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Old 01-12-2009, 16:03   #1
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Stripped Oil Vent Screw - Metal Filings in Gear Case - Help!

Hello,

While opening the lower unit screws to drain the oil in my 2002 2-cycle Mercury 15hp, I stripped the vent screw. Actually it was stripped before I got there and it looks like the previous owner gave up trying to get it out. Two broken screw extractors, some gnarled threading and some frustrating time later, I found myself left with a hole in the aluminum that needs re-tapping. I don't think I can do this easily myself and I found a local machine shop that can do it pretty cheap.

My question is... what about the filings in the gear case? I was as careful as I could be trying to remove that screw but I'm afraid some surely got in. Also, the machine shop is likely to leave a few more by the time they are done with the tap. Is it possible to open up this case to clean it out somehow? I found out how to remove the lower unit (which might be easier to give to the machine shop separate anyway) but I don't know how I would go about opening it. Is it possible to clean in out (with gasoline maybe?) and shake it around to get out trapped filings? The magnet trick won't work so well on the aluminum... Is this something I have to worry about, and if so, what can I do?

Thanks a lot!

Jack
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Old 01-12-2009, 16:41   #2
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I would flush it well with some solvent, Is it the bottom screw that is stripped? If so remove both screws and flush from top, should be no problem I believe a helicoil would repair that thread
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Old 01-12-2009, 17:41   #3
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If the original vent screw was screwed directly into the case (not a hard metal insert or something) of the motor it is a really simple process to cut new threads. Go to any Ace Hardware or Homedepot or whatever tool source you prefer and buy a tap (sometimes called a thread cutter) that is slightly larger than the hole left in the case. While you are there go ahead and buy a screw of the same diameter and pitch as the tap. Properly done a tap is used with a special wrench that has handles projecting out with the tap attached in the middle (picture something like a large wingnut arrangement). The tap cuts into the hole and cuts the threads easily.

You probably will get more metal filings in the gear case. No experience here but I would just flush liberally to rinse out any metal.

Good luck.
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Old 01-12-2009, 17:47   #4
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I had to do this on an engine block for a VW once. I think that what you should do is to start with a vaccum. After that blow air thru from the top and then revaccum. After that try to flush but I don't know what would be good to use.
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Old 01-12-2009, 17:55   #5
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It should be aluminum chips, which shouldn't hurt the gears but might raise hell with the bearings.
Do as M30 mentioned, flush from top with solvent and suck out with a wet vac. 2-3 times. DO NOT USE GASOLINE
Heli-coils are fine for one time usage but for a drain plug you should use a Keensert e.g. Keenserts® on Alcoa Fastening Systems

And install it with permatex 2 e.g. http://www.permatex.com/products/Aut..._2_Sealant.htm

to seal it. The old plug was probably metric (8 or 10mm) so you could switch to SAE if metric is hard to find. Heck! I probably have one in my tool box.

Nope! I checked.

Retapping to a larger size is a good option too, providing there is a sealing surface for the screw face! A pipe plug is not good in aluminum, in case that get brought up. Cast alum. is porous and is a week material.
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Old 01-12-2009, 18:59   #6
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I suggest USS (course) over SAE for soft metals.

Quote:
Originally Posted by delmarrey View Post
It should be aluminum chips, which shouldn't hurt the gears but might raise hell with the bearings.
Do as M30 mentioned, flush from top with solvent and suck out with a wet vac. 2-3 times. DO NOT USE GASOLINE
Heli-coils are fine for one time usage but for a drain plug you should use a Keensert e.g. Keenserts® on Alcoa Fastening Systems

And install it with permatex 2 e.g. http://www.permatex.com/products/Aut..._2_Sealant.htm

to seal it. The old plug was probably metric (8 or 10mm) so you could switch to SAE if metric is hard to find. Heck! I probably have one in my tool box.

Nope! I checked.

Retapping to a larger size is a good option too, providing there is a sealing surface for the screw face! A pipe plug is not good in aluminum, in case that get brought up. Cast alum. is porous and is a week material.
SAE threads are trickier in aluminum. Too fine. Metric is in between.

You will need a gasket under the screw head.

All good tips. I would suggest getting a factory manual for your motor (not after market). Not cheap, but worth it the first time it helps you get something apart.
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Old 01-12-2009, 19:25   #7
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Thanks for the advice, guys.

