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Old 30 May 2013, 09:07   #1
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small hole in gearbox

I have found a small hole in my gearbox today, have no idea where it has come from, could it be cavitation? hopefully its more like it has hit something submerged.

anyway do you think water will have got into my gearbox, or is this just an outer shell, the engine is 2007 mariner 60hp 4 stroke.

also can i fix it with some chemical metal? as you can see from the pic the hole is pretty small.


Thanks
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Old 30 May 2013, 09:17   #2
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Clean it out, chemical metal to repair it then change the gearbox oil to be sure. Oh, and check your anodes.
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Old 30 May 2013, 09:22   #3
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I would have thought a weld would be a permanent repair, but first drain you oil to check the colour, amount and check for debris
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Old 30 May 2013, 09:35   #4
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If I'm reading that pic right it's on the leading edge?

I bet if you look somewhere under the outsiode of your cowl (or halfway up the leg) you'll find a small rubber hose possibly with a cap in the end - it's a pitot orifice for a speedo - means you don't need a separate pitot hanging off the transom.

Mine has it too. I just parked a short length of hose over the fitting in the top of the gearbox (only visible when removed from leg) and filled other end with sikaflex.


(and if you decide to fit a speedo to it, be aware that the Teleflex ones read slightly down if not used with their own transom mount senders - the "streamlining" of the leg gives a slightly lesser pressure and so you need a Merc / Mariner guage to get a half sensible reading)
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Old 30 May 2013, 09:44   #5
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No need to worry

That is the water pick up hole for the pitot tube which is the transducer for the speedometer if connected.
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Old 30 May 2013, 10:18   #6
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What 9D280 and Ribochet said.

Most people have problems with keeping this hole open to get speed readings. It would be kind of ironic if you filled it in.

jky
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Old 30 May 2013, 10:20   #7
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thanks for all the replies guys, so are you saying that hole is meant to be there? if so i'm such a muppet never noticed it before

i shall go and hang my head in shame
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Old 30 May 2013, 10:58   #8
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Quote:
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thanks for all the replies guys, so are you saying that hole is meant to be there?
Yes - cavitation will only cause erosion on the prop itself and electrochemical corrosion would not result in a hole there

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if so i'm such a muppet never noticed it before
i shall go and hang my head in shame
No need for all that - this is what the forum is for - ask away
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Old 30 May 2013, 11:14   #9
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I thank you all very much for the help.

i do feel like a complete idiot though for not seeing it before, i've owned it for a year! Ah well, you live and learn
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Old 30 May 2013, 11:37   #10
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yep, tis a pitot hole
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Old 30 May 2013, 11:45   #11
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I'll wait for the you're a numpty replies but I've just put the gearbox back on my 135 Mariner and noticed the small rubber pipe sticking up a few inches at the front on reassembly but no obvious reason! On reading this thread I went out to look but no pitot hole on the leading edge...
Any clues please?
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Old 30 May 2013, 11:48   #12
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It's the pitot pipe

It takes the pressure reading from somewhere else. Not sure where-think it's on the front of the box by the water intakes.

I removed my pitot tubes, they're a waste of time.
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Old 30 May 2013, 11:53   #13
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Thanks for that Nos4r2, I just poked it through when I reassembled, is it ok leaving it until I change the impellor or should I take it off & plug the hole?
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Old 30 May 2013, 12:22   #14
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Drill it out, your boat will go faster!
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Old 30 May 2013, 13:03   #15
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Thanks for that Nos4r2, I just poked it through when I reassembled, is it ok leaving it until I change the impellor or should I take it off & plug the hole?
@ Davie

It'll be fine.
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Old 30 May 2013, 13:21   #16
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Cheers
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Old 30 May 2013, 19:18   #17
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I removed my pitot tubes, they're a waste of time.
They're pretty good for hosing down the inside of the console when the tube falls off the speedometer...

jky
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Old 30 May 2013, 21:26   #18
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They're pretty good for hosing down the inside of the console when the tube falls off the speedometer...

jky

I'd laugh, but thats one reason I didnt refit them after hearing that tale from someone else!
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Old 31 May 2013, 02:49   #19
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Yeah, two options are totally fill the exiit pipe or tie wrap the end of the hose so that if it did pop the blanking plug it will just throw the water overboard.

Latter option maybe preferable simply because it means that if someone subsequently buys the engine from you the facility is there, but with the cost of GPS falling all the time probably less of a "sale decider" these days.
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Old 31 May 2013, 06:24   #20
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Drill it out, your boat will go faster!
that save me buying new bigger engine ! speed is all about perception - removed GPS from boat...lol
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