[MarkS57]

Originally Posted by Joe's Garage

Those 'date' codes are on the inner flaps of the box.

There will be be 2-digit 'date code' on one flap (see the 1st pic below) that indicates the year. This box was printed in 1990.

Then on a flap from the opposite end of the box, there will be two numbers, one for the month and one for the day. Sometimes there will only be the month and no date. See the 2nd pic below - this box was printed on 8 - 10 (August 10th).

The 3rd pic is of 2nd box, also from 1990, that does not have a 'day code' but does have a 'month code' printed (again 8 for August).

The 4th pic is of a late 90s vintage Sealed Power box. It is coded to show that the box was printed in 09 of 98.

I've never seen a deciphering key for the codes on the outside of the box, although the gang-stamped digits probably do decode to something.

I believe that TRW was a reseller and not a manufacturer, so whatever dates you can decode would most likely indicate when the lifters were packaged and labeled for TRW and possibly decode to indicate who the actual manufacturer that made them for TRW was.

Although, as ponyakr has pointed out, the physical characteristics of the lifters are the best indicators of who the manufacturer is / was.

Hope this helps.

Originally Posted by ponyakr

I've read that the lifters made by Delphi have a hardened foot. You can tell that the lifter on the left has this foot, by the low groove.

Have read that Delphi use to provide lifters for lots of GM factory engines.

Thanks guys, yeah, Delphi seems to be the manufacturer of the hardened foot lifters & very much appreciated date code info. I'll check the boxes when I get home from work.

Each box has instructions for installation, for both stock & hi rev types. I'll have to see if they recommend removing valve springs on the hi rev types.