Because Owning And Flying Your Beechcraft Can Be Done Safely AND For Less Money!
  Starter Adapter Mysteries Revealed


Are you experiencing slow prop turning or slipping of your starter? Assuming that your battery, starter and electrical connections are all in good shape, you might be experiencing the beginnings of the dreaded TCM starter adapter failure!


As for my personal experiences, I've only used a SkyTec ST-3 starter for a little while (maybe 20 starts) before it died on me and they told me I burnt it up (Really??? Do you think this CSOB operates things so they don't last a long time????) So it was back to the full size monster starters for me and I have not had a starter adapter problem in 1400 hours. Oh and I use AeroShell 100W oil. PS: For a really great full size starter for your Continental engine at a phenomenal price, check HERE


Anecdotally, these two operating conditions (starter and oil weight) seem to be reported by many folks who have not experienced the dreaded starter adapter failure. No science behind this, just anecdotal references that I've seen in pireps from other Continental engine owners.




Depending on your CSOB proficiency, this might not mean a >$1,000 overhauled part purchase plus the mechanic hours to R&R the component.


Under the supervision of an A&P or IA the removal of the starter adapter and replacement of the bearings, seals and large drive spring is not rocket science, but that's my editorial opinion.


The shaft and spring interface clearances are best left to be fitted by an aircraft engine machine shop or a place like Niagara Air Parts, especially if your shaft has been buggered up or experienced inordinate wear and the shaft requires buffing or turning down, you'll need an undersized spring.


This is a key statement by the Bulletin s-2008-01 (link below) and one that you might want to check carefully if you select one of those "mini" starters:


For all old style starter adapters it is imperative that the starter adapter input shaft unwind at least one full revolution after engine start so that the clutch spring may fully release. In order for this to occur, spring forces inside the starter adapter must be able to overcome the resistance to rotation (drag) of the starter motor armature or output shaft. If the torque required to rotate the armature of the starter motor exceeds five (5) in/lbs, the clutch spring will not fully release. The rotating shaft gear will then be forced to run with an interference fit inside the clutch spring during engine operation.


Through extensive testing, Aircraft Specialties Services, Inc. has demonstrated conclusively that nearly all wear of the shaftgear and clutch spring occurs as a result of this condition which considerably shortens starter adapter life and may cause metal contamination of the engine.


Personally, I have combined ~2,800 hours (as of 4/2013) on two old style starter adapters using full size starters. You decide what starter you want turning your adapter.


Check out this article on Starter Adapters HERE


Check this out for your full size starter overhaul HERE


Read Aircraft Specialties Service Bulletin S-2008-01 HERE


See the exploded view of a TCM Starter Adapter Assembly HERE


See the mysterious Starter Adapter Spring and Shaft HERE



Doing your Own "Freshen Up" of your Starter Adapter?


Check out these Low Cost Identical Replacement Part Numbers for your TCM Starter Adapter at


Purvis Bearing Supply


Rear Seal: National 450588


Starter Shaft Bearing: Timken 204PP


Inner Shaft Bearing: Timken 203K



Where can you purchase the Main Spring?


My personal source for engine parts is Superior's Line of PMA'd Parts. Here are the spring part numbers offered by Superior.


Superior P/N
   List Price
    SA539800 M15


Caution: These springs may fit your adapter and they may NOT! Check your engine parts catalog and cross reference the TCM part number to Superior's replacement parts HERE


Check Superior's Distributors for their retail selling prices.


The recent pirep from a Bonanza owner about Airpower pricing was excellent, in that they priced the Superior PMA'd lifters at about half the price of Aircraft Spruce and the PMA'd exhaust valve was half of what the cylinder shop quoted him!


See Superior's TCM Replacement Parts listings HERE


Caution: Over the years TCM used a few different starter adapter designs! Check your engine parts catalog to be sure you get the correct parts for your adapter.


TCM GTSIO-520 & GIO-550 Starter Adapter MANDATORY SB MSB94-4G



Here are pictures of the Starter Adapter internals. Click thumbnail for a full size image.











Here is a picture of where the E-Series starter bolts to the back of the engine.



It is a completely different configuration from the current starter adapters used on the 470 and larger TCM engines. Good luck to you guys who care for these E-Series birds!


2740 North Sheridan Rd
Tulsa, Oklahoma 74115


It's been reported that Aircraft Accessories of Oklahoma has/does good E-Series starter overhauls.



Starter Adapter Kick Back Disaster



Per B55 Baron owner Chris S., "I hope someone doesn't have to get hurt or worse to make TCM get rid of this poor design.


We were flying around on this and found something was wrong when turning the prop backwards while dressing out the blades. The prop would hit a hard stop and would simply not turn backwards. The gear turns continuously on the crank gear and could have imploded the engine.


A number of owners have had similar experiences. I would not return a starter adapter back into service without this part being replaced with a new unit.


