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4JG2 headgasket change

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4JG2 headgasket change

Postby Lukenz » Mon Jun 01, 2020 2:03 pm

Hi everyone, I have recently fitted a new head to my bighorn, did everything as per the instructions, deck surface was clean and flat, tourqed the head to specs provided with the headgasket, new bolts ect and im still getting coolant in the combustion chamber, im about to tear the head back of and start over, just wondering is the any specific brand of headgasket I should be using? or anything I might be missing. the brand headgasket I used was insbe and came with my new head, cheers
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Re: 4JG2 headgasket change

Postby geeves » Mon Jun 01, 2020 5:14 pm

Was it a new head? They are prone to cracking. Did you follow the sequence for tightening the bolts? Its very important right down to the stages. Without looking at the book its all the bolts starting from the middle down to a torque then in the same order all the bolts a portion of a turn then the same again. Its not like petrol engines
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4JG2 headgasket change

Postby Lukenz » Tue Jun 02, 2020 9:37 am

Hi Geeves, thanks for your reply, yes brand new cylinder head, the new gasket came with instructions. this is all in sequence shown from middle outwards
1. 20
2. 50 Nm
3. loosen all bolts
4. 52 Nm
5. +60 degrees
6 +60 degrees
7 +30 degrees

I'm not sure what it says in the isuzu manual and if I should be following different instructions? I have pulled the head of today, i can't see any evidence of the leak since it wasn't run very long, i will order new gaskets and studs, just be nice to cover all basis so I don't have to do it another time! lol I've obviously done something wrong, just not too sure what.. I've heard people putting copper coat on the gaskets, I don't know if this benefits anything and if its something I should do, im not sure. cheers
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Re: 4JG2 headgasket change

Postby geeves » Tue Jun 02, 2020 11:16 am

That sounds about correct. Options are Warped head or block. Even new heads should be checked. Cracked head or block. Faulty gasket. Something not right with your torque or angle gauge. One option you will kick yourself if it is, Did you get all liquid out from around the rings when you put it together? It might not be new coolant leaking.
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4JG2 headgasket change

Postby Lukenz » Tue Jun 02, 2020 2:46 pm

just checked the flatness of the head and the block, can't get my smallest feeler gauge in anywhere on the head. on the block I can get the .1mm gauge in at each end of the block (lenthways) I feel like this is acceptable? but I may be wrong, definitely wouldn't want it any worse. I did not use a angular gauge when turning the bolt heads at the last stages, i just marked them so I new how far to go. I'm hoping that's what is wrong. I didn't realize I could get a gauge for only $26
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Re: 4JG2 headgasket change

Postby geeves » Tue Jun 02, 2020 5:26 pm

headgasket.jpg

warp limit is 0.2 so your 0.1 should be ok
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Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4JG2 headgasket change

Postby Lukenz » Wed Jun 03, 2020 2:57 pm

awesome cheers. the gasket my head came with was a grade 3, so the thickest one, is there any benefit from using a thinner one? I have no tools to measure piston protrusion so the thickest one is my only safe option?
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Re: 4JG2 headgasket change

Postby Lukenz » Wed Jun 03, 2020 3:24 pm

I have measured using a straight edge across piston no 1 and no 4 while at the top and packed up feeler gauges of the block, i got 1.4mm, this is a rough measurement though, should be safe to use a 1.65mm gasket that i think is grade 2?
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Re: 4JG2 headgasket change

Postby geeves » Wed Jun 03, 2020 5:43 pm

Thickest gasket would reduce compression by a little bit but not enough to matter. I have seen it suggested that if in doubt use the thickest one.
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4JG2 headgasket change

Postby isuzurob » Thu Jun 04, 2020 5:23 pm

Get the thinnest headgasket you can to work with your application, will make it drive alot better, and have all round better engine response
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Re: 4JG2 headgasket change

Postby Lukenz » Mon Jun 08, 2020 11:10 am

changed gasket and bolts, did everything to specs, appeared good to begin with, then when shutdown and on next start up big puff of white smoke.. burning coolant again. i don't know what to do now. is there any other way that water can get in exept for through the head gasket? cracked water jacket in turbo? truck runs well. no constant white smoke, only when its been idling and then on the gas. and on each startup
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Re: 4JG2 headgasket change

Postby geeves » Mon Jun 08, 2020 2:45 pm

Is it pressurizing the cooling system? Is it going through water? Is it water. unburnt diesel can give white smoke but it would stink.
Why did you do the head in the first place. A severe overheat could crack the block. A manufacturing fault could exist in that head. Are you sure you dont have water contamination in your fuel?
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4JG2 headgasket change

Postby Lukenz » Mon Jun 08, 2020 4:13 pm

its not pressurizeing the system, yet it is using water. it had a cracked head so I have a new one. it has never got hot except for once a long time ago when it blew a old hose, only just went over half. may have contamination in the fuel but I would think since it's using water and not leaking.. its burning it. I dont know what to do next. a leak down test I imagine
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Re: 4JG2 headgasket change

Postby isuzurob » Mon Jun 08, 2020 5:16 pm

Block the 2 water hoses to the turbo and try it, have had lots of 4jg2 with cracked turbo cores
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Re: 4JG2 headgasket change

Postby geeves » Mon Jun 08, 2020 5:19 pm

No pressure in the cooling system. Did all pipes go back in the right places? The only one I can think of which could cause this is the breather line although I would expect that to drain a lot more water and contaminate the oil. Next up are the oil cooler and turbo. You can bypass the cooler easy enough and even the turbo can be bypassed short term. Turbo is the only option for water in combustion and not in the oil. I hope you have no water in the oil. That leaves us back at the had and block.
When you took the head back off was there evidence of water in any cylinders?
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4JG2 headgasket change

Postby Lukenz » Fri Jun 12, 2020 8:12 am

cheers for your help guys, I blocked of the coolant supply to the turbo and it fixed the issue, I have another second hand turbo I think is good that I will install, so the last headgasket I had installed was good! o well, atleast I didn't waste money on the new head as the last one was definitely well cracked
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Re: 4JG2 headgasket change

Postby isuzurob » Fri Jun 12, 2020 4:16 pm

Just loop the hoses and leave the water out of turbo have done it on heaps, keep your spare turbo for when it completely dies
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Re: 4JG2 headgasket change

Postby geeves » Sat Jun 13, 2020 7:41 am

A lot of the cheap chines turbos dont have water jackets. If you do the above remember your idle down times
Sanding your knuckles before starting work can help. That way you cant skin them
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