Hi Christian, CJ and prd,
I have to agree with Jack (he has tools at his disposal that us mere mortals don't) that these marks are very consistent with the underside casting profile of the Briggs engine, also with the enlargements of the shots they now show that the marks are very straight lines on both front and rear rails and thus won't be fracture lines as fatigue will normally not create straight line fractures, they will radiate in all different directions away from the mount points.
Personally I think you are one very lucky chappy having a twin rail 20 inch chassis that requires none if any work in this area. Normally most 20 inch machines will have had a flogged out clutch at some point in time which will exaggerate the vibrations from a Briggs engine and thus induce much stress and flex into the longer 20 inch rails around the engine mounting points. I currently have a 20 inch machine the same as yours and it has had two massive rail failures. I will take some shots of it tomorrow and post them up onto this thread just showing what can happen due to lack of maintenance.
I will say that you've got a fairly good canvas (so to speak) to work with as a basis and it would be lovely to see that 3 HP Briggs fully restored and powering that machine again for another 40 odd years.
Cheers,
BB
