First time using them was back in the late 1970’s early 1980’s. Back then to get our junk to run 10.0’s high 9’s we ran stock valves and big cams. .695 mushroom tappet and .750 lift roller cams. If you didn’t use lash caps it rolled the valve tips so bad you had to destroy the valve to get it through the valve guides. The next time I had to run them was long before geometry issues were even talked about and very early use of Edelbrock heads and Harlan Sharp rockers I was bending pushrods way more often then I should have. A well known Stock or Super stock racer told me to run lash caps. It fixed my issue enough that I never bent another pushrod. There are two more times I use them but that will stay in my vault.
