Pre-cats: The Official MR2-ROC Information Thread

[loadswine]

Those heatshield bolts are very badly corroded, not sure there is very much for even Irwins to get hold of. I have managed to remove completely rounded bolts with them before, but they did, at least have a head.
If you were going to invest in a set anyway, then go for it, but if they will just be used for this job, then drill them out perhaps, especially if you intend using an aftermarket manifold upon re assembly.
I would say the precats really want to come out , in my opinion. It does look as if they have started to degrade.

[Roadster]

If I installed an aftermarket Manifold (  m http://www.ebay.co.uk/itm/TOYOTA-MR2-RO ... 4897.l4275 m  ) like that one, would fitting it need any adjusting to anything or would if fit exactly the same as the stock manifold? for £130 I don't see why it's worth just gutting the rotten stock one? would it affect the o2 sensors? Sorry asking far too many questions o.O

[MartinC]

If I installed an aftermarket Manifold (  m http://www.ebay.co.uk/itm/TOYOTA-MR2-RO ... 4897.l4275 m  ) like that one, would fitting it need any adjusting to anything or would if fit exactly the same as the stock manifold? for £130 I don't see why it's worth just gutting the rotten stock one? would it affect the o2 sensors? Sorry asking far too many questions o.O

Nothing else to do, just bolt on and enjoy.  You may want to wrap it to reduce engine bay temps.  However do a search on here for advice on wrapping or not wrapping, as there are many opinions on if you should or not.

[Roadster]

Toolkit required

Trolley Jack - check!
Axle Stands - check!
10mm spanner - check!
10mm socket on 6" extesnion - check!
12mm spanner - check!
12mm socket and various extensions - check!
14mm socket - check!
Hammer - check!
Vice - new manifold so don't need!
Long flat bladed screwdriver - check!
High pressure water or air supply - new manifold so don't need!
Large vocabulary of swear words - check!


Also have o2 sensor socket, PlusGas, a mechanically minded friend to help...before i start this (hopefully this weekend, if not then next weekend) can anyone recommend anything else i may need during this pre-cat removal? I'll be using a new manifold since it only cost £130. And also replacing as many stubborn bolts as possible before starting...luckily many were replaced when My exhaust was being fixed

[GT4thomas]

Possibly new gaskets and new nuts and bolts just in case you ruin the thread of a stubborn one.

[Roadster]

Possibly new gaskets and new nuts and bolts just in case you ruin the thread of a stubborn one.

New gaskets come with my new manifold I think, i removed some of the stubborn bolts today, i managed to take the annoying ones from the heatshield without ruining the threads (did break the bolts for it though which i need to buy, just waiting on my manifold and i can start ^_^


But by stubborn one do you mean a different bolt?

[Ardent]

Have no experience myself, but I tend to recall from many a past thread, that it is worth getting the proper Mr T head-to-manifold gasket.

I have removed heat shields for access and never put them back.  Does get warm back there, as my pipes are running bareback. I quiet like it that way. Even gave them bit of a rub with the Autosol.   s:D s:D

[Joesson]

The exhaust manifold to head gasket that comes with some eBay manifolds I understand has not been suitable in service and a Toyota gasket has been used.
I managed to damage some of the cylinder head studs and so replaced those.
The nuts for the studs are a tri lobal locking type and should be renewed.
The gaskets between the manifold and the cat should also be renewed.
I stripped the cat and heat shields and power wire brushed them,they came up shiny, I believe they are a low grade stainless steel. Refixed them with stainless steel nuts, bolts and washers ( from Screwfix) and refixed the shield on the bend with a jubilee/ worm drive clip.
Many remove the OE manifold as you intend and also the heat shields .
I chose to keep as near OE ( minus the precats) as I could.

[Roadster]

Mmm i'm gonna keep the heat shield, not going to wrap the manifold, seen cases of where people see cracks in the manifold, I managed to remove the heat shield without ruining the threads, hopefully i wont damage anything but will deal with that as it happens, hopefully gonna start tomorrow

[harvey718]

If your pre-cats have gone, are you able to salvage any of the engine such as the top end? I've just bought a 2001 mr2  which has white/blue smoke and is running rough. I've just ordered a 22m oxygen socket so I can check the pre-cats.

[Joesson]

The 2001 model piston oil control rings, particularly in cars with poor oil change history, have been generally accepted as the cause for excessive wear in the cylinders leading to  excessive oil consumption which breaks down the precats material which can then be sucked back into the cylinders exacerbating the situation.
Until very recently an associatevMatt Performance offered rebuilding of the engine.
Unfortunately this is not now the case.
However if you look at MattPerformance in the associate section you will see a schedule of work that was undertaken for the rebuilds offered for varying engine conditions.
You will see that the engine can be rebuilt even after severe wear has occurred.
Alternatively have a look at an engine exchange from a donor car as described under 2zz in the maintenance and troubleshooting section.
Sorry that you have not had the best start to MR 2 ownership but hope that you had planned to do some work in getting your car into good condition.

