Thread: 4BD1T Swap from Isuzu NPR

Hi everyone, long time reader here from the United States and Defender enthusiast, and back in 2019 I actually imported a 1994 Defender 110 200TDI from Brisbane. At the time I had been looking for an Isuzu County as I really wanted the 4BD1 engine but those were pretty hard to find and commanding a pretty high price. My 200TDI has been serving me well so far, but I live in the Rocky Mountains of Montana and it definitely leaves a little to be desired pulling hills/mountains even with a turned up injection pump and upgraded turbo/intercooler. At the end of the day there is no replacement for displacement, and I've found myself coming back to the 4BD1 (in this case a "T" model from an NPR truck). I've done a bunch of reading here and compiled a list of everything I think I'll need to do the swap, and I was hoping you guys might be able to verify my list and throw in any input? Here is what I am tracking so far:

• Upgraded transmission (Isuzu MSA 5 speed, more to follow on that below)
• Adapter for transmission to transfer case/shifter linkages (more to follow on that below)
• Engine/Transmission mounts (KLR, weld to chassis? Do I need new transmission mounts for the MSA?)
• Cooling package (I have a stock 200TDI radiator that I copper re-cored, and I have a double core intercooler for the 200TDI as well. Any chance I could adapt these to work with the 4BD1T, or would that be too insufficient to keep the 4BD1T cool?)
• New exhaust (I saw KLR made an upgraded exhaust system for the perentie, any feedback?)
• Power steering (I have all the power steering parts that came with my 200TDI, anything major needed to adapt it to the 4BD1T?)
• Starter (read about clearance issues with the chassis rail, any specific starter to look for?)

I did have some additional questions on the Isuzu NPR trucks as I am finding it very difficult to pull up specs on these. I am tracking the 4BD1T was in NPR trucks from 1986 to 1992, and then they switched to the 4BD2T (not interested in this engine due to the indirect injection (hard starting in cold, not ideal for Montana winters) and head cracking issues). What I can't find is what variant MSA 5 speed transmission these trucks have, as I am trying to figure out how to match it with my transfer case gearing-wise. I currently have the 1.4 transfer case, and figured I would likely need to regear it to a 1.2? Also I know the cab over NPR trucks required a specific linkage setup for the shifter to work in the cab, and this would need to be modified to work in the Defender. I saw that Sheldon made linkage adapters as well as the transfer case adapter, but I wasn't sure if he was still selling these parts. If not, does anyone make these adapters? I read that a VW shifter might be able to work with the MSA but wasn't sure how that played out.

Is there anything else I should be aware of when adapting a 4BD1T into a 200TDI chassis? I know there are a few differences in configuration with the engines from a NPR truck, but I'd be interested to hear if there are any issues on the swap, if any. Sorry about the long-winded post, I'm hoping I can get the power as well as the durability of the Isuzu going in my Defender and give it that distinctive Australian touch so it knows where it came from Appreciate everyone's help and expertise!

Originally Posted by TheVolunteers

Since the 4BD1T and the MSA would all come together from the NPR, I'd only need the transfer case adapter (plus the modified shifter), but it's starting to look like I'd have to make the adapter myself if no one is making them now. I work in a weld and machine shop so that's not impossible, but would prefer to not go down that road...

There will probably be a few audible groans from the audience when I drag up my old thread again. 4BD1T MSA5G Range Rover Classic Outcast Adaptor

If you haven't already read the thread you might find information on the Outcast adapter useful. Note the photo comparing the Outcast adapter to the original Isuzu cover plate that normally sat at the back of the Isuzu gearbox in 2wd format. You or your machinist will now have some idea of what is required to make an adapter.

I did go to a lot of trouble to make a CAD drawing of the Outcast adapter so I could test ideas for some modifications to it, but I wont pass the CAD drawing on to anyone out of respect to Outcast and the work they put into the design. Memory is a bit vague now but if you follow some other threads relating to Sheldon you will see other adapter designs.

I was fortunate to get both the Isuzu engine and its original Isuzu gearbox from a wrecker, the truck itself crushed long before.

