Hi all,

Was hoping for some advice/ help, I’ve recently carried out a compression test on my 1999 Subaru Forester stb and was a little concerned about one the readings, can anyone shed some light or is it nothing to worry about.

Readings:

Cyl 1@155 (concerned reading, is it to low compared to others?)

Cyl 2@168

Cyl 3@160

Cyl 4@165

any advice/help given will be greatly appreciated. Thanks

While I was rebuilding a ej207, I'm sure I read that it was either 15 psi or 15% difference that was within limits in the subaru service manual. 

I know yours is probably a ej205 and I can't remember the exact normal limit but I'd say if you've not got any running issues it will probably be fine .

Unless you're experiencing hi temperatures (possible h.g leak) , that particular spark plug is oily (rings ) or that plug is a different colour (possibly valve not seating) 

You could always google "leak down test" to try and diagnose a bit further , if you're still concerned 

Hi Savage Bulldogs,

Thanks for replying.

Mine is an ej205, when I removed the spark plugs they were all a little wet and on two of them the electrodes were half the size?

car has been running a little rich I think as the smell of fuel has become more apparent recently.

So possible rings? 

Cheers

Wayne

You wanna get a leak down test done rather than a comp test.

Hi Tidgy,

Looking to do that next and then go from there.

just thought I’d add a couple of pics which show what the spark plugs that I removed look like.

cheers

 

Assuming they all have the same part number - those tips have broken off

Hi,

spark plugs have the same part number.

Tips def broken then - does happen particularly if running too hot

Has it got any breathing mods and if so have they been mapped in ?

 

As jay said they look like the tips have melted, if so a bit could've scored the bore or stopped a valve seating correctly. 

 

The compression readings dont seem too bad atm ,so maybe try not heat 7's instead of the standard heat 6's if its modded and mapped 

It’s git a blitz air induction cone and as far as I’m aware it’s not been mapped or tuned in any way? 

If bores are scored what’s the most cost effective solution, re honing or new engine?

If it's running fine I wouldn't worry too much tbh .

It's only a guess that a bit of the plug might be the cause for that one cylinder being a bit low on compression but its not excessively different. 

Costing does vary , a second hand engine would probably be cheaper but you never really know how good a second hand 20 yr old engine is .

If there is a score on a bore , it depends on how deep it is as to whether a hone, 0.5mm overbore or new liner/block is needed .

The main cost of a full rebuild is in the labour to remove the engine ,both heads ,split the block halves, gaskets and rebuilding. 

I wouldn't expect to get much change from £2.5k if I had to pay someone to do a standard spec refresh/rebuild