Thanks, fingers crossed that's all it is with mine and that the light prop had nothing to do with it.

Its the combination , light prop, light starter .

motoadve wrote:Its the combination , light prop, light starter .

Close... but not quite...

The combination for better or worse is the type of light weight starter and the starter adapter. The light weight prop just exasperates the situation, but it can and does happen when the wrong combination (starter & adapter) is used with any prop.


Take care, Rob

Thanks for the info Rob, my starter is on a io520 and is TCM 646238-2 which I presume is the old 'boat anchor' you refer to - so I am hoping this adaptor failure is just a one off.

Recall that the 'start' position of your key switch shunts (turns off the right mag) until you release from the start position. Now let me walk you through a typical kick back event..engine is turning slow and getting slower as the battery runs out of juice. You decide to give the starter a rest and release the key from the 'start' position. One of those cyl is just coming up with a full charge on the compression stroke and when you release the key, both mags are now 'hot'..with typical timing of TCM engines at 23-27 degrees BTDC, the right mag fires and your engine has nowhere to release that energy except to turn backwards. Toggle switch for each mag is a sure way to prevent this. The older heavy starters (Energizer permanent magnet style) are avail for about $700 and turn the fastest. The new lightweight Skytec ST-5 turns a IO-550-N on a Cirrus SR22 at only 40rpm during cranking. The Energizer cranks the same engine at 120 RPM.

The same company who owns Cessna, Beachcraft, TCM and Macauley who just announced the 'lightest weight composite prop in the market' for use on -550 engines in the Cessna TT...so I think you will see an end to TCM trying to avoid starter warranty responsibility by attempting to link light props to the failure. It was a very poor design from the beginning made worse with a goal to reduce weight and space inside the cowling.

John Nielsen

john54724 wrote: It was a very poor design from the beginning made worse with a goal to reduce weight and space inside the cowling.

+1 John,

I can't understand the merit of that design, myself. Broken adapter parts can end up floating around inside the engine. Having a front mounted starter keeps from risking an engine strip looking for pieces of broken spring, and the starter can be removed / maintained without having to swing out the entire engine, should it break.

my starter is on a io520 and is TCM 646238-2 which I presume is the old 'boat anchor' you refer to - so I am hoping this adaptor failure is just a one off.

Nope not to be, I have just busted another one at a remote site Plane stranded there for however long it takes to find another adapter.
So 2 springs broken within 40hrs - this is unbelievable and extremely frustrating. It may be coincidence but................

Boy that sucks!

If you haven't already done so please make MT aware of your problems. It's not their fault but they have an obligation to tell those of us that have/are considering their propellor that some additional funds will need to be spent for particular starter/engine combinations. And please post the fix that finally works for you, part numbers included if possible.

Sorry buddy.

Man that sucks so bad... if one good thing can be taken from this it is the fact that you have the old style starter. I say good because many folks assume that the cure to this poor starter adapter design is retaining the big starter.

Good luck with the fix!

Thanks for the thoughts Rob and Phil, yes I know you will be watching this one closely Phil

And I wasn't going to make any comment until I had sorted the problem but given I now have a bit more time (see below) I thought I should put it out there again for anyone that can add to the knowledge base on this.
So lets start.......it's a Cessna 185F with io 520, MT prop, new style starter adapter, old Energizer starter motor and firewall forward Odyssey battery.

Scenario One. Starter starts slowing, prop hangs a bit then fires, thought it was the battery, replaced with new Odyssey so plenty of cranking. One start cold = no problem. Taxi to pumps, fill up with gas, fire up (hot start) prop swinging flat out. Didn't fire, took hand off key and prop stopped abruptly (no noticeable kickback). Turned key again just to hear the whirr of the starter motor. Aircraft luckily at an aerodrome where adapter was sent away and broken spring repaired. Aircraft out of the air for a week and I subsequently lost work which was instead done by a helicopter (just to rub salt in the wound.. )

Pick up aircraft all good, new spring and away I go.

