Question: The muffler bolts in my engine are hard to turn. I have been careful not to cross thread the bolts where they engage with the muffler. The threads on the bolts appear to be incompatible with the threads in the muffler. What is going on here?

Answer: There may be a bit of residual finishing residue in the muffler threads. The threads in the muffler holes and on the bolts are correct. Remove the residue and the bolts will work fine.

Better Answer: The muffler front section is a cast component. After the two muffler bolt holes are drilled and the threads tapped, the front section is sand blasted and treated during a finishing process. Some residue from the finishing process may be in the muffler bolt hole threads. To remove this residue simply quirt a bit of oil into the muffler holes and apply a bit of oil to one of the muffler bolts. Screw the bolt into the muffler hole about 1-2 turns and then back it out. Clean off the oil from the bolt with a paper towel and then apply a bit more clean oil. Screw the bolt back into the muffler, this time about 3-4 turns. Back it out. Clean it off, reapply oil and screw it back in about 5-6 turns. Repeat this process until you have cleared the residue from the muffler bolt holes.