Turbo BS Thread

Majority of cracked heads you find are not from people who are boosted. Number of people who are boosted with these engines still relatively small compared to the amount in service. It's possible it's just a poorly designed head with poorly supported valve seats. The common theme with heads that cracked is a lack of service. But lots of other Toyotas use the same valvetrain design too and they don't all have the issue. @Pinchaser yeah I responded quickly, echod the same information I've seen others say for years because I don't care about the topic enough dissect why it happens. But I do recognize that you and I both went to the same school of condescension and for that I have respect. But more seriously, something certainly is happening, if there were no physical change occurring there would be no reason to ever adjust the valves. If somebody wanted to I suppose they could keep removing the head and check the seat depth to the head surface measurement. I don't primarily deal with the four cylinders anymore so I have zero interest doing that. One thing about the echod information though, it does seem to solve the problem. Folks who have gotten new castings to build a head and then maintain their valve train clearances don't end up having another cracked head.

 

I don't think that would be necessary. It could be done by taking one measurement when the head was installed, recording valve clearances through the observation period, and then measuring the seat depth again when it came off. It could then be determined how much the clearance tightened because of valve wear and how much resulted from seat movement.

Valve seat retention in aluminum heads is not something I exhaustively study, but in a particular engine I have experience with, a seat insert sinking into the head occurs as a result of the seat press-fit coming loose. That same cylinder head design can also crack (not common, though) in the same way an RZ head can, although the cause is usually not obvious and assumed to be from running hot.

 

Something led Toyota to later on move away from this Yamaha derived valvetrain (was an old partnership starting back with the 3SGTE, uses the same shim sizes/diameters as their older motorcycles) setup too and move to head designs with hydraulic lash adjusters. It could be a heat related problem, but it still presents most commonly on daily driver trucks with reports of these heads cracking and people initially tearing them down to do a headgasket and then finding the cracks after sending them off to a machine shop to be pressure checked or decked.