706 replies to this topic

[The Batman]

It's a brand new engine that had major back pressure problems due to driving hundreds of miles with a blocked downpipe. I think it needs new rings and a rebore

[Bargi]

People have had that happen before without long term probs. Even on track at full tilt and driven home after. Way I see it the rings are under way more pressure on compression stroke then a semi blocked cat with blowing downpipe can provide.

[The Batman]

Whos had that problem? What Pistons did they have fitted What do you think the problem is? I think it's the oil ring of the piston rings. It's the only logical option. If valve stems where shot then they wouldn't use this much oil. So if there is no leak then it has to be the rings surely. A leak down test should rule this out.

[CHILL Gone DUTCH]

I think we should fix the back pressure issue before we start stripping the engine apart

[The Batman]

Indeed that would be a good start. What has the exhaust guy said the reason is that you have gone through 3 or 4 flexis? Do you still have Exmantaa downpipe fitted?

[MartinS]

The manifold and backbox have been checked and totally clear. The downpipe was fitted at Zandvoort and its probably just bad luck that the flexi joint has split.

Will try and get a leak down test done some time but unsure who round here will do it and not going to take another day off to get to back on track as was there again, Friday.

When we blocked the two end pipes the car carried on running with no problems and helped us confirm that there was an exhaust air leak (with strangely no audible change) from the flexi. (I was looking as exmanta had said to look for a manifold leak, and it smealt of fuel).

I would say fairly confidently that the exhaust system is not blocked. When the cat sections off will see using a camera how that looks inside to confirm all is good.

Once thats fixed and back on, I will swap the tb and do yet another fueling run followed by log files and a power run to see whats happening.

 

Oh this is all so much fun, but as ever, thanks for any comments it all helps stop me from giving up (that and the large amounts of money already thrown at this thing).

 

Martin

 

Edited by MartinS, 15 November 2015 - 02:27 PM.

[The Batman]

If you have killed 2 flexis on original downpipe and now this flexi on a different downpipe This suggest there is a problem with exhaust system angle/supports or you've killed another cat Why not decat the pipe whilst it's off

Edited by The Batman, 15 November 2015 - 02:28 PM.

[fiveoclock]

Wouldnt a build up of pressure due to a blocked exhaust cause valve problems and not ring problems?

[The Batman]

Was just looking at back pressure etc. And to high back pressure from exhaust can cause excessive heat build up which is a problem Martin has had for years! Martin does the car still run hot on track just like the z22?

Edited by The Batman, 15 November 2015 - 02:32 PM.

[Zoobeef]

Leak down tester kits are £20-30 (I should buy one really) although you will need an air supply too. If it's leaking by then listen in the intake/exhaust/oil filler cap for whistling as it'll point where it's leaking. The oil is going somewhere. If it's not pcv (blocked) then its rings, valves or head gasket. Whats normal for compression tests on that engine? If there's a decent amount of oil in the cylinders then it'll be like always doing a "wet" test.

[MartinS]

The car runs a constant 92-94 on the road so yes hot, and still hits 107-110 on track exactly as before with the ecotec.

 

How big an effect on noise and emissions is it removing the cat. Is it worth me doing that with my old 2 inch system rather than mess with the new bigger system?

 

Just had a  great idea how I can quickly improve my outlook at this moment. Yep, its pub time!!

 

Martin

 

 

Edited by MartinS, 15 November 2015 - 02:55 PM.

[Crazyfrog (Fab)]

Yep, its pub time!!   Martin    

Don't dispear martin ...the vx can be a major headhacke and a money pit I should know that one after 14 years but don't have the heart to sell it .hope you fix it and she will give you many years of happiness in the distant future.....

[Bargi]

Whos had that problem? What Pistons did they have fitted What do you think the problem is? I think it's the oil ring of the piston rings. It's the only logical option. If valve stems where shot then they wouldn't use this much oil. So if there is no leak then it has to be the rings surely. A leak down test should rule this out.

Been plenty of people over time with failed cats. About 1 in 5 people who've purchased a Tullet it would also seem. I can think of ChrisUK at a national a few years back when he was in track. I didn't think the oil rings provided any compression as such. So would be strange compression rings are ok and oil rings arent from back pressure which would have to pass by the compression rings. First to admit I'm no expert so happy for anyone who knows their engine stuff to tell me different.

[fezzasus]

I think it's very unlikely that an oil ring can become damaged while the other rings remain intact. An oil control ring contributes very little to compression, but because of that, it's unlikely to become damaged by excessive crankcase pressure.

 

A borescope will of course confirm this, as a damaged oil control ring (or any other piston ring) is likely to cause scoring on the liner. I am concerned that high combustion of oil will be generating significant oil deposits in the combustion zone.

 

Moving on to the oil itself, Martin - have you been using the same brand of oil, and where did you get it? With fuel prices the level they are, dodgy suppliers may be adulterating the oil with diesel to save money. Very unlikely, however not impossible. There's a lot of this happening in other parts of the world. Additionally, one story that comes to mind where someone's wife was putting used cooking oil into a oil canister which was, unwittingly, being used to top up the oil of a Porsche.

 

Finally, backpressure. As far as i'm aware, the 2bular backbox is unique to your car. could this be the cause?

 

So, to itemise comments so far:

 

1. Check coolant for oil/emulsion - leaks at the oil cooler or within the engine could be dumping oil into the coolant.

2. Oil type and source - is it constant since the rebuild? What happens if you top up with a different brand?

3. Borescope! You can source cheap USB borescopes, however you will need to remove the inlet/exhaust manifold to access. - Did BOT not do this when they had the inlet manifold off?

 

On a side note, i'm shocked at the price that BOT charged for the work, is it work asking if a mechanically minded member is willing to investigate the problems? 

Edited by fezzasus, 16 November 2015 - 10:00 AM.

[The Batman]

he has the TMS manifold which is where im thinking the problem is with

 

if he is killing this many flexis maybe it is damaged and making the downpipe sit at a horrible angle then with engine movement this is causing the flexi to die?

 

either that or there is a blockage in the backbox?

[fezzasus]

I struggle to blame the TMS manifold. If the standard manifold can cope with 250 bhp (let's assume that at worst case, the TMS one doesn't improve performance) then I can't see how this causes catastrophic damage at 300 bhp.

 

Perhaps the angle the flexi-pipe meets is an issue, but the TMS manifold is compatible with the standard cat section and backbox, so there won't be too much of a difference in angles. Furthermore if the issue is just the angle of the pipe causing the failures, this wouldn't have caused any engine damage through back pressure.

 

 

[The Batman]

Could the tms manifold cause too much back pressure?

[CHILL Gone DUTCH]

Unlikely the restriction is before the flexi Unless there is a mating issues causing flexi to break

[CHILL Gone DUTCH]

Also a bout of background info Martin was aiming for around 280-300 hp on m62 I personally don't think his exhaust system with a CAT is capable of this I'm not 100% sure of the size of it as its a hybrid of exhaust bits If it was a 2.5" exhaust all the way through I think it would need to have a de- cat to achieve the desired power levels. This does not explain the oil usage but I don't think it's helping with back pressure Is it possible all the oil is clogging the CAT up causing increased back pressure

[fezzasus]

The flexi might be collapsing, like this (not sure about mode of failure)