Just thought I would share. While I had some of the engine accessories off doing a rebuild on the a/c system (remanned compressor, new expansion valve, new Groton evaporator, drier, New Groton condenser, all new custom made hoses) I also did belts and poly bushings on the accessories (P/S and alternator).

The tension felt fine on all the belts but my alternator tension bolt sheared off in the block! Had to drill a hole in it and use a screw extractor to get it out... anyone else had this issue? Not sure what grade bolt I should go with for replacement :/

If your pulleys are running true the kind of bushings should make no difference.
By the way the bolt holds the tensioner arm but it is actually loaded in shear,
so it is really a "shear bolt".
--
George Downs Bartlesville, Oklahoma

I think no more than a grade 5 should do it. A grade 8 might mess up your threads and I would doubt there was a grade 8 in there. Grade 2 might be too soft. If you aren't sure what grade was in there look at top of head.

No marks is grade 2; 3 radial lines is grade 5; 6 radial lines is grade 8.

For metric, class 8.8 (on head) is medium carbon steel, quenched and tempered; class 10.9 (on head) is alloy steel, quenched and tempered.

There's more but that should be more than enough info for what you are doing.

Thanks for the posts guys. I was looking and yoshifab sells aluminum mounts, so I really don't think that the polyurethane should be any issue.

I was at the junkyard today and I went ahead and just pulled another bolt from a stock 240 along with the tension arm. Apparently at some point they added an m6 tensioner to the slot on the tension arm, so I picked that one up, because it also made more sense the way it held the bushing. I've just used a broom stick while I tightened the tension bolt in the past.