I have a TO-30 with a cracked block. It has tension rods installed by a previous owner but it started leaking coolant into the oil pan. Will a different engine, like a Z134, fit this tractor or is welding a better option?
Your leaks could be coming from more than one place. It may not be just the old cracks that are leaking. Here are some additional things to check. The piston liners or sleeves are supposed to stand proud or project above the top of the block .001 to .004″. You can check this by installing the sleeves dry, no O rings installed, in the block, placing a straight edge across the top of the sleeve and using a feeler gauge to measure the clearance between the straight edge and the top of the block. Because each hole in the block can be different, you need to check each one.
When you are installing new sleeves you may be able to move the sleeves from hole to hole to achieve the proper projection. There were shims available to shim the sleeves up to achieve the proper projection but they are no longer available. If all the sleeves sit low in the block when dry fit, you can have the top of the block planed to achieve the correct projection. That may also require having the top of one or two sleeves planed to get the proper clearance. I have been told that mechanics in the UK use copper wire under the top lip of the sleeves to achieve the proper projection. I have never done this myself and have no idea how well it works.
The sleeves are supposed to protrude just a bit in order to compress the head gasket and make a good seal. For a good seal the cylinder head and the top of the block should be checked to make sure they are flat. This will have to be done by a machine shop and if necessary, one or both will need to be ground or planed. This may also require some boring of the block where the sleeve flange rests in order to achieve the proper sleeve projection as indicated above. Before installing the head gasket, coat it with Permatex Brand Copper Coat spray, a product designed to make head gaskets seal better. Hang the head gasket on a wire or coat hanger and spray several coats of the Copper Coat on before installing the head gasket. Make sure you follow the sequence for tightening the head bolts and use a torque wrench to make sure they are tightened equally. Make sure the block is clean where the O rings rest and seal. Coat them with a silicone grease before installing them and make sure they are not twisted when you install the sleeves. As for repairing or replacing the block.
You can purchase a rebuilt short block from CT Farm & Country for $2829.06. That includes new pistons and sleeves, reconditioned rods with new wrist pin bushings, a reground crankshaft with new rod and main bearings, and a reground camshaft and bearings if there are bearings for the camshaft. When you consider the price for these parts and services, the price is not that bad if you need to rebuild the engine anyway. I believe welding the block is the best option. Be sure to use a shop or service with experience repairing these engine blocks. The cost often includes a charge for line boring which should always be done after a block is repaired.
You can replace the Z129 block with a Z134 block but there are several modifications that will have to be made to the water pump and pump casting. I have seen tractors that have had this done but I can’t recall what specifically had to be done to make this swap but believe it was just the water pump and body assembly. I think the pump body assembly from the Z129 will fit the Z134, in which case the pump will fit with no problems. The Z129 cylinder head will have to be used in order to maintain the water outlet which contains the front mount for the fuel tank. You will also need to have the oil filter canister for the Z134 as the Z129 version will not fit. The manifold, generator mount, distributor, starter etc should all fit. The Z120 block can also be used to replace the Z129 but to do so you would have to use the Z120 cylinder head and the Z120 generator. Of course you would also have a tractor with less power.