Thread: rebuilding a 4BD1, where? and improvements?

Def 90
I've worked on alot of the army defenders with the 3.9's over the years an if it's one thing that I've learned it's that the Isuzu is bullet proof, with the way that the army guys treat them (like they stole it!) I have a huge amount of respect for them.
If your friend's car still had oil pressure before it was stopped, even if it was bugger all, then it still had oil.....yea. It'd take more than that to wreack an Isuzu, Ive had them come into the workshop, an less than 2ltrs of oil was drained out, keep in mind they hold 7.5.

If he has it out anyway then first thing to check is the main bearings, if they are a copper colour then the bearings have had to much heat, they should be a light grey colour. But seriously if he had oil pressure than he'll do more damage than good to the engine by pulling it appart, by letting in foren particals. They are an extreamly heavy enginetoo, what if he drops the crank? or the head? I'm just saying that he shouldn't hasten to pull it down.

He could also refill up the oil with the new line, an test the oil pressure, if it reads above 430kpa than all's good.Standard is 441kpa from memory.

But if curiosity get's the better of him an you have some Q's, I have rebuilt a couple of them an have all the spec's and some pic's.
PM me if things get confusing and I'll give you my No.

Cheers Larns

Larns Is right, being an ex armourd corps driver chasing a leapord or apc cross country in a 110 was... well fun. The 4bd1 is bulletproof unless you run it without coolant or hydrostatic it. The machining I was refering to was for the head, mains and crank. As im relearning my trade for mechanics (dont ask nasty diatribe to follow on that matter) I looked into what I have to do for the rebuild part of the course. we have to replace one liner then rebuild with a new piston for that liner (they rotate the ones swapped out as matched sets and the engines are rebuilt every 3 weeks or so) then rebuild the rest of the engine.

My results from the first go round. No problems doing a foriegn engine rebuild so long as I fill out the paper work. this was from the workshop instructors, they prefer it when we do work on stuff we bring in as they know that we will put the effort in to make it smicko. So of I meandered to the admin side of the shop...


For those of you who have worked with buerocracies you know how this story ends...

For those of you who dont. minus the 15 minute lecture I got ranging from OH+S to Missapropriation of public monies the final answer was, "No its too much paperwork for you to do that."

Pointing out the hemi V8 that one of the instructors is having students rebuild won me no friends within the administrative side of the wing.

Round 2 starts tomorrow but will get placed on hold due to AJ field crap starting at the end of the week.

more news after fathersday... (My first one on the recieving side )

thanks for all the info guys!!

larns my 4bd1t under load runs 400-500kpa but after highway driving when not on the throttle can drop as low as 150kpa? i have seen other 'trucks' do this when not on the throttle, but i was thinking that is extremely low. once on throttle again it climbs back up quickly to usually over 400kpa. but even around town sometimes it drops to round 300kpa.

for a total non'tech person why does this happen, i would have thought the pressure may drop when not on throttle but not that much...?

Originally Posted by def-90

thanks for all the info guys!!

larns my 4bd1t under load runs 400-500kpa but after highway driving when not on the throttle can drop as low as 150kpa? i have seen other 'trucks' do this when not on the throttle, but i was thinking that is extremely low. once on throttle again it climbs back up quickly to usually over 400kpa. but even around town sometimes it drops to round 300kpa.

for a total non'tech person why does this happen, i would have thought the pressure may drop when not on throttle but not that much...?

I have difficulty following you - but oil pressure is basically set by the pressure relief valve, and will drop below this only if the supply of oil is not enough to keep up with the leakage through the bearings. This leakage increases when the bearings are worn, and when the oil is hot and hence thinner. The supply of oil mainly depends on the engine rpm and efficiency of the pump. It is normal when the engine is idling with the oil hot for the pressure to drop, and yes, 150kpa would not be out of line. Throttle position has nothing to do with it, it is engine rpm that matters. Low oil pressure above a fast idle suggests a problem, the most likely being a blocked filter, but it could be bearing wear, possibly a broken spring on the relief valve (there are two, one before and one after the filter, plus a filter bypass one), or an inappropriate oil. Oil that has been in use too long may also lose viscosity as the long chain molecules break up, but this is usually only apparent when idling - failing other problems the oil pump has plenty of capacity on this engine to keep pressure up above idling even if the oil is too thin or the engine excessively worn (and in this case there would be other symptoms!).
John

Thanks to Ben - Isuzurover, here http://www.isuzudieselswapper.com/photo.html is a link to a page of pics which show removal/replacement of 4BD1 liners without a press. Tool is relatively simple and uses threaded rod to jack the liner.

Originally Posted by JDNSW

I have difficulty following you - but oil pressure is basically set by the pressure relief valve, and will drop below this only if the supply of oil is not enough to keep up with the leakage through the bearings. This leakage increases when the bearings are worn, and when the oil is hot and hence thinner. The supply of oil mainly depends on the engine rpm and efficiency of the pump. It is normal when the engine is idling with the oil hot for the pressure to drop, and yes, 150kpa would not be out of line. Throttle position has nothing to do with it, it is engine rpm that matters. Low oil pressure above a fast idle suggests a problem, the most likely being a blocked filter, but it could be bearing wear, possibly a broken spring on the relief valve (there are two, one before and one after the filter, plus a filter bypass one), or an inappropriate oil. Oil that has been in use too long may also lose viscosity as the long chain molecules break up, but this is usually only apparent when idling - failing other problems the oil pump has plenty of capacity on this engine to keep pressure up above idling even if the oil is too thin or the engine excessively worn (and in this case there would be other symptoms!).
John

on this, check the spring in the oil pressure relief valve, attach a pressure gauge to the oil galleries while cold and monitor the pressure. Assuming perfect oil a progressive drop in pressure is caused by the spring weakening as it gets hotter as well as expanding tolerances in other engine componante..

The oil pump reliefe valve is "relatively easy" to get at and replace and I would suggest this before doing a rebuild if low oil pressure at hot ilde is one of your key symptoms, most you will be out is $50 of oil and about $2 of gasket selastic to reseal the sump.

Of course if there is lots of "uncoool" particulate metal in the sump when you pull it off (bonus of doing the spring first you get to check inside the sump and crankcase) then ID be thinking, rebuild just in case.. While the 4bdI is tough as nails, like all things overengineered, when they decide to go tits up they dont mess about in doing so.

yall have fun Im off for booko snafus and charlie foxtrots tomorrow... by then i should just about be sober..

cyall after fathers day.

Bush65
Thats pretty much identical to the liner remover that I fabricated myself, however I do have acess to a press and used this to put a new liner in.

Def 90
I recently rebuilt my Isuzu an upon first start up at idle it ran around 450kpa. so........yes you do have a problem. However don't hasten in your rebuild, if your oil pressure gauge is electric check the health of your alternator. If at idle it drops in volts this can (an have seen it) affect your gauges reading.
One of my friends rebuild his engine after trusting his gauge, only to find that the problem persisted after rebuild, he had the same symptons as yours.
Or as the others said try hooking a gauge to the engine moniter pressure then try the filter and oil.

Good luck