How to best fix cracked block

[haanzel]

I recently picked up a G4200 mower. Over the last 12 years, it has been used about 20 hours but no service since. I am going through and bringing it up to snuff. One item was flush/fill the rad. Like others, the petcock broke when I barely turned it. I tried left hand drill bits and extractors. I kept stepping up extractors and then this happened. It's cracked in 3 places - 12, 6 and 9 o'clock and goes 1/2"-1" back on a couple

I need to fix the cracks and then close up the hole. I bought a new OEM petcock but since the block open like this, I don't think tapping it is best and an expandable plug is better. I don't know what I don't know, so I am hoping some of ya'll have a better idea on how to get this back lawnworthy. Needless to say, I am a frustrated by this ordeal.

 

[BruceP]

The 'accepted' means to fix cast-iron is brazing with nickle rod.
The resulting braze repair is as strong as the base-metal and can be machined in any way you wish.

In this way, the base-material is never hot enough to melt and crystalize into glass-like hard areas which are nearly impossible to machine/drill.

Some folks claim to have success with weld-repairs on cast-iron.
BEWARE: This results in hard spots where the base-material gets crystalized and is not machinable. (even carbide-tipped tools will chip)

NOTE: ANY repair-process to cast-iron also entails slowly pre-heating the metal before starting.... followed by controlled, slow cooldown by wrapping in heatproof blankets. All of this preheating/cooldown is an effort to reduce internal stresses within the metal. (Cast-iron is inherently brittle so we take every precaution to reduce cracking)

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ALTERNATIVE: Consider simply filling that hole with JB weld... drain coolant from block by pulling lower hose.

 

[GreensvilleJay]

I'd go with the second option !!!!

In doing the first, you also have to drill small holes at the ENDS of all 3 cracks to relieve the stress, otherwise it'll keep cracking. It also may not be possible to fix the block IN the machine and need to remove 'stuff' to get proper clean access to all 3 cracks....

Also buy a second lower rad hose to keep on the shelf and two clamps....

 

[North Idaho Wolfman]

Like others have said:
Those cracks luckily are superficial, and not deep into the block, clean the area with brake parts cleaner, and use JB weld epoxy putty (or other brands) to fill the hole and the cracks.
Force a blob into the hole, then let that harden, then force more into the top and cracks.
Use lower radiator hose to drain in the future.

 

[GeoHorn]

Yep. JB Weld….. but better IMO than brake or parts cleaner, use this (or $8 at WM) : https://www.amazon.com/CRC-05103-El...ds=crc+contact+cleaner&qid=1684030081&sr=8-20

 

[haanzel]

Thanks for the replies. I had not thought about just plugging up the hole, not a bad idea. I initially drained it like that, which is frustrating since this will end up with the same result. Oh well, live and learn.

 

[Nicksacco]

JB Weld - the best tool in the toolbox!