Firewall engine mount bushings

Looking at the Piper drawings for the firewall bulkhead. The engine mount bushings call for the washer that's welded to the bushing to be 1025 steel, 1.25" diameter and .125 thick. 1025 has a yield strength of 53,700 psi. Is there any reason you could not use a grade 8 washer of the same dimension since it has a yield strength of 130,000 psi? Would they be too hard and thus prone to crack? Negatively affected by the heat from being welded?

I have been looking for a source for the 1025 washers but have come up empty handed so far. I can find the bushings already welded up for $23 each. Using the grade 8 washers and tubing I already have I could weld them up for about $2 each.

Thanks,

Mr. Ed

Personally I would use grade 5 washers since the alloy in grade 8 goes brittle when welded. The AN-6 bolt that goes through this is equivalent to grade 5 as well.

Thanks Charlie, that's what I needed to know.

The loads at those points are primarily shear and tension on the bolts. Those washers essentially act as a landing place for the tubes to weld to, not something you want to go brittle.

also be careful how you fitup those clusters and weld them(i think one area is not welded by bolt head???) so you can still get a socket on the bolt