Toyota 1HDT vs 1HDFT (1 Viewer)

[sunrk]

I know there's a thread about 1HDFT vs 1HDFTE, but I'd like to focus more specifically on 1HDT vs 1HDFT as for a basic Aussie 80 series owner they are the most common engine choices for diesel upgrades. Many 1hz 80's still exist (like mine) with the original ex-factory motor. Standard upgrade path is to get a 1hdt, but 1hdft is another valid pathway.

There are hardly any people fitting other diesels to their 80's but some do.

So what technical reasons should one consider a 1hdt vs a 1hdft? Does the 1hdt have 'design flaws'? Obviously 1hdft is 24 valve vs 1hdt being 12 valve. For a DD vehicle like mine that rarely tows big loads and doesn't so much off road, and is already 30+ years old, is there any cost-effectiveness in opting for a 1hdft instead of 1hdt?

For normal use, is it of any relevance that the power curve of a 1hdft is supposedly better at higher rpm compared to that of a 1hdt (which is basically a 1hz block with a different head and air intake design I think)?

Cost-wise, a jap import 1hdt is around $10k and a 1hdft can be up to $15k. Aussie dollar prices.

I'm not sure I'd want to get the existing 1hz rebuilt and carry on as it's too old/worn to make a good candidate to fit a turbo kit onto. If I can find a good diesel motor place I will ask about potential cost range for a full rebuild.

In hindsight it probably won't matter which engine option I go for (even 1hz + t) - cost is still going to be upward of $10k and that's 2/3 of the insured value, but I'm not in a position to justify selling my 80 to get another one, so engine swap seems the only valid way to deal with the old motor.

 

[chapel gate]

is the old motor still going strong?

 

[sunrk]

It's going yes - strong is something I have no ability to correlate with anything else. Only 80 I've driven is my own.

 

[chapel gate]

keep on trucking then..

 

[chapel gate]

the 1HDT doesnt have any design flaws, BEBs aside.

 

[Stiles]

I've heard complaints about the heated air intake on FT vs glowplugs in the T. There is a specific month at which the BEB issue was sorted out (l think 2/92?).

Manual or auto? The mention that the manual is lower geared was news to me, meaning higher rpms at hiway speeds with the MT.

A newer engine is better, right, cause its newer? But not yet EFI. More valves is a good thing? Is the FT also direct injection?

 

[gilmorneau]

For normal use, is it of any relevance that the power curve of a 1hdft is supposedly better at higher rpm compared to that of a 1hdt?

No. The jump to 24-valve was a look forward by Toyota to the future of emissions requirements and thus the need for higher combustion efficiency. If 24-valves gives higher performance, it's minor and that was probably just a bonus to them.

So what technical reasons should one consider a 1hdt vs a 1hdft?

The earlier 12-valve motors are a bit simpler and more closely related to your 1HZ--injectors are more accessible, glow plugs instead of screen, etc. OTOH, there's the BEB issue with some 12-valve motors.

In some markets the 1HD-FT came with EGR which most people recommend disabling, otherwise it's hard to find fault with the 1HD-FT.

For a working truck, the 1HD-T seems the obvious choice to me, but it's not my truck. Lower cost, easier maintenance, almost the same performance, and a huge step up from a n/a 1HZ. Monitor the BEB thing and service as required.

 

[wedgetail]

I was going to stay quiet as I felt I said my piece in the other thread, but this prompts me to reply

No. The jump to 24-valve was a look forward by Toyota to the future of emissions requirements and thus the need for higher combustion efficiency. If 24-valves gives higher performance, it's minor and that was probably just a bonus to them.

The earlier 12-valve motors are a bit simpler and more closely related to your 1HZ--injectors are more accessible, glow plugs instead of screen, etc. OTOH, there's the BEB issue with some 12-valve motors.

In some markets the 1HD-FT came with EGR which most people recommend disabling, otherwise it's hard to find fault with the 1HD-FT.

For a working truck, the 1HD-T seems the obvious choice to me, but it's not my truck. Lower cost, easier maintenance, almost the same performance, and a huge step up from a n/a 1HZ. Monitor the BEB thing and service as required.

