E51 The E51 Catalytic Converter Problem

[Lpgc]

Yes opened at the front end. I am really not sure how complex the front decoring process is. I'll try to post photos later.

I did a thread on how I decored front cats https://forum.elgrandoc.uk/threads/front-cats-decore.21762/

There are other / easier ways but they involve lowering the engine and front subframe.

 

[randomorbital]

I did a thread on how I decored front cats https://forum.elgrandoc.uk/threads/front-cats-decore.21762/

There are other / easier ways but they involve lowering the engine and front subframe.

I did read it and that's what made me give up halfway through it .

I just don't trust myself to do the job as I am sure I am going to lose a few nuts and bolts or at least round them on the way to the cats...

 

[randomorbital]

I reckon what you're thinking about doing makes sense.

If by 'opened the rear left cat slightly' you mean you opened it at the front end and that caused the engine to seem to run properly again then it's likely that a front cat has failed and the debris from it was blocking the entrance to the rear cat.

At this stage you could spend time / money decoring the front cat only to find that the engine has already been damaged by running it with the blockage before. Since you only expect to run it for a year or 2 now you might as well see if it runs OK with just the rears decored.

There is a downside though - there could still be some cat material stuck in the failed front cat, if there is no engine damage now the stuck material could cause engine damage in future. But that seems unlikely if decoring rear cats makes it run properly, because that points to debris from front cats having cleared itself.

That’s the part I opened

I don’t believe it currently have any bits on the other side because when it happens I was on a long drive uphill and I have to watch the RPM to stop the pinging.

 

[Steve Thompson]

I'm proud to say that I am one of the worlds greatest bodgers.
I've made a living out of it!!
Ha.
Haven't done this and not heard of anyone doing it but I think it's got legs -
Get a drill bit, say about 15mm.
Cut it in half or more so that it is short and the flutes are open.
Weld it to a long flexible drive.
Remove the rear cats.
Drill up & in.
Measuring depth from start of contact with the rear of the front cat (which will be a set datum).
Your only trying to remove flimsy material so should be easy.
The idea is that you create a path of least resistance for collapsed cat partials to exit through.
Doesn't need to be pretty or straight or anything professional.
Continuous use of your Elgrand should allow gentle staged self disassembly of the cat material and eliminate the back pressure associated with a blockage.
Only a bodgers idea mind you but in my mind - it works.
Someone should have a go.

 

[Lpgc]

That’s the part I opened

I don’t believe it currently have any bits on the other side because when it happens I was on a long drive uphill and I have to watch the RPM to stop the pinging.

Yes that's the entrance to the passenger side rear cat, if you opened it there and cat crap came out it'll be because the passenger side front cat has broken up. Like @dognero said, leave it disconnected and go for a drive to try to get any more loose cat material to blow out onto the floor instead of blowing into the rear cat before you reconnect the rear cat. Hopefully there's no engine damage (from ceramic cat material getting back into the engine and scoring the bores due to the back pressure when the exhaust was blocked).

 

[Lpgc]

I'm proud to say that I am one of the worlds greatest bodgers.
I've made a living out of it!!
Ha.
Haven't done this and not heard of anyone doing it but I think it's got legs -
Get a drill bit, say about 15mm.
Cut it in half or more so that it is short and the flutes are open.
Weld it to a long flexible drive.
Remove the rear cats.
Drill up & in.
Measuring depth from start of contact with the rear of the front cat (which will be a set datum).
Your only trying to remove flimsy material so should be easy.
The idea is that you create a path of least resistance for collapsed cat partials to exit through.
Doesn't need to be pretty or straight or anything professional.
Continuous use of your Elgrand should allow gentle staged self disassembly of the cat material and eliminate the back pressure associated with a blockage.
Only a bodgers idea mind you but in my mind - it works.
Someone should have a go.

Might be able to do that, probably difficult to get the drill to work at the end of such long flexible drive. Wouldn't want to go too far through the other side of the cat and take out the pre-cat lambda sensors (unless they were removed first).

