Saturday, April 10, 2021

Repowering our tired 1HZ with a fresh 1HZT engine

Our last big trip pushed our Motorhome's original 1HZ 4.2L diesel engine life beyond 500,000 kms and whilst extremely reliable, not consuming any oil or having any mechanical concerns, it wasn't the most powerful engine lugging almost 4.5 tonnes along.
This was particularly obvious when encountering any incline/mountains, attempting to overtake any slower vehicles safely or when the weather was over 30 degrees and we needed AC the most and it became a choice of keeping up with traffic or running the AC.

After researching our options, we agreed that a turbo charged option was preferable based as much as possible on factory parts so we tossed up running the factory mechanical injection turbo Coaster options of either a 94- 1HDT (HDB50-ZRMEX) or the rarer 93-96 1HZT (HZB50R-ZRMRXW1)

After weighing up the cost/benefit of buying an import/used 1HDT and then refreshing it versus a used 1HZ and turboing it, we decided on the later option after speaking with numerous importers and engine builders.

We agreed to work with Reece Diesel on our rebuild. We started with a cheap second hand used 1HZ engine core from a HZJ105R model Landcruiser.
Reece built our 1HZT to the following specifications:

Ground up rebuild of 1HZ long block - inspect, x-ray, hone, machine, complete bearing/gasket/seal kit
New 1HZ head
Rebuilt 1HZ injectors to suit 1HZT
Rebuilt compensated injection pump to suit 1HZT
Reece specification 1HZT ceramic coated pistons & rods
Denco complete turbo kit
OEM Timing kit
OEM Water pump

Freshly Rebuilt 1HZT engine




The Denco Schwitzer S2D based turbocharger kit for low boost torque and reliability




Up it went high enough to clear the engine being lowered down and rolled forward from underneath



After much preparation with a lowering gantry, removing the crossmember and steering linkages as well as engine ancillaries / wiring / hoses etc, down came the old engine






Rebuilt engine fitted with a fresh clutch kit


Up and in went the fresh 1HZT engine












Major differences noted between a Coaster 1HZ and Landcruiser 1HZ engine variants
  • 24V vs 12V - alternator, starter, glow plugs, diesel shutoff solenoid
  • Oil sump & pickup - front vs rear sump
  • Injection pumps
  • Heater coolant circuits - 1 one on  Land Cruiser head vs 2 on Coaster head
  • Harmonic balancer & secondary pulley - 4 bolt vs 6 bolt and AC offset
  • AC mounting bracket different size
  • Pilot/Spiggot bearing 12mm vs 15mm ID

Provision for water temperature, oil pressure, boost pressure and exhaust gas temperature sensors were factored into the engine plumbing for fitment of a pair of dual Redarc gauges to be able to monitor the vital engine health parameters whilst driving.

A new OEM heavy duty spec multi-pass alloy radiator is being fitted to help with cooling.

Links:

Reece Diesel
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