2LT cylinder head cross cut, the reason it cracks and fails

[crushers]

last time i talked to John he was doing a massive cleanup in the yard so sooner than later would be advised.

 

[GTSSportCoupe]

I should add: I looked at a Prado LJ78 in Victoria last year that had a cracked head. This Prado was fresh of the boat from Japan, and had cracked the head on it's first trip up a grade. Coolant was all over the engine bay from when the head cracked, as the system became so pressurized so quickly it blew open the rad hoses. The coolant was rust soup. It was the nastiest coolant I've ever seen. I'm confident that the rad was probably completely clogged. Obviously this truck had issues already when it came from Japan.

The owner had payed to have the head removed after it failed, and it was sitting in the back of his truck. I took a look at it, and it was the most severely cracked head I've ever seen. What I want to note is that the cracks were huge and in areas other than between the valves. Areas where the casting is much thicker. This demonstrates what happens when hot spots form from a failed cooling system. Where the metal gets hot and steam forms, it cracks.

 

[raboyto2]

I'm curious enough about this now I may call RADD cruisers to see if they have any cracked diesel heads around that haven't been recycled. I could pick them up, and cut them in the same manner as Fantom. I'd like to see how the 2LTE head compares to the 2LT head. I'd also like to compare to any diesel Toyota head I can get my hands on.

There is a pic of a 2lte half cut it in another thread thats not to far down. There some on the UK site and some on the Australian site.

 

[Dougal]

Thanks so much for posting these.

 

[ozwallaby]

There is a pic of a 2lte half cut it in another thread thats not to far down. There some on the UK site and some on the Australian site.

Any links to these pics you've mentioned..... thanks in advance.

 

[blis]

This perticular head came off a 2LT that had a roller valve setup. So this was an early 2LT, not a 2LT2 or 2LTE. Now the photos I have seen of the 2LT2 or 2LTE heads shows the same channel and the same divet between the valves so it gives me reason to believe it is the same.
The issue you have with this design is that you have exactly 5.7mm of cast steel seperating one chamber that contains upwards of 500PSI and over 1200F from another chamber that has virtually no pressure and around 220F.
I'm not an engineer but can ask a few friends to do some math for me, and it will likely prove what is pretty obvious, it's a flawed design. There is not enough wall thickness no matter what you do.
This is not a question of what to do so it does not fail, it is simply a question of what might prolong it from failing sooner. It will fail, eventually, if you are nice to it and run Evans you might extend the life of it but it will fail eventually.
Now if we could get to the designers and change the casting it would no longer be an issue. There is no benefit of running a cooling channe. between the valves. There is another just abouve it. If we could stop the channel before it gets to the thin section, and drill a new hole from above to reroute the flow around that section, it would solve that issue.
Now I though about cutting in threads, and putting a plug in there, the issue with that is that the thread cut would make the wall thickness even smaller and a plug, unless it is the exact same material as the head, would expand and contract at different rates and likely cause it to fail even quicker.
So unless we can redo the casting, this is a failure waiting to happen.

From engineering standpoint that wall thickness is way too much for given pressure. For example your run-of-the-mill 200 bar gas bottle is tested at 300bar pressure (~4300psi) and it's wall thickness is around 4-5mm... So frankly said, the pressure is not the problem...

Obviously the heat changes strenght values of casting but the changes are smaller by factor of two atleast in contrast to pressure...

Now, the more obvious reason in head cracking (atleast in older gen pajeros) is the fact that people dont properly let the engine cool down before shutting it off. Instead they hit the kill-switch instantly when they turn on their yard which causes huge heat-stress in the components that are really hot on the other side and are cooled fairly quick from the other side. This in turn causes uneven stress across the parts which causes cracks to form in material...

 

[Dougal]

I would think it's not the absolute thickness there that is the problem. Rather the change in thickness.

