View single post by Esprit2
 Posted: 10-01-2021 05:08 am
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 547
I'm not sure how many there are, I've just noticed an evolution in the tensioner eccentrics. Like, everytime a different front seal housing was introduced, the height of the cylindrical mounting boss changed, and a new tensioner was also introduced, in the correct length to keep the 'roller' in the plane of the timing belt. If they ALL had a 22mm hex, that would simplify things me, and be good to know... one size is far better than many.

I'm collecting the eccentric hub's hex sizes for a project I'm working on... not just some scrapbook entries. If it works out, I'll let you know. What I need is ALL the various tensioner eccentric's FRONT-mounted hex-drive sizes. Hopefully, that's 'JUST' the one... 22mm.

The J-H that I worked on a year ago had a two-piece eccentric hub... front piece with a 'hex' drive, and rear piece that mated with the stud & mount on the engine. Both were small, lightweight cast parts. I wasn't smart enough to make note of the eccentric hub's hex size.


Monday, a local J-H owner loaned a spare tensioner to me. I'm not sure what vintage it is, but it has a hefty eccentric hub that includes the rear mounting portion, plus a cylindrical boss that passes through the bearings bore. Then a second 'front' piece that, like above, is a lightweight cast part. It's a slip-fit into the front side of the bearing/roller assemblly, and includes the adjuster hex head.

The eccentric's front-side Hub has a 22mm Hex, as you mentioned


Early Lotus 907s used an eccentric tensioner that also used front & rear, lightweight cast eccentric hubs. But I don't know if it was the same as the first J-H eccentric that I mentioned above. I've never seen that version of the Lotus eccentric, so I'm searching for that one as well.


Later Lotus tensioners (1986-onward, with HTD round tooth timing belt) also used a hefty, billet steel eccentric hub, but it's long enough to extend fully through a one-piece, double-row bll bearing. It includes the adjuster hex on it's front end. It's all one piece, and a press fit through the double-wide, two-row bearing's bore. No cast front cap. A couple of years ago, Pieter Van Ruth (Qwerty) did a "Group Buy" of a one piece billet hub with the double-wide, two-row bearing. It was this 'Lotus' tensioner that he cloned in J-H lengths.
19mm = 0.7480314" -- Hex on Eccentric Hub

In all cases above, the mounting stud that threads into the block is M10, and the standard M10 Nyloc nut has an equally standard 17mm hex head.

If I'm missing any, add them to the list.

Thanks & Regards,
Tim Engel

Last edited on 10-01-2021 05:36 am by Esprit2