Model A & B

Ford Garage

Valve Lifter / Tappet Comparison

Did you ever wonder why Ford was particular about which valve tappets (push rods as they referred to them), were used with Model A and B camshafts, and why they should never be mixed?

They were dimensionally different for a reason. That is to say, they were sized to match the camshaft lobe profile requirements. Materials also matter!

The pic below shows a comparison of two reproduction jam-nut Model A tappets on the left, and the best available replacement self-locking tappet on the right.

The low quality materials and dimensionally undersized Model A jam-nut tappets (1.000 inch base diameter) on the left were (improperly) used with a Model B camshaft. Note that the one tappet base was almost completely wiped out!

How well do you suppose the cam fared? They wiped out the lobes. Game Over!

The 1.117 inch stock Model A tappet base diameter is too small for the Model B cam profile grind, as noted by Ford in the 1932 Service Bulletins.

A tappet with a 1.000 inch base diameter is completely incompatible with a Model B cam lobe profile.

The pic above shows the severe wear of the base of one of the valve tappets. Both were out of the same set, same engine.

The 1.117 inch base diameter self-locking tappet shown above is the best adjustable tappet currently available.

Pictured above is a comparison of the larger (1.187 inch) base diameter of an NOS B-6500 Model B Ford solid tappet on the bottom, with the smaller (1.117 inch) NOS A-6500 Model A Ford solid tappet on the top.

Many reproduction tappets are only 1.000 inch in diameter and will not fare well with any camshaft, nor will the camshaft lobes last long, as demonstrated in the photos above.

More Camshaft web pages on Ford Garage:

  1. Model A & B Valve Tappet Adjustment ~ Rule of Nine
  2. Model A & B Original Ford Camshaft Details
  3. Model A & B Bill Stipe Camshaft Specifications
  4. Model A & B Camshaft Timing Gear Varieties
  5. Model A & B Camshaft to Crankshaft Positioning

November 2009