I got the Outcast adapter allowing me to join the Isuzu gearbox to a Rover transfer case. Back then Outcast was only doing a limited run of about 12 adapters. Making the adapters was problematic, in terms of having to find a slot in a manufacturers otherwise busy schedule. Outcast was not going to make anymore than 12 adapters unless further interest was immediate. From memory, it was not a problem for Outcast to make any number of short spud shafts through an axle manufacturer. I may be recalling incorrectly, that Outcast originally made their adapters and spud shafts for competition rock crawling.

In the beginning Sheldon and Outcast made similar stubby spud shafts or input shafts using conventional Rover splines to match conventionally splined input gears. Later Sheldon, and a fellow called Dougal (a Kiwi) now on another forum 4BTSwaps, designed long input shafts. To improve the strength of the long input shafts Sheldon (and maybe Dougal) used finer splines on the long shaft end which mate with a fine splined input gear in the transfer case. Sheldon took conventionally splined input gears and reworked them (EDM?) as fine splined input gears in two ratios(?). Think of the Isuzu gearbox output shaft which cannot mate with the Rover transfer case. To mate the gearbox and transfer case you need to slide either the short spud shaft or the long shaft onto the Isuzu gearbox output shaft. Then the end of either of those shafts enters the transfer case and mates with the input gear. The Outcast adapter case works with both the wider diameter stubby spud shaft and the narrower diameter long shaft, but only because the passage way was cut to fit the wider diameter stubby spud shaft in the first place. If you started with a long shaft and a diameter hole in the adapter case to suit, but later decided to fit a stubby spud shaft then the adapter case passageway would have to be re-bored to a larger diameter.

You will also see my attempt at making a gear shifter, modeled along Sheldon's design. Sheldon used rose joints at the end of his mechanical linkages. The rose joints allow some flexibility where there are changes in the angular relationships between mechanical linkages and were probably better than using bolts. These mechanical linkages are located on the passenger side of the gearbox - actually you guys sit on the wrong side - lets say left side of the box when sitting in the vehicle facing forward.

Memories are a bit vague now but I recollect that maybe when experimenting with Sheldon's design the gear stick made a slight swing or arced path between gears on the same shaft in the gearbox - in most vehicles conventionally 1st to 2nd on one shaft, and 3rd to 4th on another shaft. I did not have any rose joints in my design, just bolts joining lapped components. For example, you expect when moving back and forth between 1st and 2nd gears (or 3rd and 4th) that your hand on the gear stick would simply go straight forward and straight back, not on an arced path between the two points.

It's hard to explain, but when at rest a 100mm long linkage sits in a 100mm long space. When the gear stick and linkages are in motion relationships change. The 100mm long linkage finds that the space is now only 95mm long, If the linkage is not to bind then something has to give to make up for the lost space. That give is expressed in the arc the gear stick takes. Its not a deal breaker, but could be irritating. I suspect Sheldon's rose joints helped alleviate that problem. I devised a slip mechanism at the base of the gear stick. That slip mechanism takes the stress away from the potentially binding linkage and at the same time allows the gear stick to follow a straight line. Yeah, long and boring story, but if you are interested I think I have a CAD drawing. The essential part is the slip mechanism at the base of the gear stick. The rest of the structure you would change to meet your needs. And who knows if it would be street legal. Someone did pipe in and say what a load of rubbish, all these efforts to make a mechanical linkage system, why not just buy the VW wire system.

You're 15 times our population...sorry, porous border, 16 times...sorry, 17 times...darn it, 18 times...ok, you just have a much larger population than we have. And you have as many times more machining opportunities, so hopefully you will be able get something done over there, and probably cheaper - hands up all those who want an adapter and spud shaft from TheVolunteers? Guess its better than Ukraine, where the emigrants come with guns tanks aircraft and anti-democratic intentions - at least the Ukrainians are trying to stop the boats (local Ozzie idiom)! It's past 4 in the morning, that's my excuse for the banter...

A Rover gearbox was put behind the 4BD1 in the army Perentie. I'm assuming in an engine/gearbox combination that the Isuzu gearbox is better than the Rover gearbox. However, having said that, an army chap did tell me that they loaded the army trucks to 7 tonne in exercises on army land - I assume payload and truck combined - the guys reasoned a payload of 4.5 tonnes of zero alcohol beer would be lighter than 4.5 tonnes of full strength and so keep the Rover gearboxes from being overloaded!

G'nite!