First point - the extra air flow the FT is capable of gives it much higher power potential. A tuned up FT goes much better than a tuned up T, in fact many say a highly tuned 1HZ-T can produce better numbers than a 1HD-T (it just won’t do it for long and will overheat). The increased air flow will also spoil up a bigger turbo quicker providing better low down response - all assuming optimum tuning. There’s much more of an advantage than just cleaner emissions - more air means more fuel can be added.

Apart from the valve bridge design, an FT is no more complex. Most people remove the inlet screen - it’s certainly not needed in Australia and people in Norway report east starting with no screen. Not sure what the 1HD-T without glow plugs is like though, I’ve always considered DIs don’t need any starting aid but I guess it doesn’t get that cold here.

Another significant factor is the FT pump is much better, smoother and more refined. When building an FT pump the IP shops give only a marginal discount when starting from a 1HD-T pump as opposed to 1HZ body. FT doesn’t suffer from the common 1HD-T problem of erratic idle especially on slopes, has smoother power delivery and is slightly more durable. The injection pressure is also higher, giving more power potential again.

The only disadvantage to the FT is cost. Personally I wouldn’t go to all the effort of fitting a 1HD-T when there are FTs out there - even if it’s just a work truck. What with the lack lustre performance potential, BEB issues and rough IP the FT is way it in front. Especially if you build an FTE-M…

 

[gilmorneau]

First point - the extra air flow the FT is capable of gives it much higher power potential.

Another significant factor is the FT pump is much better

The only disadvantage to the FT is cost.

I wouldn't argue any of this. Agreed on all points. I was only answering the OP's question re: a comparison of the two motors "in normal use", which I (perhaps mistakenly) interpreted to mean unmodified. In that instance, value for money goes to the 1HD-T in my opinion.

The OP seems to want more performance than his 1HZ offers (understandable) but doesn't hint at wanting to upgrade beyond a swap.

 

[wedgetail]

I wouldn't argue any of this. Agreed on all points. I was only answering the OP's question re: a comparison of the two motors "in normal use", which I (perhaps mistakenly) interpreted to mean unmodified. In that instance, value for money goes to the 1HD-T in my opinion.

The OP seems to want more performance than his 1HZ offers (understandable) but doesn't hint at wanting to upgrade beyond a swap.

Sure, and value for money when comparing stock motors probably tips it towards 1HD-T, the price of FTs is a bit over the top. Hence my mention of FTE-M, but I’d imagine this is even more pricey if not in Australia

 

[Meatpie]

the 1HDT doesnt have any design flaws, BEBs aside.

I'm curious as to why people say or think that the 1HD-T has big end bearing issues?
Given that it is part of the 1H engine group and shares the same block and crankshaft as all the 1H series diesel engines (1Hz, 1Hd-t, 1Hd-ft and 1Hd-fte) all use/have the same 94x100mm bore/stroke and bearing journal sizes (and casting numbers) and they are all SOHC. The crankshafts and blocks are universally interchangeable.
ACL list the same part numbers for big end and main bearings for all the above mentioned engines. Toyota's internal part numbers differ between engine models, However, the physical bearing shells all have the same number on them.

The only differences being the heads, conrods/pistons, injectors/pumps and exhaust (and some ancillary equipment).
The only real change was in 1998 onwards when crankshafts were factory nitrided to increase durability.
So if you have a good block and crankshaft (1998 onwards) you can build any one of these engines.

Most failures occur because of poor maintenance, mistreatment/misuse, defective workmanship when a rebuild is performed or the component is simply worn out or a combination of any of these things.

Please correct me if I am technically wrong on any of what I have written (I'm happy to further my knowledge and eat humble pie).

I have a 1Hz in my 79 series with 600k on it, factory internals and an aftermarket turbo fitted, no issues, same block and crank/bearings as a 1Hd-t and 1Hd-ft.

 

[chapel gate]

I'm curious as to why people say or think that the 1HD-T has big end bearing issues?
Given that it is part of the 1H engine group and shares the same block and crankshaft as all the 1H series diesel engines (1Hz, 1Hd-t, 1Hd-ft and 1Hd-fte) all use/have the same 94x100mm bore/stroke and bearing journal sizes (and casting numbers) and they are all SOHC. The crankshafts and blocks are universally interchangeable.
ACL list the same part numbers for big end and main bearings for all the above mentioned engines. Toyota's internal part numbers differ between engine models, However, the physical bearing shells all have the same number on them.

