Wednesday, March 21, 2012

2012 Annual Inspection (iii)

There were several things to think about after this morning's visit with Mike the IA and 31 Sierra. A good chunk of the "firewall forward" part of the inspection is done and the only significant issue concerns the muffler. It's a hard life for the muffler, with a constant flow of 1,000+ degree exhaust gas passing through it, so it isn't a surprise when problems develop.

Mike feels (and I agree) that the flame arrestor (the perforated tube visible through the exhaust pipe, at left) is deteriorated beyond acceptability. There are a couple of options available to address this – repair or replace. The decision will be affected by both price and schedule.

Dawley Aviation in Wisconsin is known to do a good job refurbishing these mufflers. They charge $225 if they can reuse the shell and $298 if they can't. The problem is that with a two to three day turn-around, sending the muffler there would require either use of extremely costly overnight shipping or accepting the idea of N631S being grounded through an extra weekend.

You can buy a brand new muffler from Cessna – but they want about $2,000 for it (I kid you not). However, a high-quality aftermarket replacement is made by Wall-Colmonoy. Their Nicrocraft line of exhaust parts is carried by Aircraft Spruce and this unit (part number 0750161-89) can be had for $332.95 plus shipping. This may cost a few dollars more than the repair but the timing will be better.

I had asked Mike to have a look at the connectors for the flow transducer (seen at left) that feeds its signal to the Shadin fuel flow computer. For about the last year, the unit has periodically suffered from erratic behavior. But it would recover after a few hours and when it is working it works perfectly. I've acquired a replacement transducer, but I'm reluctant to remove the old one while it's working. There appear to be no problems associated with the wiring, so we'll cover it back up and wait for it to fail. Fortunately, it's not essential for flight and it's readily accessible with the lower cowling removed so it makes sense to wait.

Finally (for today), we are replacing the plastic end caps on the right horizontal stabilizer and the right side of the elevator. A few "smoking rivets" have shown up there and Cessna has a service bulletin (number SEB03-1) covering the area. It calls for increasing both the number and size of the rivets. But the plastic end caps are cracked and likely not salvageable, so they'll be replaced. The image at left is from the service bulletin, showing the area in question.

I'll be stopping off at the airport tomorrow morning, of course, to see what new things are in store.


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