2F Burnt Valves reason, Carb jets, Smog air pump.

[berntd]

Hi,

A while ago. I posted here because I bought an FJ40 with burnt exhaust valves. Nobody came up with a reason for them to be burned.
Well, I know the reason now since I got a good book for my birthday yesterday about the Landcruisers.

The 2F ran on a misture of 14:1 air fuel until they did the emmision control. It then ran on 18:1 which is way lean for this motor. This causes the motor to run extremely hot internally and the exhaust valves cannot stand this, along with the hot temperatures here.

To compensate for this problem, Toyota added the air pump and its MAIN function is to blow cool air onto the exhaust valves to prevent them from burning. Hence the separate nozzles to each port in the head, aiming at the valves.

By removing the air pump system, the previous owner signed the death warrant of the exhaust valves.

I guess you all knew that already?


So, to prevent the same from happening again, I need to get the mixture back to 14:1 so the engine runs less lean and thus cooler.
For this, I need to know:

1: Does the older carb fit onto the 82 model with the newer style air cleaner housing?
2: What are the differences in the jets, venturis from the pre-emmision to the 82 model?

Has anyone done this conversion?


Kind regards
Bernt
Sydney

 

[John Smith]

Hmm, I always thought that Toyota added the smog pump to add air to the exhaust stream to "lower" emissions and help burn up any unburned gasses before they left the tail pipe.

My 40 has fine exhaust valves and I have not had a air rail installed for years. I also run a little rich though.

 

[Degnol]

"1: Does the older carb fit onto the 82 model with the newer style air cleaner housing?
2: What are the differences in the jets, venturis from the pre-emmision to the 82 model?"


If you use a E>'74 F carb on a 2F manifold it can work with the 2F aircleaner, but you need to make a little adapter with a stud and wingnut. I have one on my '74 F with a 2F intake and 2F aircleaner. I use no smog stuff as mine is a '66. I am also getting ready to install a new(rebuilt) 2F in the same truck with the same carb, unless Jim Chenoweth can talk me out of it. With the larger displacement,maybe the jets need to be tweaked, and maybe not.
I don't know if you can see the adapter or not in this pic, but I made one for Bailey. I use a small section of 3" pipe from a muffler shop swelled to fit around the throat of the carb and a little crosspiece welded and a stud welded to that with the wingnut. The adapter attaches to the carb throat with the clamp that was on the F aircleaner. Sounds Rube, but it works.

 

[65swb45]

By removing the air pump system, the previous owner signed the death warrant of the exhaust valves.


Kind regards
Bernt
Sydney

A does not equal B. Take a step back. How does air being blown into the exiting exhaust from the engine change the air-fuel mixture of gas going IN to the engine?

It does not.

If your mixture is lean, it is either because an errant source introduced air with no fuel to the engine [vacuum leak] or the carb was not supplying sufficient fuel because of an internal problem.

Changing carbs MAY solve your problem. Then again, checking for vacuum leaks and rebuilding your carb may also solve your problem, and save you having to adapt ANYTHING!

My .02

Best

Mark

 

[berntd]

A does not equal B. Take a step back. How does air being blown into the exiting exhaust from the engine change the air-fuel mixture of gas going IN to the engine?

It does not.

If your mixture is lean, it is either because an errant source introduced air with no fuel to the engine [vacuum leak] or the carb was not supplying sufficient fuel because of an internal problem.

Changing carbs MAY solve your problem. Then again, checking for vacuum leaks and rebuilding your carb may also solve your problem, and save you having to adapt ANYTHING!

My .02

Best

Mark

Hi,

I am sorry but I think you either misread or misunderstood

The air pump has NOTHING to do with the fuel air mixture and I never stated that.
I repeat, it aims cool air at the exhaust valves to cool them.
It does not inject it into the exhaust but into the head, aimed carefully at the valves (yes, it ends up in the exhaust).

I read this in a very good book about Toyota Landcruisers. It is the first proper explanation as to why the 2F exhaust valves burn so regularly (yes, they do! The shop that did my head said they have done many). What is written there makes perfect sense.

If a carb was designed to run at 18:1 instead of 14:1. Only a change in jets will change this.
My car's carb is no different to any others from the same model and year. It was designed to run that lean for emmision control purposes.

I am still hoping that someone willhave some jet sizes for me on the early 2F and the 82 2F.

Regards
Bernt

 

[Mr. Toad]

I repeat, it aims cool air at the exhaust valves to cool them.
It does not inject it into the exhaust but into the head, aimed carefully at the valves (yes, it ends up in the exhaust).

I read this in a very good book about Toyota Landcruisers. It is the first proper explanation as to why the 2F exhaust valves burn so regularly (yes, they do! The shop that did my head said they have done many). What is written there makes perfect sense.

What book are you reading? I'd like to read it and figure out why it has an explanation for the pump/air rail different from the explanation in Toyota's emission manuals. Until I read your book, I'm with 65swb45 and John Smith on this one.

If a carb was designed to run at 18:1 instead of 14:1. Only a change in jets will change this.
My car's carb is no different to any others from the same model and year. It was designed to run that lean for emmision control purposes.

You could drive around with the choke on.

By the way, what year is your FJ40?

 

[Pighead]

Interesting theory, Bernt, but...
The air rail/smog pump came out in the early '70s (my '74s had them, one of the first things I removed), I (and perhaps others) had the impression it was to lower tailpipe emissions by allowing more complete combustion of leftover fuel...
I, and perhaps others, have been running without smog pumps for quite some time without any problem of burnt valves (or Bernt valves either).
To toss in another variable, I 've heard that the later 2F heads were of a different design, lighter in weight and more prone to cracks. Wonder if it is these later heads that burn valves?
I'm still running the '74 carb, on a '74 head on a 2F block. No air rail, no smog pump, no problem.

