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This is a special order item.
Be sure to read the information below prior to ordering.
These kits are an excellent starting point for rebuilding your 12HT engine. They contain all of the basic parts you need to begin your rebuild, but are by no means contain everything that you may require.
Check the kit contents list, then the suggested additional parts list below that. There are a few performance notes towards the bottom of the page.
Important Note: Take the time to read the information provided below about preparing to rebuild your 12HT.
Engine Kit Contents:
- Pistons with pins & clips
- Piston pin bushes, set
- Piston rings, set
- Main bearings, set
- Thrust Bearings
- Rod Bearings
- Cam Bearings
- Injector Seal/Washer Set
- Full engine gasket kit
- Bore wipes & assembly lube
- Torque spec sheet
The kits are ordered for each customer's exact requirements and specifications.
The kits are made up using Japanese engine bearings, typically Taiho which is a Toyota OEM supplier, and aftermarket pistons which are designed and engineered by Engine Australia. The gasket kits are aftermarket and have proven to be reliable; there are notes below about gasket options.
These engine kits have proven to be very reliable, even under high performance conditions with higher than stock turbo boost pressures.
Note: The engine being rebuilt needs to be fully dismantled, cleaned, and measured by a machine shop for parts sizing prior to ordering an engine kit.
• Pistons are available in Standard, and in two oversizes: 0.5mm and 1.0mm
• It is possible to install thin-walled cylinder liners if your engine needs them. These are available by special request if not showing in stock.
• Engine bearings can come in sizes other than standard. Typically the sizes are 0.25mm, 0.50mm, 0.75mm and 1.00 mm.
• There are 3 different possible styles of connecting rod bearings. Connecting rod bearings need to be visually inspected to make sure the right ones are being supplied in the kit. Alternatively, if the correct chassis number associated with the engine is known, that can also be used to order the connecting rod bearings. Otherwise, see the photo regarding the con rod bearings on this product page.
• Lifters are available in standard and one oversize (0.05mm)
• Alfin pistons are supplied with all kits and recommended for all diesel engines, and especially turbocharged engines.
What are Alfin Pistons? They are pistons that have steel ring groove insets in them to prevent ring land damage to the piston which is common on these engines.
• The head gaskets that come in the kits are composite, and work very well if the block and head surfaces are properly prepared, and cleaned and used within reasonable turbo boost levels. Head and block surfaces must be within factory specifications for flatness or your head gasket will fail prematurely.
Toyota Genuine/OEM full engine gasket kits are still available and may be ordered separately (as of early 2022). The supplied gasket kits are good, but may come with any one of a few different possible head gaskets including even a factory (OEM) gasket.
It's a bit of a crap shoot as to which head gasket the engine kit will ship with. In general, the aftermarket head gaskets are perfectly fine, but if you're planning on running higher than stock boost, you may want to consider an OEM head gasket or a custom aftermarket MLS head gasket.
Custom Aftermarket MLS head gaskets may be available as a special order option. These gaskets are expensive! However, if you want to run high boost then these are your best bet. Note that the block and head surfaces must be perfectly flat and machined to the correct RA (Roughness Average) to allow these gaskets to seat properly.
The RA required for an MLS head gasket is typically 20-30RA, though some may require the surface to be a lower RA. Composite head gaskets, depending on the design, may not seal well on a surface that's too smooth, and an MLS head gasket will suffer from premature failure on a surface that is too rough. Discuss your head gasket choice with your machine shop!
• Very old, pitted, or rusty head bolts must be replaced. 12HT head bolts are not torque to yield bolts and can otherwise be re-used.
Premature piston failures in both 12HT and 2H engines: Both the 2H and the 12HT are known to experience piston ring land degradation and failure at fairly moderate mileages for a diesel. This can be due to multiple factors including less than ideal piston design, improper injection timing, worn out injectors, and infrequent oil changes among other things.
Piston ring and ring land failure of the piston will lead to the engine smoking from burning oil, increasing oil consumption, decreasing compression and poor performance. If the rings are damaged, they usually take the cylinder bores with them, so oversized pistons are needed after machining and sleeves are an option as well.
Head gasket sealing: Another issue that must be appreciated is that older 12HTs, especially JDMs that passed through our shop, tended to have head gasket failures due to poor coolant quality during their life prior to importation. This can lead to a block that is probably dished a few thou in the middle and/or a head that is not flat, and as a result the head gasket won’t seal properly.
The block and head must be carefully checked for flatness, and especially if you have had seepage of combustion gases into the cooling system or a head gasket failure.
To correct the block and/or the head material must be removed and that can affect piston protrusion heights as well as decreasing the overall height of the engine and thereby affecting head bolt hole depth. It is therefore super critical that the head bolts are checked for length vs how far they seat into the block.
A Very important note about head bolt length: Head Bolt length must be carefully checked against the stack height of the head + compressed gasket + bolt seating depth in the block. This is especially important if the cylinder head or engine block has been machined. Head bolts that bottom out in the bolt pockets due to head or block machining can cause serious problems as adequate head clamping forces will never be achieved. Some or all of your head bolts may need to be shortened, and it's generally better to just do all of them in case it has to come apart again.
Suggested items for a full rebuild that do not come in the kit:
- Rocker Shaft (check and measure first)
- Intake & Exhaust Rockers (inspect for wear at valve contact surface) - *these are no longer be available.
- Camshaft - now available as a high quality reproduction (made in Australia)
- Lifters (inspect first)
- Intake & Exhaust Valves (inspect first)
- Valve Springs (inner & outer)
- Frost Plug Set
- Injection Pump O-ring (pump to timing housing - usually comes in gasket kit)
- Updated Oil Pressure Relief Valve (longer) & Spring (this is strongly suggested as an add-on)
- Oil pump (drive gear & driven gear) - available as a kit
- Oil pump cover plate (no longer in production, though some "New Old Stock" may exist at exorbitant prices)
- Cam plug 55mm (you will require this part)
- Head Bolts
- Water pump
- Accessory Belts
- Radiator and Heater hoses
- Crankshaft pulley - available as high quality reproduction (made in Australia)
Other performance notes:
If you are going to "high performance" your 12HT it is strongly advised for you to have the injectors carefully rebuilt as a poor injector spray pattern is death to a diesel engine. The injection pump should also be calibrated by an experience pump technician who has been provided with the performance needs and desires of your engine build and your expected boost levels.
The EGT and AFR need to be set to match your desired turbo boost parameters and performance curves through careful engine tuning and then monitored closely with high quality gauges. Boost pressures should also be monitored with a high quality gauge.
AFR is monitored by using a wide band diesel engine rated Lambda sensor (oxygen sensor) and gauge this is calibrated to give you an air:fuel ratio.
Engine oil and coolant temperatures must be maintained within acceptable standards. There are a few different temperature ratings for the thermostat, and running an 82C vs an 88C is a good way to help keep things a little cooler.
A larger than stock exhaust system should be used when adding more power to your 12HT, a 3" diameter low restriction pipe is recommended to help remove heat from the engine and reduce exhaust system related performance losses.
If you are consistently running over 12PSI boost, then you should seriously consider a well-designed intercooler to reduce intake charge air temperatures, improve your power output, and extend engine life.
Engine Parts in this kit are primarily very high quality aftermarket
Bearings are typically Taiho (Japan), which is an OEM supplier to Toyota
Other items may be either OEM or high quality aftermarket
2022 09 04