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Old 05-11-2006, 09:48 AM   #1
TyranosaurusWRX
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Default leak at valves?

Looking for technical experience regarding how to determine how well a valve should seat. Getting to the point, I disassembled my heads (2.0 WRX), cleaned the carbon off of the valve seats and valves with the green scotch brite type material. I put everything back together, valves went back in the same order (ie same seats they were in when they came apart).

I had the idea to check how well they are seating by going into a dark room (absolutely no light) and shining light into the intake and exhaust ports of each head. I really don't know if this an effective practice or not, but I thought I'd try it. I noticed on a few of the valves you could see a very thin crescent of light on one side or another of the valves. By rotating some of the valves, I was able to absolutely close off the light, on others I was not. I tried using a little grinding compound, but it did not do much, maybe even made it worse.

Considering this is metal on metal, am I going to see a total perfect seal?
My engine compression tested fine before I took it apart, but it has always idled very oddly, even before the days of heavier mods. I wonder if this may be the issue. I made a diy leak down tester as well, it seemed to test fine between 3-6%...but I can't verify that the tester is working perfectly. I did notice a variation though in how each cylinder sounded.
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Old 05-11-2006, 10:12 AM   #2
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I did the same thing with my heads as far as cleaning and putting back together. I wasn't careful to put the valves back in the same orientation... i.e. they were in the same location as removed, but probably rotated. I checked the seals by spraying each intake/exhaust runner with brake cleaner 'til it puddled. Some sealed very well, some would sweat through. I figured they'd have to seat a bit once I got them back on. I was more worried about getting the lash off and developing a tick.

But after running them for just a few seconds... enough time for oil to get well circulated, all odd noises ceased. The car has run well and smoothly for 1800 miles if you ignore the spun #4 rod bearing. Spun making some tuning passes during which the car felt stronger than it ever has.

On this breakdown I checked the lash and everything was still within spec.

You might want to do the suction cup / valve grinding compound process again on the stubborn ones. I haven't done that before though so... anyone?
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Old 05-11-2006, 11:03 AM   #3
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Valves should seat and seal close to 100%

If you do a quick re-lap with a ginding compound (best way to re-seal) make sure you check the cam lash afterwards. If the seats are too bad you should get a full head job and give the seats a re-grind
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Old 05-11-2006, 12:02 PM   #4
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Thanks for input on both accounts. I am going to try the valve compound a little more extensively. That damn cheap suction cup doesn't really stick though..I need to figure out another way to spin the valves.

Oh, and as far as setting the cam lash, good point. I am going to convert to shimless buckets anyways so I need to get this situated first.
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Old 05-13-2006, 10:15 PM   #5
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You should take your heads in and have a valve job preformed. While you’re at it get a radius valve job.

The compound will make your matters worse. Compound is used to check for a seal, to make a light shadow on the valve and seat.

I am not sure how Subaru cuts there valves? But every car that I have taken apart, that has been run hard with the stock valve job, the valves are burnt. Not sure of factory quality control or just tuning of the vehicle. The seats still look good, though.
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Old 05-15-2006, 12:02 PM   #6
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Take them to an engine machine shop and have them run a vacuum test on them. They will let you know what parts need to be repalced (if any). That's what I would do as it really doesn't cost that much. Have the heads already been rebuilt?
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Old 05-15-2006, 01:16 PM   #7
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Yeah, but I did it, so taking them apart and putting them back together is no big issue. Actually I have not finished totally rebuilding them considering I need to get this issue resolved before I can re-shim. Once I know that the valves are good I can do the measurements and order new buckets.
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Old 05-15-2006, 02:23 PM   #8
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Quote:
Originally Posted by TyranosaurusWRX
Yeah, but I did it, so taking them apart and putting them back together is no big issue. Actually I have not finished totally rebuilding them considering I need to get this issue resolved before I can re-shim. Once I know that the valves are good I can do the measurements and order new buckets.
Cool...so you want to do everything. Shimming them isn't hard and straight forward out of the FSM but the rest of the head is somewhat out of my scope. Reason I say that is lack of experience and tools. Hell, I don't know if a guide or seat is still good or needs to be replaced.

FYI, I don't know about your "light test" but they should seal completely. Try putting them together and turn the heads so the valve chambers are facing up. Fill each one with water and make sure that you have spark plugs in place. They may not leak at first, but give them several hours and see what happens. It would probably be best to use a dye in the water so you can see where it's coming from, if at all. We did this on mine and had one leaking (very light drip) and it turned out to be carbon not allowing the valve to seat itself.
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Old 05-15-2006, 03:00 PM   #9
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Quote:
Originally Posted by tmarcel
Cool...so you want to do everything. Shimming them isn't hard and straight forward out of the FSM but the rest of the head is somewhat out of my scope. Reason I say that is lack of experience and tools. Hell, I don't know if a guide or seat is still good or needs to be replaced.

FYI, I don't know about your "light test" but they should seal completely. Try putting them together and turn the heads so the valve chambers are facing up. Fill each one with water and make sure that you have spark plugs in place. They may not leak at first, but give them several hours and see what happens. It would probably be best to use a dye in the water so you can see where it's coming from, if at all. We did this on mine and had one leaking (very light drip) and it turned out to be carbon not allowing the valve to seat itself.
Yeah, I do whatever I can myself to save money more so than anything (which I have found can cost you more in the long run) ...and to hone my super-fly mechanical skills.

