north east firm that will remove Pre-cats

[Joesson]

@shnazzle said
"I thought it was common knowledge by now".

On this occasion and for me this knowledge is not common. Not seen a mention of that on here.
As I mentioned my precats were perfect when removed so no personal experience only what I've read in 2011 and since.
So the theory now is that an inspection through the sensor ports will only indicate the ending of the break down of the precat? Not the start as my previous reading/ understanding.
I get it now that the material must eventually fall out from the bottom and envisage that the precat becomes saturated, the pressure of the exhaust pushing the oil into the precats. In this case the precat material acts like a sponge and the saturation is greatest at the bottom and fails upwards.
Certainly not read that anywhere, but having written it down I do get it. Thank you.

PS
This postulation differs from the photographs taken by GSB in April 2004 when he wrote his "Precat removal how I did it "thread in the maintenance section.
The picture from above shows a small area of damage, the picture from below shows no signs.

[shnazzle]

@shnazzle said
"I thought it was common knowledge by now".

On this occasion and for me this knowledge is not common. Not seen a mention of that on here.
As I mentioned my precats were perfect when removed so no personal experience only what I've read in 2011 and since.
So the theory now is that an inspection through the sensor ports will only indicate the ending of the break down of the precat? Not the start as my previous reading/ understanding.
I get it now that the material must eventually fall out from the bottom and envisage that the precat becomes saturated, the pressure of the exhaust pushing the oil into the precats. In this case the precat material acts like a sponge and the saturation is greatest at the bottom and fails upwards.
Certainly not read that anywhere, but having written it down I do get it. Thank you.

To be fair, I have a draft of a new Buyer's Guide sitting here that I've been working on bit by bit for ages. The reason for the redraft is mainly the stuff around "oval bore" and that kind of rubbish. There's still an unknown or two but we can say with some certainty that pre-cats = oval bore is a myth.


- pre-cats have been seen to break from what looks like vibration or a heavy knock (a hard split/fracture in the honeycomb and big chunks dropping out the bottom).
- pre-cat material definitely degrades quickly when hot oil is introduced to it. This is caused by oil burning, it does not cause the oil burning
- running pig rich will destroy the pre-cats over time. Which is why when people talk about "resistor fixes" for o2 sensors I lose my shizzle. Yes the heaters only matter while the car warms up, but that's still a good 5 mins or so of the car possibly running very rich (remember it already runs rich at first cold start anyway)
- oil burning is due to Toyota's crap piston design and ring material. This was helped along in the 2006 editions. The 2003 pistons aren't really even that much better. But, admittedly, better. This is why post-2003 cars definitely can still suffer oil burning (and, half-unrelated, pre-cat failure)
- there is an EGR function that the 1zz uses. It uses vvti and the cam profile to induce valve overlap which "sucks" some exhaust back into the cylinder for re-combustion and keep exhaust temps down. But... Serious doubt as to whether this is powerful enough to suck pre-cat material back up.
- I have yet to hear anybody who has taken these blocks apart mention anything about oval bore. I believe Carolyn just pulled apart a 176k block and used a bore gauge and it was straight.

And there endeth mine rant.
If it's an unknown car with iffy history, I'd replace the manifold with a readily available aftermarket equivalent. Cheap enough.
Inversely, we have a car over 100k miles that we know for a fact was meticulously maintained and oil changed frequently. It still has pre-cats in. It runs sweeter than most mr2s I've driven/heard. Courtesy of Graham Read.

[Ardent]

^^^^  Post of the day.

[AdamR28]

Some pics if my 130k manifold. Service history unknown, but the car is a wreck and this is the colour of the engine oil that came out of it...

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And the clutch fluid. Minging.

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Precats starting to look a bit flaky up top...

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But fine down the bottom.

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I'm not going to comment on the hows and whys, as I'm no 1ZZ expert, but I am struggling to figure out how they would break up bottom first.

[shnazzle]

Just for clarity; they don't disintegrate from the bottom first. They disintegrate from the bottom  as well. 
Those do look like they need to come out though

[AdamR28]

New manifold fitted already

So the one above is spare / FOC to anyone who wants it, perhaps to break the Precats out at leisure, then swap over.

