I'm a little confused on this subject. When I was reading SlantSixDan's post on adjusting valves, he lists the specs as being somthing like on the order of between .010-012 intake and .020-.022 exhaust, or something like that, I would have to look that back up again to be exact. But it seemed as though he implied that on an older engine it was up to the individual engine as to what the best setting would be. The specs I found were .010 and .020 only and that was it with no room for adjustment. So, if there is a range and I stay in that range then am I really de-lashing the valves and If not why did he say I would be de-lashing them even after he said to others in the past that it was just fine? This doesn't make any sense to me! Please bring me up to speed on this, is this a controversy, contradiction, exception or what?

Thank's for any clarity on this,
74

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Where ever you go there you are!

When lash is backed off, that is it’s loosened it changes the lift height, and opening & closing event at the valve by opening it a bit later, and closing it a bit sooner. This change by loosening reduces overlap, in other words, the time, or rotational degrees that an intake and exhaust valves are both open at the same time during filling of cylinder with air / fuel mixture. The result is sometimes a smoothing of idle, and a bit more low rpm torque.

Personal example:
I have a fairly lumpy cam that produces a big lope at 800 rpm in gear, and due to some carburetor tuning issues I was unable to idle engine down low enough to adjust lash while running. I had to set lash hot with engine not running, which no matter how many times I adjusted the valves there was a halfhearted almost miss below 1500 rpm from one cylinder. In other words, on top of the lope, there was consistent a weak exhaust pulse from one of the exhaust pipes. It’s easy to hear with only three cylinders firing down that one pipe.

After a major frigging two day carburetor tuning session, I got the engine to idle down to 500 rpm, and stay running. At 500 rpm it is easy to adjust lash, and engine oil more or less stays in lifter area, and off inner fenders & wind shield although it does rock around a bit at that speed. I was able to adjust that odd weak half miss out in just a few minutes during a relash. You can hear the change in ticking, and exhaust note as the lash adjuster is turned. All valves got fine-tuned, resulting in less ticking clatter, and much improved idle.

The reason for the slightly different adjustment on one valve from the others… I don’t know; cam height, slight rocker ratio difference, combustion chamber inconsistency?… I can’t say. But, a carful change in lash will often make a big difference in idle quality.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks wjajr,

Now I really get the purpose of the valve lash adjustment. Like I said I was green on this one! I was just thinking that it was just for the purpose of taking out play between the moving parts (rocker arms and valves), not that it was changing the operatin of the valves in relation to the other parts. This is very interesting! I'm going to let it soak in a bit before I do the valve lash adjustment.

By the way I just ordered up 2 of the three books SlantSixDan refered to and they look pretty good (reminds me of the one's in high school that I should have kept), Thank's again Dan for the good information. I couldn't afford the FSM yet, but I'll be getting that asap!

So now this helps me because although I know I have to replace the carburator (and I don't have the money to do that right now), it gives me the oportunity to lower the emissions produced in the short term and a little later replace the carburator and in the process still pass the test and use the car without damaging other parts of the engine.

Ok, I thank everyone for their help on this (and I mean everyone!) I know what I have to do now and I'm pretty sure this will do it.

Thanks,
74

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Where ever you go there you are!