Lotus Elan

Thermostat housing fasteners

PostPost by: TonyA » Thu Feb 29, 2024 3:18 pm

Looking at past posts, it was suggested to future proof the routine removabiluty of the thermostat housing by using 2 studs and nuts/ washers rather than as now, the fully threaded bolts/ washers; indeed this was allegedly factory practice on some cars

The thread is 5/16 unc and the fully threaded bolts are 7/8 inch long.

Does anyone know how long the threaded part of the stud that goes into the head needs to be, to bottom and a bit..?

Thx as ever...Tony
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PostPost by: alan.barker » Thu Feb 29, 2024 4:15 pm

Always used standard screws no problem.
They don't need to be very tight.
Just check flatness of flange.
You can put some copperslip on threads, why not.
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PostPost by: mbell » Thu Feb 29, 2024 4:52 pm

I believe the bolt penetrate into the water chamber in the housing, so likely need studs to be 3/8 to 1/2" below the surface. So would guess you want a stud around 1 1/4" long.
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PostPost by: types26/36 » Thu Feb 29, 2024 6:09 pm

Just checked a head and the holes appear to “bottom” at approx 16.6mm deep and don’t go into the water jacket on the head I checked.
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PostPost by: TonyA » Thu Feb 29, 2024 6:32 pm

Fantastic...! have already made a pair of two ended 5/16 unc studs provisionally about 1.75 inches long from A2 stainless round bar..now to trim each end : one to the head depth as you have kindly determined, the other to housing + nut+ washer height....Thx..Tony
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PostPost by: ericbushby » Thu Feb 29, 2024 7:28 pm

Hi Tony.
I think you should be careful using stainless steel in Aluminium. They are a long way apart on the galvanic scale and in the presence of moisture can cause corrosion. I believe It is possible to use stainless but it needs to be isolated with a barrier cream. Way back we used to use Lanolin on outboard motors but I think modern materials will be better now.
Ordinary steel bolts cause a lot less trouble.
Best of luck
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PostPost by: alan.barker » Thu Feb 29, 2024 7:39 pm

Hi Tony,
Why do you want to fit Studs
Alan
P.s. i know different subject but are you using Studs or Screws on the Exhaust Manifold
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PostPost by: smo17003 » Thu Feb 29, 2024 8:51 pm

Sometimes with a stud you can attempt to loosen the nut and the stud itself starts unscrewing, kind of negating the whole purpose for having a stud. This has happened to me with manifold and carb studs on the twin cam.
Perhaps cutting a screwdriver slot in the top of the stud would help keep it in place when loosening the nut?
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PostPost by: TonyA » Thu Feb 29, 2024 10:36 pm

My exhaust manifold is held traditionally; studs and copper nuts.

I put a screwdriver slot in the studs securing the thermostat housing on my Volvo Amazon 15 years ago.; likewise in the studs securing the air filter to the Zenith carb, exactly to have something to stop the stud backing out when loosening the securing nut: works a treat...Tony
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PostPost by: 2cams70 » Fri Mar 01, 2024 1:47 am

Original is best. Corrosion may have been a problem when these cars were in the “banger” class with cooling systems filled with tap water but not now as well cared for classics. If you are concerned just use some pipe sealer or low strength Loctite to seal the threads to stop corrosion by keeping moisture and air out. As others have said not a good idea to use stainless steel.
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PostPost by: rgh0 » Fri Mar 01, 2024 3:21 am

I use carbon steel hex head socket cap head bolts as easy to get at the one between the cam cover and thermostat housing. i use nickel anti sieze on the bolts and never had any problem.

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PostPost by: alan.barker » Fri Mar 01, 2024 5:54 am

Hi Tony,
I suggest to stay with Screws as original on Thermostat.
For the Exhaust Manifold Brass would be better
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PostPost by: lotusfan » Fri Mar 01, 2024 10:41 am

I also say stay with bolts. The BMC A,B and C series engines use studs for the thermostat housing and because of corrosion are always a pig to remove.
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PostPost by: alan.barker » Fri Mar 01, 2024 11:07 am

lotusfan wrote:I also say stay with bolts. The BMC A,B and C series engines use studs for the thermostat housing and because of corrosion are always a pig to remove.

+1 i was just thinking of BMC Thermostats with Studs coroding solid, they were a real pain in the butt.
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PostPost by: TonyA » Fri Mar 01, 2024 11:54 am

have just found a galvanic table : sure enough, counterintuitively, plain steel is a better bedfellow with Aluminium than is Stainless. Also, zinc will corrode preferentially when in contact with Aluminium.

I will use zinc plated steel fully threaded bolts for the thermostat housing... as Alan, Rohan Eric et al have said all along..!

BTW, be careful : our precious Aluminium castings will fizz away if in contact with salty Platinum or Gold..!

Thanks all..Tony
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