I have adjusted my valve clearances 4 times in the 14K miles I've had it. I started out using an incorrect method, so my clearances were larger than spec (https://www.s2ki.com/forums/showthread.php?...?threadid=82493). After reading some replies to that thread, I decided to experiment with valve clearances BELOW spec on the intake valves (from .008" to .006" between the adjuster screw and valve spring retainer - which resulted in an immeasurable clearance between the roller rocker and the cam lobe ). I didn't really notice any improvement from this. I am guessing that the reduced intake clearances didn't matter since my exhaust valves were still at spec. I'm wondering if the exhaust valves are now the "bottle neck", and I might notice an improvement if I reduce their clearances by .001" or .002". I am hesitant to do this, since it will increase the likelihood of burning a valve.

I know that the intake valves are cooled by the gases that flow around them, while the exhaust valves are heated by the gases that flow around them. If that is true, it seems that decreasing the clearances (increasing lift and duration) could be more detrimental to the exhaust valves than the intake valves. However, it also seems that if the exhaust valves were that sensitive, you would not be able to safely increase lift and duration on the exhaust valves via aftermarket cams.

What do you guys think the risks and / or benefits of this would be?

 

I believe that the spec is the range that the mechanism will work and valves seat properly. So you probably want to stay close.

I have heard of people adjusting the intake to the minimum looking for more lift, and the exhaust to the maximum looking to allow maximum seat time to cool the valve.

My guess is there is not enough benefit to risk additional wear.

 

Do you think that Honda designed the spec to tolerate 100K miles worth of change, which might mean that a more frequent, carefull maintenance could safely allow for tighter clearances on both intake and exhaust?

 

i'm sure UL could give the best advice about this. where is Mr. owl anyway

 

The whole point of the clearance is to insure that the valves will close all the way and not ride open a little bit. The only issue with burning valves is if they are not open long enough, i.e. you run too MUCH clearance.

The only way you could burn a valve is to run too little clearance, and I think you would have to run massive amounts of clearance (on the order of .020") to actually burn valves over time. Keep in mind that you are proportionally affecting lift- I'm not sure what it translates to (you know, though, experimentally, right?) but I know that the power is affected little enough by .002" that I suspect it's affecting the lift about the same amount. You'd have to drastically affect the lift to start burning valves.

I have been running .002" tighter than stock clearance (I/E) on the last 3 Hondas I've owned, and have raced them all. No problems yet... it's just enough to reduce the ticking to a barely-audible level and improve power a bit.

 

[QUOTE]Originally posted by marcucci
[B] The only issue with burning valves is if they are not open long enough, i.e. you run too MUCH clearance.

 

Sorry... mistyped. That should be "too much...too much."

Let's say the stock valve lash is .008" on the exhaust. If the lash is .010", there is more clearance than stock, which means that there is more distance between the cam lobe and the rocker, or the rocker and the valve. It means that you have decreased your max lift and max duration, effectively reducing the ability to flow exhaust out of the head.

Does that make sense now? Sorry.

 

[QUOTE]Originally posted by marcucci
[B]Sorry... mistyped. That should be "too much...too much."

Let's say the stock valve lash is .008" on the exhaust. If the lash is .010", there is more clearance than stock, which means that there is more distance between the cam lobe and the rocker, or the rocker and the valve. It means that you have decreased your max lift and max duration, effectively reducing the ability to flow exhaust out of the head.

 

Yeah, the valve, particularly the exhaust valve, cools by contact with the valve seat. Decreasing gap increases lift, decreases seat contact time which could burn the valves.

UL was going to decrease the gap on his and redyno sometime.

 

[QUOTE]Originally posted by Prolene
[B]Yeah, the valve, particularly the exhaust valve, cools by contact with the valve seat.