The Crossflow Chronicles

US 200ci Block Modifications - For the Crossflow Head

The Gasket Support Adapter Plate

Shot of lifter side of block showing additional head gasket support adapter plate

This plate is 1.250" wide x .250" thick. It is trimmed to fit between two square cast bosses on the side of the block so its length may vary slightly depending on your casting. Its function is to support the head gasket and seal in the lifter openings after the pushrod relief has been cut. There is nothing under pressure on that side of the block, so a high performance seal is not necessary. There may be some oil that accumulates there, so it needs to be sealed with either welding or epoxy.

This one was welded into place, but it could also be bolted thru the centers of the lifter openings. To position the plate, clamp a flat piece of steel or square tubing to the deck so that it overhangs the area where you want the plate. Then clamp the plate so that the edge is flush with the deck by butting it up against this other tube or plate. You may have to grind off the upper ignition coil mounting boss to get the adapter plate to fit flush against the block.

If welding, tack it with a nickel rod and check positioning. Continue welding by tacking at intervals until the entire lower edge and sides are secured and sealed to the block. Do not get the block too hot or weld continuously down the plate. There is no need to weld any part of the deck area itself.

If bolting, drill a 1/8" hole thru the plate and the block in the lifter opening. Insert a short 1/8" rod thru the plate and the block to hold it in place. Check for positioning before drilling the next hole. Insert a short length of rod to help hold it in position. Continue until all five holes have been drilled thru each lifter opening. One hole at a time, remove the guide rods and drill a 3/8" hole. Insert a 3/8" bolt and secure it with a common nut for the time being. When the last hole has been drilled, remove the plate and the bolts. Using a good wire brush, clean the entire area that the plate will rest down to bare metal. Thoroughly clean the plate as well.

Mix enough JB Weld or similar hi-temp steel filled epoxy to get a good seal on the plate. Coat the block area. Reinstall the plate and insert bolts. This time, secure the bolts with locknuts and tighten to approximately 25 ft-lbs. smooth any excess epoxy around the outside edge of the plate. Allow to cure. It may be helpful to turn the block on its side during curing to prevent the epoxy from running.

Intake Pushrod Clearance

The lifter opening must be widened to accommodate the six intake pushrods. A common woodworking router works well for this, but a drill and grinding stone could also be employed. The block in these pictures was milled with a router using a 3/8" carbide straight cutting router bit. Use the Crossflow head gasket as a guide to determine the openings then mill to the edge of the block.

Coolant Passages

Three coolant passages must be blocked off. The Crossflow head has no metal in those areas and you will get a coolant leak if they are not plugged. They are the holes which are opposite #2, #4, and #5 cylinders. Tap for a 3/8" pipe plug and insert plugs flush with or slightly below block surface.

The oil passage that used to lube the rockers is no longer needed, but it will be sealed by the headgasket. If you want, you can seal it too.

Coolant Bypass

One of The coolant bypass hole directly above the water pump must be blocked off. Drill and tap for a 1/8" pipe plug or a 3/8" bolt. Insert a plug or bolt flush with or slightly below the surface of the block.

Block Mods Complete

This block is complete. Note the head gasket support adapter plate, the milled pushrod reliefs, the three blocked water passages, and the blocked coolant bypass. This block must now be thoroughly cleaned and all metal chips and debris removed. It is ready to go to the machine shop for boring and decking.

Clean the Block!

This was just some of the crud that was in the water jackets. It was dug out with a screwdriver and a coat hanger. Yours probably looks the same, so while you have the block out, clean the water jackets.