ISKY CAMS and SEVERAL OTHER CAM COMPANY'S sell valve guide cutting tools, you can use to cut valve stems to fit seals, this is usually done with the heads off the engine simply because the tool uses the valve guide as a place to place the center arbor of the tool bit to keep the cutter concentric with the valve center line, so obviously the valve can,t be in the valve guide during the process
in theory brass/bronze valve guides are minimally softer and wear faster,than iron valve guides, but in reality if your using the proper valve seals, and have your oil flow to the upper valve train functioning correctly with reasonably clean oil, theres a thin coat of oil between the valve stems and the surface of the inner valve guides, that prevents any wear if your valve train geometry has the main loads centered on the valves centerline. keep in mind having proper valve train geometry, and having constant clean oil flowing over and cooling the valve springs, and rockers, plays a huge part in valve wear issues.remember the surface Finnish, clearances, valve seals and oil viscosity along with proper valve train geometry and material used in the valves also effects valve wear
btw coating the valve stems with a mixed slurry of marvel mystery oil and crane cams MOLY assembly lube during the cylinder head assembly process, tends to prevent dry start issues with the guides seizing valve stems
WATCH THE VIDEO
http://howautowork.com/part_1/ch_1/valve_spring_22.html
viewtopic.php?f=52&t=181&p=215#p215
http://www.youtube.com/watch?v=d3HksZvdMKg
viewtopic.php?f=62&t=1054&p=1990&hilit=+seals#p1990
viewtopic.php?f=52&t=1053&p=1989&hilit=+seals#p1989
http://www.vettenet.org/vlvseals.html
http://www.newenglandclassics.org/Artic ... cement.pdf
viewtopic.php?f=52&t=61
http://www.iskycams.com/onlinecatalog.html
http://www.iskycams.com/pdfcatalog/2004-05/page15.pdf
http://www.aa1car.com/library/ar696.htm
http://www.ehow.com/how_2110646_replace ... ngine.html
http://www.darklair.com/monte/howto/how ... seals.html
youll want this tool or something similar
http://www.summitracing.com/parts/PRO-66832/
a good example for the oil sludge build-up on the back of an intake valve that results from bad valve seals and loose valve guide clearances
bad valve seals and worn valve guides contribute to most of that build up, not changing oil and over heating and bad valve train geometry tends to add or speed the wear on seals and guides
CRANE CAMS SELLS TEFLON VALVE SEALS,they are commonly packaged on blister packs
