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

[GTSSportCoupe]

I would not say only the 90-94 versions crack heads.

From what I've seen the 90-94 versions crack around 100,000km or less guaranteed. The replacement part numbers last 200,000km or so on a stock engine. If the engine has an intercooler and other improvements they can last even longer. That's what we've seen in Canada anyhow....

Yup, IDI's with turbo suck. This had me revisiting the versions of this cylinder head that came with silicon-nitride ceramic pre-combustion chambers. Way more insulation between the combustion and the coolant making for better efficiency and a cooler running motor. Sort of wish I'd gone for one of them to try it out.

Here is Toyota's SAE paper on ceramic pre-cups: Toyota made ceramic pre-cups - 2L-THE

 

[Ebike toter]

I'm looking into the complete coolant system.. gonna debottleneck it throughly..
if you're interested just posted a mechanical system upgrades update...."what-did-you-do-on-your-70-series-today" let me know what you think!!

 

[Previa Diesel]

There is a way to repair these heads that I may be trying: remove the small plugs that close off the galleries beween the valves, ream or bore the galleries out smooth, and insert a hollow sleeve to seal the cracks. A high temp, waterproof adhesive would be a help, but so far haven't found anything better than Loctite. Obviously sleeve needs to be strong and relatively thin so as not to obstruct coolant flow. If I do it, I'll be tapping the ends of the sleeves (.25" Sch. 40 black pipe) and putting in set screws to plug the open ends. Will probably drill the pipe out a bit larger also. One water passage from head face needs to be bored down into the sleeves. inboard end should probably be shaped to match the profile of the existing galleries (see cut open 2LT head photos)

As for why the thin spot between the valves, this was probably to allow that area to cool more rapidly. That could be due to the need to avoid expansion and contraction that could affect the adhesion of the valve seats.

 

[Dougal]

There is a way to repair these heads that I may be trying: remove the small plugs that close off the galleries beween the valves, ream or bore the galleries out smooth, and insert a hollow sleeve to seal the cracks. A high temp, waterproof adhesive would be a help, but so far haven't found anything better than Loctite. Obviously sleeve needs to be strong and relatively thin so as not to obstruct coolant flow. If I do it, I'll be tapping the ends of the sleeves (.25" Sch. 40 black pipe) and putting in set screws to plug the open ends. Will probably drill the pipe out a bit larger also. One water passage from head face needs to be bored down into the sleeves. inboard end should probably be shaped to match the profile of the existing galleries (see cut open 2LT head photos)

As for why the thin spot between the valves, this was probably to allow that area to cool more rapidly. That could be due to the need to avoid expansion and contraction that could affect the adhesion of the valve seats.

That's a repair of limited life that has been done on many engines before. But it's not a long term cure. Cracks will keep growing until they meet air or another crack.

 

[Previa Diesel]

Yes, the cracks will extend right across that section probably, perhaps all the way to the valve seats - that may or may not be a problem. The life of the repair will depend on the seal obtained around the sleeve, and how well the heat is carried away from the area by the cooling system. I never had any problems until I got a rad leak - having a defective temp gauge at the same time was the fatal combination, that and a trip through the mountains with a heavy load!

 

[kaypang]

hello guys, i just want to share what i found on youtube...

i'm currently working on an old 2L-T head, with the same cracks... that recessed spot between the valves...
i wonder if anyone ever tried pinning the cracks with good result ?