Isuzu powered FJ140 (1 Viewer)

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So how did you determine what your ring gap should be? Did you use a formula

I put them in and went "yep, they're on the loose side". The 4BD1T manual says 10-18 thou for the top ring and 8-16 thou for the lower two.

This is from the Isuzu 4bg1t manual:
Piston Ring and Piston Ring Groove Clearance mm (in)
1st Compression 0.35–0.50 (0.014–0.020)
2nd Compression 0.60–0.75 (0.0236–0.0295)
3rd Compression 0.60–0.75 (0.0236–0.0295)
Oil Ring 0.30–0.50 (0.014–0.020)

I've got the same figures here. Plus a "limit" figure of 1.5mm (huge). I've heard rules of thumb of 3 thou per inch of bore plus 3 thou. But I prefer to trust Isuzu figures over rules of thumb. Great to have the Mahle reference too.

Interesting that they are so large. I would be really interested to compare 4BG1T pistons to 4BE1 pistons (same 105mm bore). There were truck applications of the 4BG1T and 6BG1T and also marine applications. I don't know if automotive pistons are different to marine and industrial (excavator) but it would be interesting to find out.

Did you get a look at your bores yet? If it is ring-end-cap then it should be obvious by the damage and scuffing. But even with broken rings on one cylinder I'm not getting oil soaked glow-plugs. So I'm wondering about holed pistons!
 
I put them in and went "yep, they're on the loose side". The 4BD1T manual says 10-18 thou for the top ring and 8-16 thou for the lower two.



I've got the same figures here. Plus a "limit" figure of 1.5mm (huge). I've heard rules of thumb of 3 thou per inch of bore plus 3 thou. But I prefer to trust Isuzu figures over rules of thumb. Great to have the Mahle reference too.

Interesting that they are so large. I would be really interested to compare 4BG1T pistons to 4BE1 pistons (same 105mm bore). There were truck applications of the 4BG1T and 6BG1T and also marine applications. I don't know if automotive pistons are different to marine and industrial (excavator) but it would be interesting to find out.

Did you get a look at your bores yet? If it is ring-end-cap then it should be obvious by the damage and scuffing. But even with broken rings on one cylinder I'm not getting oil soaked glow-plugs. So I'm wondering about holed pistons!

Yeah, I saw the limit of 1.5 and had to look at it a few times to make sure I was seeing it correct!

I did not know there were truck applications of the 4BG1T, I did know there were marine applications but they stopped making marine diesels a while ago for some reason. I'm pretty sure my pistons have the recessed hole with the cone in the center like this:
Nissa-BD30-Diesel-Engine-Parts-Piston.jpg


One other thing that comes to mind is this motor came out of a burned up excavator, the valve cover was literally melted into the rocker assembly of the head, I had to use a head of a different motor. I am wondering if maybe the fire damaged the pistons in some way, I never really gave it much thought at the time but if the fire was hot enough to melt the valve cover....

Pictures were supposed to be here this morning, it is frustrating not being able to do the work myself but it's either this or get a it towed somewhere to work on it and towing it was about the same price as having the shop do the work.

EDIT: this is what I found on a quick search for 4BE1 pistons:
74.4BE1.jpg
 
Here's the chassis number for a 1989 Isuzu NPR with the 4BG1 engine (non turbo): NPR61P-7102045 I found one for sale and ran the plate.

4BE1 Alfin piston: Best Portable Marine Generator for sales
Would have to check the little end pin to crown height (compression height). It may be much taller for the 4BG1. 56.4mm for that 4BE1.

Compression height 55.2 for this 4BG1 piston: [Hot Item] Isuzu 4bg1 Piston 105mm OEM 1-12111-3660 for Hitachi Excavcator Ex100-5

I believe the 4BE1, 4BG1 etc all use the same head.

A very hot fire could have weakened the pistons. But it would have weakened them all.

Regarding the marine engines, I think you're seeing them phased out of the US market due to environmental regs. They certainly still make them. I know a guy who bought a new Hitachi excavator last year with the 6BG1T in it. His last one of the same model had the 4H in it.

Isuzu marine link is broken (doesn't appear intentional), but industrial is still showing them.
ISUZU INDUSTRIAL DIESEL ENGINE
 
Here's the chassis number for a 1989 Isuzu NPR with the 4BG1 engine (non turbo): NPR61P-7102045 I found one for sale and ran the plate.

4BE1 Alfin piston: Best Portable Marine Generator for sales
Would have to check the little end pin to crown height (compression height). It may be much taller for the 4BG1. 56.4mm for that 4BE1.

Compression height 55.2 for this 4BG1 piston: [Hot Item] Isuzu 4bg1 Piston 105mm OEM 1-12111-3660 for Hitachi Excavcator Ex100-5

I believe the 4BE1, 4BG1 etc all use the same head.

A very hot fire could have weakened the pistons. But it would have weakened them all.

Regarding the marine engines, I think you're seeing them phased out of the US market due to environmental regs. They certainly still make them. I know a guy who bought a new Hitachi excavator last year with the 6BG1T in it. His last one of the same model had the 4H in it.

Isuzu marine link is broken (doesn't appear intentional), but industrial is still showing them.
ISUZU INDUSTRIAL DIESEL ENGINE

it seems to me that the 4bg1t piston recess is more ideal because it is round, I would think having a square recess would be less ideal, thoughts?

I'm going to stick with the 4bg1t pistons regardless, but I find the topic interesting.

I believe you are correct for the US and canada market and marine engines, they are a tier 2 motor as far as emissions go, and new standard is tier 3. The marine dealers in the US and Canada cannot sell the 4bg1t, but the industrial dealers will still sell brand new long blocks, if only they sold the short blocks too...
 
it seems to me that the 4bg1t piston recess is more ideal because it is round, I would think having a square recess would be less ideal, thoughts?