Yeah, the potential difficulty of getting the screw head/gasket to seal with the aluminum face is what made me shy away from doing the tap myself. I was thinking the machine shop could drill in a wider area for the head to rest against and then put the tap in below that, considering the aluminum there is pretty thick.

Do you guys think it is even worth it to remove the LU if I am just going to be flushing out the gear case afterwards? Should I bring the whole motor to the shop or go through the trouble of taking it apart?

What kind of solvent should I be using for the flushing? I'm guessing water is out of the question as well, huh....

Thanks again, this is really helpful.

J
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Old 01-12-2009, 19:34   #8
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When you tap the threads, first pack some heavy grease in the flutes of the tap. The grease will hold the chips as they are cut.
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Old 01-12-2009, 22:34   #9
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Quote:
Originally Posted by ggray View Post
When you tap the threads, first pack some heavy grease in the flutes of the tap. The grease will hold the chips as they are cut.
Bees wax would even work better but if your taking it to a machine shop, the less you take the less it'll cost. Handling of large parts always cost more. Plus, it makes it ez'r to chuck up on for precision work. Even remove the prop.

i.e.
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Old 03-12-2009, 12:06   #10
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Well, the guy at the machine shop said we should take the case apart first so he can be sure not to damage any of the shafts inside. It sounds reasonable but I am not sure how to go about taking apart the lower unit. Do you guys know what kind of obstacle I will come across as I start dissassembling this thing? Am I likely to do more harm than good, or can I just figure it out as I go along (taking care to document and photograph every step, of course)?
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Old 03-12-2009, 14:02   #11
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I am not a great mechanic by any stretch of the imagination but I was able to take the lower half of an outboard apart and put it back together when it wasn't peeing water well. There is not that much in the bottom half of the Honda I took apart. Don't know about a Mercury.
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Old 03-12-2009, 14:45   #12
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There is almost nothing in there that a couple of chips of aluminum will hurt. Retap it yourself to the next standard size and use a stainless screw with a rubber oring or washer. The grease on the tap will work fine it's an old mechanics trick. I've been doing it for years and had no failures. It's not that difficult. Take your time and you'll feel like a hero afterward.............m
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Old 03-12-2009, 16:30   #13
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There seems to be some cylindrical part in there, running vertically inside the gear case just to the aft of the vent hole. It doesn't really look like the drive shaft but nevertheless I am assuming it is important. If I just widen the hole myself around the existing center, I will endanger that part, and without a drill press I am not sure if I can easily drill the hole off to the right (forward) side where it needs to be. Even if I could, how do I create a flat surface for the new screw head and gasket to sit against? It seems like a pipe plug would solve this problem, but someone above recommended against that option. Any other thoughts on this?

So, it seems like I should consider taking the LU apart. The guy at the machine shop says they need it disassembled to safely do the tap, and it seems I would as well. (the guy recommended the pipe plug btw) After I get it off, how difficult will it be to get the gear case open? While I am doing this, what seals or gasket must I or should I replace? (sigh)


Thanks again...
Jack
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Old 03-12-2009, 21:01   #14
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Look at all the "LU's" out there. You will not find a pipe plug in any aluminum case. The wall thickness is not enough and again it's a cast alum.

That machine shop is probably not marine savvy.

The cylinder thingy may be a bearing, which is harder then any drill bit or tap. But you really don't need to use a drill bit just the next size up tap. The threads being stripped out has already enlarged the hole enough for clearance.

Can you find out what size the old plug was (O.D. & thread pitch) and I can recommend what tap to use. Any good Auto Mechanic or Machinist can tell you from the sample.

It's too bad your not here in Seattle. It would probably be just a 15 minute job.
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Old 03-12-2009, 21:22   #15
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Hmmmm... the original screw and gasket are shown on this diagram as parts #8 and #9, but they are not listed down below. I ordered the service manual but until it comes I'm not sure how to find that out.

Your advice is a big help. I agree that tapping the hole itself shouldn't be too difficult, but I still don't know how I would solve the problem of getting the gasket flush and tight with the aluminum under the screw head. The hole is a bit irregular now and the outside of the LU itself is curved. Any thoughts?
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