For the muffler to explode you had to have filled it with unburned fuel and then it ignited. I would check to see if the camshaft is really all right after ruining the rocker arms. Get a micrometer on it. A missfiring cylinder or the cold start valve staying on would be my first thoughts. You are correct in that a way off timing problem could cause this (like having the camshaft way off). To check the engine for damage I would try a compression test. This will also give you a hint if the camshaft is way off if you can't get compression on some cylinders. You may have blown out the exhaust manifold gaskets and destroyed the O2 sensor and possibly damaged the catalytic converter. You are lucky no one was hurt. I had a similar experience but in that case the engine had a burnt exhaust valve and it only blew the exhaust pipes apart when it backfired. David Teitelbaum vin 10757 --- In dmcnews@xxxxxxxxxxxxxxx, "bepositive2000" <BePositive2000@xxxx> wrote: > Hi Everyone, > > It's been a couple long weeks. > > You guys will probably get a BLAST out of this. I did?LITERALLY. > > I just finished replacing a couple of bad rocker arms on the #4 > cylinder. The oiling holes were plugged and the cam eventually made a > concave slot in the rocker arms. Cam looked fine. >