I'm going to stick with the 4bg1t pistons regardless, but I find the topic interesting.

I believe you are correct for the US and canada market and marine engines, they are a tier 2 motor as far as emissions go, and new standard is tier 3. The marine dealers in the US and Canada cannot sell the 4bg1t, but the industrial dealers will still sell brand new long blocks, if only they sold the short blocks too...

Piston bowl shape usually has to do with the injector spray pattern. So make sure you get the pistons that match. Might be worth seeing the inside of your motor before you place the order for new pistons?
 
All Isuzu 4B automotive engines I've seen pistons for are square bowl. 4BG1T are the only ones I've seen which are round. A client of mine put in a new 4BG1T industrial running a water pump a few years ago, but we don't intend to ever see the inside of that one!
My 4BD1T injectors have four jets, one to each corner of the bowl. Any idea how many your 4BG1T injectors have?

I'd back the suggestion of not ordering anything until you've seen what failed and why.

The 4BG vs 4BD history is very interesting. The 4BD came first, but only by a few years and Isuzu only put the 4BG into a truck once that I've found, then went to turbo 4BD.
 
I thought it was weird too that you had round bowls. 4BD1t uses square bowls specifically to increase swirl turbulence in the corners exactly where the injectors fire. The swirl intake ports create the swirl and the square bowl disrupts it in the corners to improve mixing. That's why I was very impressed with your mpg with the round bowl. It might be a re-entrant type bowl with a lip inside to keep the flame away from the cylinder walls. Bowl technology is very weird. It definitely has to be precisely matched with the injectors.
 
My motor has a long and terrible history with air-cleaners that leak dust, valve guides that got loose and fed debris into the oil pump and even using the wrong rings which chewed out a set of liners in 27,000km.
Currently has about 10 years and a bit over 50,000km on a set of cheap ungraded chrome liners on aftermarket pistons with genuine rings. The rings are broken on at least one cylinder from oil ingestion from a terrible oil/air seperator which sucked about 15 litres of oil out of the sump and fed it into my intake. That episode resulted in a head-gasket blown on all cylinders. I put a new headgasket in and will deal with the liners and pistons when I have more time.

Still driving great with good power/torque and excellent fuel economy. But it burns a bit of oil.

couldn't find your clay doll? :lol:
its amazing how much things can be in bad shape, and still keep going!!
 
couldn't find your clay doll? :lol:
its amazing how much things can be in bad shape, and still keep going!!


The most amazing part is I paid good money for the part which did this to my engine. I also spent a lot of time fixing other things that didn't need fixed (like rebuilding turbos) because I didn't believe a part from a reputable filter company could be causing this.

But it was.

If I had $NZ8k burning a hole in my pocket I'd go and get a new Isuzu long-block and be good forever!
 
I haven't ordered any parts yet and I don't intend on doing so until I know what is wrong.

I have confirmed in the past that the spray pattern of the 4bg is different but I am using the 4bg injectors from the motor matched to the serial number of the block and therefore pistons, so that shouldn't be the problem. I do not recall what the nozzles looked like though.

Greg, there may be a few injectors in the boxes of parts I gave you for interests sake...
 
Yes I found 5 injectors in a box of parts. Haven't looked at them closely though. They are BG injectors? I've been cleaning up a bit in the garage lately building shelves and stuff. Found lots of stuff I completely forgot about. Now that it's clean my wife wants to park in there. I told her it's technically not a garage, but rather a work shop with a garage door. Time to get it really dirty again I'm thinking.
 
Good to find the problem is not catastrophic, but still bad.

If you need a good injector shop, let me know. I have been using an old guy in Santa Ana, CA who does a great job on pumps and injectors. He is very reasonable and fast. I have referred several people to him, and all seem happy with his work.

Let me know.
 
Good to find the problem is not catastrophic, but still bad.

If you need a good injector shop, let me know. I have been using an old guy in Santa Ana, CA who does a great job on pumps and injectors. He is very reasonable and fast. I have referred several people to him, and all seem happy with his work.

Let me know.

It's definitely an injector issue, the shop it is at does injectors and pumps, but I'm going to see what new injectors from Isuzu would cost.
 
Here's the chassis number for a 1989 Isuzu NPR with the 4BG1 engine (non turbo): NPR61P-7102045 I found one for sale and ran the plate.

4BE1 Alfin piston: Best Portable Marine Generator for sales
Would have to check the little end pin to crown height (compression height). It may be much taller for the 4BG1. 56.4mm for that 4BE1.

Compression height 55.2 for this 4BG1 piston: [Hot Item] Isuzu 4bg1 Piston 105mm OEM 1-12111-3660 for Hitachi Excavcator Ex100-5

I believe the 4BE1, 4BG1 etc all use the same head.

A very hot fire could have weakened the pistons. But it would have weakened them all.

Regarding the marine engines, I think you're seeing them phased out of the US market due to environmental regs. They certainly still make them. I know a guy who bought a new Hitachi excavator last year with the 6BG1T in it. His last one of the same model had the 4H in it.

Isuzu marine link is broken (doesn't appear intentional), but industrial is still showing them.
ISUZU INDUSTRIAL DIESEL ENGINE

Hey,

So I found a few trucks with a 4bg1 but I didn't find any with the 4bg1t, thinking hard about an oem motor at this point, especially if it comes ready out of the box.

If I were to find one I see the 4bg1 is higher compression, 17.5:1 compared to 17:1 but do you know if there is anything undesirable about boosting it?
 
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