[jayplanedin]

Hey everyone,

I'm a fairly novice TIG welder but have been having good success welding mild, carbon, stainless, and aluminum lately.

I've ran into an issue with the engine block on my race car cracking, right along an oil gallery, and i want to tig weld the crack shut. In a frantic effort the day before a race, i tried to tig it with 309 rod with no preheat... Bad idea! Made it way worse and it only cracked more from that. I now plan to pull out the motor, tear it down, and properly preheat the welding area to about 500 degrees F.

Since i am just going to paint the block and don't the weld deposit to be color matched, i figured i would try tig brazing for a less expensive repair and hopefully a higher success rate without cracking, hardening, or further stressing the block. Before i start, i just have a few questions that i'm hoping someone with a bit more experience can answer.

1. Jody explained that he uses this method for cast iron, but doesn't recommend using it on an engine with lots of heat cycles. Why is this? the weld deposit doesn't need to be structural by any means where i need to seal up this crack.

2. What amperage setting is good for this filler? Do i want to see a puddle and feed it into that, or am i just heating it so that it flows in like butter?

3. Does anyone have any additional tips or experiences with welding engine blocks?

[Poland308]

The heat cycling could be an issue with your filler metal becoming work hardened or stressed to the point it will just recrack. The constant temperature swings from ambient temps when the engine isn't running to the hottest temps / after you just maxed out during a race will cause lots of stress from expansion and contraction. Even though the expansion may not be a lot it becomes an issue of how many times did it happen. This makes choosing a proper filler very important.

[jayplanedin]

Does anyone know at what temperature Aluminum Bronze begins to harden like this? It's on the exterior of the block under the intake manifold. It shouldn't see temperatures higher than 250 degrees F.

[Poland308]

The hardening can happen from a physical flexing of the material through the expansion and contraction. Like when you bend a bit of metal back and forth till it breaks off. It's not just a temperature thing.

[Oscar]

it's not the peak temperature itself, it's the constant fluctation of subjected temperatures that can yield unwanted effects.

[Arno]

Cast-iron blocks are often repaired with stitching to help with the cracking and fatigue problems of plain welds.

Some info here: http://www.locknstitch.com/engines-cast ... ustry.html

Bye, Arno.

[noddybrian]

From a laymans standpoint if this " race car " had a chance of winning BIG $$$ prize money & a racing budget I'd junk the motor as if it cracked in the first place it's not viable for racing - but as I imagine there is no / little budget & not much at stake certainly worth a try - top end of the block will obviously see a fair bit of heat but it's do-able - I would not however use any sort of stainless rod as it seems to pick a lot of carbon up from dilution of the parent metal & goes glass hard & likely to crack - your best bet will be nickel - if you can't find small quantities that's affordable for a 1off job try your local tractor parts type place as they usually keep very small packs of arc rods including 99%nickel - just knock all the flux off & scotchbrite clean - if you can't find those as others have said try old rings - I'm not a fan as they are fairly hard high carbon alloys often with very low nickel content - if you can't find any nickel I would braze with oxy / fuel - never been a fan or had much luck with tig braze - but that's just personal.

[ex framie]

Noddy has a point, will the repair handle the use?
A possibly better approach might be cast iron stitching.
lots of reading out there
Heres an example;
http://www.hotrod.com/how-to/transmissi ... ck-repair/
Might be a better option in your case.