Does anyone have any experience of the 8-valve 15B-T? (1 Viewer)

[Eurasiaoverland]

Just to be clear, I am not looking for information on the 15B-F, 15B-FT, 15B-FTE or 14B-T. These engines were all sold to public with plenty of information out there.

I am after information on the 15B-T, which was an early (ca. 1995), 8 valve 15B that externally is a 14B-T but has apparently been bored out to accept 15B pistons and therefore become a 4104 cc engine. This engine was only found in the military BXD10 Mega Cruiser and was never publicly sold by Toyota. A few complete vehicles and a number of half cuts seem to have been exported from Japan in recent years. The FB page of '4 Wheel Auto' in Canada shows at least one 15B-T transplant into an FJ62.

I have the opportunity to purchase such an engine, fresh from a half cut, and I wonder if anyone on MUD has any experience with them. My major concern would be sourcing a new head gasket as the 14B gasket would be too narrow in the cylinder bore (102 mm vs 108 mm), and the 15B gasket has different coolant passage holes and even the thickest 15B gaset (1.4 mm) is thinner than the thinnest 14B gasket (1.5 mm).

I'd be very interested to know if anyone has ever pulled one apart.

Again, not looking for info on regular 14B-T or 15B-F* engines.

Thanks

EO

 

[Hulsty]

Did you google the head gasket? I just had a quick look and it appears my local auto parts store has them in stock, not an issue.

 

[Eurasiaoverland]

Did you google the head gasket? I just had a quick look and it appears my local auto parts store has them in stock, not an issue.

When people talk of a '15BT', they almost invariably mean the 15B-FT and any off the shelf part will be for such an engine, and I imagine not compatible with the true, 8 valve 15B-T.

 

[myusername]

When people talk of a '15BT', they almost invariably mean the 15B-FT and any off the shelf part will be for such an engine, and not compatible with the true, 8 valve 15-BT.

Can you even be sure the rare 8 valve 15BT has a different bore since there's no documentation? Where did you get that measurement from; are you assuming it has the same diameter bore as the more common 16 valve 15BF variants?

It could be a stroked 14B or even the same displacement as the 14B but with other changes common in the B series (stiffening plate, cooled pistons, etc like the 15BFT?). If it was military only applications they may have named it the 15B simply to differentiate from the civilian 14B and it may not have much in common with the civilian 4.1L 15BF?

 

[Eurasiaoverland]

Thanks for your reply, some good points there.

Can you even be sure the rare 8 valve 15BT has a different bore since there's no documentation?

At this stage, no, since I have not exposed the cylinders by removing the sump.

Where did you get that measurement from; are you assuming it has the same diameter bore as the more common 16 valve 15BF variants?

Indeed, the assumption by me (and others who have examples of this engine) is that having been stamped as a 15B, it has been bored out. To support being bored out, the 14B/3Bii style piston oil squirters which are knocked through from the left hand side of the engine are absent (most likely due to a larger bore). Again, I assume it still has oil squirters and that they bolt in from the bottom on the inside of the block, as they do on commercial 15B-F* engines.

It could be a stroked 14B

Highly unlikely as this would require making an all new crankshaft. The 14B and 15B have the same stroke (112 mm). Later 14B engines use the same crank as a 15B-F*, so this stroked crankshaft would be a one-off application.

or even the same displacement as the 14B

That's possible, but I see no reason to then call it a 15B.

with other changes common in the B series (stiffening plate, cooled pistons, etc like the 15BFT?)

The 14B (and all B engines I have seen) has oil cooled pistons. My 3Bii has and I think even the older 3Bs had oil squirters. I'm pretty sure the 14B, and definitely the (JDM) 14B-T engines have the so-called stiffening plate. So none of those things are peculiar to the 15B. The commercially sold 15B-F* engines had a new block casting which looks clearly different to the 3Bii/14B casting.

If it was military only applications they may have named it the 15B simply to differentiate from the civilian 14B

But then they made a series of commercial 15B engines? Does not sound likely to me. Plus most of the military BXD10s got 15B-FTEs from what I see online. So no rationale to it being a military/civilian market distinction.

From what I can see externally, I'm let's say 90 % sure this engine has been bored out. I'm confident, though to a lesser degree, that the casting is the same as the 3Bii/14B, but that could only be confirmed by taking off the head. This engine block was cast in May 1994; that's a year before the first release of the 15B-F and 15B-FT. So I think a more plausible explanation is that the vehicle was ready to go into production but the 16 valve 15B-F* was not; so as an interim measure they bored out a 14B-T to the capacity they wanted.