Not sure what to make of the pros and cons of drilling a hole through the cat material though - Assuming the cat is good before starting the work, would drilling a hole through it make it more or less likely to collapse? On the one hand there's a hole through it which will allow gasses to go through without going through cat material, so maybe less heat in the cat and like you say a fixed hole to allow gasses to pass even if the rest of the cat material melts in a way that sees the small channels block up, on the other hand drilling a hole through it must weaken it structurally, could possibly cause cracks through it that would weaken it further. I'd expect drilling it to help prevent problems/blockages due to melted cat innards but not due to collapsed innards, and it could make collapsed more likely. The reason why some people have engine failures after decoring rear cats is because front cats can fail in a way that sees them block themselves up, not usually due to melting of the cat material (not due to the little honeycomb holes getting blocked) but because debris from broken up front cats blocks the exit from the front cats.

 

[Steve Thompson]

Might be able to do that, probably difficult to get the drill to work at the end of such long flexible drive. Wouldn't want to go too far through the other side of the cat and take out the pre-cat lambda sensors (unless they were removed first).

Not sure what to make of the pros and cons of drilling a hole through the cat material though - Assuming the cat is good before starting the work, would drilling a hole through it make it more or less likely to collapse? On the one hand there's a hole through it which will allow gasses to go through without going through cat material, so maybe less heat in the cat and like you say a fixed hole to allow gasses to pass even if the rest of the cat material melts in a way that sees the small channels block up, on the other hand drilling a hole through it must weaken it structurally, could possibly cause cracks through it that would weaken it further. I'd expect drilling it to help prevent problems/blockages due to melted cat innards but not due to collapsed innards, and it could make collapsed more likely. The reason why some people have engine failures after decoring rear cats is because front cats can fail in a way that sees them block themselves up, not usually due to melting of the cat material (not due to the little honeycomb holes getting blocked) but because debris from broken up front cats blocks the exit from the front cats.

Simon, if I understand you right - I disagree.
Surely it's the front honeycomb of the front cats that block.
Not the rear (exit) of the front cats.
That doesn't compute.
As for the drilling difficulty, I'd imagine (in my master bodge mind) that there cannot be an easier component to drill.
The honeycomb would centre and guide the drill.
Doesn't matter if its central to the cat or not.
The material would grind/flake/shatter/swarf easily.
And material 'pushed' through on the completion of drilling would take that path of least resistance straight out the back when the engine is started.
No back pressure therefore no entry into the bores.
If the honeycomb collapses in a way that re-blocks the drilled hole then "Que Sara Sara".
Re-drill.
It's quick, cheap & easy.

 

[Highway Dave]

Simon, if I understand you right - I disagree.
Surely it's the front honeycomb of the front cats that block.
Not the rear (exit) of the front cats.
That doesn't compute.
As for the drilling difficulty, I'd imagine (in my master bodge mind) that there cannot be an easier component to drill.
The honeycomb would centre and guide the drill.
Doesn't matter if its central to the cat or not.
The material would grind/flake/shatter/swarf easily.
And material 'pushed' through on the completion of drilling would take that path of least resistance straight out the back when the engine is started.
No back pressure therefore no entry into the bores.
If the honeycomb collapses in a way that re-blocks the drilled hole then "Que Sara Sara".
Re-drill.
It's quick, cheap & easy.

I like a good bodge every now and then but, have you ever noticed when drilling say a brick, the dust comes towards the drill but when near the end the brick "blows" on the other side pushing dust and particles the other way ---so possible shite either end really

 

[Lpgc]

Surely it's the front honeycomb of the front cats that block.

Some fail in a way in which the front honeycomb melts and blocks.

But we know that they often fail in a way in which the honeycomb breaks up because after a front cat failure if rear cats are in place there's loads of front cat material blocking the entrance to rear cats... Following a front cat failure if rear cats are still in place, if the front end of the rear cat is disconnected from the front pipe section it's normal to see various sized chunks of cat ceramic honeycomb material, lots of dust and bits of fluff come out from the front end of the rear cat.

