2LT cylinder head cross cut, the reason it cracks and fails (1 Viewer)

[Fantom]

As some of you know I've recently made the mistake of acquiring a 2LT for my swap. After endless nightmare failures with this engine I got pissed off and threw the cracked head onto the bandsaw to see why they suck.
The cooling chamber that runs between the intake and exhaust valves, at it's closest is only 5.1mm away from the chamber.
Between that and the endless pockets that can allow steam build up, this thing is totally useless.

 

[Fantom]

And for those who love cross sections of engines....and that's pretty much all of us...

 

[BCR4619]

Cool!... Sorry it had to come at your expense!

 

[gerg]

Hey that is cool. Never seen a 2lt cross cut before. I bet there are lots of folks that will appreciate what you did. I know I took a copy of your photos! I guess I owe you a timmys now or something.

 

[Fantom]

All good, we're all here to share our stories of misery for others to learn from
Sanded down the cut face and you can actually see the hairline crack a bit.
These idiots could have easily stopped that cooling chamber before it hit that area and drilled from above, down. Or not create that pocket between the valves.




The worst part is that there is no way or repairing that so it doesn't happen. 5mm is not enough wall thickness in a combustion chamber that deals with 300-500 psi, 1200F or more on one side and coolant running around 210F on the other. Designed to fail.

 

[GTSSportCoupe]

Fascinating! Thanks for doing that. Your pictures will be a big benefit to many people. They show just how tight this head was designed. Why Toyota did this, I do not know.

I'm curious how this compares to the later 3l head that people use as a replacement? Or for that matter, other toyota diesel engine families? Answers we'll probably never know. Maybe I'll start buying cracked heads just to cut them open on the band saw....or not.

 

[Fantom]

It was the least I could do. As for the other heads in the L series. If the have a cooling chamber like this one and recessed dimples between valves, they likely have the same problems.
If anyone around the lower mainland has a head that's cracked and is interested, let me know. I'll toss it up on the saw. At least we'll all have a chance to learn from it.

 

[cicak]

Send it to toyota with your comments and see if they reply lol.

 

[crushers]

excellent ...
thanks for confirming what has been said all along. it is a s*** head design and no matter how much money you throw at it, it will eventually crack.

proof is in the pics

 

[gerg]

Sadly though, I suspect it isnt the only head with this design. 3Bs have a tendancy to crack in the same spots, althought not nearly as often as the 2lts, and have the same cut out inbetween the valves.

Anyone running these heads should serously keep their antifreeze in good condition with at least a 30/70 mix. A 50/50 would be better, or Evans would be better yet to prevent vapor locking these weird little pockets allowing for uneven heating and expansion of the head.

 

[crushers]

yes, 3B / B / 2B heads show the same cracking, i am not sure why the 3B can put up with so much abuse even after cracked ...
it would be interesting to see a cross cut of a cracked 3B head and the thickness of the metal in the same spot.

 

[Fantom]

Bring me a cracked 3B head and I'll tell you

 

[crushers]

I am sure Steve at Extreme bends in Vancouver should have a dead 3B head to donate ...
maybe give him a call.

 

[Fantom]

I'll ask him next time I see him. It will be interesting to cut apart.

 

[MatS]

Well that looks terrifying... I've got 2 trucks with 2L engines... maybe I should sell em both before it's too late. Or drop a little VW diesel in it....

 

[Fantom]

It's funny how a little cut can change perception, or prove opinions
I'll give Steve a call this week to see if we can find the shocking truth about other models.

 

[raboyto2]

Great pics of a half cut cylinder head! Interesting to see. Im just a little over 100,000kms on this head. Guess we will see how it goes.

 

[rustybucket]

What models the 2Lt is mounted in?

About 8 months ago, there was a 3b head for sale at a engine core scrap shop next to ralphs auto wrecking on scott road. Give them a call and see if they have it, or another 3b head that is junk and then we can learn more about this problem. BTW, would polishing the head help to reflect the heat back into the chamber keeping the heat absorption down?

 

[Fantom]

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.

 

[GTSSportCoupe]

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.

Interestingly, the early 2LT (the head you cut) does not have nearly the reputation for cracking that the later 2LTE has. The 2LTE head casting may be significantly different with the lack of rockers and the bucket/shim setup instead. Perhaps it's even weaker. Or it could be similar thickness, and the increased problems are due to higher EGT's from the EFI system.

I don't think this cracking has anything to do cylinder pressures. If it was related to cylinder pressure, it would be more catastrophic (a hole instead of a crack) I would think. I think the cracking is related to heat stress. When pushed hard with continuous high EGT's and raised coolant temperatures I think that steam pockets form in the coolant passage between the valves. Once the steam pockets form, the heat is not transferred away sufficiently. This causes hot spots and high stress in the metal. This fatigues over time and eventually cracks.

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.