Rockn-Roll

OK, I am down to cleaning and inspecting my valves. The block is clean and ready to be milled, heads are clean and ready to be milled. The intake valves cleaned up nicely and are within tolerance of the valve guides. However, the exhaust valves are so pitted and covered with rock hard residue that I've ordered new valves...I checked the tolerance of the guides in the heads with the good intake valves, so I just ordered stock stems.

However, I noticed that the Clevite valves have tapered stems. At first I thought the old exhaust valve stems were worn by .001" on one end, but they could have been the tapered variety. As a note the intake valve stems are straight (not tapered). On the other hand the Sealed Power, manufactured by Federal Mogul, valve stems are straight. I don't see any advantage to a tapered valve stem...perhaps it's a way to get more oil down the valve stem? I'm going with the straight stem, but on the next rebuild I may change my mind if someone has a good enough reason.

comp

are you talking about just under the valve head??? on the tulup part?

Rockn-Roll

No, the entire stem is tapered. For example, the one in my hand right now measured with a vernier caliper near the grooves where I can see the valve was rubbing against the guide is .341" while toward the valve end is .340".

Since stock valve stems are .340" I figured there was .001" of wear near the valve end of the stem. But, it looks like it came that way.

Anyway, the valve stem on the valves I am ordering are .3414" to tighten up the gap due to the .001" of wear I see throughout the entire engine and the stems are straight....001" on both ends. I was getting a lot of smoke out the exhaust when I would first start the vette...I'm sure now that it was due to the large gap in the valve stems allowing too much oil to flow through to the cylinders.

Anyone know anything about the difference between tapered and straight?

norvalwilhelm

I have never heard of tapered valve stems? They are all straight as far as I know.

Pete79L82

The head end of the valve sees much more heat than the keeper end of the valve. That is the reason for the taper. When we use a straight stem valve we will then put a taper in the valve guide, opening up the port end of the guide an extra .0005 - .0008 to help keep the valve from sticking in the guide on high compression engines that have a lot of exhaust temperature.

Rockn-Roll

Now THAT makes a lot of sense. I'll have to see what the valves I ordered measure out as when I get them...they still could be tapered for all I know. If not, then I figure it will be time to get the guides reamed during the next rebuild...which will be in about three years...after I graduate from college and get a job that will enable me to drop a crate engine in the vette temporarily while I do the rebuild.

This is so sad being without my vette...almost like being lonely. All those cowbody songs should be re-written to replace horse, boots, girl, etc. with vette.