3sfe stubborn exhaust nutsLet’s turn the failure into the triumph.

[Doctor J]

Let’s turn the failure into the triumph.

As I was expecting before my 87 Camry wagon have had failed bi-annual California smog test (ASM, test only center). The fuel control closed loop is working and fuel trim Vf is 3.67 v, which means the mixture has slight enrichment correction, but still within the range (less then 5 Volts). The EGR system is fully functional; the intake manifold vacuum is 21 in of mercury steady, and the spark plugs of normal color.
However, the test data, which I got from the inspection report, was about 5 times higher then on one of my customer’s 89 Camry, and my car failed on HC limit. The approximate reading is posted below:


Speed RPM CO2 O2 HC ppm CO% NO ppm
15 1730 14.2 .3 135 .5 695
25 1740 14.1 .3 140 .6 670


The two speed unofficial test also have had similar readings except NO was low (no dyno load). The car may have some blow-by but because all numbers are elevated I suspected dead catalytic converter, which was confirmed by its fragments in the exhaust pipe.
The under hood cat itself is $200 and the state could contribute net $400 to do repair (test-only eligible)
This may be not a bad deal but:

• To be replaced, it must come out with the exhaust manifold (passenger side radiator fan must come out also to provide the room)
• All fasteners on the 20 year old car are stubborn
• The car has leak in the exhaust manifold gasket; someone before tried to undo one nut and broke the stud in the head near the oil sender unit.

So the shop offered just to weld-in an extra converter under body (like 88-on California cars), which will rub the power and fuel economy.
So, I decided to break the most fasteners loose, remove them one by one, replace these rusted or rounded and install them using anti-seize.
One week ago I began daily application of PB-blast on the mounting nuts and bolts.
Today I was able to remove all nuts from the head studs and three exhaust manifold to converter bolts and re-installed them using anti-seize.
The simplified design of flange nuts instead of nut and washer caused sticking of the nut flange to the manifold. Earlier cars, like my late 79 Supra had 2 mm thick washer under each nut, which resulted in even pressure distribution and good torque retaining properties due to the increased bearing (washer) area. The turning nut was biting into the one side of washer while other side was just pushing against the manifold.
Tomorrow I will show the flange nut to my CSULB professor and explain, why simple is not always better.
There are some tips, which could help to some Toyota owners deal with “welded” nuts:

• Use several applications of penetrating oil, apply when fastener is warm, about 90 degrees F
• Use 6-point sockets placed square on the fastener.
• Use pipe to extend the flex handle apply slow steady force in the plane perpendicular to the fastener
• Avoid impacts!

I would keep you posted about the smog repair progress.

[HomeGrown]

Originally Posted by Doctor J

.... Tomorrow I will show the flange nut to my CSULB professor and explain, why simple is not always better.

Economics will always prevail at Toyota (or most any manufacturer). The real economics at work here was presumably not in the price difference between a standard nut + washer vs. a flanged nut, but in reduced assembly cycle time.

Good advice on dealing with the seized/rusted nuts, Doc. Are you tempted to try and remove the studs from the head at this point, or work with the original studs?

[Doctor J]

I am going to drill out the broken stud using cordless drill, M42 drill bit and home made bushing to keep my bit centered. Then I'll use easy out to unscrew the broken piece.

[HomeGrown]

Good plan, that's exactly the way I'd approach it. Using a bushing in the manifold hole should keep the drill nicely centered so you don't end up drilling into the head itself.

[Ancientwolf13]

Yes they can be tough to get off. I had one that was completely welded to the stud. Even with 12 applications of pentrating oil, using a 6 point 14mm socket with a 1/2in drive and a breaker bar with a pipe it still wouldn't turn it just moved the whole car and started to round the nut. In that situation I had to use a Dremel to cut the nut off which even with cutting 2 sides of it completely through it still didn't come off. I broke a chisel trying to tap it off. Then I had to drill out the stud using a custom braket i made with clamps to keep the drill bit straight while drilling using a drill bit slightly smaller than the stud thickness. Then i took a thin wire brush bit and used a drill to break loose the stud remnants inside the block and used a magnetic rod to pull out the shavings. I then ran the same size tap in the hole to clean out anything left behind again and used the magntic rod again.

I put in a new stud with some antiseize and torqued it back to spec and it works like a charm. All and all it was a three hour job being it was a nut under the manifold so using the Dremel in that space was difficult. Its a long process for one nut .

[Mike Gerber]

Doctor J,

Just curious. Did the flange nut have serrations underneath the flange? If so, that is considered a locking feature. It is meant to dig in to the mating surface and thereby prevent the nut from loosening up and backing off over time, due to engine vibration. That may be what also makes it so hard to remove that flange nut.

Mike

[Doctor J]

No,the nut originally have had very smooth surface. The other end of the nut has locking sleeve with two cut-outs (the domestic car manufacturers are using "distorted" nut hole as a locking feature).

[Mike Gerber]

Doctor J,

(the domestic car manufacturers are using "distorted" nut hole as a locking feature).

Yep. I have seen them with 2 and some with 3 indentations to form a locking feature. I spent many years in the fastener industry. This is the cheapest form of a locking nut, but it does do the job. It's main drawback is that it does distort (gall) the mating male thread a bit. A nylon insert nut (with a full nylon collar), sometimes called an elastic stop nut, would be the best, but not for this type of application. It can't take heat above 250 degrees, so an allmetal locking nut is the only way to go.

Mike

[marc780]

Always use anti sieze compound or at least grease on every fastener, every time you take it out! I have even removed some fasteenrs when no work was needed to do this (I must have been very bored that day).
Exhaust system fasteners, and spark plug threads - forget the grease, anti sieze only. ALWAYS use it. high temp kind. Even if you had a new camry, it would not be a dumb thing to remove them now to anti sieze them if you had nothing better to do that day.

[Doctor J]

Update: after the cat was changed the car passed with flying colors.The old cat was ontaminated.
Conclusion:
If all readings are elevated close to the cut points and idle emissions are close to dyno emissions but CO2 is 14% and O2 sensor is working and controling the mixture, change the catalytic converter.