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lower unit drain plug torque

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I have a Yamaha F150.  Torque says 6 foot lbs.  

I bought the boat used and had a yamaha shop check the motor.  They said to change the oil.  When I got it home it was dripping black water free oil.  It had not appeared to drip anything when I was inspecting the boat.  I went and looket at it 3 times before I bought it and never saw oil on the ground.    I changed the oil but could not seem to get the bottom drain screw to set with a new gasket.  I got it hand tight, then took a small wrench and snugged it up a little.  It continued to drip oil.  I pulled the plug and tried a new gasket.  it still dripped.  I took it for a ride in a lake.  When I got it home I left it out front in the sun and a few hours later oil was pouring out the screw hole.1 trip and the oil looks to have water in it.

I took it appart tonight and really inspected the hole.  The threads look decent and the face of the hole is flat.  I put new fluid in it and this time tried to use a torque wrench to get it tight.  It just does not seem to want to tighten up.  Kind of feels like its stripping. I am at about 4 foot pounds and nervous to keep going.   The top drain plug screw stops hard.  Feels like a normal grab and stop.   Not sure if the feel on the bottom is normal.  The lower screw hole  has a slippery feel like it want to keep spinning and wont really stop.  I'm concerned the yahoo at the shop striped it out.  It did take a few hits with a reverse impact driver to remove the screw.  I hear this is normal.

Any thoughts.  Do I just not have it tight.

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Can't comment on normal, but in my F70 I could not imagine using an impact wrench.  They loosened just fine with a screwdriver.

 

FYI, stripping the oil plug on these engines is quite easy.  I followed instructions as to torque and mine stripped.  Replaced under warranty (new oil pan).  Tech said never use torque wrench (ignore instructions), tighten only till snug.

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i'm talking a reverse wrench you hit with a light hanmer to break the initial tension.  Not a pneumatic gun.

I only touched a torque when I was unsure what I was feeling,  I did not strip this.  It came that way.  It was dripping oil in my garage after they opened it to test the fluids and check for debris.   All thet said was change the fluids.   I'm pissed as hell the dealer did not note the issue in the inspection.  A mechanic via email this morning said any good mechanic should know the feel.  I'm an electrician.   I have tightened 10,000 nuts, bolts and screws.  I have made mistakes.  The service report should have noted it was not seating firm and may be stripped.

Now I have to wait many months to get in with a good mechanic who can drill, tap, heli-coil, pressure test a new drain channel.  And what do you think the guy I paid $500 to is going to say to me.  Anyone want to stand up for them.  I suspect pound sand.  I will reserve any mention of who they are till I have a comment from them and report from a mechanic validating my concern.

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If the inspecting mechanic changed the fluids, he would have had to be aware the plug issue. If not, he's not much of a mechanic.

 

That said...

Your problem sounds like when you over tighten a machine screw and it strips close to the screw head. It will go in all the way but will not tighten.

The threads in the housing may be OK and the ones on the plug might only be stripped. I cheap check is to try a new drain plug

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I took  my complaint to the company that sold me the boat. They said bring it in and then we'll take a look at it. I thought about this for a while then decided either their mechanic sucks or they lied to me. Either way I don't trust them to do the

In the end it may not be that big a deal. I pulled the lower unit and took it to Three Rivers Marine. It's a local shop here in Seattle area, and they're supposed to be very good. Provided they do it right, it's only $149 to have a helicoil installed. While there I told them to go ahead and replace the water impeller too. I was going to do that myself but figured I would let them get it done so I could get back on the water quicker.

Of course I also spent another $1,200 buying to downriggers and all the equipment to set them up for use.

FYI, I never tightened this nut to the point a pulling the threads out. But I'm sure whoever did over tighten it in the first place started the process of disfiguring their alignment in the hole. I have made this mistake myself in the field  tightening  lug nuts.  The results is the face not seating flush with the gasket there by letting oil pass by.  If you go so far as to pull the threads completely off the case, often you end up with an issue where the screw simply spins in the hole. It will not tighten nor will it back out. Then you're into a real ordeal. It can be dealt with, but you have to disassemble the entire lower unit to put reverse pressure on the screw while you turn it.  Otherwise it's not coming out.

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I took the lower unit to another local shop.  They said it was not stripped, pressure tested it and thought it was good.  It still leaks.

They also said the factory did not drill a hole that was centered in the recessed cavity.   That sucks.i wonder if the screw and washer are catching an edge as they set and getting slightly deformed at the shoulder.  I wish I knew a good machine shop that could widen the hole.  Im afraid to put it on my drill press as its a round surface and so hard to make a vertical hole to the mating face.  How they got this wrong is  beyond me.   I assume they cast this piece or use one bit with 2 cutters on a machinery mill to make the hole.  

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