1HZ HEAD TO 1HDT HEAD CONVERSION CAN IT BE DONE?
Something Shane and the Noordeman team get asked quite alot is can i fit a 1hdt head onto my 1hz?
Short answer is you can’t just swap over to a 1hdt head on its own, but with almost a complete damaged 1HDT you can convert over to a 1HDT, the differences and what you can use we have listed below to try and help you see if its worth the effort or if you just buy a complete 1HDT and rebuild it in place of the 1HZ.
You can use the 1HZ block but you will need to drill and tap the block for the oil return line
The conrods and pistons you use are the 1HDT ones
The cranks are the same
The head can be bolted on and you can use your 1hz valves and springs and guides assembly
The camshafts are different the 1hz one is a bigger camshaft on the intake lobe
The injectors can’t be used from the 1hz for the 1hdt as the 1hz is indirect injection and the 1hdt is direct injection
The fuel pump can’t be used from the 1hz for the 1hdt as the 1hz is completely different to the 12mm 1hdt pump
Fuel pump timing is different between the 1hz and the 1hdt
The injector lines are different between the 1hz and 1hdt so they can’t be used either due to the way they mount to the pump and also the injectors
The rear section of the manifold can be used from the 1hz but you will need to use a 1hdt front section of the manifold
Water pumps are the same
Timing kits are the same for the early 1hz up to 1997
The timing gears are the same
Rocker covers are the same
Intake manifolds are the same
Engine mounts are the same
Flywheel for the 1hz is smaller at 275mm diameter Â and the 1hdt is 300mm diameter but both will bolt up to the back of the engine the 300mm will only work with a H151 gearbox
The clutches are different also due to the sizes the 1hz one is 275mm diameter and the 1hdt is a 300mm diameter clutch
Oil pump assemblies are the same upto 1997
Plastic timing covers and backing plates are different due to clips or bolts but both can be used as a set