Hi all,
Couple weeks ago my v3 sti lost compression on cylinder 1 completely. No smoke, rattles or odd noises. Once splitted we found the problem, as below.
Just wondered if any one else has had the same issue.

 

End of spark plug missing?


Steve

 

Think a bit of a fuel issue. Rekon it was lean on boost, so valve got to hot and broke away

 

Think there wrx heads.

But there are many reasons why this can happen. Running lean being one of them.

Wat was spec of car? wat fuel did you use? was it mapped? was it consuming oil etc? any additives?

 

Yes it was mapped.
I have always run Shell Optimax, and it was mapped to 1.3 bar. I have walbro pump, HKS mushroom filter, and full 3" decat system. Was only running 297bhp, so I would of thought it was safe.

The heads have me worried now. whats the diffrence with the WRX and STi heads?

 

I had that, but I had a dodgy spark plug. The tip came off and got lodged under an exhaust valve and burnt it away

Graeme

 

Depends on the year.

Early WRX are hydraulic lifters, As are early STi (v1 and v2 IIRC), but I think V2 are slightly different (lighter, or anti-pump to allow more revs/lift? ).
Later Stis are bucket shims. Later WRX (post 1997) tend to be solid lifters too.

Generally speaking V1 and v2 heads are pretty much lke teh equivelent year WRX heads
but cams 'should' be differnt (depends on version I think)

V3 onwards had different exhaust valves IIRC (hollow, follwed by sodium filled...thi is in the center area, not the bit that broke!).

Not sure why you are asking, unless you think the car has WRX heads fitted for some reason. A broken valves does not warrant the replacement of the whole head!

IMO, I'd just rebuild the heads with new valves, seats/guides (if needed) and springs, and make sure they are thorougly decoked to rule out any glowing carbon issues and crack test it (i.e look like new - a simple job for any good head specialist).


edit to add:

As for teh cause? who knows, but think about it...you are looking at a 15 year old engine now!! So unless you know its past in great detail, I'd just take it as it comes and just get the heads reconned and rebuilt.

Just clean the coke off piston tops first and make sure there are no witness marks. Marks in the piston tops (and cylinder head) from debris damage can cause hot spots, causing detonation which will knacker bigs ends and melt the piston, if it look like its had valve/contact damage, maybe worth a bottom end strip-down as piston/valve contact is a sign of excessive big-end bearing play. TBH if its still the original engine, whilst the engine is out on the bench I'd be inclined to check out the bottom-end anyway for future peace of mind. Basically how far you go depends on how much money/time you want to throw at it and how long you intend to keep the car.

 

Ali-B, I was confused about heads as LegacySti commented he thought they looked like wrx heads??
Im definately doing heads as advised Im getting them checked before we do any work lol
It was running pretty high boost so think Ill make sure its mapped properly and safely when back togther

 

what does the piston look like?

 

http://i1099.photobucket.com/albums/...onepics023.jpgNot sure what exactly you want to know about piston, so I have attached a pic. Hope that helps!

 

i wanted to see if there was any signs of damage on them, can;t see the side of them though.

 

You said the car was mapped at 1.3 bar of boost, what boost were you using the car at.

 

way tooooooo much lol

 

I have seen this before on an old Kawasaki Z9 i re-built. I put it down to the valve not seating properly causing hot gasses ect blowing through and erroding the valve. Is there any seat damage? When you take the valve out check to see if its slightly bent.

 

i think they are sti valves btw. there is no difference between the actual castings of wrx/sti heads but the valves, springs and cams are different.

don`t you usually get a white frosty covering when its being running lean btw, i cant see if thats a reflection or not on the photo. the plugs usually are a good indicator , if the tip is frosty white - usually means running lean.

and 1.3 bar boost is fine if its mapped for it, should take plenty more

 

put that pic on the 22b forum, they will tell you on there whats gone wrong

 

Cheers for all the info guys.
When car broke it was running and holding 23psi of boost.

Pistons are un damaged thank god, and so to are the bores.

Ive had a look at my injectors and they are standard so,k that would mean I could only safely run what sort of bhp?? Im looking for bigger injectors but not silly big , what size should I be looking for ?

 

23psi is nearer 1.6 bar,hows it gained 0.3 of a bar?

sounds like its been running too much boost for a long time.

 

standard are 440s,witha fuel reg can probably do upto 400hp but better to get 550s to do that, without reg i`m guessing but probably about 350.

were you running 23psi or 1.3 bar, if you were running 23psi, thats your problem

 

I dont think that would cause this type of damage to be honest. Firstly its only one valve damaged, secondly i would have thought the head gasket would have failed first if it were down to too much boost.

As i said before, i have seen this before on an old motorbike (that was not a turbo) and standard. This was also on just one valve with no other damage. My bet is for some reason that valve was not seating correctly in that area causing a blow through.

 

The valves are STi/Type R - should have the codes EH and IH on them.
The exhaust valve looks like it has suffered from high temperature/thermal shock.
Can be caused by cooling system problems but more likely to be det related - rapid increase in temp causing uneven heating of the valve, a radial crack will appear and allows the combustion gas to escape subsequently opening/burning the crack wider.

Mick

 

Faulty injector or ign fault would be my guess. Poor valve seating can cause a hot spot under the valve but any such issues will be resolved with the rebuild of the heads. I would rebuild it with new injector plugs & coil & then take it to a local fuel injection or Scooby specialist to check it is all running ok.

 

When we removed the valves, the second exhaust valve in the same chamber was cracked to, so has got hot.
The additional boost was created by a Dawes device, naughty I know, but that does seem to be half the cause.
The 550 injectors might be an idea, running at half potential is better than maxing out standrads I suppose ;-)