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  Baron 55 Fuel Selector - Separate Main & Aux Tanks (TC-1 to TC-1607, TE-1 to TE-942, Except TE-938)




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Applicable to TC-1 to TC-1607, TE-1 to TE-942, Except TE-938



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 (Click HERE if you need Bonanza fuel selector O-Rings).


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). However, it is a rather tedious and critical process as you will see in this teardown narrative.


Hopefully, the below narrative and high resolution images can take some of the intimidation out of the opening up of one of these beasts by a qualified A&P mechanic.


The removal was tedious, especially with nearly full tanks , which required AN plugs and a very quick hand on the MAIN and AUX feed lines going into the selector valve.



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 (stubby 11/16" and 9/16" wrenches were essential to me in this aspect) 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.




It is EXTREMELY CRITICAL that the orientation of these


components is preserved for proper functionality!!!! My IA and I


match marked and photographed everything to insure a proper




See the B55 MAIN/AUX/CF 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/Bo Owner (Bob B.) 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!


But anyway, for those who insist, HERE is a link to a sizing chart for the MS29512 "boss gaskets" in case you want to "roll your own in M25988/1-XXX Flurosilicone".


Be sure to secure A&P approval prior to any O-ring substitution and return to service!


Below is the rat's nest of fuel lines for the B55 fuel selector 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 orientation! THIS IS ABSOLUTELY CRUCIAL! Digital photos are also a big help.


Tips I learned:


1. Have proper size AN plugs on hand (and be quick of hand to insert plugs) for MAIN and AUX lines or drain fuel tank(s).


2. Wear appropriate eye protection with splash guards.


3. Match Mark and/or photograph all parts and their orientation to each other. Starting with both valves in the OFF position was helpful in a baseline orientation and prevented fuel from also coming out of the engine feed port at the bottom of the valve.


4. Beware of burrs induced in center shaft (which can damage interior o-rings) as a result of driving roll pins out (a rat tail file can deal nicely with these).


5. Leaving top mount screws in mounting frame aids in loosening lines to valve.


6. Allowing valve to "float" upon re-installation, without the top three mounting frame screws attached to mounting frame, aids in attaching lines to valve.


7. Match mark fitting orientations to enable proper line orientation and ease of reattachment.


8. Upon final tightening of each line apply torque putty to identify it as a torqued line.


9. Count the number of fittings on each valve and confirm that the total matches the number of lines that have torque putty applied


10. Leave left selector valve out to remove right fuel selector which allows easier access to MAIN/AUX/CF lines on left side of the right valve. Re-install right selector valve first


11. Right selector valve is of similar design but orientation of lines and shaft positioning is different. AGAIN, match mark/photo everything related to orientation of the valve body housing, center shaft and port fittings.


Another watch out is to be sure to use some form of Torque Putty or marker pen or indicator to indicate that you final tightened each line.



This will help you confirm that all fittings have been properly tightened.




Baron 55 Fuel Selector Cover Placard Makeover


~TC-191 THRU TC-1607


TE-1 THRU TE-942 (Except TE-938)


Since you've made it this far in the B55 Fuel Selector Valve narrative, you might be interested in buying an extremely custom set of placards to freshen up your fuel selector cover panel.


If you're diving into your fuel selector valves for o-ring replacements and your 50 year old cover plate has seen better days, you might like to give it a fresh look.


Check out the before and after pics of how my custom placard design came out and click the PayPal Buy It Now Button if you'd like a set:




After Replacement Placards



Cover Plate Backside View


For $95 (includes FREE USPS Priority Mail US Shipping), you will receive the full width top main selector valve roadmap placard and the red "WARNING" placard (as shown below) that sits below.



It does NOT include the intercom placards since these may or may not be how your cover is configured for your intercom setup.


The 37 gallon Main marking is in compliance with the latest POH published limitations (all us 55-Series drivers know it is a 40 gallon tank but 3 gallons became legally deemed unusable in later years).


Applicable ONLY to the following 142 Gallon/136 Gallon Usable SNs:


~TC-191 THRU TC-1607


TE-1 THRU TE-942 (Except TE-938)

NOTE: Using the existing cover plate as a template, you will need to drill your own holes in the large main placard to insure that the placard fits your exact fuel selector cover and any post lights that are in your original cover. The large holes for the selector valve shaft bushings are approximately 11/16" and are easily done with a step drill like THIS.


Your purchase also helps to supports the site.

This placard will NOT fit Early 95-55 Models with a fuel selector as shown

below. It is believed that the 95-55 Aircraft are SN: TC-1 thru TC-190.


Shipping Options



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.



If this narrative has helped you, please donate to keep Free