The front cat bodies (in fact all cat bodies including rear cats) are wider than the incoming and outgoing exhaust pipe, there is an upside down funnel shape from the incoming exhaust to the cat body, the wider (than exhaust pipes) cat body, then at the bottom of the cat a narrowing correct way up funnel shape to the exit pipe. The internal cat material is brittle, easily cracked and broken up into smaller pieces, and in the process creates lots of white ceramic dust. I reckon that some front cat blockages are caused by broken up cat material blocking the narrowing exit funnel shape and smaller broken up pieces / dust blocking any gaps between bigger pieces, there's also a lot of heatproof padding/fluff like material sealing the interface between the ceramic core and the metal body which (if we imagine a chunk of ceramic broken away from the outer edge near the padding/fluff) can come loose and help to block any small gaps between big chunks of ceramic blocking the exit.

I've decored many Elgrand rear cats and a few front cats, really brittle stuff, removed by tapping into it with something like a chisel which splits it and then (on the short nearside rear section that doesn't have to be cut open to decore it) you end up with lots of dust and loose chunks inside the cat that won't come out of the exhaust inlet or exit hole until you've broken the bits into progressively smaller pieces. Bits can get wedged in an inlet / outlet hole even without trying, sometimes difficult to free by intense shaking etc, seems reasonable that with exhaust gas all trying to flow one way through a cat with broken bits of various sizes, dust and padding/fluff inside all trying to be pushed out of the exit that the exit can get blocked up and the stuff blocking the exit compacted and made even more gas tight by the exhaust pressure.

 

[Steve Thompson]

Some fail in a way in which the front honeycomb melts and blocks.

But we know that they often fail in a way in which the honeycomb breaks up because after a front cat failure if rear cats are in place there's loads of front cat material blocking the entrance to rear cats... Following a front cat failure if rear cats are still in place, if the front end of the rear cat is disconnected from the front pipe section it's normal to see various sized chunks of cat ceramic honeycomb material, lots of dust and bits of fluff come out from the front end of the rear cat.

The front cat bodies (in fact all cat bodies including rear cats) are wider than the incoming and outgoing exhaust pipe, there is an upside down funnel shape from the incoming exhaust to the cat body, the wider (than exhaust pipes) cat body, then at the bottom of the cat a narrowing correct way up funnel shape to the exit pipe. The internal cat material is brittle, easily cracked and broken up into smaller pieces, and in the process creates lots of white ceramic dust. I reckon that some front cat blockages are caused by broken up cat material blocking the narrowing exit funnel shape and smaller broken up pieces / dust blocking any gaps between bigger pieces, there's also a lot of heatproof padding/fluff like material sealing the interface between the ceramic core and the metal body which (if we imagine a chunk of ceramic broken away from the outer edge near the padding/fluff) can come loose and help to block any small gaps between big chunks of ceramic blocking the exit.

I've decored many Elgrand rear cats and a few front cats, really brittle stuff, removed by tapping into it with something like a chisel which splits it and then (on the short nearside rear section that doesn't have to be cut open to decore it) you end up with lots of dust and loose chunks inside the cat that won't come out of the exhaust inlet or exit hole until you've broken the bits into progressively smaller pieces. Bits can get wedged in an inlet / outlet hole even without trying, sometimes difficult to free by intense shaking etc, seems reasonable that with exhaust gas all trying to flow one way through a cat with broken bits of various sizes, dust and padding/fluff inside all trying to be pushed out of the exit that the exit can get blocked up and the stuff blocking the exit compacted and made even more gas tight by the exhaust pressure.

Understand.
However (there's always a however), from what I've seen, photos (not real life I'll give you) of fresh failures and mechanically removed ceramic bits are all jagged with straight edges.
However (told ya) keep searching and you see photos of ceramic bits that have been swirling around loose within the cat enclosures for a while.
These bits are often smooth, even quite round.
This tells me that they are self grinding themselves into dust.
When like for like brittle materials collide then damage is rapid.
So providing that that path of least resistance (the drilled hole) is available, then that self created dust will shoot straight out and through the full exhaust.
Probably no good for the following drivers lungs mind you! (Just thought of that!).
Wish I had a workshop and opportunity to at least have a pop at this.

