Lotus Elan

Brace across rear turrets +2S

PostPost by: rgh0 » Tue Mar 17, 2020 7:33 pm

From memory its about 5 mm thick plus a couple of mm of the suspension leg material for the thread length of about 7 mm. If the threads are substantially damaged then helicoil or solid thread insert or drill and tap it out to the next largest size. The bolt works mainly in shear so the clamping load does not need to be high so the thread length is OK even if a bit shorter than desirable

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PostPost by: Matt Elan » Tue Mar 17, 2020 7:36 pm

Here is a picture of my Spyder chassis looking towards the rear cross member. You can see the two holes for the cross brace at the top of the turrets above the springs. You can just about see the plate which the hole is drilled in; it is (IIRC) about 4mm thick on top of the turret. Hopefully the thread is OK and just needs a clean up by running a tap down it. If you don't have a tap then file a flat or two and a point on a bolt an use it with lots of lube. If the thread is gone then I'd see nothing wrong in drilling it and the bobbin hole bigger, then running a tap down the next size up so the bobbin and chassis are both tapped. For a helicoil you'd probably need to move the body out of the way but you may be able to pop one in the chassis - use some locktite to fix it in place mind. You could run a long helicoil through the bobbin as well but I suspect it would snap if the body shifts slightly, so probably best just to helicoil the chassis.
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Front of rear turrets
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PostPost by: alan.barker » Tue Mar 17, 2020 8:07 pm

Sorry Matt but
Never ever use Loctite on Helicoils that's a no no. Also clearance hole in Bobbin, only Tap Chassis.
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PostPost by: mbell » Tue Mar 17, 2020 8:19 pm

Interesting, my Spyder chassis doesn't seem to have any thing for that bolt....

Maybe there enough thickness there or something in the tube to drill/thread. There is a lone spot weld on the tube.
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Spyder rear turret
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PostPost by: Matt Elan » Tue Mar 17, 2020 9:36 pm

Mine's an early chassis (#250 IIRC) and I'm pretty sure it had a plate but I may be mistaken - the body's sitting on the chassis ATM so its hard to check....
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PostPost by: HCA » Wed Mar 18, 2020 8:43 am

rgh0 wrote:From memory its about 5 mm thick plus a couple of mm of the suspension leg material for the thread length of about 7 mm. If the threads are substantially damaged then helicoil or solid thread insert or drill and tap it out to the next largest size. The bolt works mainly in shear so the clamping load does not need to be high so the thread length is OK even if a bit shorter than desirable

cheers
Rohan


I pulled the bolt completely out and it is a bit manky, so my thoughts are with replacement of the plate, but this is not staight forward as it means replacing the plate and then remounting to body to get an exact point to drill and tap the plate, remove the body and replace it again!

7mm is not a lot of meat for a 7/16 bolt to get a tight grip on. maybe there should be a beefier captive nut behind...

If there is enough movement on the rear turrets to warrant such a brace, I then got to thinking about the fronts where of course there is nothing. Then reading up on the subject, I see many of your serious competition bretheren say there is movement and manage to squeeze in a cross brace between the engine and radiator. Now, I guess if you are regularly cocking the inner wheel in corners this might be necessary, but for road driving?
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PostPost by: rgh0 » Wed Mar 18, 2020 9:28 am

Lotus never added a component like the cross brace without a reason but whether the reason was to stop chassis cracks or body flex and noise versus the chassis or to maintain rear suspension geometry or all three we wont know unless you talk to the original designers and they are no longer around and did not leave any substantial formal engineering design records that would help explain.

if you dont want to drill and tap the next size up bolt and dont want to remove the body I would find a new bolt and fit it gently and lightly tighten it and leave it alone for road use unless some other problem develops as the criticality of the cross brace at the rear for road use especially with a stronger Spyder chassis would certainly have to be questioned.

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PostPost by: alan.barker » Wed Mar 18, 2020 9:49 am

Imho you don't need to replace the Plate. Fit a Helicoil/ Armstrong or other Wire Thread Insert.
For sure to drill and tap the Plate for the Insert will mean increasing the clearance Hole in the Bobbin but that's not a problem.
to fit a Stainless Wire Thread Insert is easy BUT buy a Kit which includes: Pilot drill for Insert, Insert Tap, Fitting Tool, Special dia Punch to break Tang off Insert.
You need the Special Punch to break off Insert or when you break off the Tang the last Thread of the Insert will jump out of position.
NB: Before you assemble the Wire Insert into the Tapped hole, drill a Hole in a piece of scrap metal the same thickness as the Pad on the Chassis. Drill and Tap this and do a trial assembly of an Insert counting how many turns you need. That is to have the Insert 1/4 turn below front and back surfaces. You can adjust the length of the Insert with the Wire Cutter on a good pair of Pliers.
Then take this Insert with it's custom adjusted length, put a little Oil on it and slowly assemble COUNTING the turns.
For the now large dia hole in the Bobbin you can make a Bush to take up the Slack.
Have fun
Alan
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PostPost by: HCA » Wed Mar 18, 2020 10:34 am

Thanks Alan - first, not sure I have the patience do do this and second, not sure how it is with you, but here it is total lockdown, so buying anything car related is not going to happen unless available on ebay! The army seems to have deployed all their 19 yr old rookies down here and with their new found power, it is more dangerous to face them than walking amongst the virus.. :lol:

I have maqnaged to get a clean bolt, albeit a stainless one, back in as suggested by Rohan and tightened it up until I can feel it is about to slip and will worry more later... 8)
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PostPost by: alan.barker » Wed Mar 18, 2020 10:41 am

Hi Hal,
pleased to know you have fixed it.
I live in Morbihan France where there have been several Clusters.
At least it gives me more time on the Forum and try to share our knowledge :wink:
Amicalement
Alan
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PostPost by: Donels » Tue Mar 24, 2020 11:29 am

In my Lotus +2 chassis I need to clean the threads in the rear turrets. I measured the thread and reckon it’s 7/16 x 20 UNF. Can anyone confirm before I order the tap please.
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PostPost by: oldelanman » Tue Mar 24, 2020 12:50 pm

Donels wrote:In my Lotus +2 chassis I need to clean the threads in the rear turrets. I measured the thread and reckon it’s 7/16 x 20 UNF. Can anyone confirm before I order the tap please.


Yes. The bolt part no is XUFB0724 which is 7/16" UNF x 1 1/2" long
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PostPost by: alan.barker » Tue Mar 24, 2020 2:27 pm

7 for dia 7/16
24 for 24 16th long
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PostPost by: Donels » Tue Mar 24, 2020 6:15 pm

Thanks guys. Brilliant nugget of information.
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PostPost by: Matt Elan » Wed Mar 25, 2020 8:13 pm

Just a quick comment - the workshop manual points out that this mount may need to be shimmed. There may be clearance between the body and the chassis at this point as it’s the only mounts that is in the fore and aft plane. If you tighten it without shimming you can distort the shell; lotus suggest making up shims from 16swg thick steel to fill any gap.
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1969 Plus 2S - Currently undergoing nut and bolt restoration
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