Hi All

I have been trying to get to the bottom of a smoking issue that my 2wd cossie has had for a while now, and am about to pull my hair out!

I have been able to isolate what provokes the most smoke which is over run.

This is the problem:

As a drive, for example down a hill in traffic. If the car is in gear, and my foot is not on the throttle, when I next engage the throttle, it will blue smoke badly - enough to be embarassed! Boost is absolutely irrelavant. It doesnt matter how the car has been driven before hand.

If a boot it up to any speed with any given boost, then when I achieve whatever speed (say 100mph), then dip the clutch, there is no smoke at all when I re engage the throttle in or out of gear.


The car had a completely rebuilt bottom end only twelve months ago, after about 12k miles. The problem has been steadily getting worse.

The rebuild included new oversized pistons and rings, placed into oversized bores to match. Std compression, and all was fully balanced.

The chap who carried out the work was competent (ie I didnt do it!!), and the car has bronze valve guides, and was fitted 12k ago with new stem seals. The car has been apart since for a head gasket failure.

HELP HELP HELP HELP HELP

I am at my wits end!

JJ

 

bump

 

Sounds very like valve stem seals to me or 2nd choice would be vlave guides!

 

as above i would say

 

Thanks for your input, this was my first choice as well.

The guy who built the engine is beating himself up about the Rings though, but fact remains that we trusted that the bronze valves previously fitted were okay, and the piston rings this weekend just passed a leak-down test with flying colours.

Doh!

 

i'd say valve guides,very basically what can happen is when your on over-run (downhill,no throttle as you put it) the engine is under vacuum and sucks oil past the guides,then when you boot it all that oil is blown out

i'd do guides (and obviously stem seals whilst the heads off,and also check the bores for heavy glazing)

then last but not least is turbo,but i doubt it's that

 

Thanks bud-weis

That is a really good explanation of what happens

One question though, couldnt the vacuum also suck oil past the bores? We did have the head off recently, and the bores looked okay, no signs of glazing that we could see.

I think you are right. I checked the turbo not long ago, and it was fine.

 

There may not be anything wrong with your guides, etc...

What exhaust are you running ? An aftermarket one which flows better can reduce the amount of back pressure the turbo is seeing, leading to a little more smoke than usual.

Also, Stu once said that while you are off throttle (or light throttle), there isn't enough pressure flowing through the exhaust which leaves deposits in there. As soon as you step back on it, the extra pressure is enough to push everything out, making it look like you are burning oil like no tomorrow.

Try and get a leakdown test arranged, it's a little more advanced than a compression test and the person doing it should be able to tell you what is leaking if anything

 

Hi Frog

We did the leak down test last weekend, and the bores only yielded a 5% maximum leak at over 3BAR air pressure!

The exhaust on the car is the magnex all the way from turbo back. I take your point about the exhaust, but it is using a lot of oil as well.

 

A leak down test should enable you to find out where it's leaking from, you say the bores only yielded 5%, how do you know this wasn't going through valves/guides, etc... ? Did you positively identify the bores as being the source of the leak as opposed to inlet/exhaust ?

I believe a leakdown test can tell you if you have inlet, exhaust or piston leaks by listening () in various places while you run the test, come to think of it, it may not be able to tell if guides are leaking...

I would have thought that blocking the inlet manifold, opening the inlet valves and closing the exhaust while pushing air into one cylinder would tell you if any air is getting past the guides.
This might well be a load of drivel though

 

The reduced exhaust back pressure may let oil past the turbo oil seals too Explaining the increased oil consumption.
(I am pretty sure I read that somewhere here too )

 

Only thing is, that if it was the turbo seals, you would expect to see residue in the induction pipes would you not? (between turbo and intercooler etc. And these are clean as a bell

I may be wrong about this though.

 

Sorry, just read your other post,

The test was done with the cylinder set so both the exhaust and the inlet valves were closed. So as such, any escape would either have to be due to a poorly seated valve (unlikely as car runs reasonably well), or running past the piston.

My understanding from speaking to the chap involved was that the 5% was so insignificant, that it was not likely to yield a telling result.

I will ask him if the test can be carried out with the valves open to see if that can yield a result with the inlet/ exhaust suitably blocked. I know nothing of leak down testing, so have no clue as to whether this is realistic!

JJ

 

That sounds right, however, the leak could be diagnosed as an exhaust valve leak by listening for air flowing out into ex. manifold, inlet valve leak by listening on the inlet side.
If no sound from either it's either HG or rings.
I *think* it's possible to know if it's HG by watching for bubbles or something like that in coolant, but I am not 100% sure.

The reason for doing a leak down instead of straight forward compression test is that it allows you to find where the leak is, rather than just state "compression" is low, which could have nothing to do with rings if you see what I mean.

By opening the inlets and somehow sealing the inlet manifold, I guess you'd know how much the guides are leaking.

I am only trying to use common sense here, I have never done this sort of thing before

 

I appreciate your input! At least you are prepared to stick your neck out and have a guess!

I think my guys problem was basically that with both valves closed, there was not enough air leaking to identify where it was going. Again, I am guessing.

I have been told by wife I am not allowed to touch cossie this weekend, so when I get back, I will have a long chat with tuner, and see if he can think a little harder on what is causing this damn smoking.

Its enough to drive you to Japanese!

 

hi mate my s2 has done loads of miles and in a morning it smokes a little this is the stem seals, iv recently done over 400 miles in one day and it used no oil so def stem seals for mine , so if u do alot of miles one day see how much oil it uses, if its the rings it will use a fair bit

andy

 

For the last week, I have been using it as my main form of transport (whilst the usual car was fixed)

It has done in one week about 1000 - 1200 miles. I would guess that in that time it has used between 1 and 2 litres of oil!

Doh!

 

Good luck with the tuner, and the wife