Pontiac Block Main Cap Identification

We get many questions on main cap types on Pontiac blocks. This causes much confusion when choosing dip stick tubes with and without a windage tray.

Lets take a look at the different ways main caps came on Pontiac blocks.


All Center Mains Drilled

This block is the most universal block for use with or without a windage tray. Notice mains #2 and #4 are drilled for use with a windage tray. Main #3 is also drilled on this block so that a windage tray is not required and the AAU-N302 (without windage tray lower tube with bracket) has a place to be bolted in place.


Only Center Main #3 Drilled

This only has the option to use a lower dipstick tube without windage tray. Notice that mains #2 and #4 are not drilled. This is where the windage tray would normally attach. To use a windage tray on these blocks the main caps would need to be replaced or drilled if the caps have the cast embossment which has the capability to be drilled and tapped. (the block pictured has main caps #2 and #4 without the embossments)


Example of a either of the above blocks with an AAU-N302 installed.

After installing the block tube (AAU-N304) first, insert the lower tube (AAU-N302) into the block tube positioning the bracket into place over main cap #3. Secure with 5/16 x 3/4" bolts with washers using thread lock.


Only Main Caps #2 and #4 Drilled

This block is for use with a windage tray only because the main cap #3 is not drilled but #2 and #4 are. The windage tray is installed using main caps #2 and #4. This version requires a windage tray and lower dip stick tube without a bracket. The main cap #3 can be drilled for use without the windage tray so it can accept the AAU-N302 lower dipstick tube. See the section below on how to do this.

In this case the lower dip stick tube was held in by the windage trays. See the images below to see how the tube is held in place. This lower dipstick tube is part number AAU-N300 (for use with windage tray only, does not have the bracket).

After installing the block tube (AAU-N304) first, insert the lower tube (AAU-N300) into the block tube. Slide the windage tray over the tube and into position.

Some blocks came with windage trays from the factory. We do not recommend reusing a 40 year old windage tray. The metal can deteriorate and pieces can be introduced into the oil pan and rotating assembly area causing catastrophic failure. With the relatively inexpensive cost of replacement, it is worth replacing.


Blocks with Aftermarket Billet Main Caps

Our aftermarket main caps have the #2, #3, and #4 main caps drilled for use with and without windage trays. They can accept the AAU-N302 when not using the windage tray.


Drilling Main #3 for use with the N302 Lower Dipstick Tube with Bracket (No Windage Tray)

Main cap #3 will need to be removed then follow the directions below

Drill the center #3 main cap in the center using 17/64th drill bit at a depth of 1"

Tap the hole using a 5/16 18 tap. Ensure you clean the main cap and threads thoroughly before reinstalling so no trash gets into the block.

Install the main cap and temporarily fit the N302 so you can mark the bracket for the corresponding hole to be drilled.

Using a 5/16 x 3/4 bolt and washer, install the N302 using thread lock.