Chrysler Filter Adapter #21250 Maintenance Bulletin

January 2010


Big Block Chrysler oiling systems with the filter in the stock location use the #21250 filter adapter. The gasket used for this filter plate should be the "green" gasket. A green Kevlar material gasket is used to seal the pump cover to the filter adapter plate. Replacements are available in the Oil System Gasket & O-ring package Milodon #21590. During each engine rebuild, the oil pump assembly should come apart for inspection and be reassembled with new gaskets and O-rings.


Baring in mind that Milodon oil systems have been in use for over 40 years and many of those systems are still in use, there is a rare occurrence of failures with the early "gray" gasket. Any occurrence however is unacceptable.


The green gasket has been supplied in all kits since 1996. Milodon oil systems have been in production since 1965 so there were many early gray gaskets supplied. These systems were used on everything from street cars to the Hemi Pro Stockers of the 70’s without incident. While the majority of applications worked fine, if the filter plate clamping force is not sufficient there is a possibility the gasket could be pushed out by oil pressure. The green gasket contains Kevlar fibers and has increased internal strength to resist fracturing and being pushed out of place. Adequate clamping force is a necessity however. 


Clamping force of the filter plate may be diminished by several factors.

  1. The two filter plate bolts must be tight enough initially.  Being countersunk bolts that are torqued to 35 ft/lbs, they will then require a substantial effort to loosen them. When assembling the cover - Make sure the bolt threads are clean and go all the way down by hand. Then remove the bolts, coat with oil and torque down for final installation.
  2. The bolt inside the filter cavity sits about 1/8" deeper that the outer bolt. If bolts are replaced over the years then the length must be checked or the bolt could bottom in the hole before it properly clamps the filter plate. While appearing tight it would allow a loose gasket and subsequent failure.
  3. Check that there is enough flat sealing are around the oil ports in the cover. There should be a minimum of .130 sealing surface for the gasket to seat on.