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Filling aluminium head with brazing rods?

General engine tech -- Drag Racing to Circle Track

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BLSTIC
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Filling aluminium head with brazing rods?

Post by BLSTIC »

Are those aluminium brazing rods usable in a cylinder head reliably? Particularly in the exhaust ports?

I'm looking at a few different engine designs and thinking 'wow those ports are way too big', 'so are the exhaust flanges', and 'If only this thing had some tumble flow...'. Filling the ports would fix that right quick...

I have spare heads to try the technique on, but they are too soft to actually test on an engine.

Thanks
Ben
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Re: Filling aluminium head with brazing rods?

Post by mag2555 »

Your concidering doing things that should not be tried out with out a flowbench at hand other then maybe cutting down on excess expansion rate of a Exh port out to the flange once the flow has cleared its way around the short turn, at that point any drop in the floor path is likely not needed in general.
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Re: Filling aluminium head with brazing rods?

Post by cncguy987 »

The exhaust temps are way hotter then abrasing rod melting point.
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Re: Filling aluminium head with brazing rods?

Post by treyrags »

cncguy987 wrote: Sun Nov 01, 2020 7:56 am The exhaust temps are way hotter then abrasing rod melting point.
We filled the floor of stock Cleveland exhaust ports with brass to raise them before aftermarket heads were allowed in our Comp class in the early 80's. If your exhaust is melting the brass out of your exhaust ports you have bigger problems....
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Re: Filling aluminium head with brazing rods?

Post by V12MECH »

Are you thinking about the aluminum rods sold at the typical tool discount store? They have a very low melt point.Check out Muggy Weld supply, I have used some of their products with good results.
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Re: Filling aluminium head with brazing rods?

Post by cncguy987 »

I also was assuming you meant braizng rods you can by at home depot etc. Melting point is 750f. I seen exhaust temps near 1000f.
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Re: Filling aluminium head with brazing rods?

Post by BLSTIC »

cncguy987 wrote: Mon Nov 02, 2020 8:18 pm I also was assuming you meant braizng rods you can by at home depot etc. Melting point is 750f. I seen exhaust temps near 1000f.
If those are the ones on tv where they "weld" any non ferrous metal and filled the holes in the coke can, then yeah, that's what I was talking about.

mag2555 wrote: Sun Nov 01, 2020 6:02 am Your concidering doing things that should not be tried out with out a flowbench at hand other then maybe cutting down on excess expansion rate of a Exh port out to the flange once the flow has cleared its way around the short turn, at that point any drop in the floor path is likely not needed in general.
And yes, that was pretty much it. It seems like most older 4v heads I see have massive ports compared to the valves. Going from what Exhausted has been saying I'd do well to keep them smaller, which also works well for turbocharging. Flow bench won't help me on the intake side, or at least not used traditionally. Need some tumble flow metering in there...
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Re: Filling aluminium head with brazing rods?

Post by Geoff2 »

The exh gas might be 1000*, but the metal temp is much lower...
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Re: Filling aluminium head with brazing rods?

Post by BCjohnny »

BLSTIC wrote:Are those aluminium brazing rods usable in a cylinder head reliably? Particularly in the exhaust ports?
If I'm thinking about the right product, melts around 300 deg c (~ 600 deg f), then the bulk metal temperature will in normal circumstances stay below that, but I've a funny feeling you might experience localised erosion or scouring

I'm not sure there's enough of a temperature cushion that you won't experience problems, but there's only one way to find out and it's unlikely to be catastrophic to the rest of the engine

I've used those Aluminium 'brazing' rods on many other jobs, and they can be a lifesaver where 'normal' TIG welding won't cut it ....... correctly done
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Re: Filling aluminium head with brazing rods?

Post by BLSTIC »

BCjohnny wrote: Tue Nov 03, 2020 2:40 am I've used those Aluminium 'brazing' rods on many other jobs, and they can be a lifesaver where 'normal' TIG welding won't cut it ....... correctly done
What situations would TIG not 'cut it'? I'm looking at these brazing rods as a budget alternative, I didn't think there was a place they could be better
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Re: Filling aluminium head with brazing rods?

Post by BCjohnny »

BLSTIC wrote:What situations would TIG not 'cut it'? I'm looking at these brazing rods as a budget alternative, I didn't think there was a place they could be better
I've used it on occasions where TIG had 'failed' and another method was needed to repair the repair

One job was continuing crack propagation along the line of the weld

All the usual methods, cutting out and drilling the end, pre-heat, different filler etc, had been tried ...... but the crack would always eventually propagate afterwards ...... a common model of gearbox casing that came in

I guess you could have thrown weeks of fannying around at it and came up with the solution, but the economic answer was to use another method, hence the brazing

In hindsight I'd guess the more malleable nature of the brazing process allowed a softer interface for the repair than the harsher TIG ...... or the higher tensile strength of the filler distributed the stress into a larger load bearing area ....... I dunno, it worked so it's all kinda moot :wink:

Alum brazing rods aren't for everything but, despite the usual 'expert' internet babblings, they do have their uses
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Re: Filling aluminium head with brazing rods?

Post by enigma57 »

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,

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Re: Filling aluminium head with brazing rods?

Post by ProPower engines »

BLSTIC wrote: Sat Oct 31, 2020 8:10 am Are those aluminium brazing rods usable in a cylinder head reliably? Particularly in the exhaust ports?

I'm looking at a few different engine designs and thinking 'wow those ports are way too big', 'so are the exhaust flanges', and 'If only this thing had some tumble flow...'. Filling the ports would fix that right quick...

I have spare heads to try the technique on, but they are too soft to actually test on an engine.

Thanks
Ben
The real question is what or who's heads are you working with. ](*,)
There is no real good solution till that is known. [-X
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Re: Filling aluminium head with brazing rods?

Post by Krooser »

How about using a MIG gun with a spool gun?

I've seen blocks repaired with these units and have been OK for many seasons of use.
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BLSTIC
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Re: Filling aluminium head with brazing rods?

Post by BLSTIC »

Krooser wrote: Thu Nov 05, 2020 9:10 am How about using a MIG gun with a spool gun?

I've seen blocks repaired with these units and have been OK for many seasons of use.
I didn't even know such a tool existed. They have such a tiny nozzle you could almost weld from the valve side if it came down to it...

I need to see if those are compatible with my Cigweld 135 or if I need to use a different machine

Thank you for that
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