Part Number: 18-2959
• Part Name: Cylinder head gasket
• Manufacturer: Sierra Marine
• Engine Configuration: V4 cross-flow, Johnson / Evinrude
• Location: between the cylinder head and the cylinder block
• Quantity required: 2 per engine — one per cylinder head
• Warranty: Sierra Limited Lifetime Warranty against defects in materials and workmanship
• Sold: see listing quantity
• Aftermarket replacement, engineered to meet or exceed OEM specification

Gasket overall dimensions, bore size, bolt-hole pattern and thickness are not published in the catalogue data available for this number and are deliberately not stated here rather than guessed. If you need these confirmed before you buy, message us and we will measure the actual gasket and send you the figures.

Superseded & Cross Reference Part Numbers

Sierra 18-2959 interchanges with the following. Always confirm against your own application guide before ordering.

• Sierra Marine: 18-2959
• OMC / Johnson / Evinrude: 306048
• GLM Products: 34030

Do not confuse this with the later V4 head gasket. OMC used a different head gasket on the V4s from 1973 onward:

If your motor is a 1973 or later V4, you want 18-2956 / 318358, not this gasket. If it is 1972 or earlier, this is the one.

Features

• Sierra Marine quality, engineered to meet or exceed the original OMC specification — Sierra has supplied marine replacement parts for over fifty years
• Sierra Limited Lifetime Warranty against defects in materials and workmanship, which is more coverage than an original OMC part carries
• Seals combustion pressure in the cylinders and cooling water out of them, at the most critical joint on the powerhead
• Correct compressed thickness, which sets the final squish and combustion chamber volume
• Intact fire rings and correctly sized water passages, so cooling flow is unrestricted and the seal holds at the bore
• Flat, uncreased, never-torqued stock that crushes to its design thickness on first installation
• Cures the cylinder-to-water-jacket breach that is the classic failure on these older V4 powerheads
• Single-use by design — reusing a torqued head gasket is how a rebuild fails the first time it is run
• Covers a wide span of the early OMC V4 range on one part number

Application

Fits Johnson and Evinrude V4 outboard motors:

• 75 HP — 1960 through 1965
• 80 HP — 1966 through 1967
• 90 HP — 1964 through 1965
• 100 HP — 1966 through 1972
• 115 HP — 1969 through 1970

One retailer additionally lists 85 HP (1968–1972 and 1979) under this number. That does not appear in the specialist OMC head gasket references we checked, so we are reporting it but flagging it as unconfirmed — if you have an 85 HP, message us with your model and year and we will check it properly before you buy.

Remember: order two per engine. These are two-head V4 powerheads.

Because OMC ran several head gasket variants across the V4 family, buyers should confirm 18-2959 or OMC 306048 against the exploded cylinder head diagram for their specific model and year before ordering. If you send us your model number and year we will check it against the parts catalogue for you. On a head gasket it is worth the two minutes, because fitting the wrong one means the heads come off again.

Why Choose Sierra?

Sierra Marine has produced marine engine and drive replacement parts for over fifty years, engineered to meet or exceed the specifications of the original engine manufacturers, and supplies both the aftermarket and OEM channels. Sierra's catalogue is one of the most comprehensive and best cross-referenced in the marine industry, and Sierra parts are backed by a Limited Lifetime Warranty. On gaskets for motors whose manufacturer no longer exists, Sierra is frequently the only source still producing to the original specification — and in many cases Sierra stock has outlasted the OMC originals entirely.

Returns

We accept returns through eBay's standard 30-day return request process. If the part is not what you need, simply open a return request through eBay within 30 days of delivery and we will take care of it.

Thank you for looking. We are a small parts business and we take real care in identifying, describing and packing every item we list. If anything about this part is unclear, or if you want additional photos or measurements before you buy, please message us — we would much rather answer a question up front than have you receive something that is not right for your machine.

If there is any problem at all with your order, please contact us first and give us the chance to make it right before leaving feedback. We respond quickly and we will resolve it.

QBS Parts, Inc — Gardena, CA