Mercury 25 hp bottom cowl

I bought a 1980-1981 25 Mercury yesterday and got it running this morning but the bottom cowl seems to be loose and I don't see any missing screws. Are they supposed to free float a little? This is one of those deals you come across every ten years so I didn't ask a lot of questions.

Is this the model you have:

https://www.boats.net/parts/search/Merc2/Mercury/25%20%282%20CYL.%29/5705532%20THRU%206416712/COWLS/parts.html

I know on my 1984 there is a seal down there that when degraded really allows it to buck & wiggle like crazy (just replaced mine). Looks like if that's the right model your seal is still available (part #11), if not I'd drop the s/n into the search & look @ your cowling components, you probably have something similar that is either gone or in need of replacing.

That looks like mine but it's hard to tell if #11 is the seal between the top and bottom cowl, which I also need to find. The bottom cowl on mine wiggles with the shaft housing. Just got off the phone with a guy at Mercury and he said something needs to be replaced, probably a gasket under there somewhere that I can't find a picture of.

Use the serial # & look up the exact diagram for your motor, if it's not on the mounting bracket any more Mercury puts them on freeze plugs on the engine as well, so you'll have to look around but you'll be able to find it.

I'll check the motor for more numbers. The guy at Mercury found my motor from the number I gave him, 5884149, and the name of the original owner but he couldn't say what might need to be replaced.

That's definitely your serial #, however for some idiotic reason you need to put a zero in front of it to find the parts online...so for boats.net you want to search using 05884149 and you find your motor.

You're missing the same adapter plate seal I was missing in the drive shaft housing sub assembly. Well, not missing, but chances are the adapter plate has cut through the side of the seal rendering it useless. Manufacturer's part # 87357 which is, of course, discontinued. I found mine on Ebay. You could for the time being get a piece of 1/2" vinyl hose & cut it lengthwise on one side & fit it in place of your worn out seal until you find a new one. You might need to set a piece of 1/4" hose cut the same way inside the 1/2" to make it thick enough to hold up once in place. It will be a temporary fix but should help with the vibration in the mean time.

Don't buy this one
https://www.ebay.com/itm/USED-MERCURY-MARINER-99702A3-ADAPTOR-PLATE-87357-SEAL-96248A1-WATER-TUBE-HOUSING-/281695034399?hash=item4196551c1f:g:6V0AAOSwZd1VWKSc&vxp=mtr
In the 4th picture you can see where the adapter plate has cut through the side of the seal - that's what's happened to yours.

Try some used parts suppliers, https://www.northernoutboard.com/ might have one, I've ordered parts from him in the past & they've come in great condition.

Replacing it will fix the cowl vibration issues you were experiencing

Great ideas. Thanks very kindly.

https://www.boats.net/parts/search/MercuryMarine/0g136178/368/160/Driveshaft%20Housing%20Assembly/parts.html

Looking at the newer motors the part # 87357 was replaced by 15866-2, which is now also discontinued. However, on the newer 25hp motors there is a seal 15866-4 (1st part in the link above) that looks to be the same as the adapter plate part # is the same (at least it is for my motor & the newer one). Better yet that part is still available.

A local dealer ordered me a #15866-4 and saved me a few dollars so we'll know soon enough. Looking at the motor and the diagram I can't tell for sure how it goes in. I did see part of the old seal still under there.

When you separate the two halves of the lower section of the cowl you will see there is a stainless retainer above it cinching it down with 4 or 5 screws per side. Just loosen those up & it comes free.

I think on mine I had to detach the fuel connector from the cowl to gain access to the screw on the side facing the boat to split the lower section of the cowl - the side facing away from the boat was easily accessible. It was pretty straight forward and simple. I didn't need to remove it completely.

The retainers are part #18 in this diagram of your cowl:

https://www.boats.net/parts/search/MercuryMarine/05884149/676/2/COWLS/parts.html

That is great to hear. I was afraid the bottom cowl was one piece.

I put it on this morning. It's not squared like the old one, it's one straight piece so I cut part of it to fit the rear and two to fit the sides and I think it'll do fine. It for sure doesn't wiggle anymore which is all I needed. Thanks very much for the tip.

That's probably why the part# with the -4 at the end doesn't cross reference against the older motors. You said it comes as one straight piece, so the only difference is that it hasn't been formed yet --- the length was sufficient to encompass the entire adapter plate right?

It would cover 90% of it but I didn't put a piece across the front because there wasn't much left over and there wasn't a lot of access.

I also looked at the choke since it didn't seem to work when I had it running. I used a spray bottle to squirt mixed gas in it which is what the previous owner did. The choke knob pulls a lever forward but it doesn't retract. The outer choke knob itself is broken so I bought one of those too but replacing it looks more involved than I wanna tackle right now.