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Discussion Starter · #1 ·
Disclaimer: I am not an expert of the 2JZ head, but some advice was past from my machinist to me that I would like to share with you all.

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A while back I bought a built bottom end I bought from Supraforums. The bottom end was built with Crower Rods and JE Pistons.

Well, being as picky I was, I dropped it off at my machinist to go over the specifications and double check the clearances. He completely rebuilt the engine and I am very very happy with the results.

When I left, he recommended me to replace the cam sensors on my head when I put the engine back together to prevent from burning oil, excessive oil consumption or detonation. I said okay and left.

Well, I thought about that last comment and I couldn't think of how the cam sensors would cause more oil consumption and detonation.

My head has a bent intake valve. So I had to have my head rebuilt. A friend of mine also had a head he wanted rebuilt with Ferrera valves and to clean up the pits on #1 and #6 from detonation. His #6 was pitted badly from lots of detonation.

When I dropped off both heads to be rebuilt at my machinist and explained to him what I wanted, I also asked him about the cam sensors comment.

Well, well, well........now please read carefully. This information is crucial and the cam sensors is something that is very easily over looked and possibly an engine killer if not addressed.

Some of you might know that the cam sensors on the 2JZ are plastic. They do have rubber seals. However, even if the rubber seals are good, the cam sensors can still leak through cracks on the inside of the can sensor that are not visible from the outside. How do they get cracked? Well, I will come back to this later.

When I was at the machinist shop, he explained the cam sensor recommendation in detail. He grabbed my engine head and said, "Here, see you should replace your cam sensors. They are leaking".

Holy shit! He was right. Here below is a picture of my head. You can see the oil trails from where the front cam sensor was and how it drips and collects onto the intake manifold.




Here is the photo of the my head again but with the cam sensor between #5 & #6




My machinist then looks at my buddies head and points out this head show more of the evidence of leaking cam sensors to a higher degree.




Here he shows me a closer look at #6 and it's intake port.





Now, he explains even further how leaking cam sensors can cause excessive oil consumption. He explains that the intake flange gasket was designed to seal air and it does a great job of it. However, so much air is drawn in that the gasket and flange does not prevent from fluids being drawn in.

From the last picture above, you can see where the oil is drawn in into the intake. This oil is dry and not fresh. So this oil has been there for a while. This is evidence that oil is being drawn into the intake of number 6.

This is how a leaking cam sensors can cause your engine to burn oil.

Great, so that could explain the smoke and oil consumption, but it goes even further than that.

Remember when I mentioned about detonation?

Well, almost every Supra that has cylinder issues will most likely be #6. Supporting reason as to why can be pointed the fuel rail and setup. Some fuels rails are setup where the fuel is feed through the front of the fuel rail and the fuel return is from the end of the rail at #6. Some have mentioned that the fuel pressure drops from across the rail and injectors causes #6 to be leaner than the other cylinders.

Luckily, my fuel rail is setup where the line from the tank is split in a "Y" formation and the center of the fuel rail is tapped and is used as the fuel return line. The helps spread the fuel pressure across all 6 cylinders.

Now, my machinist explained to me that oil can cause detonation as well. I'm no expert so I recently learned this. Some of you might already know this. When oil is drawn in from the intake flange from a leaking cam sensors, the oil entering the cylinder can change the fuel characteristics dramatically. Essentially, the oil increases the chances of detonation. It's kind of like lowering the octane level of the fuel you are using if oil is present in the cylinder. This his how oil entering the cylinder through the intake flange can cause detonation.

Now, why #6 more than others?

Well, more than likely if your cam sensors are leaking then the cam sensor by #6 will leak more than the front cam sensor.

Why?

Well, my machinist kindly explained to me as to why it would by pointing out the oil feed and oil return passages in the head.

Here is a picture of the oil feed and oil return from the bottom of the head by #6.



Now, I don't know the GTE head at all so I might be wrong on pointing things out on this head.

As you can see, there are oil feeds on one side of the head all the way down to the end of #6. However, do you notice there is not a oil return passage at the end of #6 but the last one only between #5 & #6? My machinist states that because of this configuration, during hard acceleration all the oil is slung to the back of the head. Since there is no oil return passage at the end of #6, oil starts to accumulate at the back of the head acting like a reservoir.

