This additional heat is caused by the increased power, and the increased speeds demanded from today’s engines. The federal exhaust emission laws have also required a much leaner fuel-air mixture than before, which bums at an increased temperature. We also find the new non-leaded fuels increasing combustion chamber temperatures.

These temperature increases directly affect valve guide wear. The valve is in direct contact with the combustion chamber. The heat the head of the valve is subjected to must be dissipated through the valve stem, guide, and subsequently the waterjacket. So as the temperature is increased it becomes more and more difficult to have controlled lubrication and prevent guide wear.

There has also been an increase in friction in the valve guide area. The camshaft lift has been increasing, as well as the rocker arm ratio and valve spring rates. These create increased thrust on the valve against the guide and the increased stroke generates more frictional heat and wear.

The cylinder heads on most automotive engines today, are cast with the valve guide a permanent part of the casting. This type of guide is referred to as a integral cast guide. Excessive wear on this type of guide has caused the head to be scrapped and replaced.

There have been for some time, methods of valve guide repairs for heads of this type. One is boring out the guide and replacing with a valve with on oversized stem diameter. A second is guide knurling which displaces the metal in the guide closing the bore up, and it is then reamed to proper size. These repairs however, are applicable only in guides with less than .006 wear.

For guides worn in excess of .010 only very time consuming repair has been possible. The guide had to be precision rebored, centering from the valve seat and then resized with a cast iron sleeve to bring the size back to standard. This operation demands a large investment in equipment and valve guides.

Hastings has developed a method of guide repair utilizing a phosphor bronze sleeve to bring the guide back to standard size.

Phosphor bronze Is an excellent bearing material, having far better wearing qualities than the cast iron guide, as well as having superior heat transferring ability.

The worn guide is bored to desired oversize, and the universal length bronze sleeve is driven into the guide. The sleeve is then trimmed to the proper length. A spiraling arbor is passed through the sleeve which provides a positive lubrication area and also forms the sleeve firmly to the valve guide bore insuring proper cooling and heat dissipation. The guide sleeve is then reamed to a finished diameter which can be as little as .0005 larger than stem size with no danger of valve sticking or seizure. When finished the guide has a far better precision fit, with wearing qualities many times superior to that of the standard cast iron guide.

(P11)