[Roadster]

OK, just spent the day replacing the manifold.....quite inpressed with myself but i'm having one problem....the 5 bolts which connect the gasket...i can't get the last one in...the other 4 are in fine (took a lot of annoying lining them up to fit....anyways anyone had any problems fitting the manifold and gasket to the car? it's one of these  m http://www.ebay.co.uk/itm/TOYOTA-MR2-RO ... 4897.l4275 m


I havn't put in my o2 sensors yet to see if it works! but i'd prefer to get the 5th bolt in if i can first....any tips?

[Joesson]

These must be the head to manifold studs.
The studs should first be screwed into the head.
If any came out when you removed the OE manifold or you are replacing the studs screw these in by hand first ensuring all threads are clean.
The studs can be tightened home by putting two ( old )nuts on the stud and locking the nuts together with two spanners. Then tighten the stud, a torque wrench can be used for this.Then remove the nuts with the two spanners.
When all studs are in then offer up the manifold . This should go straight on.
If not you will need to adjust the holes in the manifold.
To do this you need to determine where the interference is.
This can be done with a strip of masking tape ( light colour) applied over the face of the manifold that faces the head.
Find something sticky and dark coloured,  engineers blue is the traditional thing to use. But improvisation with a dark grease such as Copaslip or a marker pen or a dab of paint will do the job. Apply the marker to the end of the studs and again offer up the manifold and press the manifold against the studs.
With a modicum of luck when you look at the manifold you will see the marker where the manifold holes need opening up.
I suggest a round file for this as the idea is to remove the minimum material necessary

In short you need to fit the manifold to all 5 studs in the one go.

Clean up before fitting the manifold and beware that no swarf or material enters the exhaust ports on the head
ADDENDUM:
The above is engineering practice for aligning items where no template is available.
In this case you have the old manifold and the new gasket!
The gasket is probably easiest to use, so place the gasket on the face of the new manifold and accurately locate the gasket with the holes that you know are in alignment with the studs. This can be done for instance with two drills or two bolts of suitable size. You will then see the error in position of the one hole( maybe more slightly out also). Mark the manifold with a marker pen or similar. Remove the gasket or it will get damaged. Then file out the hole/s as required. You can use the gasket to check progress but be careful that it isn' t damaged.
The new flange is likely thicker than the OE flange and so take care that you open the hole out square to the flange face.
If you have a Dremel  tool this may speed up the process.
As above take care to remove only what material is necessary and use eye protection when using any power tool.

[Roadster]

These must be the head to manifold studs.
The studs should first be screwed into the head.
If any came out when you removed the OE manifold or you are replacing the studs screw these in by hand first ensuring all threads are clean.
The studs can be tightened home by putting two ( old )nuts on the stud and locking the nuts together with two spanners. Then tighten the stud, a torque wrench can be used for this.Then remove the nuts with the two spanners.
When all studs are in then offer up the manifold . This should go straight on.
If not you will need to adjust the holes in the manifold.
To do this you need to determine where the interference is.
This can be done with a strip of masking tape ( light colour) applied over the face of the manifold that faces the head.
Find something sticky and dark coloured,  engineers blue is the traditional thing to use. But improvisation with a dark grease such as Copaslip or a marker pen or a dab of paint will do the job. Apply the marker to the end of the studs and again offer up the manifold and press the manifold against the studs.
With a modicum of luck when you look at the manifold you will see the marker where the manifold holes need opening up.
I suggest a round file for this as the idea is to remove the minimum material necessary

In short you need to fit the manifold to all 5 studs in the one go.

Clean up before fitting the manifold and beware that no swarf or material enters the exhaust ports on the head
ADDENDUM:
The above is engineering practice for aligning items where no template is available.
In this case you have the old manifold and the new gasket!
The gasket is probably easiest to use, so place the gasket on the face of the new manifold and accurately locate the gasket with the holes that you know are in alignment with the studs. This can be done for instance with two drills or two bolts of suitable size. You will then see the error in position of the one hole( maybe more slightly out also). Mark the manifold with a marker pen or similar. Remove the gasket or it will get damaged. Then file out the hole/s as required. You can use the gasket to check progress but be careful that it isn' t damaged.
The new flange is likely thicker than the OE flange and so take care that you open the hole out square to the flange face.
If you have a Dremel  tool this may speed up the process.
As above take care to remove only what material is necessary and use eye protection when using any power tool.

Thanks very much  s:) s:)  i'll try sourcing new studs first, I noticed when I replace the gasket that there is now no place for the heat guard to be replaced, I didn't heat wrap it because I read up on some cracking the manifold...how much of an issue will it be driving without any heat shields/guards?

[bluesmoke]

I've got loads of spare nuts and bolts but I bought them so long ago I can't take them back now lol.

Like you, I wanted to make sure I had everything in case I had any issues during the process.

I found it quite strange that the manifold to engine nuts have been changed:

[Joesson]

When you removed the manifold nuts did they came off with the studs attached?

