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In order to keep the exhaust valves from burning out, the stem seals on these engines were changed a couple of times. Originally the umbrella type seals on the exhaust valves were found to allow more oil to go down the stems than not having any at all. They slid up and down on the guide and acted like a little oil pump. The first service bulletin on this problem said to leave the seals off the exhaust valves. The square seals are to go on the intakes. With the valve spring compressed you work the square seal onto the second groove, put the keepers in the top groove and release the spring compressor. The seals are to keep oil from running down the stem from the top of the spring. The last service bulletin dealt with a new style exhaust valve seal. The exhaust guides have to be machined on top to accept the newest style seals from IH. They fit over the guide and seal on the stem. If the guides are not cut lower they will catch in the groove that the unbrella seals were in originally. The other option is to have the guides machined and have Perfect Circle stem seals put on. They are similar to the IH seals but take a different guide cutter to make them fit. The IH cutter has a stop that allows cutting until the guide is the correct height from the head. On the PC cutter you will need to make sure the guides get shortened enough so the seal will not catch on the lower stem groove. The problem with the exhaust valves on these engines is the oil going down the exhaust valve stem gets turned to carbon and builds up on the lower part of the stem. A short time under heavy load will cause the temperature of the valves to increase and the stem will expand enough so that the carbon buildup on the stem keeps the valve from seating completely. When that happens the air going past the open valve will burn it like a cutting torch. It only takes a second to burn out the valve. This is also the reason that use of low ash oil is so critical on these engines. The low ash oil is much less likely to leave carbon deposits on the stems. When choosing oil look for something that has 1/2 percent or less ash content.
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