Bad running after new head gasket - cause?

[rogerthechorister]

Thanks for the input guys.

I am returning to the expert...

[Diesel-do-nicely]

sorry roger, just read your pm and i dont drink .

[rogerthechorister]

A Scotsman who does not drink? And in particular does not drink whisky? What else can I bribe you with?

[rogerthechorister]

A mechanic I know (not the one at present working on the car) has suggested the problem might be valve stems. It makes no sense at all to me but has anyone any views?

[Laird Scooby]

Not sure what he means by valve stems - i know what valve stems are but does he mean the valve stem seals, the valve stems themselves and if so in what respect? Is he suggesting they're worn?

However, a silly thought just entered my head and i wouldn't mind betting it's been overlooked.

The PCV filter/flametrap.

After the head gasket failure it's almost certainly blocked and probably the hoses connected to it and their respective stubs where they connect to things like the inlet manifold. Even if it doesn't fix things, it's worth inspecting it to make sure it's not blocked, replacing it if so.

I'm not sure if i've picked the right one here as i seem to recall your car is turbo'd and don't know if "one breather fits all" or not but that's the wee beastie i mean. Even on my n/asp K-Jet B230E, when mine was blocked it ran like a bag of camel-dung. Add a turbo to the mix and it might be enough to cause a serious problem like you have. It's also possible that it is clear/clean but leaking - again in the right place this could cause an air leak into the inlet manifold. Got to be worth checking it surely?

[rogerthechorister]

Thank you Scooby. I am told the breather stuff has been done. I may perhaps not fully believe it...

Suggestion was valve stems not the stem seals.

AFAIK stem seals result in puff of blue smoke when starting and/or on re-applying throttle after overrun: not happening.

Worn stems/guides would result in valves slopping about, poor compression because of bad seating, but I see no reason how they could cause a flat spot at 4,500 rpm.

[baggy798]

Are you still using the Turbo+ system? I was going to suggest bypassing it.

[Laird Scooby]

Originally Posted by rogerthechorister

Thank you Scooby. I am told the breather stuff has been done. I may perhaps not fully believe it...

Suggestion was valve stems not the stem seals.

AFAIK stem seals result in puff of blue smoke when starting and/or on re-applying throttle after overrun: not happening.

Worn stems/guides would result in valves slopping about, poor compression because of bad seating, but I see no reason how they could cause a flat spot at 4,500 rpm.

That's exactly what i would have said but for the valves to slop about to that degree the valve stems would surely have to be worn to almost nothing.
I wonder if the filter element was checked in the breather/flametrap - it's only a gauze and the pipes leading in might be clear but that might be blocked.
Assuming you can get your arm in to where it usually lives (under the inlet manifold on the side of the block) you could pull it out and check it yourself. It is a fiddle and a spare door mirror glass comes in handy to peer through the manifold branches at what you're trying to do. Because of the fact it is fiddly, i wonder/suspect it may have only been checked visually to make sure the hoses were attached.............

[Diesel-do-nicely]

just replaced a turbo for a chap today,940 hpt, his had split inside the exhaust casing between the wastegate mechanism and the impeller housing, flatspot from 3000rpm and wouldnt boost more than 6psi.what a difference, like 50 horsepower difference, and the crack was visually thinner than a matchstick.
wonder if doing it sideways has nackered his garret in similar fashion

[rogerthechorister]

I learned only today from mecco that the flat spot only appears when the engine is warm/hot. When cold no flatspot.

That rules out a fuel pressure issue as such, in my opinion.

He is going accordingly to change the Lambda sensor again as (he says) there are two different ones, one for cars with EGR and one for cars without and maybe the wrong one is in there (even if it is new) and he is also going to change (again) that temperature sender under the manifold.


Just as well I was going to have bits resprayed though as some bar steward has keyed her up while he has has her!

My plans to buy another have fallen through.