<snippity>

By removing the air pump system, the previous owner signed the death warrant of the exhaust valves.

I guess you all knew that already? <snip>



Kind regards
Bernt
Sydney

 

[1Fine40]

One other thing to be sure of is the vacuum line that goes from the intake manifold back by the firewall to the brake booster....my old 2F had a rotten hose connection there, which introduced more air into the last two cylinders, which I'm pretty sure is why those two valves burned. All the rest of them were fine upon disassembly and inspection. (eventually went the evil SBC route anyway....)
Cheers!

 

[Roadnoiz40]

I'm with 1Fine40. Leaky vac hose/vac valve leans out the mixture. Which exhaust valves were burned? Back ones?

 

[Steel]

I am still hoping that someone willhave some jet sizes for me on the early 2F and the 82 2F.

Regards
Bernt

http://www.sor.com/sor/cat042d.tam?xax=24288

HTH

 

[65swb45]

I'd also like to see the book that suggests 18:1 was EVER a target mixture from ANY auto manufacturer.

 

[Pin_Head]

I'd also like to see the book that suggests 18:1 was EVER a target mixture from ANY auto manufacturer.

X2.

It is possible that what the book means is when the EGR valve opens, the mixture is leaned, but this is with exhaust gas, not air, so the combustion temperatures are actually lower.

The primary purpose of the air injection is to provide air to burn any unoxidized hydrocarbons leaving the cylinder, not to cool the valve.

 

[berntd]

Hello all

The book is:

Toyota Land Cruiser Gold Portfolio and can be found here:

http://www.themotorbookstore.com/tolacrgopo19.html

The angle of the injectors aimed against the flow, at the valve instead of with the flow, into the exhaust spaeks for itself.

Whatever the emmisions manual says, could be true or was a clever stunt to give the impression that it works.
I am peronally also of the opinion that the air simply adds to exhaust gas volume, so that the emiisions measured at the exhaust appear as a lower percentage - hence cleaner.


My book further states that the burnt valves are the single greatest failure of the Landcruiser from the mid 70s onwards. 23% of all recorded problems evaluated over 150 different cars were burnt valves.


Another question is: What is a simple test without a CO meter to see if it runs too lean at say 50% load?

Regards
Bernt

 

[Pin_Head]

I am peronally also of the opinion that the air simply adds to exhaust gas volume, so that the emiisions measured at the exhaust appear as a lower percentage - hence cleaner.


Another question is: What is a simple test without a CO meter to see if it runs too lean at say 50% load?

Regards
Bernt

The volume of air put out by the pump is pretty small compared to the engine exhaust.


Read the plug color. Mocha brown is 14:1. White is lean, black is rich. They also make a gizmo that looks like a glass spark plug where you can actually see the flame color while it is running at night.

 

[berntd]

hi

Thanks for that. You are right, they do make a see through plug, and I have one! It is called Colortune. However, you can't test the car under load while driving unless you have a dyno test bench or something. It only really works for idle and for ONE cylinder under no load conditions.

I used to do everything with plug colour but since the unleaded fuel has taken over, I have developed problems with that. I just can't seem to get proper plug colour like in the old days.

I 'll try that again and see what happens.
The snag is that you have to drive for a couple of miles and then suddenly cut the engine quickly to get the correct colour. That can be a real pain, next to the road with the engine steaming hot...

I guess CO tester is the only easy way...


Regards
Bernt

 

[65swb45]

Bernt

If you have reason to suspect that the truck is running lean under heavier loads, you might want to have a closer look at the power valve circuit. The power valve is designed to suppliment fuel flow to the primary emulsifier under heavier loads, and if it has a physical impediment inside the carb, or an ineffective vacuum signal, then you could be experiencing a 'lean' condition because of that.

 

[FJ40Jim]

I'd also like to see the book that suggests 18:1 was EVER a target mixture from ANY auto manufacturer.

Many new cars run at that level under light cruise condition. This only is used on cars w/ DBW throttle and wideband feedback. The goal is to reduce pumping losses by opening the throttle under cruise.

This definitely is not done w/ a conventional carburetor.

 

[Nomis]

I also read in the book, "The LC Owner's Bible" that burnt valves would result from removal of the factory Air Pump - is this not the case?

 

[berntd]

I also read in the book, "The LC Owner's Bible" that burnt valves would result from removal of the factory Air Pump - is this not the case?

Ditto, another source with similar info!



Bernt

 

[FJ40Jim]

I also read in the book, "The LC Owner's Bible" that burnt valves would result from removal of the factory Air Pump - is this not the case?

First, I must point out "The LC Owner's Bible" is crap. It should be called "The mini/runner bible w/ minor errors and the occasional sidelong error-riddled reference to Cruiser".

No, that is not the case. The AP injects air into the exhaust stream, after the combustion event and downstream of the valve.

There are 2 things which burn the exhaust valve:
1. Tight adjustment, which does not let the valve come into solid contact w/ the cold seat long enough to drop the temp of the valve.

2. A lean combustion event that leaves superheated oxygen in the chamber. When the exhaust valve pops open and the glowing hot oxygen goes past the exhaust valve it attacks it in the same manner as an oxy-fuel cutting torch.

The AP can not stop the valve burning, because the valve burns when it is open. When the exhaust valve cracks open and cylinder blowdown begins, flaming hot gas is leaving at near sonic velocity and several hundred PSI. A little squirt of fresh air downstream of the valve is less than insignificant at that critical moment.

The valve can not burn if there is no free oxygen left in the chamber after combustion. If the mixture is correct or richer, valves don't burn. If the mixture is 18:1, and the valves are not Stellite or another inox alloy, then they are toast.