This is a new set of 8 bronze valve guides and 8 viton valve stem seals for the BMW K100 series '83-'90. Valve guides are precision machined from C63000 nickel bronze (Ampco 45) for superior wear, friction reduction and heat transfer. They have been machined to use a .475" valve seal which is a more robust and widely available type used in both the motorcycle and automotive industry, insuring future availability and wider range of choices. Valve seals are metal clad viton construction containing 5% Teflon for reduced friction and wear. Viton is the leading seal material with the greatest resistance to high temperature and chemicals found in fuel and oil. These are +.001 oversize from the stock guides which is perfect for most applications. Custom sizes can be made to order. Satisfaction guaranteed or your money back! We offer custom valve train components and full cylinder head services. Please contact me if you have any questions. Thanks for looking!