 

[raboyto2]

Any links to these pics you've mentioned..... thanks in advance.

https://forum.ih8mud.com/diesel-tech-24-volts-systems/761593-2lt-head-cracked-sleeved-can-work.html

I guess thats the only one I can find. I specifically remember one on the Australian forum that I cam across 2-3 years ago, but cant seem to find it. It was also cut with a band saw, but was super super rusty.

 

[Fantom]

Without debate the primary cause of the crack is an issue with proper cooling, the reason it happens there is because of what the photos show, weakest section of wall in the highest stress area.
Yes, gas bottles have even thinner walls and deal with higher pressures, but they don't do that under the same conditions of vastly fluctuating temperatures combined with such variable pressures.
Considering that you are going from suction to pressure of up to 500psi around 2500-3500 times a minute you essentially just attached a vibrator to the cylinder wall, which is much worse than a gradual increase of pressure. Add to that the large temperature fluctuations and it becomes 100 times more stressed.
Also you are dealing with cast steel, which can often times have weaknesses that plate steel never sees.
It is a combination of factors but at least we know why it happens where it does and why coolant always enters the combustion chamber.

 

[crushers]

why it happens is not important, is it the basic s***ty engineering of the head that is the issue.
unless you pull off the interstate and immediately shut it down the egt readings are well below any issue even if you only drive a mile after a hard run.
the s***ty design work allowed for the week spot. i have seen these heads blown after bucking an alberta head wind WHILE driving it. the engine heated up while working to move the LJ78 up antler hill between Calgary and Canmore, she crested the hill and on the flats hit the head winds (as some of us know, the S bends are really bad for head winds) coming out of the S bends the truck over heated. we had it towed to the shop where it was pulled and the cracks were very visible.
she had a pyro and kept an eye on the temp, sadly, the weak spot left her stranded.

i have yet to see one of these crack in the driveway, in my experience they have always left the owner stranded on the side of the road miles from the last pit stop.

although i agree sudden shut downs isn't a good practice, that isn't what is killing these crappy POS heads.

 

[Fantom]

Well of course the head will crack while driving, because it's under stress at that time. It won't do it while chilling in the driveway because it has no pressures to deal with. But the effects of not cooling it down properly do add to it over time as well.
All those factors are important, but I agree with something Crushers said a while ago, it's not a matter of if it will break, just a matter of when. You can run Evans, you can have a great cooling system, over time that area will fail again and again because of a weak design.
I've talked to a regional expert on this stuff, John Voo at ATEB, and he's ran his 2LTE for a while now, highly modified (and I think it has a 3L head) and pushing upwards of 20PSI with great results. He agrees it's the fault of the cooling system inadequacy that causes it and if it is maintained it's more reliable. I agree, and when it fails, which eventually it will, it will do it in the weakest spot. So from a design standpoint, why not remove that spot? No logical design reduces material thickness in the most critical place of the structure. This is like taking a bridge and cutting out half the beams and supports in the middle, brilliant!

 

[crushers]

yes, i agree with your assessment, the heating and cooling will cause the cracks eventually.
as long as the egt is under 600F then you can shut it down with no issues and that drop in temps can happen VERY quickly once you are off the highway or no longer putting the engine under heavy load.

i am sure you are familiar with the Choqu, long long steady uphill climb, then forever back down the other side ... this stretch of highway is brutal on heads. you get to the top, stop for the toll and some guys shut the engine down. that would be a serious no/no. high heat from the climb, sudden pressure drop and a recipe for disaster.

 

[MatS]

I know everyone says the 3L head is an improvement... but how much are we realistically talking? Do they bolt onto any 2L engine block or are we just talking 3L non-turbo fits 2L non-turbo and 3LT and 2LT interchange? I'm just trying to decide it running it till it blows is the option and swap something after or will a 3L head and constant maintenance save me some headache.

