Should brass or stainless bolts be used in a brass boiler?

[bill]

I have a question for all the technicians on the forum. My commercial Gaggia machine has just experienced a burned out heating element and while waiting for the replacement to arrive I decided to remove the boiler plate and check the boiler. The boiler and the boiler plate are brass and the bolts are brass, too. The bolts are threaded in to holes in the boiler. Since one of the soft brass bolts had already broken off and two others had leaked a little, I thought about going back with stainless.
My concern, though, is that it might be very easy to strip out the holes in the brass boiler with the stainless bolts. Maybe that's why the brass bolts were used in the first place?
Any thoughts from folks with more knowledge in this area then me?

[starry]

I think the issue of threads stripping is a matter of the amount of torque applied. Brass is weaker and therefore cannot sustain the same amount of torque as harder materials such as stainless. Another factor using different metals in this application is thermal expansion. Different materials expand and contract at different rates and may 'work' against each other during heating and cooling cycles. Seems like the safest approach is to use the brass bolts and don't overtorque them. I don't know off-hand what the torque specifications are for brass, but they can be obtained from the 'Machinery Handbook', a reference book probably available at most libraries.

[jesawdy]

Bill,

That is a valid concern, but I think not a big issue. The Silvia brass grouphead has a stainless #6 Allen screw, and the E61 groupheads are chromed brass and have stainless screws. I thinks its a matter of trying not to be too ham-handed.

If I am reading this Table correctly, Bolt Torques - Stainless Steel, Brass Aluminum Bolts, you would certainly torque a brass bolt to a slightly lower torque. I would assume the converse would be true, for steel into brass.

Hopefully someone that has done exactly what you describe will chime in with their experience.

[bill]

Ralph & Jeff,
Thanks for your responses; you both have good points. If I do go back with the s.s. I'd planned on torquing it like it was brass. Also, I know I can easily find the right size in stainless but not so sure about brass. That may end up being the critical factor anyway. Hopefully, someone who's had to go thru this will give some input.
Bill

[bill]

Another option I thought of was to use s.s. socket head cap screws rather then regular bolts. My thought is that I'd be less apt to overtorque the bolts with an allen wrench? Any thoughts?
Bill

[HB]

I like the flat profile of Allen screws and they're nearly impossible to round off, but I don't think the choice is crucial. If I was concerned about over-torquing, I'd use a torque wrench and a criss-cross pattern when tightening.

[starry]

You can get just about ANY type of brass bolt or machine screw in metric or not from http://www.mcmaster.com Try entering metric socket head cap in the search. They also have the best selection of stainless fasteners I've ever seen depending on your final choice.

[gtrman]

Bill,
I'm not totally sure if this applies to brass and SS, but in every experience I've had, unlike metals corrode each other...
This leads me to believe you should go with the brass. But again, maybe there's some anomaly between brass and SS that this does not apply.
good luck
-jeff

[gscace]

Bill,
I'm not totally sure if this applies to brass and SS, but in every experience I've had, unlike metals corrode each other...
This leads me to believe you should go with the brass. But again, maybe there's some anomaly between brass and SS that this does not apply.
good luck
-jeff

Depends on voltage potential of the 2 metals in contact with each other. Brass and stainless steel are very similar, so you can use both together without fear of galvanic corrosion. Dunno why brass was used here except for the business of thermal expansion, but even that shouldn't be too big an issue. I suspect the real issue here is people thinking too much and being too tricky. I'd be perfectly comfortable with using stainless steel fasteners.

You might try Maryland Metric as a source of metric fasteners. McMaster Carr is also good and very fast.

-Greg

[bill]

Thanks to everyone for their input. It seems the consensus is that s.s. bolts should be fine as long as I'm careful not to over-torque. A plus is that my local hardware store has a good selection of metric bolts and socket heat cap screws in stainless.

[cannonfodder]

Put a drop of 'anti seize' on the bolts and they will break free when you open up the boiler again, 10 years from now. Stop by you local auto parts store and ask them for it, they will have some. Since the bolts do not contact water, I would not have a problem with it, but don't use it on something like the dispersion block. It is a bit toxic, that lead and lithium grease combination does not taste good. Don't worry about the boiler heat affecting it, it holds up well with spark plugs and engine heads which get a lot hotter than a boiler.

[bill]

Good idea! I'll do that. In ten years I'll be pushing 75 and will need all the help I can get.
Bill