Looking forward to learning more about this engine.

EO

 

[ceylonfj40nut]

Seems like its a poor unicorn in many fronts which raises flags of all kinds if reliability and repairability are your goals when overlanding the way you do on your trips.

 

[Eurasiaoverland]

Seems like its a poor unicorn in many fronts which raises flags of all kinds if reliability and repairability are your goals when overlanding the way you do on your trips.

Not sure about 'many' fronts - could you be specific? The head gasket issue is potentially serious indeed. But the reason for buying such an engine is that as far as I'm concerned there is no susceptibility to head gasket failure outside of serious, sustained overheating, like any engine. They are not like the poorly designed 1KZ-T or 2L-T engines which are very sensitive to overheating and commonly crack heads. A two-valve, direct injection cylinder head is about as robust as a cylinder head can be - much more material than a 4 valve head and no nasty pre-combustion chambers (hateful things which damaged my otherwise immaculate 567,000 km 3Bii).

Aside from this the components are standard as far as I can see (filters, belts, thermostat, power steering pump, vacuum pump, flywheel, clutch, water pump, manifolds, turbo etc etc etc). I fully expect the crank, rods and pistons to be off-the-shelf items. And while the 15B-F, -FT and -FTE are no longer in production, the 14B is

EO

 

[ceylonfj40nut]

Not sure about 'many' fronts - could you be specific? The head gasket issue is potentially serious indeed. But the reason for buying such an engine is that as far as I'm concerned there is no susceptibility to head gasket failure outside of serious, sustained overheating, like any engine. They are not like the poorly designed 1KZ-T or 2L-T engines which are very sensitive to overheating and commonly crack heads. A two-valve, direct injection cylinder head is about as robust as a cylinder head can be - much more material than a 4 valve head and no nasty pre-combustion chambers (hateful things which damaged my otherwise immaculate 567,000 km 3Bii).

Aside from this the components are standard as far as I can see (filters, belts, thermostat, power steering pump, vacuum pump, flywheel, clutch, water pump, manifolds, turbo etc etc etc). I fully expect the crank, rods and pistons to be off-the-shelf items. And while the 15B-F, -FT and -FTE are no longer in production, the 14B is

EO

Seems like your are trying to answer the parts availability questions which will give you peace of mind. I speak generally. When stranded, you need to know you can get parts quickly. If it does not have piston oil squirts, thats a downgrade.

 

[Eurasiaoverland]

Seems like your are trying to answer the parts availability questions which will give you peace of mind. I speak generally. When stranded, you need to know you can get parts quickly. If it does not have piston oil squirts, thats a downgrade.

I don't for a moment believe that they removed them from the engine design. They are merely internal (only visible/accessible by removing the sump pan), just like on all 15B engines (and L engines). Oil nozzles are not really serviced items so having to remove the sump pan to get to them is a non-issue.

 

[myusername]

According to people who have compared the 15BF and 15BFT, the 15BFT has gallery type pistons. Sorry for not. being specific

The 15BT appears to be more 14BT than 15BFT, I think it's a stretch to assume it has the same displacement as the 15BF even if it is bored out. It very much appears to be a modified 14BT which would very much explain why they labelled them 15B to differentiate (but doesn't explain why they didn't make an effort to differentiate the labelling of the 15BT from the clearly very different 15BF aside from the idea that military 15BT were possibly never intended to be in civvy hands)

Military Megacruisers seem to have been made with several different 15B series engines through their production, even the later NO4C. Since ex-military assets are sold in batches it's possible you just saw pics of a later batch that were fitted with the 15BFTE and as a result assume most of them were fitted with this engine (eg, the now notorious thread exporting ex megacruiser 15BBFT[E] engines). It's also likely that all or most of the older 15BT and 15BFT military Megacruisers have already been disposed of prior to the english speaking world forming an interest in them, and only later ones fitted with 15BFTE are coming on the western market now.

