Strange item in engine bay

[Snarks]

I found what I can only describe as a hot water bottle top in my engine bay the other day. It doesn't have a screw thread though. It was resting on top of the gearbox. Does anyone know what it is?

I had some diagnostic work carried out on the engine and a Forge dump valve fitted a few weeks ago so I'm wondering if it is related to that?

 

[Math]

yes, funnily enough i found mine lying in my engine bay too, its a plug that sits in the top of the gearbox, ive not got round to seeing hwere it goes/put it back but ill scan a diagram up for you later

 

[Math]

no.19 circled sorry about poor quality, been in my pocket for 2 weeks

 

[goble]

the plug is there to check the timing with timing light

 

[Snarks]

I'm struggling to match the diagram to what I see under the bonnet. I can see this at the moment (ignore the arrow, I stole the picture from elsewhere) :

Which direction am I going in the find the hole?

 

[Math]

the plug is there to check the timing with timing light

nice, im going to have a look at puting mine back in tomorow so will let you know

 

[ArosaRacer]

stops dirt and muck getting in gear box, best done with cold engine when putting it in