85 force lower unit drain plug

[sidewing]

Hi everyone.

Let me start by saying this forum has been a gold mine of information and thank you all. I can't find a boat shop around here that will work on an 85 force for some reason.

I purchased a new to me 88 Bayliner with an 85 force outboard about a month ago. It ran and didn't sink, but none of the electronics seemed to be working for various reasons.. anyway, we took a chance on it as our first boat. I'm fairly mechanically inclined and do electrical as well so I've been putting some work into it. Here's what I've done so far:

spark plugs, impeller, lower gear oil, fuel sending unit (to fix gas gauge), automatic bilge pump, stereo and speakers (wired into a shutoff switch), new accessory switch (wired into shutoff switch), solar panel, bimini top, gps fish finder, swivel jack, led tail lights, license plate holder, 4 front led spotlights, horn, tachometer, new battery posts, fishing pole holders, stern light, bow light, boat ladder, add tell tale.

The issue I'm having right now is when I did the lower unit gear oil, I couldn't get the bottom drain plug to come out. I ended up just removing the fill and vent and pumped a quart of fresh oil into the fill and let it spill out of the vent (nice chocolate oil water)... I also didn't have fresh gaskets for those screws (which I have now).. so I'm wanting to properly remove this drain plug, replace the gaskets and get all that watery oil out of there. It seems like the Allen head is stripped cause I can't get it out.

Any advice on how to get this thing out, and what I can replace it with that is easier to remove going forward? Here's a couple of pictures. If I could convert it to a flat head like the fill and vent, or even a hex head that I can get a socket on, that would be much better..

Any advice or tips is appreciated. Oh, we have taken it on the lake about 5 times already and it's running great. I just want to make sure the lower gear oil is doing it's job in properly lubricating so it doesn't cause an issue down the road.

Thank you.

 

[racerone]

Use an impact screwdriver to get the drain plug out.-----Or use a small punch on the drain screw.----Filling a gearcase from the top is a common mistake.----Do not run this motor until you verify good gear oil in the lower unit !

 

[Jiggz]

Because the drain plug is installed at the bottom, some people continue to use the leftie loosey method without noticing it only works while you are facing the back of the screw. So instead of loosening they are actually tightening the screw as ever. Or it could also be because the screw has not been touched in years. But with this screw soaked in gear oil, very seldom it gets frozen stuck. But more like from mistakenly tightening it instead of loosening it.
The original allen wrench size for this plug is 5/32". If it is worn out or stripped try using a little bit larger allen wrench and the next closes one is metric size 4mm. You may have to hammer it in lightly to get to fit. Remember you need to soak the plug with pb blaster oil overnight (raise or trim the motor as high as it'll go and support it with a 2x4 wood if need to). And then prior to turning it, apply a little heat around it. Do not overheat as there are oil seals around the "bullet" that can get affected. If you have an impact driver (small cordless one is preferred as pneumatic one will be too strong and would just strip the plug) with socket allen wrench, use that instead.

Replacing the drain plug is close to impossible as it has pipe threads instead of regular machine screw threads. The only other option is to drill the hole out and rethread it with regular machine screw thread and just use a gasket to seal it off.

 

[racerone]

I doubt that the drain screw is a pipe thread !!!-----And the screw has a gasket , doubt that PB blaster will help here !

 

[sidewing]

I ordered a impact screwdriver set, gonna give it a try tomorrow..
I tried spraying it, letting it sit for a bit, hit it with a good 60 seconds of heat from my heat gun and tried 5/32, 4 and 4.5 (too big) in hand tools as well as my DeWalt cordless impact.. no luck on any of them.. the 5/32 feels like it wants to grip, but once force is applied, it just starts stripping it some more.. same with the 4mm.
Can't find my easy out set.. not sure if that would be an option.. if so, I'll probably have to buy a new one..
I hope the impact screw driver works.. if not I don't know what else to do other than just pump as much clean oil into the fill as I can..
I don't understand why they'd put such a crappy screw head on this thing.. and why the boat shops around here won't work on the engine, even if it's something like removing a stuck drain plug.. that seems like something that shouldn't be an engine unique talent for any boat mechanic.

 

[racerone]

I do not like the drain plugs that need an Allen wrench either.-----Using a small punch will remove this screw !

 

[roscoe]

If I could convert it to a flat head like the fill and vent, or even a hex head that I can get a socket on, that would be much better..

It should be an allen head screw.
It is way under the gear case.

Do NOT remove the phillips head screw near the front of the gear case.

 

[sidewing]

It should be an allen head screw.
It is way under the gear case.

Do NOT remove the phillips head screw near the front of the gear case.

Yep, the Allen head one is the one that is giving me problems.

I saw in another post from 2016 that a guy was pulling the prop, removing the bottom 2 carrier bolts, tilting the engine down so 90 percent of it drain's out.. maybe thats an option once a year.. I haven't looked up how much of a task that would be to remove yet.

 

[Nordin]

Try with heat from a propan torch around the allen screw and then try to drive it out with a small punch.
Heat will help as the screw is made of steel and the LU case is aluminium alloy. The will expand different when heating.
The allen screw has fine threads and if been in salt water it will get really stuck.
Fine threads is making it harder to get loose.

 

[racerone]

I think these use the 3/8-16 NC thread.----So not a fine thread !

