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 Posted: 09-27-2021 10:24 pm
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Esprit2
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The timing belt eccentric tensioner hub's hex drive size went through a series of evolutionary changes. What hex sizes were used when... or on which eccentric hub?

If there are six sizes, it would be nice to hear about each one once. But we probablly don't need to hear about one size six times... right?

Hmmm... I suppose we could throw the Nyloc nut in there too. Did it's hex size change as well? If so, which nut size with what hub hex size.

Thanks for any help,
Tim Engel

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 Posted: 09-28-2021 05:45 am
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discogodfather
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I had the one with the dual bearings (which was the early kind?) for years and it is 19mm (for a 19mm wrench). The nyloc nut was a 17mm (for a 17mm wrench) and I think an M10 internally.

I now use Garry Kemp's updated kit (with the single integral bearing setup) and it uses a 19mm to adjust, but the nyloc nut takes an 18mm wrench now. Still an M10 internally.

BTW Kemp's kit (with the special spacer) is 100% bolt on for the Lotus 907 and it works great, not to plug anything but it's been a year and a half and 3k miles and it never has slipped and feels 5x stronger than the stock setup.

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 Posted: 09-30-2021 05:54 pm
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browndog9
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How do you procure said device ?

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 Posted: 09-30-2021 08:54 pm
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redracer
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The very early ones with the hex behind the bearings was 35 or 36 mm.(I no longer use those, although I do have the tool for it).
Later, they used 22mm(7/8" will work fine) with the 17mm locking nut.
These are the only ones I have ever seen althpugh you say there are 6?

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 Posted: 10-01-2021 04:08 am
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Esprit2
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Bruce,
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.

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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 04:36 am by Esprit2

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 Posted: 10-01-2021 04:30 am
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Esprit2
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browndog9 wrote:
How do you procure said device ?
Garry Kemp (Kemp High Performance Engines) is a Lotus specialist, and has an eBay store. You can sort through what he has listed there, or contact him through eBay. He's pretty agreeable about taking any conversation started on eBay to an email, or a phone call... but you can make contact there.

https://www.ebay.co.uk/itm/272070049030?hash=item3f58a37d06:g:xXoAAOSwnipWZhU0

Regards,
Tim Engel

Last edited on 10-01-2021 04:52 am by Esprit2

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 Posted: 10-01-2021 04:30 am
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Esprit2
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Oops... screwed up.
Would a moderator please delete this blank message.

Last edited on 10-03-2021 06:20 pm by Esprit2

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 Posted: 10-01-2021 06:30 am
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discogodfather
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Garry Kemp's kit, full bolt on for 907, 910, 912. I spin to 8500 rpm on this all the time, it works. Apparently this is becoming a thing to replace many of the later Lotus spring based tensioners.

Only drawback is that it is sensitive when setup precisely when you tighten it, slips a lot when you give the nyloc the final torque. Have to spend time getting to know it, and the Burroughs is a must have.

Tracks great, but a little inward of where the stock setup tracks (meaning the stock is centered, the Kemp kit is about 2mm towards the engine).

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