Doc Talks: Evo Cylinder Stud and Head Bolt Update

This week, Doc Harley demonstrates the evolution of cylinder studs and head bolts.

Now, here's a brief video summary from Doc;

Allow me to share some lessons I've learned over years of working on Evolution or Evo engines. One common problem customers would experience is failing base gaskets, usually due to issues with the cylinder studs or head bolts.

Early Evos from 1985-1994 used head bolts made of soft metal that was prone to stretching over time. The service manuals at the time did not recommend replacing the head bolts during repairs. This often led to customers needing repeated repairs as gaskets would fail again after a season. These Evos also installed the cylinder studs with a shelf above that the long head bolts could bottom out on. Between the stretching bolts and potential bottoming out, it created problems.

In 1995, Harley made some important changes. They started installing the cylinder studs upside down, which prevents the head bolts from bottoming out on the shelf and provides better clamping force. However, the earlier manuals did not specify this updated installation method. I've also found issues like this on other models, where the manuals were later updated with improved repair techniques learned over the years.

I demonstrate some tips for safely removing old studs and show how to properly install the new upside down studs. Using an old bolt and special Harley bearing tool as an installer prevents bending or damaging the new stud during installation. Following the latest service manuals and updates can help prevent the frustrated repeated gasket failures customers were experiencing on their Evo engines. Proper replacement of parts like this, learned from experience, is key to reliable long-term performance.


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