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Filling aluminium head with brazing rods?

General engine tech -- Drag Racing to Circle Track

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cncguy987
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Re: Filling aluminium head with brazing rods?

Post by cncguy987 »

Geoff2 wrote: Tue Nov 03, 2020 1:51 am The exh gas might be 1000*, but the metal temp is much lower...
I would just go ahead and try then.
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Re: Filling aluminium head with brazing rods?

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For a little added insurance you could have the ports TBC'd.
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Re: Filling aluminium head with brazing rods?

Post by Truckedup »

enigma57 wrote: Wed Nov 04, 2020 1:30 am Have you considered machining some port stuffers of similar material and expansion coefficient as heads? Perhaps make them a slight interference fit to port walls (couple thousands) and use the manifold(s) to lock them down when assembling engine?

Just a thought,

Harry
I think this might work in some situations.
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Re: Filling aluminium head with brazing rods?

Post by MadBill »

How about like this? Tip: use heavier gauge stainless! :oops: I'm in the process of beefing them up with stiffener tabs and 1/4" dia. SS 316 'spines'. The ports were quieter and picked up ~ 20 CFM @ 0.700" and before turning inside out at ~ 4,500 RPM on the dyno, were good for 15+ lb-ft.

There is/was a guy making them for BBCs from cast iron and there still was someone a couple of years back doing them for BBFs. I believe they're popular with Pullers.
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Re: Filling aluminium head with brazing rods?

Post by n2omike »

Project Farm tested several different aluminum brazing rods against each other. Below is a link to his tests and results. They seem to work surprisingly well.

https://www.youtube.com/watch?v=fKIKsDfRAcs
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Re: Filling aluminium head with brazing rods?

Post by BCjohnny »

n2omike

Good vid, yes some of them do ...... but the detail is in the prep beyond that

By all means grind out the repair conventionally, but finish off with a Stainless cup brush and make flakes fly

Get in quick otherwise the oxide start to form again, heat only accelerates the process, and don't labour the job

Won't replace TIG, but as said has it's uses

Most brazing processes require skill, or a knack, and are often difficult to pull off ...... that's why people who 'can weld' often scorn them
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Re: Filling aluminium head with brazing rods?

Post by n2omike »

BCjohnny wrote: Wed Nov 18, 2020 4:00 am n2omike
Good vid, yes some of them do ...... but the detail is in the prep beyond that
By all means grind out the repair conventionally, but finish off with a Stainless cup brush and make flakes fly
Get in quick otherwise the oxide start to form again, heat only accelerates the process, and don't labour the job
Won't replace TIG, but as said has it's uses
Most brazing processes require skill, or a knack, and are often difficult to pull off ...... that's why people who 'can weld' often scorn them
You make some great points. Prep is everything with these! A fresh, rough finish is KEY to making these work. A grinder/sander does a great job. If a wire brush is used, it MUST be stainless. Regular steel will leave a dull gray finish on aluminum that interferes with the bond. The guy in the video above looked like he used a belt sander, and did the job right after.

His tests left me very impressed... and he is no expert, nor is he sponsored or selling anything. I was impressed that with some of the products, it was the parent material that failed, and not the brazed joint. I didn't see that coming. With the aluminum 5/16" bolt... He brazed the bolt head to a pulling device that measured force, and with the better products the bold shank broke before the bond let loose. Yes, it's the threads vs. the bolt head, but still...

I bought some some similar rods at a flea market 20 years ago, and didn't have much luck with them. After watching the video, I purchased some of the Hobart rods to try at some point. Curious to see how they work!
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