Studs vs. bolts for group head

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negrocorto
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#1: Post by negrocorto »

I'm in the process of finally getting my Conti Prestina back together. Is there a real advantage to using studs, threaded on both ends, to attach the group head onto the boiler, then tightening those with nuts, as opposed to simply using bolts to fasten the group head onto the boiler? What did the engineers who designed this machine have in mind when they chose to go this route? I wasn't sure where to post this question, having kept abreast of drgary's Prestina restoration, but chose to open a new topic since, I assume, other machines apparently use studs also.

Thanks

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drgary
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#2: Post by drgary »

Congratulations on having a Prestina to restore. My first thought on the advantage of studs over bolts is that you screw the stud all the way in until it bottoms out. Then you've got enough threads supporting the weight for sure. If there's enough stud left for securing it with a nut and washer, you're good. By the way, be sure to use marine grade hardened stainless (type 316 aka A4) and slather it with anti-seize compound.
Gary
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Paul_Pratt
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#3: Post by Paul_Pratt »

Yes I agree with Gary, with a bolt you can never be sure how many threads you have, a stud will make sure you have as many as possible. Studs for me are always the best choice.

jonny
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#4: Post by jonny »

Another, less obvious issue I've run into: the difficulty of aligning the group head to the mount while using screws. It's a minor inconvenience, but it's difficult to justify when the studs have the advantage of already being in place to guide the group into position effortlessly.

negrocorto (original poster)
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#5: Post by negrocorto (original poster) »

Thanks guys. I was eager to bolt the group head on this weekend, but I'll wait a few more days. I'm guessing Allann Bros has them....

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drgary
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#6: Post by drgary »

Use Allann Brothers for Prestina parts. But I would upgrade from stock parts for bolts and standardized hardware like that after my rusted bolt ordeal. You'll find what you're seeking at eBay or McMaster-Carr or a large industrial fastener supplier that has full inventory of metric sizes.

Off topic for a moment, how about some photos of your Prestina and your rebuild?
Gary
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hankbates
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#7: Post by hankbates »

Having studs semi-permanently in the boiler also reduces the amount of wear of the threads in the boiler, as they will not be disturbed when the group is removed for cleaning.
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jonny
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#8: Post by jonny »

You can also look at Ace Hardware if you have one near you. They have a decent selection of stainless metric hardware, but I remember not finding those studs there and hence I bought screws to get me started. Richard brings up a good point too. Brass is soft, so the lower the frequency of stressing those threads the better.

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rpavlis
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#9: Post by rpavlis »

It is also possible to decapitate long bolts to use the threaded parts for studs.