 

[Eurasiaoverland]

According to people who have compared the 15BF and 15BFT, the 15BFT has gallery type pistons. Sorry for not. being specific

The 15BT appears to be more 14BT than 15BFT, I think it's a stretch to assume it has the same displacement as the 15BF even if it is bored out. It very much appears to be a modified 14BT which would very much explain why they labelled them 15B to differentiate (but doesn't explain why they didn't make an effort to differentiate the labelling of the 15BT from the clearly very different 15BF aside from the idea that military 15BT were possibly never intended to be in civvy hands)

Military Megacruisers seem to have been made with several different 15B series engines through their production, even the later NO4C. Since ex-military assets are sold in batches it's possible you just saw pics of a later batch that were fitted with the 15BFTE and as a result assume most of them were fitted with this engine (eg, the now notorious thread exporting ex megacruiser 15BBFT[E] engines). It's also likely that all or most of the older 15BT and 15BFT military Megacruisers have already been disposed of prior to the english speaking world forming an interest in them, and only later ones fitted with 15BFTE are coming on the western market now.

Ah, got you on the piston design. I know the -FT pistons have a 3 mm top compression ring cf. a 2.5 mm on the -F but I have never held either piston in my hand so don't know more than that (though have heard the same regards oil galleries).

I believe the 15B is bored out to a 4.1 because it is the simplest answer to the problem. I am not familiar with all Toyota's engine series, but from those that I do know (B, L, H, K, R, RZ, JZ, VZ, UZ, KD etc), it's clear that Toyota do not label two engines in the same family with different displacements with the same generational number. Similarly, I am not aware of any instance where two engines of the same displacement in a family have different generational numbers. Therefore your assertion that the 15B-T might not be bored out, or might be bored out to an intermediate size between the 14B and 15B would mean that Toyota have violated this rule. Not impossible, but highly unlikely in my opinion.

Again, the simplest answer is that the 15B-T is a 4.1. You are trying to invoke alternative (not impossible) scenarios where, in addition to the above, there are bespoke parts that were not used on any other engine (a stroked crank or intermediate sized pistons). This is something of an irrational approach. Why are you so against the idea of the 15B-T being bored out to the same 108 mm bore as a 15B-F*? I realise this is a large increase in bore size (for reference, 3Bii/14B aftermarket liners are 106 mm OD) but given that the 14B and 15B-F* use the same crankshaft, the distance between the centre of No.1 piston and No.4 piston must be identical. Therefore, it's clearly possible to fit them in the space of a 14B block, though that would depend on the casting. You can compare pictures of 14B and 15B gaskets and see that there is much less material between the cylinders on the 15B. You can also see that the 15B has more coolant passages whereas the 14B would seem to be solid between the cylinders. I somehow doubt Toyota would supply the military with an engine with paper-thin cylinder walls. It is possible that they used wet liners I suppose, but Toyota ditched liners in 1988 on the B engines so it would be a step backwards technologically.

On the use of '15B' on both the 15B-T block and the 15B-F* blocks and Toyota not making an effort to label them separately, that is not without precedent. the old 3B (cylinder liners, stink pipe etc) and new 3B (unofficially 3Bii) are labelled identically on the block, despite being very different engines. Same for the 11B. The 14B and 14B-T are not labelled differently. I imagine the same holds for the 15B-F and 15B-FT though I have never looked for the engine number casting/stamp on a 15B-F* block.

As for which engine is most common in the Megacruiser; you make a very good argument of recency bias. However, you assume that I am limited to the English-speaking world/Western market, which I am not. I live in Asia where used Japanese imports are extremely common and have been for decades as far as I know. The supplier across the border in Malaysia currently has four BXD10 half-cuts, 3 of which have the -FTE. There are also Russian-language sites selling parts (e.g. baza.drom.ru) and I can tell you from experience that Vladivostok in eastern Russia is a very large importer of used Japanese vehicles and parts (it's just across the water from Hokkaido), and has been since the 1990s. So my impression that the -FTE is the most common engine in the Megacruiser is not just from MUD threads, but from several years of perusing online parts sites, forums and visiting engine import warehouses. I could be wrong, but as stated, my impression is that the -FTE is the most common Megacruiser engine. Thanks for sharing the W04C picture - I was not aware that they came in the Megacruiser and don't think I have ever seen one (being electronically controlled it is not on my radar).

 

[myusername]

Ah, got you on the piston design. I know the -FT pistons have a 3 mm top compression ring cf. a 2.5 mm on the -F but I have never held either piston in my hand so don't know more than that (though have heard the same regards oil galleries).

I believe the 15B is bored out to a 4.1 because it is the simplest answer to the problem. I am not familiar with all Toyota's engine series, but from those that I do know (B, L, H, K, R, RZ, JZ, VZ, UZ, KD etc), it's clear that Toyota do not label two engines in the same family with different displacements with the same generational number. Similarly, I am not aware of any instance where two engines of the same displacement in a family have different generational numbers. Therefore your assertion that the 15B-T might not be bored out, or might be bored out to an intermediate size between the 14B and 15B would mean that Toyota have violated this rule. Not impossible, but highly unlikely in my opinion.

