Because Owning And Flying Your Beechcraft Can Be Done Safely AND For Less Money!



  Baron Fuel Selector - Separate Main & Aux Tanks (TC-1 to TC-1607, TE-1 to TE-937, TE-939 to TE-942)




Got blue stains in the tray underneath your fuel selector? Got blue staining on the body of your fuel selector? See HERE for examples of fuel staining of a Bonanza fuel selector body. Did someone quote you an incredibly high price to OVERHAUL your fuel selectors (I can't understand why, because there's only o-rings in there that any A&P is authorized to remove and replace)?


Unless you have some form of bent shaft or selector body warping (highly unlikely), you're in luck, because a simple fix might just be to replace the o-rings in the selector body. It's a rat's nest of fuel lines in there and a not so great place to access but it is doable to extract these items from their home and open them up on the bench and replace the o-rings. Be sure you have the work done by an A&P/IA or are well supervised by one, as this, like many areas of certified birds, is not an area for unsupervised amateurs.


See the fuel selector parts extract HERE for o-ring details.


See a narrative HERE written by B58 owner and A&P, Larry O., on his B58 fuel selector R&R.


See HERE for some flurosilicone o-ring options for the shaft and body o-rings if your A&P will authorize a substitution. Flurosilicone o-rings have been shown to deliver much greater service life than their 1940's nitrile rubber versions.


An IA friend of mine reminds me that the so called "o-rings" in the fuel line fittings attached to the selector body are in fact "BOSS SEALS" (Item #26 MS29512-6 in the above fuel selector extract) and are different dimensionally AND in chemical resistance than conventional o-rings. He says:


"They have a cross section almost square. MS 28778-xx (in the case of my B55, MS29512-6). They are a different hardness/durometer than an o-ring also. The size is a reference to the tubing size for the affected fitting.  Thus a -6 is for a 3/8 fitting which is for most Beechcraft fuel selectors. O-rings are sized by cross section diameter and inside diameter and classed as fuel or oil. It is not unusual for mechanics (ought to know better) to assume a 'standard' o-ring is used. In a way that is correct if one uses 'standard' in reference to the correct part for the application. This is the Readers Digest version of the Parker Handbook.


The IPC calls them o-rings, yes. Thus the confusion by many to use a 'standard' o-ring. The part number MS29512-xx uses a number '4' or '6' to indicate tube size. It is a tube fitting in the Mil Spec and fuel resistant, very important distinctions. This is why using the parts manual is usually the best source for part identification.


Many of us (A&Ps) learned to use the part needing the o-ring to determine what to order-Measure the cross section, measure the diameter, look it up on a chart. I have a 20+ year old chart.  It gives an explanation of the applicability for the part numbers and calls the AN & MS (o-rings) - Boss Gaskets.




Not really a tomato-tomato issue. but this is one of many things that come up the industry will never truly eliminate. When I was in Corona, only a mile from Aircraft Spruce, this very issue caused a great deal of heartburn with their parts department. The boys in back packed the o-rings in a baggy and I refused them.The actual single packages give lot, expiration date, and clear identification. You can not tell the difference between a MS29513 and a MS 28775 the same size but one is fuel and the other oil. Although I have seen them used interchangeably, it is not BEST practice. Many parts are commonly called by the Brand name regardless of actual manufacturer-Sheet metal screws called PKs for instance."


"A rose by any other name would smell as sweet"


So be careful not to just replace these BOSS GASKETS with a conventional o-ring that looks like it fits!


Below is the rat's nest of fuel lines that you'll be looking at:




Be sure to put whatever markings, tags or numbers you feel are needed to get EVERYTHING back in the same place! Digital photos are also a big help. Another watch out is to be sure to use some form of marker pen or indicator to indicate that you final tightened each line. This will help you confirm that all fittings have been properly tightened.



As always, if you have no idea what a fuel selector or an O-ring is or what a good one is supposed to look like or what a bad one looks like, close this browser page and ask your A&P licensed mechanic to have a look at your fuel selectors and let you know if they are leaking.



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