Scenario Two. About 40hrs later. Fly into a remote airstrip with punters, shut down to drop off and attempt start up for a second load. Hot start, prop swinging well but didn't fire as per usual straight away on the hot start. Took hand off key and exact same chain of events as scenario one with no noticeable kickback. Except this time I'm stranded at a remote airstrip. and I'm not willing to risk flying it with a broken spring in there.
Call in another aeroplane to extract ourselves and get on the phone to get this problem sorted (Niagara, MT etc etc). In the meantime weather forecast at remote strip looks decidedly rough with high winds, thankfully got a couple of friends to fly down by helicopter to lash it down better and dig in the wheels while I wait to get engineers in there. IF I have an aircraft still tied down by the time the engineers get there this is what I'm planning to do.

Replace 'new style' adaptor with an overhauled 'old style' adaptor
Check starter motor torque before refitting (and fly a spare in in case mine is out of spec)
Check mags, impulse coupling and timing
Cross my fingers and toes

If there is anything else that could be suggested that I should be doing please let me know. I have been forced to learn a whole bunch of stuff since this has happened about TCM starter adapters so there is some reasoning behind my plans and think I am on the right track

I will post about the outcome good or bad.

On my IO-520 I have Slick Magnetos with Impulse Cuplings on both Magnetos.
I had the Iskra starter and had a Backfire(?) and broke a spring.
I put a lightweight starter on the thing afterwards, but believe the problem was not priming the engine enough when it was cold. The backfire was attempting a start with a cold engine (35/40F).
Haven't had a problem since.
Might not be the best system, but there are a bunch of these engines out there with this start system and not a bunch of problems based on percentages.
I would be looking for problems other than the start adapter.
If you have an earlier model that only had one magneto with an impulse adapter, maybe the wrong magneto is coupled to the starter switch ??
IMO, the TCM 470/520/550 is a pretty good piece!

237

In my case Iskra starter and MT prop.
Bought old style starter, also sent the magnetos and they retarded the impulse couplings, been flying like this for more than 400hrs and its good. ( knock on wood)

Thanks guys,
Agreed SkyTruck the broken adaptor spring is the end result but not the cause. I need to get to the bottom of the cause. I figure guys operating on floats wouldn't take too kindly to this situation and yes, plenty of Continentals doing that every day.

Motadve, so the only difference with my situation is that you have retarded the impulse couplings (same starter and prop etc), definitely on my list then.

So does the TCM impulse coupling retard to TDC from 25 degrees BTDC, in which case just a few degrees more would be enough to prevent any possibility of a kickback?

A backfire on the other hand would suggest the impulse coupling isn't working consistently when hot, or at all?

I had a sticky impulse coupling on my L-mag to start with - too much grease in the Mag. You could hear in when you turned it over by hand. Flushing the grease out solved the problem. That was a Bendix installed on Lycoming.

That's right Battson and I think John described the scenario very well in a previous post, especially when stopping the start and suddenly having 2 hot mags. Obvious avoidance would be both mags impulse coupled like SkyTrucks and of course......working correctly. I'm still not completely convinced it was a kickback, it certainly wasn't obvious like some of the kickback clips I've seen online and certainly no backfire. But I am willing to try anything that will prevent this in future. Problem with doing multiple fixes is that you may never discover which fix it was.

Some good info here and some major over analyzing of the problem going on.

We are talking 470 520 and 550 installations common to Cessna's.

1. They are all started with the mags in the BOTH position. Even when you have a key start these engines start on both magnetos. If you only started on one magneto then you would not have two impulse couplings. Typically Lycomings or little continentals have only one impulsed magneto and in that case you would start it on the impulse mag only.

2. The impulse winds a spring that catches slightly before 22* BTDC and winds for a total of 30* degrees of rotation.

3. Retarding the internal timing is going to make a weaker spark and retarding the magneto to crank timing is going to lead to poor performance and decrease in fuel economy. This will not help kickback whatsoever. Crank timing is pretty irrelevant to the problem when you have impulse couplings retarding the timing to somewhere around TC.

4. I really dont know why the new style starters suck. I dont know of any air taxis that depend on their big continentals that run anything but the older starters. We have all tried the improved torque, lighter weight, higher RPM, longer life BS but after the millionth time warrantying them you go back to the old style because you are sick of remote field starter changes. I know the old style works and rarely has a non pilot/ maintenance induced failure.

