In ordering ‘60’ pound springs for my 5.9, I see there are valve guide seals available, which are not even discussed in my Service Manual. Is this a necessity as our engines age or just another gimmick?
The cylinder heads do have valve guide seals and it can be prudent to replace them if you're tearing into it. Seems like there was more than one style of seal used. Do you have the serial number? If so I can look up the part #.
Ed, according to Quick Serve the head gets 2 different ones. It take 6 of part 3901097 and 6 of part 3921640. I'm assuming one is intake and the other the exhaust but it doesn't specify which. I checked my 4bt industrial catalog and they have the same seals. 3901097 is for the intake valves and 3921640 is the exhaust valves. Since the exhaust get much hotter that one is probably made of a different material. Below is the diagram of your head. Part #8 is the valve seal.
PS. Most places show the 3921640 can be used on both valves. Probably a better grade seal. See prices ranging on that one from about $8 each to $1 each. Someone is making a serious profit. Of course the $8 one come in a Cummins package and the cheaper ones are aftermarket.