Eccentric bushing bolt

[GearheadEE]

Hey everyone,

I am in the middle of refurbishing a post 1991 mark V 510 and ran into this issue. The bolt that clamps the eccentric bushing does not seat flat on the casting ears. I was following Bill Mayos guide on headstock improvement where you put a lock washer under the head of the bolt, but the washer doesn't sit flat, and neither does the square nut(in the picture it is backwards, but I flipped it and the same thing happens. In the second pic I am holding the square nut flat on the ear and pushing it as high as it will go against the casting.

The only paths forward I can see is:
1) leave as-is, which isn't good
2) grind down square nut and get smaller lock washer
3) drill larger hole in ears in casting, which isn't good as well
4) grind/file down the shoulder of the casting to allow the nut & washer to have the room it needs
5) some stack up of spacers, not great

What do you guys think? Thanks!

139984744_10105471599632335_8558846445854866174_o.jpg (101.6 KiB) Viewed 660 times

140382420_10105471663918505_607221330427763963_o.jpg (120.63 KiB) Viewed 660 times

[JPG]

My first suggestion is to remove the washer under the head of the hex head screw. The head is large enough to retain the bearing in the eccentric which is it's only purpose.

Second forget about adding washers under the clamping bolt head and nut. However the nut should have a split washer between the nut and the ear. A split washer has a small od.

You may also add a split washer under the bolt head if you desire to do so.

Now regardless do not over torque the clamp!!! Barely compressing the split washer is adequate (another good reason to use them here).

[GearheadEE]

That washer under the bolt head is a split washer, sorry for leaving that detail out.

[edma194]

It takes minimal torquing on that bolt to hold the eccentric in place. Finger tighten it, watch the washers and see if they compress or bend at all, at that point you should be done. I'm trying to describe how I turn a wrench to tighten something like that, it's not going to move more than 10 degrees after finger tight. There isn't much area on the ears, it would be nice if a spring washer like Belleville, or just a bent washer would fit in there to apply some gentle pressure without cranking it down hard.

[chapmanruss]

The purpose for putting a lock washer there is to keep the Allen head cap screw (or bolt on early Mark 5's) and the nut from loosing up as with any bolt/nut assembly. There should be a washer with the nut according to the parts lists and exploded diagrams going back to the original Mark 5 Manual. I don't recall if it is a split washer or not and the parts list simply list washer. As others have said here and in other threads DO NOT OVER TIGHTEN the cap screw and nut. Their purpose is only to keep the eccentric from rotating which changes the belt tension. The eccentric is kept in place by the screw and washer in the main casting and the screw and washer in it. The Idler Shaft assembly is kept in place by the set screw in the eccentric. Unless you have an early Mark 5 which has a couple differences in that area with the first having nothing but that bolt, washer and nut using the casting clamping to hold it in place. That was soon changed.

I think in this case you are getting hung up on having everything "fit perfectly" but worry less about that and focus on function. There may have been some over tightening causing the cast "ears" of the housing to bend together some already.