5. I really dont know why the new style starter adapters suck. I do know that when the new style adapters came out all these " kick back" issues started. Everyone was in a panic to figure it out. Well there are approvals to run the old style adapter now with a shim on new style crank gear engines. Some people take factory new/ remans yank the brand new adapters off and install an overhauled old style adapters.

Sure you can get warranty on a burnt out starter or a busted spring on your low time engine. Lots of down time, a repair, wait to get paid and have it all happen again in a few hundred hours. Or 4.5 hrs once My OPINION is new stuff sucks or stuff good.

There was a discussion about this at CPA forums, all the guys who reatrded the impulse couplings had good results, it only retards the sparks during the starting process.
Give Cliff a call from aircraft magneto service, he knows about this problem and will explain to you why retarding the impulse coupling does work. His number is (206) 780-3099

Righto as promised I'll let you know how I got on.......

Aircraft was dug in well and remained upright. The engineers managed to fly in there the following week once the winds abated with an overhauled Old Style adapter and the necessary shim for the new style crank gear - replaced the new style adapter with that and flew it out.
Sent the magnetos away and received this info back.......
"Defect - engine kicking back on start. Rare to find this problem with impulse magnetos but probably the lightweight prop fitted caused this when the impulse cam not fully engaged up to the specified minimum 150 rpm. Both magnetos tested as received and both found to be well below this minimum. In all other respects both snap ring cams serviceable. One S/N impulse cam was able to be reworked until the fully engaged impulse speed was 160 rpm. The other S/N required a new impulse cam and spring to reach the same fully engaged speed of 160 rpm...... both magnetos tested serviceable"

PAMR MX had some good points on the adapters and I'll be one of these when it comes time for engine overhaul.....

5. I really dont know why the new style starter adapters suck. I do know that when the new style adapters came out all these " kick back" issues started. Everyone was in a panic to figure it out. Well there are approvals to run the old style adapter now with a shim on new style crank gear engines. Some people take factory new/ remans yank the brand new adapters off and install an overhauled old style adapters.

So what have I learnt .......
1/. If your adapter spring breaks it could be just bad luck OR it could be a timing problem to get checked out. It would certainly be cheaper to get it checked first. If it breaks TWICE in a short amount of time you'll be kicking yourself for not getting it checked out after the first breakage and you still need to get things checked out .....oh and BTW bring lots more $$$

2/. The old adapters and old starters have been tried and true for years, why change a 'relatively' good design for a flawed one (new style adapter). Unfortunately my newer overhauled engine had the new style adapter on it because of the new style crank gear. It's now got the old style adapter with the same old style starter

3/. Between changing adapters styles, checking timing, magneto inspection and reworking impulse couplings I think I have it sorted. The 'pucker factor' every time I engage the starter is starting to go and I'm getting a bit more faith back in my machine. I hope by posting this I don't jinx myself but it just might save someone else from the same predicament

I know a couple guys who run 470's who installed Skytec starters & had some issues with them. They both then bought a Hartzell brand starter and were very pleased. I'd never heard of a Hartzell starter before,only props, so I don't know if this is a new product or maybe an existing product rebranded as Hartzell.

Maybe I answered my own question-- the latest Spruce catalog shows Hartzell starters but refers to them in the text as Lamar. FWIW my new skywagon has a p/n 646238 TCM Energizer starter and a firewall-mounted Odyssey. Generally the prop stops when it comes up on the first compression stroke, and I have to bump it a few times with the starter button. But once it's past that first blade, it swings on through (none too fast) and fires. I ran the battery down yesterday trying to bump that first blade pas though-- a buddy had to hand-prop me.
No indication in the logs of how old the battery is-- it's a Hawker SBS J16, not a Powersafe Odyssey SBS J16 if that means anything as far as age goes. I believe the starter hasn't been off since factory reman 1150 or so hours ago. So I'm thinking of replacing the battery and either having the local auto-electric guy freshen up the starter, or else just buying a new one. What's the consensus-- a Hartzell or a TCM Energizer? (or are they the same thing?)