Force lower unit oil plug

[sjaltobelli]

I recently purchased a used lower unit from a 1986 Force 125HP engine to replace my cracked lower unit on a 1990 90HP. When I purchased the lower unit, the oil drain plug at the bottom was not tightened all the way. I changed the oil and put the allen plug back in. I am wondering if there is a stop for that oil plug. It appears to continue to screw in deep into the unit. I am concerned that if I keep going it will run out of threads and end up inside my unit. Does anyone know if there is some sort of stop for the plug? Should the plug be flush with the unit or does it go deep into the unit? Thank you.

 

[Matthew A.]

Re: Force lower unit oil plug

On some LU's the plug will seat completely. On those that do not seat and the plug can be screwed all the way into the LU housing can be easyly dealt with. Depending upon whether or not the female threads are in good condition, it is important that the plug fit snug into the female threads. If the plug can be screw all the way and into the housing [do not allow plug to come loose inside the housing] remove it and make sure it's length is within an 1/8 inch + or - of the depth of the female threads of the LU. A plug that is the same is ideal. Wrap the plug threads two or three times with teflon thread tape. While the plug is seated on the correct size allen wrench apply thread lock on the the last 3/16" to 1/8" inch of threads that will be threaded into the port last. The thread tape helps to insure the port is relatively water tight. Using thread lock helps to keep the plug from exiting or working it's way in and moving about inside the housing. Sealing the threads also helps to prevent the plug from becoming frozen in the port from corrosion by reducing electrolosis between the stainless steel plug and the aluminum housing.

 

[sjaltobelli]

Re: Force lower unit oil plug

So there is a chance that if I continue to screw the plug in, it will end up inside the housing?

 

[Frank Acampora]

Re: Force lower unit oil plug

There is a stop inside BUT If the screw has been overtightened and the stop broken, then YES there is a chance of running the screw all the way into the lower unit.The screw itself is 5/16 threads so if you get a 5/16 bolt with 1 inch of threads, you can check to see if the bolt stops or continues in. Only about 1/2 inch or less of threads should run into the threaded hole.

Don't worry! Those lower units at various times used a 5/16 set screw, a 3/8 flar headed screw exactly like the drain and fill plughs, and a 1/8 NPT pipe plug.

If the setscrew will not stop, then simply buy a 1/8 NPT pipe plug in either stainless or brass (Allen head if you can find it). Buy or borrow a 1/8 NPT tap, and re-tap the hole. NPT threads are tapered. Do not go too deep or the plug will not seal. Tap in stages and test with the plug until the correct depth is gained.

Then a little teflon tape and your problems are over.

 

[Mark42]

Re: Force lower unit oil plug

This is a great thread with great info on that darned drain plug. Today I went to remove the drain plug in my 1985 85 hp and saw its the alen head screw. Before making a mess of things, I was wondering just how difficult it is to remove the plug, and how easy it is to strip out the threads or head of the alen screw.

Any tips or tricks to getting out the alen screw without breaking something?