Hi All,


I have a Mercury 20HP 4 stroke outboard (Model - 20ML, Serial - 0R255347). While changing the lower unit oil I have managed to strip the threads in the aluminum casing while tightening the top (vent) plug. I have done some research on how to fix this and it seems the options are either Heli-Coil or Time-Sert. I was thinking that Time-Sert would be better since it is a solid insert rather than a coil… that way I can use thread locker on the outer threads without having to worry about it seeping through to the inner threads. Questions I have are as follows…


1. Both Heli-Coil and Time-Sert come in either stainless steel or carbon steel. The drain plug for this outboard (part # 953683) looks like it is zinc coated rather than stainless steel… can anyone confirm? This leaves me wondering should I go with a carbon steel insert since it is more compatible with the aluminum casing and the drain plug according to the anodic index? Or is stainless steel the way to go? Would galvanic corrosion even be an issue here given that the insert should not come into contact with salt water etc?


2. The plug itself is a slotted 5/16 pan head type. It is really short (only has 5 threads) whereas the casing looks like it has enough thread for double that length and more if the hole was tapped out to it's entire length. This leaves me wondering if there are any alternative plugs available that could utilize more of the threads. This would be an easier fix if a longer plug is available.


Thanks for any help and suggestions.


Ken.