 

[crushers]

the 3L "upgrade" head is still the same design as the old 2LTE head.
sales gimmick is all that is.
we have had installed the 3L head onto a couple LJ78s and they blew a couple years later.

engineered design is poor ... no, not poor, down right s***ty.

drive conservatively, watch the pyro, watch the water temp (completely unrelated in response time and application) install a pyro and aftermarket water temp and drive accordingly.

don't believe the hype.

 

[MatS]

Sounds good. This is why I ask you before I make $3000 decisions haha. Thanks for the advice. If you noticed since last time I messaged you I now have 2 trucks... '87 in the foreground has 213k on it, 2L, SUPER clean rust free cab with a new OME suspension on 33" BFGs. The '88 in the background will be listed for sale soon and that is the truck I did all the cab reconstruction on and full POR 15 interior... that thing will not rot away again and only has 171k on it.

 

[crushers]

i love those trucks ...
just the engine turns me off, otherwise i would have one.

 

[raboyto2]

I know everyone says the 3L head is an improvement... but how much are we realistically talking? Do they bolt onto any 2L engine block or are we just talking 3L non-turbo fits 2L non-turbo and 3LT and 2LT interchange? I'm just trying to decide it running it till it blows is the option and swap something after or will a 3L head and constant maintenance save me some headache.

God, iv wanted one of these for a while. But a pickup doesnt suit me.

On this topic of cracking L series heads, I just wanted to toss this out there. The 3L head is the same as the 2LTE head as far as we know. They do carry different part numbers but I could not find a difference between the two when I had them side by side. Id love to see one cut open. Im assuming the 3L heads do no crack as often as the 2lte simply because they are in a slightly higher displacement engine that is not turbo charged.

The expense of the issue is a little blown out of proportion also. 3000$? Well, if your in there and doing the whole timing system, new fuel injectors new this and that I guess it could add up. But then again I was talking to my neighbor who just dropped 1250$ on new "brakes" for her Avalon at a local shop. Pads and rotors in the front and just pads in the rear. . I guess it pays to do things yourself. 1sttoyotaparts is still selling OEM 3L cylinder heads for 650$. (I guess they dont ship to canada anymore). 60$ for a head gasket and 70$ for a headbolt set from most canadian JDM parts sellers, or other. Hell you can even be more cheap and buy a complete cylinder head on ebay (with valves, cam, shims, headgasket, headbolts) for 680$ (shipped to my location). I dont know the quality of these units, but Im assuming not the greatest. I emailed a few people that have purchased these and so far no problems YET. Of course if it cracks far from home it will be expensive. Just like when we blew a tranny on the Coquihalla, but that was in a ford.

I've been running Redline Water Wetter because of this head issue. It lowers the surface tension of the coolant. This reduces the size of hot spots which are the cause of steam pockets which dont allow good cooling of the metal thats touching it. Is it a solution? No. Will it help? Probably.

 

[gerg]

So I drilled into my spare smashed 3B head I had lying around and measured the depth between the valves in the same spot the 2lt head cracks. The 3b heads crack there too but dont fail near as often. Well its at least 8.5mm on the conservative side. Maybe 8.75mm. Tuff to measure through a hole, but its at least 8.5.

Incidently, what is a common depth for this area in normal diesel heads?

Sorry for no cool cross cut like Mat. I only have a chop saw and im not about to sit there for an hour doing this, plus I still use the old one for turbo builds.

g

 

[Fantom]

Thanks for checking that out, and all the good turbo info.
Since the 2LT head is only 5.71mm, that's a fairly large difference. It may be greater still if the overall diameter of the hole is smaller than the 2LT. I will have to harass Steve, Ciaran or Greg (G&S) to see if anyone has a junk head.
Still trying to track down an engineer familiar with thermal and pressure effects on metal

 

[deaddrift]

What a cool thread, thanks!

So... I run a someday-to-be-turbo'ed 3B and I want to know what is this Evans coolant thing all about? Why better than 50/50?