Stage II On Center Block 4.1 Liter
Casting number 25500153



86-87 Production Block Top View
86-87 Production Block Bottom View
Features of Note:
  • Buick's latest on center casting
  • Notice the lifter bores have not been drilled for oiling
  • The galley has no holes for drain back, and also notice how the oil port (tower) just in front of the lifter galley comes out of the block at an angle
  • All on centers are like this , all off centers have the port facing straight up
  • Notice the knock sensor provision at the rear of the block
Features of Note:
  • Four bolt mains
  • Thicker pan oil pan rails than production block
  • Cross bolted main caps on 1 and 4 earlier on center castings did not get this treatment.
  • The cylinder walls are much thicker on the newer blocks
  • All on center blocks use a BBChevy rear main seal.

Submitted by:

Bill Anderson