If so you may be able to rescue the studs.
Put the studs into a small container and soak them in Plusgas or similar.
Then put the nut in a vice with the stud vertical above it.
Put two nuts onto the other end of the stud and tighten them together.
Put a spanner on the lower nut and undo the stud from the original nut.
New nuts should be used for refitting the manifold these are a self locking type.
The new nuts Bluesmoke has do not appear to be self locking.

As for the heatshield I understand some members run without that refitted.
Of these some have heat wrapped the manifold and some haven't.
There is a recent thread on that subject.
Your car will run with or without the heatshield and with or without the heat wrap.
I doubt you will notice a huge difference either way within  the restrictions applicable on your island home.  s:wink: :wink: s:wink:

[Roadster]

When you removed the manifold nuts did they came off with the studs attached?

If so you may be able to rescue the studs.
Put the studs into a small container and soak them in Plusgas or similar.
Then put the nut in a vice with the stud vertical above it.
Put two nuts onto the other end of the stud and tighten them together.
Put a spanner on the lower nut and undo the stud from the original nut.
New nuts should be used for refitting the manifold these are a self locking type.
The new nuts Bluesmoke has do not appear to be self locking.

As for the heatshield I understand some members run without that refitted.
Of these some have heat wrapped the manifold and some haven't.
There is a recent thread on that subject.
Your car will run with or without the heatshield and with or without the heat wrap.
I doubt you will notice a huge difference either way within  the restrictions applicable on your island home.  s:wink: :wink: s:wink:

Had to buy new ones, too hard to fit properly without putting them in fisst, managed to get some in though, seems secure now, hopefully they won't take too long to come to my 'Island home' lol

Before
 m http://postimg.org/image/gpk7hb1dv/ m

After
 m http://postimg.org/image/dnottlyv7/ m

Seems to be driving ok was a little smoke to start with from the PlusGas which is expected but seems fine now, engine sounds a little better too but no noticeable change in power as predicted

[Joesson]

I agree with what has been said on here before: It would be a shame to cover it up!
Hope all continues to go well for you and your 2.

[harvey718]

I've just got round to removing the oxygen sensors on the pre-cats to discover the left 1 had a light coating of soot but the right 1 was caked in oil.

Any ideas to what would cause this before I start taking the head off??

[harvey718]

Neither side of the pre-cats had any sign of a matrix inside and I don't have any history to know whether or not they have been removed a previous owner.
Surely some fragments of the matrix would still be seen if the part has failed?  Any info would be much appreciated.

[Joesson]

I saw my complete pre-cat matrix before removing it.
I have also seen photographs of pre-cats that have started to break up when there was still some honeycomb material to be seen.
If there is no sign of any honeycomb material at all then it is likely that this was removed at some prior time.
The soot coating on one sensor and oil coating on the other would be indicative of what is exhausting from the relevant cylinders.
The soot could indicate a poor fuel/ air mix but the oiling indicates wear.
Firstly, check your spark plugs.
Are these similarly two sooty and two oily?
What year is your car and what mileage?
Has the car been using oil?
The cars built 2003 to 2006 had a series of changes to the pistons and oil control rings each to improve there function.
Engine wear typically increases with mileage.
Frequent topping up of the engine oil is an indicator that the engine is worn, typically an ovalling of the bores causing oil to be drawn from the sump, burnt during combustion and exhausted via the pre-cats which when contaminated with oil begin to break up.
In certain modes the engine rebreathes the exhaust introducing the abrasive precat material into the engine and exacerbating the wear.
If this fits the profile of your car then I suggest that a previous owner has removed the precats, either as a preventative measure or an attempt to cure the problem.
A test of each cylinder compression will give you a good indication of the condition of the engine.
If the compression readings are low or differ greatly then excessive wear of the pistons is most likely.
This may not be the scenario you wanted to hear but is unfortunately sometimes the case.
There are remedies however which vary from partial to full rebuilds or replacement of a similar or higher performance engine.
Very much information can be found on here via "search" and there are good people on here that have been where you are and have worked through a solution that I am sure will offer advice as you uncover your mysteries.

[harvey718]

Thanks Joesson, I will be checking the sparkplugs tomorrow and be looking to get the head off to see whether the head gasket is gone or for some more clues to the white smoke and oil.

I was after a project and I paid £400 for 2001 which has a smoking engine, but the rest of the car is almost perfect, a small scratch on drivers door and a small chip to the front bumper. I'm in no hurry to get her on the road so will plan to work through the engine and rebuild it if viable.

[bluesmoke]

Just a quick one, the gasket rings for pre cats to main cat pipe, they're coated with paste by the looks of it, so you don't need to do anything else when replacing them, right? Just sit them in place and bolt everything up?

[spit]

Nothing else required. The furry bluey-green paste does the business.

Go slow and even across the three amigos in several passes to keep everything square. Torque is, um.... in the region of 46 ft lbs.

[Joesson]

Excellent recall spit!
46lb ft in old money
62 Nm for the metricated.