Nathan Plemons

I just thought I would share some observations that raise some interesting questions. After having my heads CNC'd and new valves installed I find myself with a good deal of leftover parts.

I brought a pair of valves up here to the office to use as decorations. I've been looking at them and have noticed something interesting that tends to make one ponder. For example, the intake valve has deposits around the back of the valve while the exhaust does not. I suppose this makes sense because the gasoline mixture is hitting the back of this valve while the exhaust flows the other direction over that valve.

So then look at the combustion chamber side of the valves. I notice that the intake valve has deposits on that side while the exhaust valve has virtually none. Can I assume that because the intake valve is closed after combustion that the exhaust valve just attracts less depostis because it is actually open at that time, allowing the exhaust gases and solids to exit the valve rather than settle on it?

I also have to wonder about the long term usage of swirl polished valves. Sure when they are brand new they might help out some, but after the deposits start to gather on them I can't see them being effective anymore.

I always run premium gasoline of a good quality, at least I feel like it's a good quality, but I have some deposits regardless. Now obviously I can't take my engine apart every week and see how my valves are doing as far as deposits. I've got 8 intake valves with similar deposits, I was thinking about buying 8 different types of fuel system cleaner and soaking the valves in the stuff, and see which ones do the best job of breaking the deposits loose. Would anybody else be interested in an experiment like this?

0ski_dwn_it

I think what you are seeing is normal.

The deposits on the back of the intake could also be oil burned off residue from leaky valve seals.

I have a valve from the miller high life top fuel dragster. This valves live was probably only ~2 minutes of runtime max. It looks like a mushroom! I too had it in my office.

:cheers:

Nathan Plemons

I figured it was normal enough. My motor has been extrememly healthy so far. I'm just trying to make sense out of what I'm seeing. The thing that seems so wierd to me is how two valves, which are in the same combustion chamber can have such different deposits on the combustion chamber side.

SPD DMN

My stock valves looked like that as well. It takes a long while for the deposits to build up anything major though. When I pulled my heads after having them redone with around 2500 miles on them, they were a little discolored but they did not have any deposits on them whatsoever. I actually used a buffing wheel to clean off those old valves that had that crud on them (ended up not using them though, just playing around) and that stuff is harder than you may think.

SPD DMN

The intake valves will have the deposits from the entering gasoline. The exhasut valve gets much hotter than the intake valve because it gets surrounded by the hot gasses leaving the combustion chamber. That is why exhaust valves almost look burnt and intake valves generally have a little glazing on them.

65Z01

Consider what your intake looks like.

The incomming charge is low (relatively) temp with EGR components that sits momentarily on the back of the intake valve; the outgoing charge is much higher temp and moving much faster.

Do the deposits on the OEM valves look to be deeper than the "swirl" on the backs of the new valves?

Nathan Plemons

Would that also explain why they are heavier and seem to have a thicker base?

One more question, what's up with the grooves for the locks? Why does the intake have two and the exhaust always have one?

Nathan Plemons

Yes. The swirl on the valves isn't really very deep at all. I guess that's good or it would tend to actually trap deposits. Don't get me wrong, I don't have big chunks of deposits or anything but it would be enough to disrupt the swil effect I would think.

Here is the URL of a picture of one of my new valves It's just enough out of focus that you can't really see the swirl pattern.
http://www.wku.edu/~nathan.plemons/heads/valves.jpg

65Z01

My stock L98 intake and exhaust valves both have double grooves, the lower is for the O-ring upper oil seal and the upper is for the keeper retainer ring.

Nathan Plemons

Upper oil seal? That's a new one on me. The LT1 has one valve seal that slides down over the valve and snaps into place around the valve guide. This is why I posted this thread, I figured it would turn into a nice knowledgebase.

Nathan Plemons

What does the Y on the bottom of the intake valve mean? I would first think for the Y body car, but this valve is no different than an F-body valve, I'm pretty sure they have the Y on them as well.

Can you guys tell that my job is boring? I get to sit around and intensely study a pair of valves.

scorp508

They have a Y on them? I don't remember seeing that on any of mine.

Nathan Plemons

Maybe L98's don't. But mine sure do.

sinistervette

The exhaust valves need to be heavier/thicker due to the fact that they need to withstand 2-3 times the heat of the intake valve. The exhaust valve opens into the just burned fuel/air mixture, allowing all the gasses to exit throuhg the exhaust. During this time, the intake is closed, only getting a flash of heat against it's face. Then when the intake opens, is has a cooler fuel/air mixture going past it actually cooling it down. This continuos heat/cooling is the main reason for deposits building up on intake valve, and just being burned off of the continually hot exhaust valve. As for the oil seal grooves, the exhaust valve doesn't actually need to have a seal on it, that is why you only have a o-ring at the most on the exhaust valve. The intake valve needs to have the best seal possible, in the "old days" :D they would install both a o-ring and umbrella type seal! Since the positive type teflon seals came along, you no longer need o-ring or umbrella seals, the positve ones seal just fine. The reason for the exhaust vale not needing a seal, and the intake needing a good seal is vacuum! The exhaust valve only sees pressure on the stem area of the valve, from the exhaust gasses being forced out of the cylinder. The intake however, sees a vacuum or draw as the piston goes down into the cylinder, pulling the gasses past the valve stem into the cylinder. Also, just a little note. If you have positve seals on your exhaust valves, make sure that the valve guide is a sintered bronze type(self lubing like a pilot bushing), and not cast. If you seal the exhaust to good, no oil will be able to get into valve guide and lubricate it. The exhaust valve guides tend to tighten up, expecially under hard use :D , and need oil to keep them from galling and inevitably seizing up! I learned the hard way, and had an exhaust valve hang open and introduce itself to the piston! :cry Very costly learning experience! Oh well, poo happens! :yesnod: You shouldn't need to worry about deposits on the stainless swirl polished valves, all of them I've used and worked with over the years stayed very clean. I had one set come back to me after 5 or 6 years that had some deposits on them, but the guy had put 60000+ miles on the motor! :cheers:

sinistervette

It's just me again! I forgot one other thing about the thickness of the exhaust valve. The egde thickness around the head of valve is refered to as the margin. If the margin is to thin on an exhaust valve, it will burn out quicker. Kind of like using a torch and holding it by a piece of 16ga. sheet metal, and then by a piece of 1/8". The 16ga. will burn out almost immediately, and the 1/8" will withstand quite a bit more heat! Another lesson learned the hard way! :D DON'T LET ANYBODY CONVINCE YOU TO BACK CUT THE EXHAUST VALVE FACE TO INCREASE FLOW! :lol: :lol: I did it to a pair of heads I was experimenting with, and lets just say that a flatbed bill from "BFE" Kentucky to Holland Michigan cost $320+! :eek: :cuss :cry

sinistervette

If I understand correctly, I was told that the letter designation was only on certain valves that GM was checking up on the tooling that forged the valves. Evidently they were having some issues with quality fromone of thier suppliers. It was a long time ago, but I'm sure that was how it went. :cheers: