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Old 04-17-2014, 06:06 AM   #1
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Default Frequency of valve adjustment on race motor???

How often are you guys with race motors adjusting valve lash?

I have some pretty aggressive cams and was thinking of checking them now with 8hrs on the new motor. How often from here on out?
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Old 04-17-2014, 08:44 AM   #2
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It is one of the things I do after a National event as part of my "post race inspection" I also keep a log of where each valve was. Keeping a close eye on lash and keeping a record of it, helped me find and fix an issue with the motor last year that would have resulted in a massive failure. I had two intake valves that "tuliped" and I was able to see it in the valve lash before the valve broke and destroyed the motor. The process takes less than an hour and imho is very worth it.

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Old 04-17-2014, 09:13 AM   #3
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I did it after every race- which was usually 6-10 hours of track time. With pretty aggressive cams and shim-under-bucket.
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Old 04-17-2014, 12:44 PM   #4
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Thanks guys!

I like the idea of creating a record and looking for unusual patterns of wear. With the 6 speed trans I still struggle with mis shifts and over revs.

TNT: what were the symptoms of the tuliped valves? Were those 2 constantally getting loose? Why do you think that happened? Over revs?
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Old 04-17-2014, 05:48 PM   #5
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Exactly the opposite. The lash was getting tighter. It is to be expected that the valve lash will tighten up a small bit on a brand new valve job. But it should tighten up 1 or 2 thousandths and stabilize. I had two that started to tighten up 2 to 3 thousandths a race. After the second time seeing get this tightening I knew there was something serious going on so I pulled the head and found the valves to be very worn and on the verge of total failure.

My theory as to the cause was weak valve springs. The car only turns somewhere between 7500 and 8000 rpm....but is making 23psi boost. I think the boost pressure and high rpm was allowing the valves to float on the seats causing the erosion. I had the head rebuilt, put in stronger valve springs and everything has been fine. I lash my intake valves at .010 and the exhaust at .014 for what that's worth.

I have accumulated a small stash of shims and have gotten pretty good at changing them. My behavior is probably a little OCD....but I spent 10 years working in aerospace propulsion where you checked everything twice and then a 3rd time for good measure. You could question the need....but I have already saved the motor once.

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