Can somebody tell me why the briggs parts diagram for my 2010 35 hp engine model 613477-0157-E1 only shows one part number for the crankcase bolt (M8 x 50mm) but two of my bolts (by each cylinder) are slightly longer and use a 12mm socket head vs a 13mm socket compared to all the others? The two that are longer also have a flat washer and the others don't.

Sounds like someone put some different bolts. If it's not the bolts for the crankcase cover and they are actually going into the cylinder then they're just for the muffler bracket. All the cover bolts are the 13mm.

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It had cam installed before I owned it so it's possible that is when they were switched. They are crankcase bolts. Just wasn't sure if all the bolts were really one part number M8x50mm. I don't see a reason I can't go back to having all 11 be the same.

Stock bolts have a 12 mm head. aftermarket have 13... Now some years of stock bolts had 13.