Critical Note:

400EX Head studs will pull the threads loose in the cylinder anytime that the cylinder gets too hot breaking down the aluminum. There are several causes of this including overheating of the cylinder during resleaving and poor matching of fuel octane to the engine.

Critical Note:

These heavy duty studs cannot be used if the cylinder was drilled and tapped for Helicoils or drilled and tapped for any other oversize studs with a differant thread diameter and pitch.

Installation Instructions

  You need to first drill and tap the cylinder to accept the new studs. 

Hole machining

7/16-inch course thread. Drill holes with a 3/8 inch bit. It is always best to have a machine shop do this procedure in a vertical mill to ensure proper alignment.

Be sure to hone cylinder after studs are installed. 

Install the new studs using Permatex sleeve retainer on the threads. 

Be sure to install to the correct height. 

The studs must be the correct distance out of the top of the cylinder. 

Front – 2.436”

Rear – 3.188”

Sides – 1.929”


Stock vs. Heavy duty


400EX Exhaust

Highest Power Exhaust for the 400EX!!

Yes its loud!!