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Old 12 January 2020, 05:35   #1
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Merc 4hp flushing port thread damage

I have a Merc 4hp Saildrive that I use as my aux.


The hose flushing attachment fits into the bottom of the engine casing, you take out a small threaded plug and screw in the hose attachment which has the same thread. Mine has a short tail of hosepipe and a normal hose connector that I then fit onto the garden hose.



Unfortunately over a number of years of use taking the plug out and fitting the adaptor, the threads have badly worn on the engine side (guessing it is probably just aluminium), and it now barely grips. Apart from worrying about the plug popping out and losing cooling water, it means I dare not remove it again to flush the engine, and I don't want to have to set up a tank each time as it is a pain.


I am pretty sure a helicoil type thread repair won't work as the engine obviously has a cavity on the inside and helicoils are not really designed for that. There's also dissimilar metal corrosion to think about with a stainless helicoil against whatever the engine casing is, plus hot salt water!



My other thought is to try and find a thread adaptor and drill it through, drilling out the engine port and tapping it to the next size up (e.g. M8 to M10), fit the adaptor in with loctite and then just screw the blanking plug or the flushing adaptor into the thread adaptor.



This sort of thing https://www.jpldirect.co.uk/catalog/...rs_E30400.html


Before I order some (nothing like that available locally) I wondered if anybody might have other ideas that I hadn't thought of, or had come up with a solution to the same problem in the past?


Thanks.
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Old 12 January 2020, 18:23   #2
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Time sert? Helicoil will just corrode. Fine if it was fit and forget, but you're likely to be flushing after every trip, so not up to the job.

I had steel inserts fitted on my Tohatsu cylinder head for threaded spark plugs. Stronger that the surrounding alloy.
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Old 13 January 2020, 04:26   #3
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Thanks, not something I have come across, looks like a good idea but quite expensive on Amazon as a one-off (£150 for the set) - will look around and see if I can find it from another UK supplier.


That's what I think, the helicoil option will swell with corrosion and probably seize/repeat the problem.
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Old 13 January 2020, 04:50   #4
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I'm not sure the helicoil will be the problem you think if you insert with something like loctite it should fill the voids between the stainless coil and the aluminium case. Volvo penta use helicoils as standard in a lot of their outdrives so it must work ok. I've used timeserts in the past and iirc they are carbon steel which will corrode worse than the stainless helicoil. If it was mine I'd install a helicoil with plenty loctite and put plenty of aqualube grease on everytime i flushed it
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Old 13 January 2020, 04:52   #5
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Is it possible to permanently seal the port & flush using muffs?
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Old 13 January 2020, 10:42   #6
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That's the issue about unscrewing, screwing back on constant basis said bolt located under the powerhead. Install a Helicoil and grease the bolt to prevent corrosion if any.

If the flushing is done on dry land, preferibly use a bucket of a regular size with motor sitting vertical on a motor stand to avoid using the flushing port constantly.

Happy Boating
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Old 13 January 2020, 11:44   #7
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https://www.amazon.co.uk/Thread%C2%A...27060789&psc=1
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Old 17 January 2020, 18:59   #8
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OK, thanks all. I'll come up with something from one or other of the above ideas!
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