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
7/16-14
course thread. Drill holes with a 25/64 inch bit. Drill to a depth of 2.000" minimum and 2.200" max. It is always best to have a
machine shop do this procedure in a vertical mill to ensure proper
alignment.
For best results, use a roll form tap. Tap drill for this type of tap is 25/64, can be done with 3/8" but use plenty of Tap Magic for Aluminum tapping fluid.
Be
sure to hone cylinder after tapping the holes but before 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”
You must use a drop or two of oil on the top threads and the between the washer and the nut!
You must use a torque wrench!
Factory torque is 32 Ft-Lbs
With these studs and oiled nuts torquing to 35-40 for up to 87mm bore should be fine, and 40 to 45 for 89mm bores.
Stock vs. Heavy duty
If installed correctly original acorn head nuts will work just fine.
Clutch Note: I have
seen a lot of clutch problems develop once
performance work is
done to this engine. The 8 plate clutch setup has 15% more friction area than stock and additional
spring pressure.
Critical Note: I have
seen several clutch basket backing plates break sending hardened
steel pieces thru the engine , doing considerable damage. I now replace my clutch
basket with a new one once per season on the 400EX.
Fix your weak stock threads with these heavy duty head studs. Note: will not work with helicoiled or other thread insert repairs! Can be over torqued some for big bores. Made of 4140 alloy steel are more then strong enough. Reduced upper section allows for easy install and no head drilling, just cylinder drilling and tapping. Works with all the original hardware.
GT Head Studs in stock ready to ship.
see side bar note at left..............................#01-001...........$65.00