Again, the simplest answer is that the 15B-T is a 4.1. You are trying to invoke alternative (not impossible) scenarios where, in addition to the above, there are bespoke parts that were not used on any other engine (a stroked crank or intermediate sized pistons). This is something of an irrational approach. Why are you so against the idea of the 15B-T being bored out to the same 108 mm bore as a 15B-F*? I realise this is a large increase in bore size (for reference, 3Bii/14B aftermarket liners are 106 mm OD) but given that the 14B and 15B-F* use the same crankshaft, the distance between the centre of No.1 piston and No.4 piston must be identical. Therefore, it's clearly possible to fit them in the space of a 14B block, though that would depend on the casting. You can compare pictures of 14B and 15B gaskets and see that there is much less material between the cylinders on the 15B. You can also see that the 15B has more coolant passages whereas the 14B would seem to be solid between the cylinders. I somehow doubt Toyota would supply the military with an engine with paper-thin cylinder walls. It is possible that they used wet liners I suppose, but Toyota ditched liners in 1988 on the B engines so it would be a step backwards technologically.

On the use of '15B' on both the 15B-T block and the 15B-F* blocks and Toyota not making an effort to label them separately, that is not without precedent. the old 3B (cylinder liners, stink pipe etc) and new 3B (unofficially 3Bii) are labelled identically on the block, despite being very different engines. Same for the 11B. The 14B and 14B-T are not labelled differently. I imagine the same holds for the 15B-F and 15B-FT though I have never looked for the engine number casting/stamp on a 15B-F* block.

As for which engine is most common in the Megacruiser; you make a very good argument of recency bias. However, you assume that I am limited to the English-speaking world/Western market, which I am not. I live in Asia where used Japanese imports are extremely common and have been for decades as far as I know. The supplier across the border in Malaysia currently has four BXD10 half-cuts, 3 of which have the -FTE. There are also Russian-language sites selling parts (e.g. baza.drom.ru) and I can tell you from experience that Vladivostok in eastern Russia is a very large importer of used Japanese vehicles and parts (it's just across the water from Hokkaido), and has been since the 1990s. So my impression that the -FTE is the most common engine in the Megacruiser is not just from MUD threads, but from several years of perusing online parts sites, forums and visiting engine import warehouses. I could be wrong, but as stated, my impression is that the -FTE is the most common Megacruiser engine. Thanks for sharing the W04C picture - I was not aware that they came in the Megacruiser and don't think I have ever seen one (being electronically controlled it is not on my radar).

Not trying to make an argument, just pointing out that it's pure assumption to assume it shares anything in common with the 15BF variants

Per your comments about export, JDM imports are common to Australia and NZ as well there are just more limitations than some Asian countries so there aren't many/any megacruisers. Due to practicalities within Japan it appears that most military Megacruisers are wrecked / parted out

NB: as noted previously, ex military surplus is sold in batches, so it's possible and likely that entire batches are sold with the same engine. Those pictures I passed on of 15BT and 15BFT engines in megacruisers are not recent, I think I saved them from a thread that was 10-15yrs old. AFAIA the 15BFTE had the longest production run and was the most recent variant, the 15BFT version was only made in a short period over 20yrs ago

Unfortunately it's impossible to tell how many military variants were made with which engine as this information simply isn't available AFAIA. notably, popularity for export has increased significantly over time thanks to the internet , forums and social media etc, so the later 15BFTE variants likely had tenfold global demand for export vs the earlier ones to come up in military surplus auctions

 

[MauricioR]

Hi, a friend on mine has a 8 valve 15BT. Here is a photo of the Engine Gasket:

similar to the 14BT but not the same....
Also similar to the 15B-FT but not the same....

I cannot seem to find any part ID or information on it. Even the Toyota dealer here in Costa Rica has no info.

 

[Eurasiaoverland]

Hi, a friend on mine has a 8 valve 15BT. Here is a photo of the Engine Gasket:
View attachment 3494835

similar to the 14BT but not the same....
Also similar to the 15B-FT but not the same....

I cannot seem to find any part ID or information on it. Even the Toyota dealer here in Costa Rica has no info.

