#1 Head gasket retorque YES or NO?

[professorbob]

I am in the process of freshening up my supra 1987 MarKIII turbo. I just had the transmission rebuilt and have the engine on the stand doing exhaust gasket replacement and replacement of hoses.
The vehicle never indicated there is any issue with the head gasket. I do not want to go through the process of removing all the intake stuff to replace the head gasket when there has been no problem.
I am unsure about checking the torque on the present head and even if it can be done without having to remove lots of additional stuff.
I heard that there have been problems with blown gaskets on this engine.

Can anyone offer suggestion about how to proceed.
Leave it be.
Torque the head while on the stand.
Remove the head and install new gasket.

Understand, I am not trying to increase performance here. I just want to have a reliable daily driver.
Any suggestions are appreciated.
Thanks
Prof.

[bgrieger]

Welcome,

Given you have the engine removed, if you are going to do the gasket now is the time. You are at an interesting decision point.

First, the HG is a known problem...well known. You have correctly identified most of the solutions. If you leave it alone, it will fail eventually. It might live longer than you will own it though. A re-torque of the gasket has the risk of being a cure or just as often, it may be the straw that breaks the camel's back and cause it to fail (you may unseat the fire rings as they do shift a little).

Now, we get to replace. To do this with a stock gasket, you should get the head machined, and have the block inspected. The gasket rings leave impressions in the aluminium that need to be skimmed before installing a new gasket. The block though often is fine to install without work if the marks are light enough. You might want a professional to inspect it.

Now, if you are going for a stock reliable build, torquing the gasket to 72-80 ft/lbs on a new gasket with machine work is going to work well for you. You need new bolts though.

Now, if you want absolute reliability, you can consider a metal head gasket, though the block and head need to be machined, and not every shop can do it well either. You need a shop that can deal with the very smooth finishes a steel gasket requires. The gasket itself is fairly cheap compared to a genuine Toyota one, and if you get the machine work, the additional work really doesn't cost a lot more. Yes it is the foundation of a performance build, but it is bulletproof when done right too.

Bob

[professorbob]

Thanks for the rapid reply and sound advice.
I have another question.
Since I have the valve covers off, what is the best process to check the cam shaft clearance and what should those reading be to make sure they are still in spec.
The interior of this engine looks very clean and seems to have hardly any ware, but think a check now could reveal any potential problems before I get the engine back in the car.

ALSO:
What is a good way to check the operation of the turbine blow off valve actuator.
I note that is spring loaded. Can you tell me what amount of pressure is required to actuate the rod.

Thanks for any assistance.
Prof.

[bgrieger]

The lifters clearances can be checked with feeler gauges, but generally the caps and journals are fine. If you take one out it will look scored, but they are indeed 99% of the time alright. Toyota used a material on the journal surfaces that off hand I cant remember the name of that makes them look scored and more worn than they are. Many a machinist has misdiagnosed it because it is unusual.

If you have the deck machined, just make sure to insist they do it while the head is bolted to a jig - the long heads warp over time with heat cycles (the cause of the gasket failures...coupled with low torque values that allow the movement in the first place) and if they simply skim it they will leave you with banana shaped cam journals!

The clearance from lifter to cam lobe should fall in the range of
Intake: .15-.25mm (.006-.010 inch)
Exhaust: .2-.3mm (.008-.012 inch)

If they are over this, you take the current lifter thickness and add whatever is needed to get back into this range. Then order the correct ones from Toyota (you may need to go plus or minus a couple of thou as toyota doesn't sell every possible size, but you should be able to find one that gets you inside the range).

If you can blow through the bov without vac, it's bad. If not, it works. If you apply a vac pump you can see. I'm not sure what they will cleanly open at, but it's not much.