Diagnosing a valve seal problem
 

After ruling out other parts of the car (Turbo - went for service, rings - got a compression test done, all at 120psi) I am thinking that I have worn valve stems/seals in my heads which the cause for the smoke beign produced from the back of the car.

The problem is been happening for the last year or so but has become noticably worse in the last few months with smoke appearing from pulling out from junctions not just from conditions under boost.

It there any way of checking to be sure that this is my problem before I pay to get the engine taken out and the heads replaced? Its gonna get expensive if I do....!

Nezz.

wouldnt worn valve/seals cause a loss of compression through?

worn valve seals wont cause a compression loss. normally when these go you get smoke for a minute or so after start up (talking bikes and cars here with verticalish cylinders, not sure if it would be the same with horizontal scoob pots) but then it goes.

we run some race bikes without any seals deliberately and you still only smoke on start up, so i dont think your smoke is down to this.

worn valve guides wont cause it directly either, but this will give your valve seat and valve 45deg sealing angle a harder time, making them recede/wear quicker. then obviously you may get compression losses and/or a bit of smoke.

if your valve to guide clearance is like a c0ck in a bucket, you may get a bit of smoke but yours does sound a bit more than that.

i think you are gonna have to take the engine out and whip the heads off to confirm though unfortunately

it sounds very possible :(

Could just be a build up of oil in the intercooler/inlet manifold from the breathers that come from the crankcase and rocker covers.
Probably not this , but worth a look before you go stripping the engine.

yeah good point andy. whip the IC off, i should think it would be dripping in the neck to cause that much smoke.

how many miles has the motor done? had a hard life? lots of short journeys etc.?

Usually, valve stem seal failure is recognised by the engine momentarily smoking after a period at idle. The high idle manifold depression pulls oil down the valve stems into the tract above the valves and thence into the combustion chamber, which, at idle is not hot enough to burn the oil. When you press the loud pedal and put the engine under load, the temperature rises and the oil burns and blows out as a brief puff of smoke.
Very often, it is possible to change the stem seals (and springs) without removing the head, but I think accessibility would rule this out on a Subaru.

IC is front mount, all breather lines connected to catch tank and none back into the inlet pipe. Motor is a MY00 UK turbo with 60K on the clock.

Standard block and heads, MD304 turbo, gruppe-s headers, HKS exhuast parts, HKS air filter blah blah.

If sitting at the lights or cruising for a little then blast it, lots of smoke.

Coming off from crusing on the motorway then floor it down a dual carriageway gives off less smoke but still a fair bit - mostly as the turbo spins up and at top revs it gives out more but increase flow thru the engine woudl do this to.

Once the car has had a bit of boost thru it then it seems to be a lot better with minmal to no smoke.

Turbo has been sent back to TD for full repair and is still 3 months under warranty, as said above compression check came out at 120psi all round. Has has a fairly hard life being tuned to 300ish HP for the last 4/5 years. Wouldnt say a lot of short journeys really just normal road useage and a few track/airfeild days.

Tempted to try another turbo just to make sure its not that first!!

it doesn't sound valve related to me. Valve problems don't usually present such consistent results accross all cylinders. Depending on how much you want to try and diagnose yourself, you could try and remove the inlet manifold and turn the engine over by hand with some fluid in the inlet ports (brake cleaner for instance) and see if you get air hissing past the valves, obviously harder to test the exhaust side like that.

A leakdown test may also be useful, and you can also try the leakdown and compression tests with some oil squirted into the bores before hand, which will help seal the rings and show up a ring seal issue (ie if oil makes it much better then valves probably not the problem).

Paul

For my money, the turbo seals have gone. take the car to the manufacturer / supplier ( Turbo Dynamics was it ?? ) for a diagnosis, or else others like Zen Performance, Xtreme Scoobies, APi, Scoobyclinic, Lateral, ASPerformance etc.

For oil smoke out of the exhaust it needs to get IN to the exhaust stream, so that's either in the combustion chamber/ cylinder, or else afterwards.

Oil via valve stems on these flat engines is not too likely, not in significant quantities despite high vacuum in the cylinder - not that much oil about there and at no pressure. Ditto oil via rings unless rings really shot - no pressurised liquid oil feed at piston ring surface ( maybe more for engines with under piston crown oil squirters )

So probably from turbo via the turbo seals / bearings.


My puffs of smoke came on lift off from hard boost on OEM D04 turbo, was due to to worn turbo.

Turbo came back from Turbo Dynamics, they said they couldny find anything wrong with it but replaced the seals as a precaution.

Hmm Leakdown test next then....

Everyone's assuming it's oil but you haven't mentioned what colour the smoke is. Oil = blue; fuel = black; water = white :)

Also, condition and consistency of the plugs, i.e. colour, wet/dry, oily, may indicate where to look.

Gerry

Smoke = light grey/blue

hmmm, not good. Blue smoke is deffo something that needs to be investigated. I may be massive overfuelling which causes oil in the cylinder to be diluted and ingested past the piston rings. But blue smoke is most like to be linked with some positive leak, like a piston or valve stem seal problem.

Paul

Gets my vote too.

David APi Engines / APi Impreza
www.apiengines.com

David,

Turbo went back on today but havent had chance to try to replicate the problem again yet.

You may be getting a phone call from me in the week to discuss how to progress with this.

Neil.