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Silver Soldering help - crankshaft

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Matt Stevens 126/02/2021 03:04:03
97 forum posts
11 photos

Hi All,

So i have just pinned and silver soldered my Stuart Triple Crankshaft. I am happy with about 50-60% of the joints but some of the others did not capillary into the joints....i think because i did must have 'burnt off the flux'

I have pickled the crankshaft and cleaned up up the best i can with 400 grit, but i am concerned that because i can't disassemble the joints now that i cannot clean them up you think it will solder up again if i reflux the outside and try again?



Edited By Matt Stevens 1 on 26/02/2021 03:06:19

not done it yet26/02/2021 05:45:20
6444 forum posts
20 photos

Because it cannot be guaranteed, I have to say ‘doubtful’. Could do but....

Silver soldering and pinning is belt and braces, so it should not be too important, even if only partially soldered.

Probably a good deep clean in pickle, followed by careful rinsing and trying again looks to be the best option you have, short of removing the pins.

Personally, I would not have pinned until soldered satisfactorily. That way it could have been relatively easy to ‘unsolder’ it in order to start again, from scratch.

Experts will be along shortly, so I, too, am looking forward to their comments.

Speedy Builder526/02/2021 06:50:34
2454 forum posts
196 photos

What pickle, did you pickle hot or cold?

For me, the brick behind your flame would have been more effective it it were closer to the work, so that the flame "licked" around the workpiece.

Hopper26/02/2021 07:05:33
5505 forum posts
137 photos

Is that a metal V block you are soldering on in the pic? That would be sucking up all the heat from your torch. Not to mention doing the V block no good.

Edited By Hopper on 26/02/2021 07:15:15

fizzy26/02/2021 07:14:23
1827 forum posts
120 photos

I occasionally get the odd joint which wont take (I do this every day near enough). You need tenicity flux, not easyflow, then get it real hot. Get it hot enough and the flux will do its stuff. It will flow into the joint by capillary action before the solder melts but it needs to be a lot hotter than normal - no idea why, but it works.

Keith Hale26/02/2021 09:23:40
329 forum posts
1 photos

Hi Matt,

Silver soldering is a skill made impossible by not sticking to the basic principles of the process. At least you appreciate the role of capillary flow.

The problem and solution to it lay in the same place - behind the torch!🤔

The picture indicates that your heating technique is flawed. Do other problems lie ahead? Do you appreciate WHY you have to do what you do to make successful joints?

I suggest that you seek professional one on one advice. Talk to someone who does it for a living, or your equipment or material supplier. A 30 minute conversation could prove to be revolutionary🙂

The real answer to this and future problems does not rely on a pickle but getting things right first time! There are plenty of books available. Seek more than one line answers.

Give a man a fish, feed him for a day...... Teach him to fish......👍

SMEE used to run a course.



PS Keep clear of grit. If you don't get rid of it all afterwards, the alloy won't flow. Not the same problem but a problem all the same.


Edited By Keith Hale on 26/02/2021 09:25:42

Keith Hale26/02/2021 09:38:44
329 forum posts
1 photos

Hi Matt

See personal message.

The only charge goes on your phone bill ☺️


JasonB26/02/2021 09:54:39
21649 forum posts
2495 photos
1 articles

Which may be high as I think matt is in the US

Brian H26/02/2021 10:26:58
2242 forum posts
113 photos

Hello Matt, what kind of flux are you using?


Dave Halford26/02/2021 10:41:39
1820 forum posts
19 photos

A brand available in Ontario? smiley

Matt Stevens 126/02/2021 14:09:56
97 forum posts
11 photos

Hello All,

Thanks for the responses.....firstly I am based in Ontario, Canada. It is below zero out which likely doesn't help!

The flux i am using is a LucasMilhaupt Handy Flux which is disolved in a little filtered water to make a thick paste. I also have a LucasMilhaupt Tec flux which is for high temperature soldering and is a liquid and quite runny....i was thinking this might help to 'pull' into the joints?

I have used the paste type several times before without issue.

The V-blocks didn't take to much heat, they got warm but not hot. None the less, i could use something else and for sure i can try more firebricks that are closer as well.

I am assuming there is nothing to lose by trying again after a good clean up anyway....

PatJ26/02/2021 16:03:41
141 forum posts
104 photos

There is definitely a bit of an art to silver soldering.

Using a good flux is critical, as is cleaning the metal before applying the flux.

I have only silver soldered a few items, but all were successful.

I have done a lot of soft soldering, and so the technique is the same, but with a lot more heat.

The art is to get the metal hot enough without burning up all the flux.

You have to get the overall part pretty hot, and then focus on one joint at a time to bring it up to the wicking temperature.  There is a certain sweeping motion required to spread the heat a bit on the joint.  You don't want to create a hot spot on the joint that will overheat the flux.

It takes a very surprising amount of heat to get the metal up to the temperature where the silver solder will wick, and for that reason I don't like to silver solder things, just because refilling the oxygen and acetylene bottles is expensive.

I generally use a shaded welding goggle when silver soldering due to the brightness.

If you are not seeing a wicking action starting on the surface, then the metal is not hot enough.  Don't feed in the silver solder if the wicking action has not started, else you get the cold blobs.

Without a clean joint and good flux, and sufficient heat, there is no wicking, but rather just blobbing on the surface, which has very little strength.

The strength in a silver solder joint relies upon having a thin joint, and a completely wicked joint.

Thick silver solder joints are not nearly as strong as thin ones.

I am no silver solder expert by any means, but I can successfully solder with that material.

Too much clearance and the joint is not as strong as it could be.

Too little clearance and the joint may not wick.

I have seen some folks cut a step on the end of the pins, which they fill with silver solder.

A step would work, but a longer thin step would be stronger.

Pinning the crank will take the solder joint out of shear, so the solder is basically to keep things from moving, and not so much for strength.

And keep in mind that many motorcycle crankshafts are pressed together without any soldering or pins, so from that respect, I would say the pins are probably not necessary.

Certainly on a model engine operating under no load, the stress on the crank would be very minimal, and silver solder alone is probably overkill.

For a launch engine operated for a considerable amount of time under full load, you would have to pay much more attention to the crankshaft.


Edited By PatJ on 26/02/2021 16:05:11

Edited By PatJ on 26/02/2021 16:06:50

Edited By PatJ on 26/02/2021 16:07:40

Edited By PatJ on 26/02/2021 16:09:33

Edited By PatJ on 26/02/2021 16:11:02

Keith Hale26/02/2021 21:45:13
329 forum posts
1 photos

Hi Matt

Lucas Milhaupt?


See personal message.


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