Mercury 20HP Lower Unit Oil Plug Size?

[KiwiKen]

Hi All,


I need to buy a timesert kit to repair the threads for the lower unit oil plug on my 2008 20HP Mercury. The part number of the plug according to this site is 953683 and to me it looks like it is size M8 - 1.25. However when I called the mercury number (in Fond du Lac, WI) and quoted the part number the tech support told me it was UNC 1/4 - 20 and made of zinc plated steel.

Before I order the timesert kit I need to find out the correct size. Can anyone help me confirm the correct thread size etc of this plug?


Thank you,
Ken.

[KiwiKen]

I called tech support again to confirm. This time I got confirmation that the plug is M8 - 1.25. This matches up with what I see with my thread gauge etc so problem solved.


Ken.

[KiwiKen]

Hi All,


Finally getting around to following up regarding my thread repair. I decided to go with a regular carbon steel timesert to fix the thread and am very happy with the results. I purchased the timesert kit with a few inserts of varying lengths, a tap guide (helps to make sure the thread tap goes in exactly straight) and some loctite. The instructions that come with the timesert kit are pretty straight forward but still I took my time (checked everything multiple times etc) since it was my first time using timesert or any thread repair for that matter.

The tap guide is basically a piece of machined steel rod with the outside knurled and with a hole down the middle sized to take the tap with minimal clearance. The idea is to hold the tap guide securely against the hole being tapped so that the tap starts off straight. I have to say that the tap guide is quite expensive for what it is but for this application I think it was well worth the expense since the oil plug needs to be straight to make sure the seal is good.

I also followed advice I found in other forum posts… namely I loaded the tap with grease before cutting the threads to trap aluminum shavings etc and I also cleaned the threads afterwards with cotton swabs which seem to do a good job of snagging any remaining aluminum shavings. I also ran the old gear lube through a couple of times straining it each time to remove aluminum shavings. This all seemed to work well for me. The new thread seems really solid and no issues when changing the gear lube at the end of the season (no water in the gear lube and absolutely no sign of aluminum filings etc).


Ken.