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Old 11-21-2015, 03:17 AM   #1
92SS
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Default False knock from loose valve lash with aftermarket cams?

So I have a built motor running GSC S2 cams and GSC beehive springs. Getting false knock between 2000 - 3200 rpm at out of boost loads which is dropping spark timing by 12 deg (max allowed) and bogging the engine. I'm thinking its caused by the valvetrain since that's the same rpm range at which the valves are noisiest. It makes a lot more noise than when it was stock.

Right now I have valve lash at .007-.009 intake and .013-.016 exhaust. Cam card says to use .008 intake / .010 exhaust. Engine has around 5000 kms on the build.

The stock spec for sodium-filled exhaust valves I'm running is .014. Is there any risk of burning a valve if I bring the lash down to .010? Maybe average out the specs and shoot for .012? Car is mostly street driven and I want to do the occasional track day. Turbo is sized for 60+ lb/min.
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Old 11-21-2015, 09:46 AM   #2
spoolinsti05
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Get the adjustments in spec. The closer the better.
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Old 11-21-2015, 11:14 AM   #3
ALOKIN
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Are you sure that's what's causing it? ~.015 exh isnt terrible. I have my exh at ~.013 and there's no noise or false knock issues.
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Old 11-22-2015, 08:31 PM   #4
92SS
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Quote:
Originally Posted by spoolinsti05 View Post
Get the adjustments in spec. The closer the better.
Well which spec? .014 or .010? I guess since I'm already close to .014, then I should just try .010 since that's probably what the cam ramp rates are designed for.

My only concern was the .010 spec is for regular valves but I'm running sodium filled so I have less safety margin with regards to burning the valve.
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Old 11-22-2015, 08:32 PM   #5
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Quote:
Originally Posted by ALOKIN View Post
Are you sure that's what's causing it? ~.015 exh isnt terrible. I have my exh at ~.013 and there's no noise or false knock issues.
What cams are you running? I also had no problem with .014 exhaust on stock v9 EJ207 cams. They were a bit noisy but no knock sensors issues.

My other option is reduce the knock sensitivity in the tuning but I always like to address the mechanical issues first if possible.
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Old 11-22-2015, 08:33 PM   #6
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Billet gsc S1s
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Old 11-22-2015, 10:06 PM   #7
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Hmm, S1's probably have equal or more aggressive ramp rate with the shorter duration.

Found I can't get one of the lifters out, it moves freely for the first .2" but then hangs up on something hard (makes clink sound). Even a big magnet didn't work. Maybe it bottomed out on something and mushroomed the edge a bit. This could be the cause of the noise. Gonna be risky to cut it with a dremel...
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Old 11-23-2015, 09:36 AM   #8
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Yikes. Can you weld a bolt to it and use a pulley puller?
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Old 11-23-2015, 02:17 PM   #9
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vise grips
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Old 11-26-2015, 08:40 PM   #10
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Ok update time.

Vice grips were a no go, couldn't get enough space to pull on it. So I ground a slot in the side of the lifter and pried it out with flathead screwdriver.

Underneath I can see the jaggy edge of the valve spring sticking out and its not sitting right on the retainer anymore.

Think I'm going to pull the engine and remove all valve springs for inspection.
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Old 11-26-2015, 09:50 PM   #11
Patrick Olsen
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FWIW, I used to have timing being pulled through the mid-range on my N/A EJ25D with aftermarket cams. I never did figure out what the issue was - it was stock short block, stock (ported) heads, Cobb reground cams. Even running 93 octane and even at light load it would pull timing - it was very noticeable in the ol' butt dyno and on the actual dyno.





(I only had primitive data-logging capability, no way to see knock counts.) For a while I dummied the knock sensor with resistors and it worked like a champ. Eventually I went back to running a knock sensor and it didn't pull the timing anymore - I don't know if the valves had tightened up over time (and thus weren't creating noise anymore) or what?

Last edited by Patrick Olsen; 11-28-2015 at 11:58 PM.
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Old 11-27-2015, 02:28 AM   #12
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Yeah, that graph shows exactly what I feel happening. Retards timing up to the max allowed (-12 deg) randomly at the start of a pull. It happens during regular driving too, maybe 2-3 times for a 30 min drive.

On a side note, on my previous build I had enough piston slap when cold to trigger the knock sensor too. To counteract this I raised the knock control enable temperature which worked perfectly.

I will call up GSC in the morning and see what they're going to do about the broken spring.
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Old 11-30-2015, 11:51 PM   #13
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sodium filled vavles stay cooler don't they ....so that would mean they expand less so .010 should be fine. yikes I just saw you had a broken spring ...changing spring is a "B" with the heads off the motor . I hope you have one of those sweet Subaru billet spring compressors...I did mine with a DIY tool and a regular type spring compressor ...not fun but doable.next time i'd pop for the bolt on compressor.
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Old 12-01-2015, 02:39 AM   #14
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Well the sodium valves transfers heat better, so the stem will heat up more vs a solid valve. I think it may grow more because there is more of the length getting heated, but that's just my theory. I should ask GSC about the lash see what they say.

Yeah I have the Company23 bolt-on spring compressor on order. Last time I assembled them on my drill press lol. Made it really easy using the lock.

So GSC got back to me and there's a bunch of reasons why it could have broken which I can't confirm until I get them out. Anyway once the tool shows up I'll remove the springs and send them to GSC for testing. I haven't seen any other EJs break a spring so I assume it's a rare one-off occurrence. They did say if a spring fails it's usually within the first few hundred miles, so that kind of alleviates my fears about the rest of the springs.
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Old 12-01-2015, 07:08 PM   #15
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I just bought a set of Brian Cower springs and Ti retainers ,they are working great.
did you make any kind of tool to use your drill press to swap springs?
I used a piece of alum pipe with a window cut out in it to do mine ...it was a paintheass but it got the job done.
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Old 11-14-2019, 07:24 PM   #16
pcampbell
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I am getting knock from 5200+ on my Delta 1500s. I've pulled between 5 and 10 degrees of timing and still the ecu says it is knocking. I'm going to try 1 last ditch ,fat AFRs and 10deg total advance up there (I was running 22 before Deltas) before I call it false knock. Is there any work around for this?
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Old 11-15-2019, 03:21 PM   #17
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Quote:
Originally Posted by pcampbell View Post
I am getting knock from 5200+ on my Delta 1500s. I've pulled between 5 and 10 degrees of timing and still the ecu says it is knocking. I'm going to try 1 last ditch ,fat AFRs and 10deg total advance up there (I was running 22 before Deltas) before I call it false knock. Is there any work around for this?
What knock detection equipment are you using to verify?
Which ecu are you using and how are the knock thresholds set?
Throwing fuel at it and pulling timing out can cause high egts and start to create other issues.
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Old 11-15-2019, 06:12 PM   #18
pcampbell
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Stock 05 DBW ECU and stock knock sensor. I can't adjust knock sensitivity.. it's just by load and by rpm on or off. It seems to have stopped knocking when I pulled enough timing. From 20.5 degrees advance down to 14.5 and it is no longer knocking. It seems like a lot of timing to have to pull but I don't know what is expected. It is clear that there is a lot more air going in because it leaned out a lot. Guessing it's about +25-30whp gain based on MAF readings @ redline (it is a centrifugal supercharger) over the Stock cam setup with 20.5 degrees of timing at the same RPM. It is a 10:1 EJ25 motor (running 33% water meth) so this may all be normal behavior. I've never done cams before...

Last edited by pcampbell; 11-15-2019 at 06:29 PM.
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