That's good info, I will try it out.
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Old 05-16-2006, 10:49 AM   #10
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Well, I tried it. After sitting 8-9 hours, only my number two chamber lost any water. More specifically it was the exhaust valve closest to the cam gear. I did notice however that even though none of the others leaked, there were at least a couple of valves (intake and/or exhaust) that did form a ring on the underside of the valve at the seat. You could see it if you looked up in the port. Apparently the viscosity of the water was thick enough to retain the water as none of them showed to have formed a drip.
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Old 05-16-2006, 01:50 PM   #11
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I like the light test better Very super-fly!!

I've heard of people sonically testing valves with these high pitch sources and a very narrow band mic. Can't remember the name of the device.
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Old 05-16-2006, 06:52 PM   #12
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If the crescent of light isn't concentric and you can get it close completely off, I would suspect the stem may not be straight at worst or a worn valve guide. Take some time now to make sure these areas are good to go and save the heartache later on if they aren't.

Props on the light trick....I hadn't heard of it until now but surely will use it at some point!


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Old 05-16-2006, 07:01 PM   #13
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Thanks guys. If I am going to make it worth my money to buy new shims, I am definitely going to have to do this right the first time.


Just a word of advice about the flashlight thing, make sure it's a small thin one that will go right up in there to check all the angles.. because if you just shine it into the port in general it wont be enough.

Last edited by TyranosaurusWRX; 05-17-2006 at 01:45 PM.
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Old 05-16-2006, 07:07 PM   #14
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I say shim'em if you have the heads off. The valves do wear and the factory can shim pretty loose which just leads to a noisey engine that's hard to hear knock on--almost all stock engines would be improved with new buckets IMHO.
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Old 05-16-2006, 11:20 PM   #15
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Quote:
Originally Posted by Hopper

The compound will make your matters worse. Compound is used to check for a seal, to make a light shadow on the valve and seat.

.
sorry?? you say that valve seat grinding paste is not used to make a good sealing surface?? the compound is used to help re seat the old valves if you reuse them! and is something i allways do!


tyr you asked about an easy way to relap your valves? do you lot get variable speed chuckless cordless drills? the valve stem fits rather well in the end and as long as you very gental and go super slow and remember to lap in both rotations it works rather well, also rather than scrape your valves clean give em a 2 hr soak in caustic soda itll wash off without damaging the valves
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Old 05-17-2006, 12:50 AM   #16
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FYI, you can't get caustic soda in the states.
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Old 05-17-2006, 12:56 AM   #17
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Quote:
Originally Posted by eastcoastbumps
FYI, you can't get caustic soda in the states.
serious?? why on earth not lol what do ya use to de-coke engine and exhaust bits?
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Old 05-17-2006, 01:05 AM   #18
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Brake cleaner is very popular. I haven't tried caustic soda on any car parts before. I've got a couple bottles so I'll give it a shot next time I've got something nasty to clean. What else do you use it on?

My Mum is in Ireland right now. I may have to give her a ring and ask her to bring back a few more bottles.
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Old 05-17-2006, 01:24 AM   #19
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anything covered in carbon that need cleaning! its realy good for cleaning out exhausts before repacking, de-coking blocks and pistons
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Old 05-17-2006, 08:46 AM   #20
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Quote:
Originally Posted by TyranosaurusWRX
Thanks guys. If I am going to make it worth my money to buy new shims, I am definitely going to have to do this right the first time.

Good, you got to re-shim to do it right

Also, just something to think about, if you have the heads professionally rebuilt it'll increase performance since they ordinarily cut them at 3 angles, thus increasing airflow.
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Old 05-17-2006, 08:50 AM   #21
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Quote:
Originally Posted by bboy
I say shim'em if you have the heads off. The valves do wear and the factory can shim pretty loose which just leads to a noisey engine that's hard to hear knock on--almost all stock engines would be improved with new buckets IMHO.
You would not believe how tight the clearances on the valve lash became on my 02. I actually checked them last summer, after owning the car for 3+ yrs. I am assuming it just broke in/seated that way, which would put the shim closer (tighter) to the cam lobe. More so on the intake valves. I think you should see approx. .007" - .008+", and I had like as tight as .004" on some of those. I suppose after a long period of time that would loosen up due to wear, but that seems a bit much. I have new aftermarket cams too, so I don't want to mythbust the spit-or-split theory on my shimmed lifters.
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Old 05-17-2006, 08:54 AM   #22
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Quote:
Originally Posted by tmarcel
Good, you got to re-shim to do it right

Also, just something to think about, if you have the heads professionally rebuilt it'll increase performance since they ordinarily cut them at 3 angles, thus increasing airflow.
That would be sweet. But I think too much more debt -related to my car- is going to put a strain on my marriage. At least Visa will still love me.
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Old 05-17-2006, 09:20 AM   #23
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Quote:
Originally Posted by TyranosaurusWRX
You would not believe how tight the clearances on the valve lash became on my 02. I actually checked them last summer, after owning the car for 3+ yrs. I am assuming it just broke in/seated that way, which would put the shim closer (tighter) to the cam lobe. More so on the intake valves. I think you should see approx. .007" - .008+", and I had like as tight as .004" on some of those. I suppose after a long period of time that would loosen up due to wear, but that seems a bit much. I have new aftermarket cams too, so I don't want to mythbust the spit-or-split theory on my shimmed lifters.
Actually, the valve lash tolerances tighten up as they wear. The valves wear into the seats causing the stems to protrude further out towards the buckets.
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Old 05-17-2006, 09:31 AM   #24
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Well, that's what I was saying, they tightened up to about .004". Stock valve lash tolerance on the 2.0/WRX is about .007~.008'' according to the repair manual. On the other hand, if the shim itself wore down but the valve/seat didn't, tolerance would loosen, I imagine.
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