3 cyl 2 stroke C40TLRV what is the purpose of the large plug on the cylinder head?

[bedwar44]

I am in the middle of doing some routine maintenance, replacing gaskets, seals, etc., and I was curious if anyone could tell me the point of the large 14 mm plug with red gasket (like an oil plug) on the left of the cylinder head. No. 4 in picture (3 is gasket). Parts list and service manual calls it a "straight screw." It doesn't appear to have ever been removed (I haven't ever needed to), and I can't really figure out what the point would be, other than possibly to do some kind of flush with cleaner on the water passages. I searched and looked in the service manual, but could not find any answers. I was just curious if anyone knew what it was for.

[a387673]

Sacrificial (zinc) anode?

[99yam40]

not sure, but I think it is a place to put a optional temp gauge sensor

[bedwar44]

Thanks for the replies! It is not an anode, as those are under screwed under the head. I was thinking it might be for some type of optional sensor or diagnostic procedure also, but cant really find any mention of it. Thus, the curiosity.

[KayKatz...]

Just curious, did you remove the plug, and if you did, were the threads the same as what you would find on a garden hose?

[bedwar44]

No, I did not remove it. It didn't really want to budge very easily. So, since I don't really see much use for it, I decided it was't worth it to possibly mess up the head, etc. trying to get it out. Just, figured next time I have the head off I would see about lubing up the threads from the inside and removing then. Anyway, it is a metric bolt (14 mm) so don't think any North American hose fittings would fit it.