Lower Unit Drain Plug Seals

**97mirage** · 03-23-2023, 06:58 PM

On Mercury engines, what are the small seals on the lower unit’s drain plug and vent screw made of? Are they cardboard (which makes no sense) or some kind of rubber or what material? Thanks for any response.

**WaterZebra** · 03-23-2023, 07:30 PM

Originally Posted by 97mirage

On Mercury engines, what are the small seals on the lower unit’s drain plug and vent screw made of? Are they cardboard (which makes no sense) or some kind of rubber or what material? Thanks for any response.

Gasket material

**97mirage** · 03-23-2023, 07:40 PM

WTF does that mean, Zebra? What kind of gasket material? There’s plastic, metal, cork, rubber, reinforced, unreinforced, etc. I need to understand the material composition. If you don’t know, don’t reply.

**25two.stroke** · 03-23-2023, 08:01 PM

Originally Posted by 97mirage

WTF does that mean, Zebra? What kind of gasket material? There’s plastic, metal, cork, rubber, reinforced, unreinforced, etc. I need to understand the material composition. If you don’t know, don’t reply.

Figuring that mercury has used 4 or more types of gasket material for said drain plug seals over the years its hard to answer your question. You needing to know exactly what it is is even more confusing.

What are you up to?

The cheapest black gaskets on the oil drain screws are un-reinforced fiber. Just basic ass gasket material you would buy in bulk at the hardware store. The most expensive seals, on the other hand, are rubber coated metal. The soft metal core is similar to the compressive metal used on 4stroke oil drain screws (not sure but I think its aluminum cause it is not magnetic). The coating on the outside of the metal is rubber.

**25two.stroke** · 03-23-2023, 08:05 PM

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**Jim Speros** · 03-23-2023, 08:34 PM

There was even an o ring for a short while. Mercury used a blue gasket for years. Sierra and other aftermarket had the worst gaskets IMO grey or black.

**97mirage** · 03-23-2023, 08:36 PM

The OEM vent screw hole stripped. Because of its location right next to the shaft, I was reluctant to open the hole slightly to install a helicoil. So I abandoned (filled with liquid weld) the original vent screw hole and retapped a new one nearby. The helicoil and stainless screw that comprise my “new vent” work great, but I need to fabricate a seal for my screw. So, I want to choose the “best” gasket media to fabricate my seal, hoping to use the same media as on OEM vent screw seals. That’s why I asked this question. Maybe someone can just tell me what a good gasket material is for this application and that’s what I’ll use. Thanks for helping me, 25twostroke!

**Jim Speros** · 03-23-2023, 08:40 PM

I like the yellow Merc gaskets best. However the aftermarket nylon? Clear hard plastic something may work well in your case. IMCO uses them. I believe at some point OMC did too.

**97mirage** · 03-24-2023, 06:31 AM

Thank you for your response, Jim Speros.

**XstreamVking** · 03-24-2023, 07:45 AM

Make your own with some viton rubber sheet to resist oil.

**WaterZebra** · 03-24-2023, 09:00 AM

Originally Posted by 97mirage

WTF does that mean, Zebra? What kind of gasket material? There’s plastic, metal, cork, rubber, reinforced, unreinforced, etc. I need to understand the material composition. If you don’t know, don’t reply.

Next time be more articulate in your question and you will get the same level answer. By the way, good luck with JB weld, a aluminum gearcase and hypoid gear oil. Over time, it will seep like a wounded critter. F moron.

**97mirage** · 03-24-2023, 02:36 PM

Yes…thank you. All good points. I will certainly keep my articulation for future posts in mind. In the interim, maybe you should consider working on your knowledge of the English language. The article “a” is used before words that begin with a consonant and the article “an” is used before words that begin with a vowel. So your kind response should have said “an aluminum gearcase” versus “a aluminum gearcase”. And you call me a moron…?

**25two.stroke** · 03-24-2023, 06:15 PM

Originally Posted by 97mirage

Yes…thank you. All good points. I will certainly keep my articulation for future posts in mind. In the interim, maybe you should consider working on your knowledge of the English language. The article “a” is used before words that begin with a consonant and the article “an” is used before words that begin with a vowel. So your kind response should have said “an aluminum gearcase” versus “a aluminum gearcase”. And you call me a moron…?

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**4Speed** · 03-25-2023, 07:13 AM

I just checked a bag of 10 I just purchased as well as a spare plug that came with a new seal and no mention of material on the packaging, but they are all blue (that really doesn't help much). I do dip the blue ones in lower unit oil before I install them as I have had them stick & separate before while trying to remove them with a pick when installed "dry".

**97mirage** · 03-25-2023, 08:22 AM

45speed: thank you for your efforts to search for any material type on the packaging.

Xstreamviking: I went with your suggestion and bought a sheet of Viton. I then used circular gasket punch cutters to fabricate new seals. The combination of cutters (I have an assortment to choose from) and good Viton medium resulted in perfect-fit gaskets for the hardware that I installed for the new vent.

I appreciate all of the responses, men. Thank you.