Lotus Elan

Tricky sheared off bolt

PostPost by: nmauduit » Wed May 24, 2023 2:05 pm

good job ! I would first try operation just after passing a tap in, it is more likely to maintain original alignment than with an helicoil if that can be avoided (once it's redrilled no quick way back), and the function is not to fasten but only to pivot a light (...) part...
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PostPost by: USA64 » Wed May 24, 2023 3:04 pm

Just a caution; the bobbins are aluminum, do not use Copaslip or such. It will form a weld.
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PostPost by: smo17003 » Wed May 24, 2023 3:15 pm

USA64 wrote:Just a caution; the bobbins are aluminum, do not use Copaslip or such. It will form a weld.

That's good advice, I have used nickel anti-seize on all of my aluminium (aluminum :D ) threaded parts.
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PostPost by: alan.barker » Tue May 30, 2023 7:42 pm

Copperslip is not a lubricant it is antiseize.
Should not be used as lubricant for moving parts.
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PostPost by: JonB » Tue May 30, 2023 7:52 pm

I propose stainless bolts and waterproof marine grease.

Hopefully not too contentious...?

But of note - if the car's pods still move up & down easily after 52 years (they did), I imagine ordinary zinc plated bolts will outlast me.
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PostPost by: mbell » Tue May 30, 2023 8:44 pm

JonB wrote:I propose stainless bolts and waterproof marine grease.


The bobins are Ali, so that is bad combination for galvanic corrosion. I'd stick with standard zinc plated and suitable lubricate.
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PostPost by: Gazzerb » Tue May 30, 2023 9:01 pm

Worth checking the galvanic table for relative metals;
Aluminium and stainless steel are fine whereas zinc and aluminium are likely to corrode.
Aluminium and copper also okay.
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PostPost by: Craven » Tue May 30, 2023 10:20 pm

When I replaced the pivot bolts I used a longer bolt with enough room to add a half nut behind the bolt head, this nut can then act as a lock nut against the bobbin. Stops any chance of a slow unwind out of the bobbin.
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PostPost by: snowyelan » Wed May 31, 2023 1:12 am

Hi Gary,

Can you share some insight on the charts you mention? From what I am seeing Aluminium is between zinc and stainless.
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PostPost by: JonB » Wed May 31, 2023 7:45 am

mbell wrote:
JonB wrote:I propose stainless bolts and waterproof marine grease.


The bobins are Ali, so that is bad combination for galvanic corrosion. I'd stick with standard zinc plated and suitable lubricate.


I think they are mazak (pot metal).
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PostPost by: Gazzerb » Wed May 31, 2023 4:14 pm

The bobbins seem to work like aluminium when being drilled & tapped but I do now recall that they are potentially made from Mazak...... 'base metal of zinc and alloying elements of aluminium, magnesium and copper'.....
That leaves us a bit stuffed when looking at the corrosion tables and scuppers my plans to use stainless steel!

I have extracted a table from the internet credited to Struct X which is a handy reference when considering any dissimilar metals and the risk if corrosion.
There is only one thing for it. Eliminate the electrolyte and keep the car dry :lol:
Gary

Perhaps on second thoughts, with the Mazak being mostly zinc, the stainless steel bolts will be fine after all. :D
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Galvanic Corrosion Table by Struct X.pdf
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PostPost by: snowyelan » Wed May 31, 2023 4:34 pm

Hi Gary,
I believe your chart is for situations where there is active current present (like in a steel bodied vehicle) based on the anode and cathode columns. Mid way through the article in the link below is a table that may be more appropriate for the isolated headlight bobbins. I'm no expert, so if we have one here on the forum, please feel free to correct me!

https://www.corrosionpedia.com/an-intro ... ion/2/1403
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