Wow, there is someone out there! Thank you very much for your reply. That is very clearly bored out beyond the diameter of 14B cylinder bores.

If I needed a new head gasket, my first try would be Cometic for a custom made version. You could send 15B-F* and 14B* gaskets and highlight which elements need to be integrated.

Next option would be to machine a 15B-F* gasket for the 14B-T coolant passages. It might be necessary to skim the pistons to make up for the difference in gasket thickness, and any machine work done to the cylinder deck.

Last option is to get a 3Bii/14B* block, 14B-T pistons, and make the engine a 14B-T.

Toyota will be no help at all. I have a suspicion that the part number was 11115-58120, but this part is no longer available. Is there a number stamped on the gasket? It should be on the top surface, exhaust side, between cylinders 1 and 2 I think.

Very interested to see any more pictures on the engine teardown, is there a thread anywhere I can see?

Thanks again,

EO

 

[MauricioR]

Wow, there is someone out there! Thank you very much for your reply. That is very clearly bored out beyond the diameter of 14B cylinder bores.

If I needed a new head gasket, my first try would be Cometic for a custom made version. You could send 15B-F* and 14B* gaskets and highlight which elements need to be integrated.

Next option would be to machine a 15B-F* gasket for the 14B-T coolant passages. It might be necessary to skim the pistons to make up for the difference in gasket thickness, and any machine work done to the cylinder deck.

Last option is to get a 3Bii/14B* block, 14B-T pistons, and make the engine a 14B-T.

Toyota will be no help at all. I have a suspicion that the part number was 11115-58120, but this part is no longer available. Is there a number stamped on the gasket? It should be on the top surface, exhaust side, between cylinders 1 and 2 I think.

Very interested to see any more pictures on the engine teardown, is there a thread anywhere I can see?

Thanks again,

EO

I do not think we are going to make a post about, but surely I can share some photos.

This engine is mounted on a 40 series and it is used to compete in 4x4.



No idea exactly on what was this engine running on before this since it was imported directly from Japan as it is.
It seems that we will have to fabricate the gasket with the cometic folks.

 

[MauricioR]

From Cometic:

"Unfortunately, it does not appear we will be able to build a reliable gasket for that engine.
The bore size is too large for any of our combustion chamber rings,
and we cannot produce it in steel at the current time."

 

[Eurasiaoverland]

From Cometic:

"Unfortunately, it does not appear we will be able to build a reliable gasket for that engine.
The bore size is too large for any of our combustion chamber rings,
and we cannot produce it in steel at the current time."

Thank you for sharing pictures and video. I can see from the picture of the block that there are small pairs of coolant passages between the cylinders, which the 14B does not have. Did you confirm that the bore is 108 mm?

I know that these engines came in the earliest Megacruisers (mine came from a Megacruiser) but I have also heard that they came in some military trucks and maybe Coaster busses supplied to the Japanese military, but I have no evidence of this.

That's bad news from Cometic. As I posted above, it might be possibe to modify a 15B-F* head gasket to fit, but one issue is thickness. On the 14B*, the head gasket can be 1.50 mm, 1.60 mm or 1.70 mm thick. On the 15B-F*, they can be 1.20 mm, 1.30 mm or 1.40 mm. So it will depend on what controls the piston protrusion from the block. I assume the 15B-T uses standard 15B-FT pistons, but I am not sure of that. If the 15B-F* and 14B* blocks are the same height and the 15B-FT pistons are shorter, then a 15B-F* gasket could work. If the 14B* and 15B-FT pistons are the same height, but the 15B-F* block is shorter than the 14B* blocks, then there is another problem.

If you find a place who can make these gaskets I would be very intereted, but Cometic were the only place I came across.

Thanks,
EO

 

[myusername]

That's bad news from Cometic. As I posted above

Try CHK Thailand, they supposedly get steel headgaskets made for 15BFT (can't confirm that they're not rebranding a pre-existing product)

They might be able to arrange a batch for you. If you can find a few other owners willing to contribute it might be worthwhile, especially if you were the only worldwide source!

 

[myusername]

Try CHK Thailand, they supposedly get steel headgaskets made for 15BFT (can't confirm that they're not rebranding a pre-existing product)

They might be able to arrange a batch for you. If you can find a few other owners willing to contribute it might be worthwhile, especially if you were the only worldwide source!

Just be aware they may be prone to confusing 15BFT and 15BT

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[Dougal]

Surely anyone selling a half-cut can supply engine numbers and those numbers would be enough for diagrams and part numbers?