Looking at the schematic of the tensioner it looks like there is no reason to remove the sealing plug to install the tensioner.

I don't see how it would make any difference.

And the directions don't mention it either.

Is there any way to tell if my tensioner is applying too much tension to the chain?

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1987 300SDL 167k
1992 Volvo 740 140k
1990 Volvo 740 250k
1989 Volvo 240 269k

Anyone want to trade an old Volvo for an '87 300sdl?