Two of those teeth were in the sump and the third was sitting on top of the mag drive housing in the accessory case section only to fall out wend we removed the housing. It could have fallen into the cam and crank gear or the crank and starter adapter gear resulting in a catastrophic failure.


If you experience a kickback (on a 470) a way to check to see if a tooth has broken off is to remove the top plugs. turn the prop backwards while checking the alternator pulley back lash. A missing tooth will result in a noticeable amount of travel."



A Beech Lister/owner of an N35 Bonanza has provided a pirep on Niagara's starter adapter repair kits and shaft and spring services:



Their fee to turn down the shaft to fit a new spring is reported to be $75 and a new spring is from $140 to $250 (personally, I'd call one of Superior's Distributors for a quote on the spring). Niagara could be a place to get your shaft machined to specs for your CSOB sourced spring.


Check out these Starter Adapter Overhaul Kits from Niagara as a possible one-stop shop:



Kit reported to be approximately $100



Here is an 08 September 2020 pirep from B55 owner, Jim M. of Florida on his starter adapter removal process:

"We did not need to completely remove the throttle body but we detached some brackets and clamps to jockey it sideways. Then we could slide the adapter straight out the back from the engine. We could not remove the pully since it was so tight and there was not enough room to attach a puller. Once the adapter was out of the engine we used a puller to remove the pulley held in place with a Woodruff key.  

So, the removal sequence was:
1) Remove engine cowlings 
2) Remove alternator belt
3) Remove starter
4) Disconnect Air-box brackets on left side of engine
5) Disconnect angle brackets (under the engine) holding intake manifold to throttle body
6) Remove bolt on bracket holding throttle body the engine
7) Move the throttle body/Air-box assembly sideways
7) Remove (carefully) the starter adapter.

For reference, Niagara supplies a new Woodruff key, new engine gasket and new starter O-ring for repaired units. 
Niagara quoted a price of $1,062 with no core issues. TCM has had problems with pitting on the gears so that is always a concern." 


Per Beechcraft owner and buyer's broker Bob S. of Arizona, here is another potential source of good starter adapter repairs/parts:




Here is what Beech owner John P. says about his starter adapter experience:


I've done a couple of these the past few years.  First was on an IO-470K.  Used Niagara parts and had the drum turned down locally/gear machined locally.  Did the reassembly myself.  Kind of a PITA.  The last one I did I got the parts from Aircraft Specialties and then took the unit over to LyCon in Visalia, Ca.  Think the total for parts & labor was in the $400 range.  He had a special tool over there that made installing the spring on the gear and getting the final assembly into the drum a snap.  You do need to pull it first before ordering any parts.  Have to use a micrometer on the drum to see what size spring to buy.  The shaft WILL have a taper out of spec so machining will have to be done.  Anyone can grind the gear it's the shaft that requires a "tool post grinder" to machine it and very few shops have one.  Overall easy job, assuming especially if you can find someone who has the special tools to install

the spring.


PS: Check above for sources on the spring.



Here is what BeechTalker Paul M. says about his starter adapter experience:



"I am a starter adapter vet. I think I saw some advice on Niagara on this site when the adapter started giving problems in my IO-550. We had a terrible ISKRA starter which eats these adapters. It started slipping and then I made the mistake of going from W100 to W100PLUS and the prop barely turned over despite hearing the starter going full tilt.


I put a Niagara replacement adapter on and it blew apart before two blades went by. Niagara blamed it on bad mags. I was suspicious and spoke to other people who have experienced the same failure and had the same blame by NIagara. Not only were my mags not "on" but the mags were subsequently checked and found in perfect condition. Niagara took its new broken adapter back and that was generous of them.

Subsequently, we disassembled my slipping adapter and measured the wear according to the manual, found the shaft and spring to be worn beyond limits.


I sent the parts to Aircraft Specialties and they ground the shaft and drive gear then supplied the new M15 undersized spring for about $300 roughly. My A&P and I re-assembled and tested the unit thoroughly and replaced it and it has worked perfectly for about 250 hours now.


The biggest change was going to the old Prestolite starter which performs wonderfully. The spring needs high torque to operate without slipping and the older TCM/Prestolites can do that.


The other IO-550s in my hangar still use the ST-3 and ST-5. The ST-3 is about to fail shortly and the ST-5 already had his adapter fail and he upgraded his ST-3 to a ST-5 and it works much better.


I've included three pictures of the product returned by Specialties, they did a really good job at a reasonable cost.





I was happy with the existing components in my relatively new starter adapter and did not want to swap them out for an unknown core."



Spruce Creek


I Found Your Oil Leak!


This is not going to be a good day.

(Contributed by Dave B. from an IO470-C in a J35 Bonanza)



Here's what happens when the starter fails to DIS-engage!

Not a pretty story.



See more troubleshooting info from Niagara on starter adapters HERE


See Lew Gage's Starter Engaged Warning Light Article HERE


A55 Baron owner, Jon B. reports that a Sloan 855 light fixture from Allied Electronics works nicely.