Modern Vespa

Got my rebuilt motor back from Scooter Mercato and it was packed really well.
Removed it from packing and put it in the engine stand since I need to change out the brake arm for the T5 cable conversion.
Went a outlet straightening around the shop and in about there was a snap and a bang and when I looked the lower shock mount had snapped in half. A very clean break.
Better on the stand than on the road.
Went to the local welding supply to ask for a repair resource and was given a good one.
The question is what filler rod is best used for making the repair.
Thanks
Rick

That is extremely unfortunate, and better on the stand than on the road

Nooooooo! Bummer....

From that picture it looks like it's been cracked for awhile. Break on motor side is shiny, break on rear is dull metal that has had time to corrode.

4047 filler rod


The filler metal should be something that is paired to the parent metal. What is the case made of?

Does anyone know exactly what alloy it is? Percentage of magnesium? I know it is not pure aluminum but does it have anything else besides magnesium?

All steel for example is an alloy, there is no such thing as pure steel, steel is composed for various elements so it is by definition an alloy. If the alloy has above a certain percentage of carbon in the recipe for instance then it is stainless steel and there are varying grades of stainless usually depending on percentage of carbon.

Just using google and some general welding knowledge this website recommends 4047 for use as a filler metal and I think welding tips and tricks is a reliable source.

https://www.weldingtipsandtricks.com/cast-aluminum-welding.html

This is a good place to start. Ideally we would have an experienced welder experiment on a garbage case of the same manufacturers alloy and have him make some test welds. Then we take it apart and do some testing for tensile strength, penetration, and porosity.

While the test weld is made we measure machine settings (volts/amps) and gas flow the specifics of the tig rig setup, and we ask the welder how each of the different settings we try feel and look going in and compare the visual aspects of the different test welds.

This is basically how you qualify a procedure, and a welding procedure specification (WPS) is the recipe for the best setup for the application.

From the link..."What is the best tig rod for cast aluminum?
here is a little known resource for selection of tig welding rods for cast aluminum

5356 is stronger than 4043 but tends to get porosity when used to weld aluminum castings.

4043 is fine and usually a pretty good choice for castings because the silicon content makes it a close match for most aluminum castings.

Maxals 4943 is a fairly new alloy that is touted as a great replacement for 4043 on aluminum castings. it works pretty good.

But in my opinion, 4047 usually is better for preventing porosity.

Why?

Because of the higher silicon content.

Silicon is a deoxidizer but also lowers the melting point of aluminum alloys.

A lower melting point means the filler wire will flow at lower amperage...and that means it will be less likely to draw impurities out of the cast aluminum base metal.

4047 aluminum filler wire contains around 12 % silicon and although has a slightly lower tensile strength than 4043, tends to make welds that have considerably less porosity than welds made using 4043 filler metal."

Good catch, you have the makings of an inspector!

Would have been nice to magnaflux before rebuild maybe? Better to find out before than after and why was that not done by the rebuilder?

Not trying to badmouth just asking questions.

Look for Gickspeed on here, he does case repairs often.

You would have to use a dye I think, don't think magnaflux will work on aluminum.

Yeah that only works on the iron blocks, another good catch. Nothing gets past you does it?

It is normal for engine rebuilders to do a magnaflux before rebuilding, I have heard this many times as a standard check but as you say won't work with aluminum alloy and I haven't heard of dye penetrant tests with alloy blocks. I my self have had to do some dye testing with stainless for the same reason, good stainless with lots of carbon content in not very magnetic.

Change of direction. Welder wanted motor disassembled.
Spoke with David at SM will send it backdown and Matt will put parts in another set of P200 cases.
Better solution

Oh that's a kick in da coins. :-/
Sorry Mayor.

Thought... this would be a GREAT time to learn to disassemble a set of cases.

Split 'em and take it down to the bearings. Send all your internals back to Matt (Bagged and labeled proper.) and take your case halves to the welder.

If he does a good repair you have an extra set of cases for the shelf or for sale, AND you will have learned something along the way. (Shoot.. you might even decide to reinstall all the bits and bobs yourself.)

IJS
You can do it!
We're all here to help.
Ya know you wanna!
Everybody's doing it!
Just say no Yes!

So does the welder want the case stripped so that he can preheat any impurities out of it?

Over the last nearly 60 years I have built small block Chevy's, MG Midget, Austin Healy Sprite and Triumph SCCA race motors, VW sand rail motors and various 2 and 4 stroke motorcycle motors.
It's not a mater of if I can, I simply don't enjoy that part of the pastime any more.
So I do what I enjoy and send the rest out.
As you get into your mid 70's with the energy one has to do things you pick your battles.
Intruly admire the folks that choose to do all aspects of it.

Regarding the welder when I spoke with him he said he didn't want to be responsible for the whole motor. His shop his rules. I'm ok with that.
Regarding shelf stock, when we downsized homes 9 years ago I no longer have a garage just a 10x15 space in the back corner of the walkout basement.
Don't have space to store spares and usually pass along excess parts to others that can use them.

Totally fair and totally understand.
I just wanted to encourage ya in case you did have the bandwidth.

After Hurricane Harvey flooded all my bikes (except the one on the lift) I sent my flooded p200 engine to Gick to rebuild BC I just didn't have the mental space for it at that time. Glad I did bc it was an easy way to put a working bike back on the road while we put the rest of our lives back together.

Looking forward to seeing that glorious white P back on the road!