 

[jerryjerry05]

The allen headd set screw is a fine thread machine screw.
Easy out is a way to go. You drill the set screw then use the appropriate easy out and heat it with a propane torch.
Once you drill it the oil will drain out so be careful when you use the propane torch. Use the torch before you drill is an option, your breaking up the corrosion around the screw, heating it and then an oversized allen wrench might do the trick??? Remove the vent screw before you add heat as the oil will expand and the pressure might cause problems.
Filling the oil from the vent/ fill screws doesn't get the oil at the bottom of the case.

 

[sidewing]

The allen headd set screw is a fine thread machine screw.
Easy out is a way to go. You drill the set screw then use the appropriate easy out and heat it with a propane torch.
Once you drill it the oil will drain out so be careful when you use the propane torch. Use the torch before you drill is an option, your breaking up the corrosion around the screw, heating it and then an oversized allen wrench might do the trick??? Remove the vent screw before you add heat as the oil will expand and the pressure might cause problems.
Filling the oil from the vent/ fill screws doesn't get the oil at the bottom of the case.

Is there a specific size/thread for a replacement if I drill it out? Or a size that is compatible if I need to tap and replace?
I ordered a drain plug with a magnet that is 3/8 16 with a flat head (like the ones on the fill and vent) in the hopes that maybe I'll be able to drill and tap to use it.. but I don't know if it's gonna be too big until I see it.
I can't seem to find an exact replacement anywhere online.

 

[sidewing]

Just to provide an update.. I tried kroil, a butane torch, impact screw driver, easy out and nothing worked. I just drilled it and it's draining. Hoping that I'll be able to thread it so I can use the new 3/8-16 magnetic drain plug. Will update.

 

[Jiggz]

Sometimes you just got to do what you need to do to get things done. Let us know how it works out with a replacement screw. Goodluck.

 

[sidewing]

alright, so we appear to have success..

i want to start by thanking everyone on this thread for your input.. it's very much appreciated.

so i haven't taken it on the lake yet obviously to test.. but its looking like a very big success... i drilled out the hole, threaded it, and its using a much more standard (easier to find today) mercruiser drain bolt with a crush washer... here's what i used and what i did, in case it helps anyone now or in the future:

New drain plug is a 3/8-16 flat head top with a magnet. part # 22-8M0058389.. ordered a 2 pack off amazon for $12.99. It also fits/is a match the upper fill and vent holes as well.

crush washers i got a 20 pack from amazon for 7.99.. part # 18-2945.. inner diameter 9mm, outer diameter 14mm. these also fit all 3 plugs (fill, vent, and new drain).

i drilled and tapped the hole with: Kobalt 3/8-in-16-in Standard (Sae) Tap and Drill Set.. which is a 3/8 16NF tap and a 5/16th drill bit. i got it from lowes, part # 5036564... i coated the drill bit with Forney 20857 tap industrial pro cutting fluid.. i used "Kobalt 0- 1/4in Adjustable Carbon Steel "T" Style Tap Wrench" from Lowes, which is item # 5036558 to hand thread the hole after drilling.. i also coated it with the cutting fluid to assist with the threading, and it helps to holds onto the metal shavings. the bit and tap were 6.98 at lwes.. the T tap wrench was 7.98 from lowes.. and the cutting fluid i got from amazon for 6.80 for a 4oz bottle.

the new drain plug with the crush washer screwed on as smooth as can be.. i tightened it with my dewalt drill set to '9' (not sure if that translates to 9ft lbs.. but its a turn knob scale of 1 to 15 on the drill)...

Looks real clean on the bottom, and shouldnt have any issues getting it off in the future vs that stripped allen head that was on there prior.

 

[Jiggz]

Thanks. Looks like a success story and a good reference for the future. Thanks again for sharing.

 

[sidewing]

took it out to the lake yesterday... ran better than it ever has. i just need to figure out why my boat doesnt seem to go super fast.. like 8 to 9mph.. the prop tips are a little bent from what looks like many dings.. i was thinking of getting a new prop to see if it makes a difference, but for a quality stainless steel one, kinda pricey.

 

[racerone]

Sounds like it is running on 2 of 3 cylinders.---Are carburetors clean ?----Does spark jump a gap of 3/8" (1 cm ) on each lead ?----And post you actual compression values.----Checked flywheel key ?--Checked reed valves ?------Do not run the motor if carburetors and jets are not confirmed clean.----Serious engine damage can happen.---

 

[sidewing]

Sounds like it is running on 2 of 3 cylinders.---Are carburetors clean ?----Does spark jump a gap of 3/8" (1 cm ) on each lead ?----And post you actual compression values.----Checked flywheel key ?--Checked reed valves ?------Do not run the motor if carburetors and jets are not confirmed clean.----Serious engine damage can happen.---

i ran a compression test and read about 120 on each of the 3 cylinders.. ill need to research the other mentioned items. the guy i bought it from said he had just done the carb before i bought it... hopefully his word was honest.

 

[Jiggz]

Does the motor has tach? Any idea how fast is the RPM at full throttle while in the water? Or even at half throttle? It takes a little experience to detect one misfiring cylinder by sound alone. A quick drop cylinder test will let you know if there's misfiring.
Have you installed a clear fuel filter between the fuel pump outlet and the carb inlet hoses? This is a very useful troubleshooting tool especially for fuel related problems. A simple Fram G2 or G3 for less than $5 will suffice.

Lastly, has the motor run great before like making at least 4500~5000 RPM and maybe at least 30~40 MPH that you know of? Have you checked the timing?