So, possible scenario might go something like this...

With the excess amount of oil building up at the back of the head during hard acceleration, the leaking cam sensor would leak more than the front. Then drip into the intake flange and drawn into the intake through the hard vacuum under the hard acceleration and boost. This oil is then entered into cylinder #6 (or #5). This oil in the cylinder increases the chances of detonation of the fuel at this point.

Now, remember I said about how the cam sensor could crack back in Paragraph 8 of this post? Well, the cam sensors are made out of plastic. What can commonly happen with these sensors is that from high mileage engines, these can crack from the heat over the long periods of time. Also, the cam sensors can leak immediately after a brand new rebuild by the cam sensors being easily over torqued when installing them back in. The cam sensors only require 78 INCH lbs of torque (8.8 Nm or 90 kgf*cm). This is not much at all. So again, these bolts can be easily over torqued.


Again, I don't know a lot about the 2JZGTE head, but I do believe my machinist and everything he says really makes sense. I am just writing down what he said and I do not claim to be an expert at all. I am just trying to look out for my Supra bothers.

So if your can inspect your cam sensors for signs of leaking, I suggest replacing them and when rebuilding your engine I recommend replacing them anyways. They are about $40-$50 a piece. To me this is with the investment to prevent consumption of oil and possible detonation under high demands of boost.

What my machinest is doing to both heads is putting in grooves on the side of the head under the cam sensor so that the oil leaking can drip past the intake flange and not accumulate on it.
 

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Interesting write up, makes sense and I would have never thought of that as well. Good info to know. Thanks :bigthumb:
 

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Allen, that is BY FAR AND AWAY one of the most interesting posts I have ever read. I am going do a bit more research on it. WOW! your machinist sounds like he has been doing this for YEARS. The only question I have is how is oil drawn in under boost? With a positive pressure in the manifold runners, wouldn't that actually help keep oil out? Of course an explanation of that could be the lovely venturri/siphon effect. Reguardless, it does make sense. Somebody should sticky this.

The most insitefull thing I've read in several months. And the most insitefull thing I've EVER read on supra forums. An A+ for a good writeup. :bigthumb:
 

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Discussion Starter · #5 ·
Rotarytoy said:
Allen, that is BY FAR AND AWAY one of the most interesting posts I have ever read. I am going do a bit more research on it. WOW! your machinist sounds like he has been doing this for YEARS. The only question I have is how is oil drawn in under boost? With a positive pressure in the manifold runners, wouldn't that actually help keep oil out? Of course an explanation of that could be the lovely venturri/siphon effect. Reguardless, it does make sense. Somebody should sticky this.

The most insitefull thing I've read in several months. And the most insitefull thing I've EVER read on supra forums. An A+ for a good writeup. :bigthumb:

Well, under full boost, you are correct that the pressure would not draw in the oil. However, durng idle or low RPM, the vacuum from the cylinders drawing in air from the manifold would draw the oil in. Then after a while from idling or easy driving, you could accumulate oil in the manifold just sitting in there collecting. Then when you get on it at full boost, all that oil get's pushed into the cylinder from the boost pressure.

That's a more likely scenario.
 

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Discussion Starter · #6 ·
Rotarytoy said:
Allen, that is BY FAR AND AWAY one of the most interesting posts I have ever read. I am going do a bit more research on it. WOW! your machinist sounds like he has been doing this for YEARS. The only question I have is how is oil drawn in under boost? With a positive pressure in the manifold runners, wouldn't that actually help keep oil out? Of course an explanation of that could be the lovely venturri/siphon effect. Reguardless, it does make sense. Somebody should sticky this.

The most insitefull thing I've read in several months. And the most insitefull thing I've EVER read on supra forums. An A+ for a good writeup. :bigthumb:
Is this Brian?
 

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I might have to check mine as well... Good Write Up... Can we make this a sticky???
 

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i noticed a leak in the center one and when i checked both bolts were less
than finger tight and the rear one only had one bolt!!!wtf!

so i fipg both sensors inplace with their washers and locktighted the
bolts. i dare those bitches to leak again!
 
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