The Lotus Grand Tourers

Hi I am trying to fit a new timing belt to my 1990 ( G ) Excel with a new tensioner bearing. The belt is on all the pulleys in the correct position.

I have purchased a SATRA S-XTBT adjuster but it comes without instructions on how to use it.

Can somebody please tell me how to set the correct tension and at what figures or force using this tool ?

Or is there another way to set the tension without this tool ?

Regards
Ian.

I would suggest a forum search as there is lots of info already on tensioning the can belt. Try this one, particularly the article by Tim Engle
viewtopic.php?f=33&t=9874&start=15

I asked how to use the SATRA S-XTBT tensioner gauge as it came with no instructions.

I had already looked at a number of past threads on here and video's on Youtube all talk about other types of gauge or
semi-automatic adjusters or even twisting the belt 85-90 degrees To me that doesn't sound to accurate for such a important belt, as you can twist anything with enough force.

Please can someone tell me exactly how to do this with the said device as I have only just got my Excel and if I'm going to blow the engine I may as well not bothered to change the belts or do the shims on the valves.

Ian.

A quick Google search gives the first video, of how to use the device.
https://www.youtube.com/watch?v=Qf-zgjyEcMs
At approx 8mins there's a table which may not be clear enough, but I guess the same is available elsewhere, that will hopefully give you the conversion figures.

I would guess that you've not received precise help as nobody else is using the same device on the Excels. I had these and Esprits for years, been on forums for them for years, and don't recall anybody posting that they have one of these. I guess most use the Burroughs type(which is the Lotus one), a generic one which is pre-defined by belt thickness, or the Krikit (which isn't for timing belts but can be used with a bit of know-how).

You can set the tension by frequency. Lotus introduced this for the V8, but it can be used on the 910/912 as well. Base setting is 100-110Hz, but the type of belt (mass etc) will have an effect on frequency.
More info on https://www.thelotusforums.com/forums/t ... lt/?page=3

Filip

Ian,

Use of the SATRA S-XTBT depends upon having access to certain belt tension data/ specs provided by the engine manufacturer. Unfortunately, Lotus never used that method of setting tension, and therefore never published the required data.

The Satra works on the premise that for a given force applied perpendicular to the belt at mid-span, the belt will deflect a certain distance. For instance, a typical spec might be that for an applied force of 52-57 N-m, the correctlly tensioned belt will deflect 2mm. It's that sort of data that you must know before you can use the Satra, and it's that information that Lotus has never published.

Here's a Youtube video on how to use the Satra. It's 22 minutes, and in the end, just tells you what I wrote above. With out the Force Vs Deflection specs for the Lotus timing belts, you can't use the Satra.
https://www.youtube.com/watch?v=Qf-zgjyEcMs

The video link AndyC posted is a short version of the same video, starting at the 18:57 point.
https://www.youtube.com/watch?v=Qf-zgjyEcMs&t=1132s

It's possible to 'back into' the required Force Vs Deflection spec; but first, someone with a proper (and recently calibrated) Lotus tension gauge (Burroughs BT-33-86J, or Clavis Frequency Meter for the HTD belt only) is going to have to take the initiative to do the work. First, accurately set the belt's tension to Lotus spec, then immediately take a tension reading with the Satra. Using the result, back through the math/ logic to get to a Force Vs Deflection spec for that combination.

The same was true for the Krikit KR1. If you apply one to a correctly tensioned 9XX timing belt, it will not yield the same reading as the Burroughs. Back in the early-mid 1990s, Ian in Canada and myself, working independently, did similar correlation work for the KR1. Later, when we learned of each other's efforts, we compared results and found that they agreed. So I started promoting the KR1 on early mailing lists as an inexpensive alternative to the Burroughs.

You're now in the same situation with the Satra, in that it has not been calibrated for the Lotus 9XX applications. And as was done for the Krikit, someone is going to have to make the effort to determine a corelation for the Satra. Once that is done, it will probably be a reasonable alternative to the Burroughs. But today, NO, the Force Vs Deflection spec for the 9XX belts hasn't been published, so you can't use the Satra to tension the belt.

Note that the Satra is thickness sensitive, and the HTD belt is thicker than the trapezoidal belt... and the new Gates Blue belt is thicker yet. It will be necessary to correlate Satra Force Vs Deflection for each belt. Once that's done, it might be a dumb stroke of luck that all three are so close that the difference can be ignored, and one common spec used. That's wishful thinking, and it would be very unwise to simply do the correlation on one belt, and then presume it's correct for all Lotus 9XX belt options.

Regards,
Tim Engel

And all of that assumes that everything is properly calibrated.

Absolutely. 'Garbage in/ garbage out' applies.

Regards,
Tim Engel

If this is similar to the Draper tool then I did use that... Or at least check it against the Burroughs type. If you cut the old belt and staple a loop at either end you can then hang weighrs from it to provide a known tension... in my case it took a toolbox and spare wheel! You can then use the gauge to find out what it reads when the correct tension is present. This may only apply to that type of belt so make sure your repl is the same. I described what I did right at the end of this post..

https://majcd213.blogspot.com/2016/05/r ... inued.html

Or, you could visit one of us with your gauge and get the SATRA reading off our correctly tensioned timing belt.
Tony

Yep. That's how I checked my Optikrik.