Looks like my head probably isn’t cracked after all - there are no visible cracks and the head passed a pressure test. But the head has issues:

1. Valve clearances. Two exhaust valves had only .002” of clearance. These were the ‘good’ ones - none of the other six could even muster .0015”.

2. Exhaust valves. Two are overtly burnt. NONE look good. I wouldn’t reuse ANY of them. So eight exhaust valves at $10 a pop.

3. Valve shims. All are around .1102-.1142 range. Smallest available is .0984 and largest available is .1299. Not much adjustability before running out of shims - especially after seats are cut. Not sure if new valves will give back much (if anything).

4. Exhaust side needs a valve job - the second one this head has had in its lifetime. That means moving the valves up even more.

5. The machine shop proposes solving this problem by cutting down the tips of the valve stems in order to avoid running out of shims. Not sure how much can be taken off before the lifter and retainer shake hands, or whether this is even a good idea.

6. Head will need to be resurfaced. It likely already has been by an unknown amount for the last valve job. Not sure how much is left to safely take off. Cost: $50.

7. Valve job and valve adjustment (ie cutting the valve stems) will cost $320. In other words, this is no cheap fix.

8. Valve stem seals will be extra, as will other
potential items such as retainers, keepers, or any other unforseen issues.

So what do you say? Fix it or go with a brand new head?

 

I'd buy OEM exhaust valves and rebuild the head.
There's nothing wrong with taking a bit off the end of valve stems, if needed, to stay within the shim assortment.
The new valves should stand shorter than the old ones though.

 

Depends on how nice you want it to be and for how long? Best case, lots of machine work and new valves, it'll be like new.

A few years ago we bought our neighbor's 200K mile Highlander with a V6 that was running on 5 cylinders for practically nothing. After a little diagnosing, one front cylinder leaking all the compression into the exhaust. So I just went to the pick-and-pull style yards in the area (there are 4 or 5 of them around), found a nice lower mileage Camry/RX300/Highlander/etc of the right year, and whipped a head off it. $75 bucks or so. That and a nice oem t-belt/WP/gasket set and it ran perfectly.

 

Too bad 3RZ stuff isn’t as common in junkyards as Camry stuff. And what stuff there is is beat to hell. But I guess that’s what you get when an engine spends SO much time running close to maximum MEP.

 

There is, or you have a need to run a 3RZ at 4000RPM full throttle for extended periods?

BMEP = 150.8 X Torque (ft/lbs) / Displacement (ci)

3RZ...150.8 x 177 / 164 = 163psi
5VZ...150.8 x 220 / 206 = 161psi

As for the rarity of 3RZ stuff part of the reason is, as most of these engines were in 1997-2004 Tacomas, and if you recall the frame recall, those that weren't re-framed were scrapped. Scrap yards were instructed to crush the truck and under no circumstances to part it out. You are also dealing with 19 to 27 year old engines / trucks that the owners are holding on to them.

 

Peak MEP may be fairly similar between the 3RZ and 5VZ. BUT, I guarantee you the 3RZ is going to be spending a hell of alot more time there (or at least close to peak MEP). Remember that these 3RZ’s were used only in 4Runners, T100’s, and 4wd Tacomas. Compared to, say, your basic 2wd Tacoma, these are all heavy vehicles. Not to mention that they are going to carry heavier loads of cargo and/or people and run big wheels, etc. Also, unlike, say, a 2wd Tacoma, these vehicles are less likely to be used for light duty work such as commuting. If you put a smaller, four cylinder engine in these things, it is going to live a MUCH harder life than a larger V6.

As for the 3RZ stuff being rare, the use of this engine in these large vehicles is part of it. Let’s face it. The 5VZ is just a MUCH more attractive option for a 4000 pound 4Runner or Taco 4wd. More 5VZ’s sold = more available in junkyards and from private party sales. And the fact that these engines lived an easier life means the engines are likely in better shape when they get there (they are probably ending up there as a result of an accident rather than engine failure)

 

BMEP is not a measure of stress on an engine. It is, as the "mean" in the acronym says an average of cylinder pressure, which at wide open throttle can range from a vacuum to perhaps 800psi in a street engine. Note that during "normal" operating conditions, cylinder pressure may peak at 300-400psi. The number assigned to BMEP is a good indicator of how efficiently an engine produces torque, the higher the better. The low BMEP numbers that most Toyota engines of the past exhibited, explain to a point their relatively poor fuel efficiency and torque. For example the BMEP of a 22R comes in around 135psi (129ft/lb of torque @ 2800RPM)...if that's not a strained engine in a truck I don't know what is. More "modern" engines such as Toyotas 1NZ-FE sit around 180psi.