[Call the midlife!]

As it was my, possibly badly-worded post that started this in the first place I should point out I wasn't suggesting that ALL failed precats fail at the bottom first but they can ALSO have a tendency to break up from the bottom due to vibration or knocks or whatever reason they suddenly decide they'd be happier in the main cat.
As previously discussed the general consensus is if they look good on the top they're probably even better on the bottom.
Should still smash them out at your earliest convenience though...

[bigfootisblurry]

More great info/knowledge from this place. Thanks for sharing.

[MisterK]

@shnazzle said
"I thought it was common knowledge by now".

On this occasion and for me this knowledge is not common. Not seen a mention of that on here.
As I mentioned my precats were perfect when removed so no personal experience only what I've read in 2011 and since.
So the theory now is that an inspection through the sensor ports will only indicate the ending of the break down of the precat? Not the start as my previous reading/ understanding.
I get it now that the material must eventually fall out from the bottom and envisage that the precat becomes saturated, the pressure of the exhaust pushing the oil into the precats. In this case the precat material acts like a sponge and the saturation is greatest at the bottom and fails upwards.
Certainly not read that anywhere, but having written it down I do get it. Thank you.

To be fair, I have a draft of a new Buyer's Guide sitting here that I've been working on bit by bit for ages. The reason for the redraft is mainly the stuff around "oval bore" and that kind of rubbish. There's still an unknown or two but we can say with some certainty that pre-cats = oval bore is a myth.


- pre-cats have been seen to break from what looks like vibration or a heavy knock (a hard split/fracture in the honeycomb and big chunks dropping out the bottom).
- pre-cat material definitely degrades quickly when hot oil is introduced to it. This is caused by oil burning, it does not cause the oil burning
- running pig rich will destroy the pre-cats over time. Which is why when people talk about "resistor fixes" for o2 sensors I lose my shizzle. Yes the heaters only matter while the car warms up, but that's still a good 5 mins or so of the car possibly running very rich (remember it already runs rich at first cold start anyway)
- oil burning is due to Toyota's crap piston design and ring material. This was helped along in the 2006 editions. The 2003 pistons aren't really even that much better. But, admittedly, better. This is why post-2003 cars definitely can still suffer oil burning (and, half-unrelated, pre-cat failure)
- there is an EGR function that the 1zz uses. It uses vvti and the cam profile to induce valve overlap which "sucks" some exhaust back into the cylinder for re-combustion and keep exhaust temps down. But... Serious doubt as to whether this is powerful enough to suck pre-cat material back up.
- I have yet to hear anybody who has taken these blocks apart mention anything about oval bore. I believe Carolyn just pulled apart a 176k block and used a bore gauge and it was straight.

And there endeth mine rant.
If it's an unknown car with iffy history, I'd replace the manifold with a readily available aftermarket equivalent. Cheap enough.
Inversely, we have a car over 100k miles that we know for a fact was meticulously maintained and oil changed frequently. It still has pre-cats in. It runs sweeter than most mr2s I've driven/heard. Courtesy of Graham Read.

I've been reading about pre-cats ever since I joined the forum after buying my car new in 2004.  The car has now covered 67k miles and still has the precats.

I completely agree and hold with the comments made in the last paragraph. My car runs as well, if not better than it ever has, it does not burn a drop of oil (I've never had to personally remove the oil cap!), it has been serviced with oil change every 12 months without fail, either by Toyota or the experts below.

I have discussed precat removal with a number of knowledgable Roadster experts - Steve Nugent (D1 Customs), Matt Lee (Silverstone Performance) and Rogue Motorsport. Because of the history of the car, the advice from each was the same 'if it ain't broke, don't fix it'.  My view from the hundreds of posts I've read and feedback on the subject, is that precats fail because the engine burns oil.  Therefore, I'll continue to follow the advice I've been given and keep things as Toyota built them i.e. a standard engine which does not burn any oil and has a Toyota manifold complete with precats.

I think that these sentiments agree with Shnazzle's post 🤞😀.