 

[LeStempy]

The trouble is that dust can still be sucked back into the engine during the valve overlap due to the resonance.

 

[Lpgc]

However (there's always a however)

For sure, and I hope you don't think I'm out of order for keep replying on this mate.

I'd say jagged in fresh failures implies breaking up rather than melted at the front end, for sure some debris bits will be rounded if flying around inside the hollow bits of cats (the funnel shape bits don't contain any cat material, at least not until the cat starts to break up, all the cat material is in the cylinder shaped bits between the funnels) - But what if they grind down to a size where they then block gaps between bigger bits of already broken cat at the bottom of the funnel, or the dust from them grinds down to finally block smaller gaps that previously allowed exhaust to flow out of the exit. Drilling a hole straight through the centre of cat material would certainly help protect against blocked cats due to melting, I agree that drilling a hole would be beneficial if it were just a case of cats failing due to melting. But I'm not so sure it would help protect against blocked cats due to cats breaking up, especially not if drilling the hole causes the break up of a cat that wouldn't otherwise have broken up, or is the root cause of (say) a section of honeycomb from around the drilled hole to crack off / fall out and slot straight into the exit pipe. When manually decoring a cat that hasn't failed it seems that the honeycomb seems more likely to crack along it's length (parallel with the little holes that run the length from inlet to exhaust end of the cat) than across it's width, whole longitudinal sections of honeycomb become dislodged and are then free to drop towards the exit, it only takes 2 full length longitudinal cracks to allow a cat cylinder long section of honeycomb from the outside of the structure to become dislodged and then it's going to go down toward the exit either due to gravity or due to being carried by the flow of exhaust gas.

 

[Lpgc]

The trouble is that dust can still be sucked back into the engine during the valve overlap due to the resonance.

I think resonance will play some part in exhaust getting sucked back in, if it were an older design engine (or particularly a race engine with long duration cam and small lobe to lobe separation) such aspects could play a slightly bigger part in exhaust getting sucked back in. But still in both cases there's a definite overwhelming direction of exhaust flow which points from the engine towards the exhaust pipe when the engine is running... Nobody fits a filter to their tailpipe in case dirty air from the atmosphere gets sucked into their engine via the exhaust pipe.

That said, I've got a boat with an inboard American V8, I could make it a lot more powerful and faster by fitting a cam with longer duration but that would be at risk of it sucking some water in through the exhaust valves during cranking the engine, not really when the engine was started and running because then the overwhelming flow is towards the tailpipe (which is underwater), mainly just during cranking if the engine doesn't fire and there is no exhaust pressure to push the water away.

But I think what happens with Elgrands is when there's a blockage the area of exhaust from the engine up to the blockage becomes pressurised, then when the driver lifts off the throttle (or particularly at that point) there can be more pressure in the exhaust than in the engine cylinder, a situation you'd never really get under normal conditions without an exhaust blockage, which then causes exhaust gas from the blocked exhaust to flow back into the engine cylinders through exhaust valves carrying with it the ceramic stuff.

 

[sg66]

I'm proud to say that I am one of the worlds greatest bodgers.
I've made a living out of it!!
Ha.
Haven't done this and not heard of anyone doing it but I think it's got legs -
Get a drill bit, say about 15mm.
Cut it in half or more so that it is short and the flutes are open.
Weld it to a long flexible drive.
Remove the rear cats.
Drill up & in.
Measuring depth from start of contact with the rear of the front cat (which will be a set datum).
Your only trying to remove flimsy material so should be easy.
The idea is that you create a path of least resistance for collapsed cat partials to exit through.
Doesn't need to be pretty or straight or anything professional.
Continuous use of your Elgrand should allow gentle staged self disassembly of the cat material and eliminate the back pressure associated with a blockage.
Only a bodgers idea mind you but in my mind - it works.
Someone should have a go.

I've already had many a thought on doing similar things, I was working on a Flexi sleeved hole cutter to rake out a bigger section of material.