I am not aware of any first generation Tacoma that weighs 4000lbs. All numbers are base Xtracabs...fairly common.

• 4X2, 2950lbs. It's a 2RZ so is it really applicable?
• Pre-Runner, 3270lbs
• Base 4x4 4cyl, 3470lbs...checked this on the door jamb by subtracting the payload from the GRVW
• Base 4X4 6cyl, 3515lbs
• Base 4 Runner 4cyl, 3616lbs...the only one that I am aware had the 3RZ

Just for comparison a first generation pickup (78-83) came in at 2660lbs.

Mentioning that...

1978-83 pickup (22R, torque peak of 129ft/lbs) is 20.6lbs of truck per 1 ft/lb of torque
1997-04 Tacoma (3RZ, torque peak of 177ft/lbs) is 19.6lbs of truck per 1 ft/lb of torque

So a 3RZ Tacoma is less strained then a 22R pick-up because its BMEP is higher by 25psi and it has a somewhat flatter torque curve and has greater thermal efficiency. As a reference the 5VZ is 15.9lbs of truck for 1lb of torque.

So I have to state that it doesn't matter what engine is in a vehicle, you need X amount of torque to move Y amount of weight at Z speed. It's simple physics. That engine can be a 4, a V6, a V8 or a V16.

The average engine doesn't work as hard as we would think. This as explained by the average amount of fuel used. Both my Tacoma and 83 get an average of 25mpg (those are Imperial gallons). Using that in 1 hour going 50mph they will use 2 gallons of fuel. 2 imperial gallons of fuel weight about 15lbs. By re-arranging the following formula we can get the horsepower...

Fuel flow, pounds per hour = .1339 X HP/ thermal efficiency (the thermal efficiency of most Otto cycle engines is 25-30%. I used 27.5%)

We arrive at what seems to be a shockingly low number...about 30hp. However in an old text book of my dads states the ratio of .4-.5lbs/HP/HR appears for normally-aspirated engines and confirms this. As this book was a publication of the "Commonwealth technical air crew training" I believe its trustworthy. Running out of gas in a Lancaster over western Europe in 1943 had more dire consequences then running out gas at the mall in your Tacoma...where most are seen! (Yah the Merlins were super-charged so about .7-.10lbs/HP/HR)

Using the formula, Torque = HP X 5252/RPM (Charles Watt came up with this one 200 years ago) we get roughly 75ft/lbs of torque which is a BMEP of 69psi driving at 50mph, roughly a third of its maximum BMEP of 163.

If these engines are strained its not the engines fault, its the fault of what sits behind the steering wheel. It's like buying a Yaris to haul gravel then complaining its a piece of ****!

EDIT...

Some after thoughts...

No the vast majority of these trucks are not climbing Everest, fording the Amazon or racing across the Mojave at 100mph. They are being used for the daily commute, getting groceries, picking up the kids after soccer or taking the dog to the vet. After all the weekend chores are done they may go off road. They may haul a few bags of topsoil for the garden. They may go into the bush so you can go fishing or hunting. Occasionally they may haul a heavy load or tow. That four wheel drive will come in handy on those snowy days. Gee they're doing what they were intended to do. Yah we modify them, sometimes beyond what the original engineering accounted for...that's not the engines fault. Even the most modified truck, proportionately is used very little for the modified purpose.

Now I have to put on the "Captain Obvious" hat but...and I apologize ahead of it...if the 3RZ is such a piece of crap, why are you rebuilding it rather the swapping in a "better" engine? That's what I'd be doing. If there's "all kinds" of 5VZ stuff out there that seems to be way to go.