Guest bastaad525 Posted October 25, 2004 Share Posted October 25, 2004 Okay maybe this is a silly question... I was just wondering, if you were to adjust the valve lash clearances to be tighter than spec, would this not result in slightly more lift and duration, and hence make slightly more power? I'm talking, if hot setting is .010 and .012 intake/exhaust, then how about doing .008 and .010, or maybe even a little tighter? Tight enough where it wouldn't cause problems i.e.: not so tight that the cam is resting on the rockers full time when cold? Of course I know this might bring some negatives... like a lumpier idle, but, would there be any other drawbacks you guys could think of? I mean... would it break anything or risk any damage? Also, one more question... I guess it's time to adjust my valves as they're getting pretty loud.... the odd thing is, when the motor is cold it is dead quiet, all you hear is injector noise, then as it heats up it starts tapping louder and louder. This means they are adjusted to loose right? Of course I'll be adjusting them with a feeler gauge, but was thinking of going just a little bit tight on them to quiet everything down... just not sure if I have that right. Quote Link to comment Share on other sites More sharing options...
Thumper Posted October 25, 2004 Share Posted October 25, 2004 I ran my 83 280zx n/a tight for about a year. I forget what gap I ran. I had heard that it would cause more wear and tear, but about a month ago when I sold the car I took the valve cover off and it looked the same as it did a yr ago. On the other hand I really didn't notice any difference in power but the valve noise was much quieter than my previous gap I ran. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted October 25, 2004 Share Posted October 25, 2004 yeah I wouldn't expect a really noticeable increase in power I gues... not from only .002 or .004 tighter gap... really just want the thing to quiet down more than anything. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 25, 2004 Share Posted October 25, 2004 The valve needs to sit on the seat firmly to transfer heat out of the valve and into the head. If you adjust the valves too tight you'll burn a valve. That being said, the cam card that came with my cam said .008/.010 hot, so there is a little variance out there. A lot depends on the guy behind the feeler gauge too... easiest thing to do is to get the stepped feeler gauge so you know you're going tight enough. The right one fits, but the thicker part doesn't. http://shop.store.yahoo.com/bradystools/fegablty0to01.html Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted October 26, 2004 Share Posted October 26, 2004 yeah I've noticed when I used to have other people adjust them for me... everyone goes by feel and interprets their results differently. I usually tighten the gap just until the feeler can't go in and then loosen just a tad so I can get it in there with a little bit of force, so it's tight and has some drag on there. So if I go even .002 tighter than spec to quiet the tapping is that enough to risk burning valves?? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 26, 2004 Share Posted October 26, 2004 I don't think so. I think .002 is pretty safe. Especially if it takes you a long time to get through them all. The longer it takes you to finish the looser they'll be. Not passing judgement or anything, just saying. I was taught to hold both the 14 and 17 in my left hand, and the feeler gauge in my right, and kinda tighten and then lock it down all in one motion with the left while constantly feeling the resistance with the right. I also use a piece of chalk or sometimes a dot of white out to mark which ones I've done, and do it as quickly as I can so the engine doesn't cool down too much. I'm still not that good at it to be honest, probably because I don't drive my Z enough. I know a guy who can do all 12 valves in an L6 in about 10 minutes, start to finish. He always pointed and laughed at me because it took me at least twice as long, probably more like 3 or 4 times as long now. I'm out of practice Of course he races a 510, worked in a Z shop for a couple YEARS, then became a Nissan tech... IIRC he used to say that if the temp gauge went under 160 you were going too slow (Autometer). If you're really slow you might want to wait until they're totally cold and do them .002 tighter than the hot spec. That's the way they do 911 valve adjusts and it seems to work for Gunter. If they're still noisy you can always pull the valve cover and check the hot gap, and tighten your cold gap as necessary. Quote Link to comment Share on other sites More sharing options...
DAW Posted October 26, 2004 Share Posted October 26, 2004 You could fudge toward the tighter side of spec but it's not worth the risk of burning a valve to go tighter than that. I set valves by grossing in on the setting before I finalize, e.g., if the setting is to be 0.010", I check with 0.009" and make sure it passes, then confirm that 0.011" won't pass without significant pressure, then go for the consistant drag with the 0.010" feeler as the fine tuning tie-breaker. I set cold and double-check hot. Eventually you get the feel for the action of the final snug of the locknut in that cinching down doesn't bring the post down; it actually elongates the effective length of the post a bit, and you can plan accordingly. DAW Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted October 26, 2004 Share Posted October 26, 2004 yeah I got my technique down pretty good, I think. Timed myself once, from the moment I shut off the motor and went to remove the valve cover, until the moment I checked/finished adjusting the final valve, was about 20 mins. I figured that was plenty time to get them done before the motor cooled significantly to affect adjustment. I too am out of practice though, and was planning on doing them cold to start. I finally figured out just the right tightness to set to so that tightening the locknut got them just right... man that used to PISS me off though! Always used to tighten the locknut and then the feeler wouldn't fit.... #*@!^!!!! So the valves really transfer some significant amount of heat to the head during the tiny fraction of a second they stay closed? It seems odd that tightening up the gap a smidge would significantly affect that (changing the amount that the valve stays fully seated by mere thousandths of a second I"m sure?). But I'm sure that info was confirmed when someone was rebuilding a head because of it Quote Link to comment Share on other sites More sharing options...
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