Thermostat housing bolts

[GrahamFountain]

At the moment I can't foresee any situation where I'd sell the car.

I did download the specification for the Evans Vintage 180, and it looks fairly impressive. But I don't think I use the doly in a way that requires a waterless coolant.

I've also been having a bit of a look for studs to use instead of set screws, but I haven't yet found any that have more than 3/8ths inch UNC thread that don't have too large a saddle section as well.

I wanted more than 3/8ths of UNC into the manifold. It ought to be enough: a pretty rough calculation shows the area of alloy in 3/8ths depth of 3/8ths thread (once coiled) is nearly twice that of the CSA of a 5/16ths stud. And the difference in tensile strengths should be well less than a factor of two (even not knowing the specs of the alloys). So if the torque setting given won't risk shearing a 5/16ths stud or screw, it shouldn't risk stripping 3/8ths of 3/8ths thread out of alloy either. But I'm still a bit concerned that, given the years of thermal cycling and chemical action, there could be some stress cracks round the top of the hole in the manifold. It's probably not an issue, and the helicoil should spread the stresses out along the thread, and maybe a bit further down the hole as well. But...

I suppose I could make a pair of studs to the spec I want, i.e. 1/2 – to 5/8ths inch of UNC thread, from some 5/15ths bar. But as I have nearly none of the tools, I'd have to have it done, and that's liable to be a lot for a pair of studs. Yes I could just use bits of 5/16 UNC roll threaded bar, and chop off above the UNC nut, but if I'm putting that much into the job, I'd like it to look right.

So I'm swinging back to using the 1" SS set screws I've got. I did talk to a qualified chemical engineer (my father in-law) about it, and his experience is that stainless screws can be difficult to remove from aluminium after a year or two in the air and rain. But with the holes coiled with AS7245, 302 stainless inserts (and in a continuously acidic environment), that shouldn't be the same problem.

Graham

[tinweevil]

So I'm swinging back to using the 1" SS set screws I've got. I did talk to a qualified chemical engineer (my father in-law) about it, and his experience is that stainless screws can be difficult to remove from aluminium after a year or two in the air and rain. But with the holes coiled with AS7245, 302 stainless inserts (and in a continuously acidic environment), that shouldn't be the same problem.

Graham

Go with your instinct and a good slap of copaslip (That's proper copaslip not cheapo copper grease). If you're still worried how it'll be after a year set an alarm or mark it in a calendar then remove and check them. The cost of a gasket is pennies.

[Karlos]

Myself I would do what Tinweevil suggested, plenty of Copaslip but I would stick with bolts or setscrews. I think if you get a seized thermostat housing on studs it is much more difficult to remove than if it was fixed with bolts or setscrews.

[tony g]

Have you thought about helicoiling to M8 metric? Opens up plenty of options for studs or bolts. All my inlet manifold threads are now M8 (ex are 10mm).
Cant be arsed to look for unf/unc bolts I guess

Tony

[GrahamFountain]

That's a good point about the cover ceasing to studs that I hadn't thought of.

But the 5/16 UNF helicoil kit arrived today. Not happy about that. But for time reasons, I've had to order another UNC kit and send that one back in parrallel.

GRRRaham

[GrahamFountain]

Have you thought about helicoiling to M8 metric?

I had enough trouble with the TR7 being an imperial spanner engine and a metric spanner body. Never did work out if the engine mountings were metric bolts with imperial nuts or vice versa.

Graham

[GrahamFountain]

The rain finally held off long enough to helicoil the inlet manifold. I had a good look and it was only the RH one needed doing.

I hadn't done one of these since day release at Tech collage, in the 70s, but it all went as I expected, with the drill that came with the £12 coil kit being smaller than the clearance hole in the thermostat cover. So I was able to drill out the hole with the cover in place, and held down by one bolt, to keep all the swarf out of where it shouldn't be.

Both the setscrews are now tightened down to 20 lbf ft (thanks Jon) with no problem and, so far, no leaks.

I did use the copper slip on both the stainless bolt into the stainless coil and the one into the alloy manifold. I'll try to remember to pull them both in a few months, see if there's any obvious pitting or other signs of corrosion on either, and report the results.

Graham

[dursley92]

Slightly off topic, but continuing studs versus bolts, what do folks think about changing to studs for the exhaust manifold?
My current Sprint engine had studs when I got it and I have a stainless tubular manifold. I was wondering if it was worth fitting studs on a "new" engine and the 10mm metric option helicoils sounds like a good idea.