 

[LeStempy]

I think resonance will play some part in exhaust getting sucked back in, if it were an older design engine (or particularly a race engine with long duration cam and small lobe to lobe separation) such aspects could play a slightly bigger part in exhaust getting sucked back in. But still in both cases there's a definite overwhelming direction of exhaust flow which points from the engine towards the exhaust pipe when the engine is running... Nobody fits a filter to their tailpipe in case dirty air from the atmosphere gets sucked into their engine via the exhaust pipe.

That said, I've got a boat with an inboard American V8, I could make it a lot more powerful and faster by fitting a cam with longer duration but that would be at risk of it sucking some water in through the exhaust valves during cranking the engine, not really when the engine was started and running because then the overwhelming flow is towards the tailpipe (which is underwater), mainly just during cranking if the engine doesn't fire and there is no exhaust pressure to push the water away.

But I think what happens with Elgrands is when there's a blockage the area of exhaust from the engine up to the blockage becomes pressurised, then when the driver lifts off the throttle (or particularly at that point) there can be more pressure in the exhaust than in the engine cylinder, a situation you'd never really get under normal conditions without an exhaust blockage, which then causes exhaust gas from the blocked exhaust to flow back into the engine cylinders through exhaust valves carrying with it the ceramic stuff.

It may be a minimal chance but it's a minimal chance of total engine destruction. Making a load of cat dust with a drill so close to the engine is surely not a good idea.

 

[Lpgc]

It may be a minimal chance but it's a minimal chance of total engine destruction. Making a load of cat dust with a drill so close to the engine is surely not a good idea.

It's not a great idea to do it because there is a chance of a bit of cat dust being sucked in during starting the engine the first time after the drilling but I don't think we'd be talking anything like the amount that would enter cylinders during tip-out (lifting off the accelerator) with a cat blockage.

Edit - I'd be more concerned about making the honeycomb more likely to crack and block the exit.

 

[sg66]

It would be fairly easy to shove an modified hoover tube up there too to keep some negative pressure and suck up dust as you go.

There would only be one real way to find out

 

[Steve Thompson]

For sure, and I hope you don't think I'm out of order for keep replying on this mate.

I'd say jagged in fresh failures implies breaking up rather than melted at the front end, for sure some debris bits will be rounded if flying around inside the hollow bits of cats (the funnel shape bits don't contain any cat material, at least not until the cat starts to break up, all the cat material is in the cylinder shaped bits between the funnels) - But what if they grind down to a size where they then block gaps between bigger bits of already broken cat at the bottom of the funnel, or the dust from them grinds down to finally block smaller gaps that previously allowed exhaust to flow out of the exit. Drilling a hole straight through the centre of cat material would certainly help protect against blocked cats due to melting, I agree that drilling a hole would be beneficial if it were just a case of cats failing due to melting. But I'm not so sure it would help protect against blocked cats due to cats breaking up, especially not if drilling the hole causes the break up of a cat that wouldn't otherwise have broken up, or is the root cause of (say) a section of honeycomb from around the drilled hole to crack off / fall out and slot straight into the exit pipe. When manually decoring a cat that hasn't failed it seems that the honeycomb seems more likely to crack along it's length (parallel with the little holes that run the length from inlet to exhaust end of the cat) than across it's width, whole longitudinal sections of honeycomb become dislodged and are then free to drop towards the exit, it only takes 2 full length longitudinal cracks to allow a cat cylinder long section of honeycomb from the outside of the structure to become dislodged and then it's going to go down toward the exit either due to gravity or due to being carried by the flow of exhaust gas.

Absolutely not Simon.
Nice to have an adult discussion on an interesting subject.
You, with your immense skills, knowledge and experience & me with my bodge based immature idea.
What could go wrong!

 

[Steve Thompson]

I've already had many a thought on doing similar things, I was working on a Flexi sleeved hole cutter to rake out a bigger section of material.

Whaay!!!
Someone on my side.
Not sure about the hole cutter though.

 

[Steve Thompson]

It would be fairly easy to shove an modified hoover tube up there too to keep some negative pressure and suck up dust as you go.

There would only be one real way to find out

We need a brave soul to have a go.
Or better still someone who has access to the bits to test on a bench.
Exhaust guys.
Scrappie.
Anyone know anyone?