First post here, have a quick question: If you set a bare Cooper motor and a bare Cooper S motor side by side on the ground, is there any quick way to tell one from the other? Someone wants to sell me a spare and says it's an "S", but how would I know? It's supposed to be a long block, valve cover to oil pan with no manifolds or bolt on accessories. I realize there are internal differences, but how much external? Thanks in advance!

 

the usual give away on a bare block is the the water pump outlet. The R50 is close to the timing cover end. The R53 is back on the flywheel side and they have a block off installed on the front hole for the R50.

The block itself is actually the same, the internals are what is different. R50 has cast internals and the R53 is forged with dish pistons.

 

Does the R50 have flat top pistons? The reason I ask is because if the block was stripped of all accessories AND the blanking plug was removed from the outlet in the block they would externally look alike, correct? A borescope would reveal dished versus flat top pistons fairly quickly. Where are the motor numbers located? Does the "S" have a "W11B16" stamped on it? Sorry to be a nuisance, but I don't have any to compare and I don't want to spend my money on the wrong motor.

 

Assuming the source of these images are correct:


R50 piston


R53 piston

 

Thanks for the pix! That helps a lot. A quick poke down in the spark plug hole with the BS and see if it has a step in the piston crown. That a fairly easy and foolproof way to tell the difference.