I have my EJ205 out of my 2003 WRX. I pulled the engine in the first place to troubleshoot a 90% pressure loss in Cylinder 4 (measured via a leakdown test with the Engine still in the car). The remaining cylinders all had ~5% pressure loss. After removing the heads, I found that Cylinder 4 had a burnt out exhaust valve. I took this opportunity to replace:

  • All intake/exhaust valves (lapped)
  • All valve springs
  • All valve stem seals
  • Ordered new bucket cover (shims) to put all valves in spec
  • New head gaskets on head install

After putting the heads back on, getting the timing belt together, and valve covers on, I decided to run a leak down test while the engine is out and before I do any further work.

Here are the results of the leak down test, each cylinder couldn't exceed 75 psi. Using an endoscope, I put each cylinder to TDC for each test:

  • Cylinder 1: leaks ~90% pressure loss from intake valves
  • Cylinder 2: leaks ~25% pressure loss from both intake and exhaust valves
  • Cylinder 3: leaks ~25% pressure loss from exhaust valves
  • Cylinder 4: leaks ~25% pressure loss from exhaust valves

This is the second time I've done a valve job and I'm a bit alarmed. Did I mess things up that bad? Is excessive leaking on a new valve job (with engine outside of car/before first start up) expected?

My first guess might be the timing belt? After installing the timing belt and engaging the tensioner, I verified that all the timing marks lined up. Any other theories before I remove the heads again?

Edit: Verified timing belt is aligned correctly.

  • Either you have not lapped them properly or you have the timing wrong.
    – Solar Mike
    Jul 31, 2020 at 7:19
  • Or not shimmed correctly.
    – HandyHowie
    Jul 31, 2020 at 7:55
  • Are you rotating the engine while doing the leak test? If so, are they leaking through the entire stroke? The air is definitely leaking out of the exhaust/inlet ports?
    – HandyHowie
    Jul 31, 2020 at 7:58

1 Answer 1


You state you "lapped the valves" when replacing them? If you have replaced the valves, you need to do more than just lap the valves. You actually have to do a valve job. This entails machining both the valve seat and the valve itself so they will mate properly. Once this is done, then you lap the valves in to provide the seal you're looking for. The machining procedure is more than you can do at home. Since you make no mention of having this done, I believe this is where your problem lies.

  • 1
    Thanks, I checked with my local machine shop as well and they've confirmed this. Heads are at the shop now! Thanks!
    – Joe
    Aug 1, 2020 at 1:20
  • 1
    Glad you're getting them fixed. Hope it all goes back together well and with no more leaking :o) Stop in at The Pitstop and tell use how everything went! It's our chat room where we are a lot more open to talk about things like that. Aug 1, 2020 at 1:25

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