There's basically two types of oil injection. The old type which was used up and into '91 has one hole in the cases for the oil pump drive, and the oil is fed into the intake side of the carbs.

Later model NSRs (most MC21 and all MC28) have an extra oil feel direct to the RH main bearing, and use a different oil pump.

On early models (single hole) you only need to plug this one hole, but on the later models you need to plug the main drice hole and the extra feed hole.

The 2T plug (TYLY-0012) is just held in the main drive hole with some RTV sealant to stop leaks. Plug holder (TYLY-0015) can then be fitted to hold it in. Never had one come loose. The plate with two holes is supplied by another manufacturer.

The extra feed hole can be blocked in a number of ways. HRC supply a little alloy plug that you ram down the feed hole, and is pretty much impossible to remove. I like to use epoxy, and have never had a problem. Even removing the epoxy to return the cases back to oil pump use is not too difficult. I've also seen it done with various silicone sealants etc. The feed hole does need to be blocked as it's a direct link to the crankcase.

Removing the 2T plug can be done by drilling and tapping into the centre of the plug and using a slide hammer or something to break the sealant.

Maybe on the next batch I'll redesign it, and the holder, to keep the standard o ring, so removal is easy. It's just that when I build a race engine it usually stays a race engine, so I like to make sure everything's sealed and tight.

How many people out there actually revert back to oil pump after doing the pre-mix conversion?