Finally I made first samples of chain tensioner plug.
The idea is that you insert the plug, and by turning the srew you compress the O-ring which seals and holds the plug in place. There is also a small pin holding two parts together so there is no danger of parts falling into the engine.
Also one of the goals was to make the plug thin enough that it can be inserted without removing the fan pulley assembly.
Nice machining job! Cute job with the pin and the slot it fits into.
I can’t say I’ve seen a retention scheme that involves squeezing an O-ring. I don’t see why it wouldn’t work. It might work best if you go with a really fat O-ring, but I suppose that’d make it harder to find.
I’d still prefer a simple plug and O-ring with a tang under a nearby bolt head for retention.
Given that the timing cover is aluminium, why not just tap the hole with a suitable thread and insert a bolt with a copper washer underneath it just like the oil pan has?
The etype v12 already has this arrangement for the oil gallery to oil cleaner connection on the front timing cover.
kind regards
Marek
Thanks Kirbert 
Yes when I look at it I also think that I went a bit overboad and overengineered the plug… it will be a good match for jaguar’s overengineered radiator drain plug with lever :))
Let’s see how it will work in real life.
Unless you have your timing cover off I wouldn’t dare taping it on assembled engine…
Final version of chain tensioner hole plug 
With stainless steel bolt and copper washer just in case and everything assembled with use of non-metallic anti-seize also just in case 
Why non-metallic anti-seize?
Well this the best anti-seize I could get 
It has the widest temperature range and is compatible with all metal combinations. Also it is not hazardous as nickel based anti-seize is. And I don’t like the idea of using copper anti-seize due to possible galvanic corrosion between aluminium and copper as those two metals are quite apart on galvanic series table.
After multiple requests I have made another batch of chain tensioner plugs:
is it possible that some positive crankcase pressure could maybe weep some oil out the threads and past the copper washer??
just askin , nice work!
ron
Hi John
the plug arrived during the week, and was fitted today : easy fitting , the most difficult part was taking the old plug out
@Robros : I doubt there’s a risk, as the oil is mostly spread around the crankcase and drips , it’s not pressurised
Great! And yes rubber plugs can be real PITA to remove even when they are flexible. Some aftermarket plugs are made from crappy rubber and swell from engine oil which makes them even more difficult to remove.
Reg. oil seepage through bolt thread, I don’t think so as copper washer is there to seal it.
