Can I run the 1/4-20 tap in without tap drilling first? I just checked and its one of the bottom two and there's not enough room to get a drill in there. I may have to pull the jugs. If I do will I have to replace the cylinder base gasket and head gasket? I just intalled them yesterday.
I'm pretty sure yes you don't have to drill. First check that a 1/4-20 bolt will pass thru the hole in the tensioner. usually uses a 7/16th socket or an 11mm, same diff. PRactice on something if you can. A 6mm nut in a vice if no old engines around.
Its been a while. But at one time I had all my cam tower bolts as 1/4-20s. They are only slightly more diameter than a 6mm and slightly coarser thread.
The standard T handle on the tap likely won't work, same clearance problem as the drill, you'll have to use a 3/8 ratchet with a tap holder.
If you pull the jugs, its a new head cheeze and base gasket for sure, IMO Or you're taking a chance...which others have taken and survived, I'm just saying...
If you can get a 1/4-20 bolt to catch about 3 revolutions, with or without the tap, I'd bet money it will seal. 4 to 6 would be better, 8 revs is standard. But there is so little pressure on that tensioner, 2 good 6mm and a lame third hole ought to do it.
So check it out and ... don't blame me. Sorry for your pain. Been there.