TheBrickLayer:

Which style of MDS 40 do you have? There are the ones that the muffler bolts on from the exhaust side and then there is the bolt through style (like OS -TT motors). The mds .40's I've got are the standard FS series (has black head) that has a bolt on muffler from the exhaust side (the block is actually threaded not the muffler). If you have one of the newer series (40-48-58-68 with a silver head) those had the bolt through design for the exhaust.

Here's a pic of the black head 40 FS series that has a bolt on muffler:


Here's a pic of the silver head 40 FS PRO series that has a bolt through muffler design:


Hope that helps,
Madd_Maxx