Head gasket/Valve job question

[Stelth]

I just got a '91 4Runner from a friend. She gave it to me because it needs a head gasket. I found her a mechanic who would do the job at a good price, but she decided not to do it. So I was talking to the mechanic today, and mentioned that the heads had been replaced previously. He said that if they had been previously milled, that the compression might be too high if they need to be resurfaced again, and that would result in high NOx and not passing smog.

I'm wondering if I can tell by measuring the volume of the combustion chambers and comparing it to what they should be, assuming I can find out that info.

Not sure what to do here.

 

[Trav]

Is this a V engine? No problem to cc the heads but the intake may need machining also.
Thicker head gaskets are another possibility.
Consult a good automotive machinist.

 

[Gabe]

Originally Posted By: Stelth
the compression might be too high if they need to be resurfaced again, and that would result in high NOx and not passing smog.


Is there any truth to this?? I am having a hard imagining how this could be...

 

[eljefino]

NOx is the curse of the thermally efficient engine. I could buy this, though it would all be theory to me.

If you look at how EGR works, it cuts pinging and NOx while letting you get away with more compression. Take that a step further and here's what you get.

You might be able to cheat and run a cooler thermostat and slither through that way.

 

[Chris142]

The heads would have to been massivly surfaced to have raised the compeession that much. You may be able to put thicker headgaskets to prevent the problem. If this is the 3.0l v6 plan on doing the heads and gaskets often as they were very problematic.

 

[wirelessF]

The only way to prevent the HG issue is to change the exhaust manifold or modify it. Its an unusual design that superheats the 6th cylinder and warps that area of the head causing the HG leak. Later generation engine fixed that issue with exhaust manifolds exiting to a y-pipe.

That engine blows headgaskets like a [censored] so I swapped mines out for a lexus v8.

 

[Stelth]

Well, I can't swap the engine with something different and pass smog. In Kalifornia, we have to use the same engine the vehicle came with (with a few, very narrow exceptions). Right now, I feel that my best option is to get the heads off, check the combustion chamber volumes, and if things are OK, reassemble with the redesigned gaskets.

 

[Trav]

Like someone posted you would have to give them a heck of a haircut to bump the compression high enough to cause any problems.
IMO the only thing you may need is a point or two higher octane fuel if anything.

Fel-Pro gaskets were a little thicker than stock on many applications, probably for this reason.