Hello peeps..

story goes, my mate bought a very cheap 97-98 wrx sti because its got a running fault. he did a compression check, which showed 3 cyl had 130-150 psi , but No4 had 50psi. he seemed to have it in his head it was a valve problem, so i agreed to have the heads off and take a look for him

it's stamped EJ20 and is now in my garage with the left head off it and i can't seem to find anything majorly wrong with it.

cylinder bores both look the same, no noticable marks or scoring, like a pinched ring. i can't get any play out of the pistons in the bores.

No4 combustion chamber in the head was noticably more carboned up, but there are no cracks that are visable. there is quite a lot of well baked on carbon in the faces and lower stems of all the valves, but little difference between the cylinders


number 4 wirebrushed off

also, the valve sealing faces seem quite eaten away and concave? is this damage or just how they are? the inlets look normal, where the exhausts seem like they have been 3-angled.


one ex valve on each pot is slightly smaller than the other, is this normal? the smaller one has a ring around the top face, that looks like a crack, but i'm guessing could be a casting mark?

both No4 exhaust valves

i did check for leakage by filling the exhaust ports with brake cleaner, but it leaked from all 4 valves, so i figured it wouldn't be enough to cause such a large difference in compression.

the head measures nice and straight in all directions and the head gasket looks ok. its a 3 layer item, stamped 482. is this something i should be looking for when getting the right replacement?

Thanks for reading, sorry about the essay
Dave

 

Be worth removing the piston and checking for any det damage to the ring lands if the compression is that low.
The valve seats and faces are pitted,so will need cutting/facing to restore a good seal.
Did you check the valve clearances when you stripped it to check for tight clearances?
The head gasket sounds right and should measure 1.6mm in thickness for a STi Version 3~4.
What are the valve codes out of a matter of interest - if the engine is a STi V3~4 the head codes should be RH-B and LH-B (not LHC 007 as in the first pic).

Mick

 

God has spoken

 

Cheers for the reply, bud.
is there a way of popping out the pistons/rods without spliting the block? heard this is a bit of a can of worms

i didn't check the clearences when i took it apart figured they were hydraulic

i will have a look at the valve/head codes. he told me its a 97 or 98 car, but thats the head from it in the picture, maybe an earlier one or something?


cheers
Dave

 

There are some slight differences i think between the v3 and the v4 engine (though both are phase 1.5's), can you confirm if the car is a version 3 (MY97, pre facelift interior) or a version 4 (face lift interior)?

Ta,

Tony

 

Sounds like a piston problem as said above. Check the ringland, I've had one thats melted slightly with no wear to the bore.

 

Pistons will come out without splitting the block - remove the 14mm hex access plug on the front of the block and the small oval plate on the back to gain access to the gudgeon pin circlips on Cylinder 2+4.
You need a long round bar or 1/4 drive extension ( i use 6mm Silver Steel round bar) to drift out the gudgeon pins - remove No.4 pin by going through the front access hole and drifting it out the bell housing end.

Looks more like a Phase 2 head going by the combustion chamber shape - if it has under bucket shims and ED3/ID3 valves, then its originally from an STi V5~6 (WRX if it has outer bucket shims) but will wait for you to confirm the valve codes and shim type.

Mick

 

thanks for that, bud. Thats a big help. The head does have under bucket shims and id3 and ed3 written on the valves, so i take it it's a later engine.

 

If ALL 4 valves leak, do the others? Surely this would say that the lower comp COULD possibly be a valve problem???

 

all 4 ex valves leaked, which puzzled me. The inlets were ok

 

Possibly not been burning right, possibly to rich?? Getting to hot on exhaust cycles? Strange, check the ehad for cracks before taking pistons out, much as I've done it a lot of times, its not an easy job, putting them back in a 5 minute job though

 

all 4 ex valves leaked, which puzzled me. The inlets were ok

 

Yeah, you have STi Version 5~6 heads there Dave - got any pictures of the piston crowns ??
Exhaust valves normally 'let by' due to valve seat recession,tight valve clearances,distorted valves(and they do quite often despite being sodium filled) but would expect to see a burnt valve to drop the comp that much on No4 cylinder.

Mick

 

you reckon i could get away with cutting the valves, then? or is that 'would' a wouldn't?