The only differences being the heads, conrods/pistons, injectors/pumps and exhaust (and some ancillary equipment).
The only real change was in 1998 onwards when crankshafts were factory nitrided to increase durability.
So if you have a good block and crankshaft (1998 onwards) you can build any one of these engines.

Most failures occur because of poor maintenance, mistreatment/misuse, defective workmanship when a rebuild is performed or the component is simply worn out or a combination of any of these things.

Please correct me if I am technically wrong on any of what I have written (I'm happy to further my knowledge and eat humble pie).

I have a 1Hz in my 79 series with 600k on it, factory internals and an aftermarket turbo fitted, no issues, same block and crank/bearings as a 1Hd-t and 1Hd-ft.

my own gut feeling has always been the 1HDT BEB issue was a "bad" batch of bearings, but there appears to be plenty of evidence from oz, of folk inspecting bearings that have been changed after 100000 odd miles of use, to be pitted and showing signs of early delamination.
i have changed dozens of bearing sets for customers over the years and installed many on engine rebuilds.
the time has not yet come to revisit what condition these are in, but it will. sump replacement is pretty common in the uk due to corrosion.

then i will be able to come to my own conclusion.

 

[TheBussman]

I'm curious as to why people say or think that the 1HD-T has big end bearing issues?
Given that it is part of the 1H engine group and shares the same block and crankshaft as all the 1H series diesel engines (1Hz, 1Hd-t, 1Hd-ft and 1Hd-fte) all use/have the same 94x100mm bore/stroke and bearing journal sizes (and casting numbers) and they are all SOHC. The crankshafts and blocks are universally interchangeable.
ACL list the same part numbers for big end and main bearings for all the above mentioned engines. Toyota's internal part numbers differ between engine models, However, the physical bearing shells all have the same number on them.

The only differences being the heads, conrods/pistons, injectors/pumps and exhaust (and some ancillary equipment).
The only real change was in 1998 onwards when crankshafts were factory nitrided to increase durability.
So if you have a good block and crankshaft (1998 onwards) you can build any one of these engines.

Most failures occur because of poor maintenance, mistreatment/misuse, defective workmanship when a rebuild is performed or the component is simply worn out or a combination of any of these things.

Please correct me if I am technically wrong on any of what I have written (I'm happy to further my knowledge and eat humble pie).

I have a 1Hz in my 79 series with 600k on it, factory internals and an aftermarket turbo fitted, no issues, same block and crank/bearings as a 1Hd-t and 1Hd-ft.

search for the thread on these. Its a pretty well documented issue. Two of the most popular theories: first bearings from 90-92 were not as good as later on. second: for some reason the 1hdt makes just the wrong frequency and cavitates oil in the rod bearings. I've seen plenty of bad bearings for oil staved or abused engines the pictures people have of their bad 1hdt bearings look a lot different. There is something going on there its not just bad maintenance, I'm going to try coated bearings.


Back to the main focus of the thread: I considered all 3 motors for my swap, went with 1HDT because it's the "right" motor for my 93 truck, and i do like the idea of external easy to get to fuel injectors, as well as being able to remove a glow plug for testing or evacuating water from a cyl on the trail. ( i have a snorkel so that shouldn't happen but still) the glow screen seems like a restriction and you could remove it but i do like running a glow system to keep the smoke down on cold starts especially if your not going to have ASCD. Oh yea and cost.

 

[Hulsty]

Common knowledge, 1HDT eats big ends, they are a 100k service item. None of the other variants of the engine have the issue.

 

[KiwiDingo]

Yep, very common. It's not the bearings, it's the sh1tbox design flaws of the DT.

 

[J1083444]

Yep, very common. It's not the bearings, it's the sh1tbox design flaws of the DT.

All 1hdt conrod journals stretch and become oval, particularly boosted engines. Barely anyone replacing bebs bothers to check this and therefore there is a constant issue of beb failures. On top of this, the genuine 1hdt conrods can bend over time. Throwing new bearings in whilst the engine is still in the car contributes to the above failures.