GT6 / Spitfire DIY alternator bracket improvement

Problem: Years back when I first did an alternator conversion on the GT6 the very rudimentary ‘pull it hard and tighten the nut’ fan belt tensioning method really annoyed me. It seemed there should be a way to achieve finite adjustment, and not risk noisy, slack or dangerously tight belt tension.

Solution: I don’t remember where now, but somewhere I saw a rigging screw (sometimes called a Turnbuckle). They are available in a load of sizes, lengths and materials from chandlers (sailing suppliers). So I used one of these to solve the problem. I then went on to sell them for a while on eBay under the name Mere Components.

Type: The type I chose for this job has two ‘jaw’ ends which usually come with a removable pin. Other types of end available are hook, eye (round and oval) and swage, so be specific when ordering.

Size: Rather fortunately there’s a commonly available 8mm size. It has M8 threads, 8mm pin and 8mm clearance drilling in the Jaw, and the Jaw gap is also 8mm which suits the flange on a Lucas A127 alternator which you’re probably using… right?

Material: Given that Turnbuckles are used in sailing, many are available in marine-grade stainless steel. Galvanised steel is available but… nope.

Modifying  an ‘off the shelf’ turnbuckle: The alternator-end can be used as-is, bolted to the alternator with a stainless M8 bolt, nyloc nut and washers. See the following image:

The other end needs to attach to the head via one of the water pump housing bolts. This is a 5/16″ bolt which is near-as-dammit 8mm, so perfect for the 8mm clearance hole in the Jaw. To avoid having to use a longer than standard bolt, and fouling the water temperature sender attachment, one half of the Jaw should be cut / ground off. I found that a new hacksaw blade, and several passes over a bench-grinder made a nice neat Job of it. See pic:

Finally, the two nuts that came with the turnbuckle I bought were very weedy, so I found a ‘normal’ sized stainless M8 nut, and a reverse-threaded one, to replace them with. There are not nylocs, so two 5/16 fibre washers are performing locking duty.

Here’s a pic showing the whole thing installed:

These pics are courtesy of Roy Lacey, showing the one I made for his GT6 as a prototype years back.

Side-note: I see that Quiller Triumph still have these listed as for sale at £32! Goodness… they used to buy them off me a few at a time for about£10 or something back in 2008, crazy. Here’s one of my old photos that they’ve ‘borrowed’ it seems for their website:

alternator adjustable bracket stainless


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3 thoughts on “GT6 / Spitfire DIY alternator bracket improvement”

  1. Hello,
    Great job on the tensioner! I’m looking to do something similar on a 6v to 12v conversion,on an old Ferguson tractor. I’ve seen numerous variations,but I like the jaw ends on yours. I’ve seen the jaw ends,but I haven’t been able to find a single sided one. I found Quillers,but like you said,it seems a bit pricey! Can you provide me the names of some other sources. I’m not opposed to buying the pieces individually and assembling my own.
    ThankYou & Have A Good One😃

    1. Hi Kevin,
      Glad you like it. I’m still running one on my GT6.
      You mention “single sided” jaw end. I bought the rigging-screws in bulk as normal double-sided jaw ends, then sawed one side off (just with a hacksaw and good quality stainless blade) and cleaned up the cut on a bench grinder. A 10 minute job. Also mentioned above is the fact I replaced the nuts with better/bigger ones. It’s all stuff that’s readily available, and there’s nothing ‘special’ about the Quiller ones, and I imagine that if you ordered one they would also have to make it and send it to you 🙂

      I can’t find the original source of the rigging screws used in the pics above, but a search for “M8 stainless riggings screw” returns this site:
      As long as you check the ‘L1’ and ‘L2’ open and closed lengths listed there suit the Ferguson, and that the ‘E’ jaw gap suits the dyno/Alternator you’re using, I think you’ll be fine.

      If you can’t find reverse-threaded M8 nuts and suitable washers, let me know as I still have some knocking about.

      Cheers! Ben

  2. Fantastic idea, & many thanks for the link to GS Products, I have ordered one today.
    Regards, Andy

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