The International Cessna^® 170 Association

I have a Sky-tec starter kick back problem on my Cessna 150L O-200 that I would like to discuss. I am hoping the knowledgeable people on this site may give me some troubleshooting help. I have gone through quite a bit so far to try and fix this issue. In a nutshell I will get a strong kick back every ten or twenty starts that will either brake the starter shear pin or worse yet knock teeth off the crankshaft gear.

Here is some data on my current configuration:

- Upgraded Sky-tec starter with shear pin (old Sky-tec startes don't have it) Starter has been back to the factory for overhaul.

- Stock Cessna 150L key starter switch

- Stock O-200, 1500 SMOH, 4 new Millenium cylinders 500 STOH / motor runs great/ only use 100LL

- Prop is a Climb prop, max static RPM is on the upper range of allowable rpm range for this prop. Motor runs strong and smooth.

- Both Bendix mags have had their 500 hour inspection within the last 5 hours (I asked them to look for anything that could cause a kick back problem. They said they found a sticky impulse coupler and replaced some parts)

- new battery

- Replaced all crappy old ground cables with 5 or 6 new grounding cables (made by my local FBO and used on their C-150 fleet) I am starting to wonder if the grounding cables are letting this starter work too well??? The FBO added one extra cable that was not included by the factory. Yes this starter will crank this motor over pretty fast compared to the OEM starter.

- Timing set to 28 deg BTC per STC SE8675SW

- Yes my P-leds work great. I get about a 75 rpm drop from either mag switching to right then both then left.

- If you google 'impulse coupler' the first thing that comes up on google is a page called 'kickback' from Sky-tec's own page.

Is it possible that things are working too well and I am turning this motor over fast enough to not properly advance the timing during a start?

Looking around Sky-tec's web site I quickly found the following disclaimer...pretty scary if you ask me.

CAUTION
PLEASE READ THIS CAREFULLY BEFORE INSTALLING
YOUR NEW ST-2 STARTER
Make absolutely sure of the following:
__ Both magnetos are within manufacturers specified limits.
__Timing is correct and that there will not be any detonation before
Top-Dead-Center during the cranking procedure.
__P-leads correctly enable and disable the magnetos.
__‘Start Switch’ operates normally and is not intermittent.
__ Battery and aircraft electrical system are capable of handling the
surge of your new starter (approximately 250 Peak Amps).
If you have any doubts about the condition of your aircraft systems or its
compatibility with this new Sky-Tec starter, DO NOT INSTALL THIS STARTER.
Return it to your dealer for a refund.
Sky-Tec does not accept any liability or responsibility for damage to the
starter or your engine caused by kick-backs (detonation before TDC), low
battery pulsating of the engagement system, prolonged cranking cycles
causing the starter to overheat or any component failure of the starter which
might possibly cause ancillary engine damage.
Through the years Continental engine starters have had many problems. The
old ‘pull start’ systems were difficult to adjust and many gears were broken or
worn down as a result. The newer ‘key start’ systems employed a sprag clutch
that would ultimately fail. Both systems had the same results: upon starter
failure, parts and metal fragments would fall into the accessory case gear train
and oil. Many of these failures were either caused or contributed to by the
engine kicking back during the cranking cycle. Continental has redesigned
their starter to minimize the possibilities of these occurrences. Sky-Tec has
always adopted similar improvements to its Continental starter designs with
the enhanced capability of retrofitting older engines with minimal
modifications. More than 1,500 ST2 starters have been installed and are in use
by Sky-Tec customers today. Properly installed and operated, there is no
reason you shouldn’t expect the same levels of reliability, performance and
enjoyment from your ST2 starter purchase. Enjoy!
An important note from the Sky-Tec family scrap book: Please Read!
In February of the the year 2000, our own beloved Ercoupe 415C-D, N93543.s factory
OEM heavyweight pull-type Delco starter suffered damage from a kickback and the results
weren.t pretty as the ensuing engine teardown is now documented in the plane.s logbook.
Your Sky-Tec starter can break.
High-torque preignition events (kickbacks) can
and typically do damage starters. A piston
producing over 20 HP trying to make the engine
go backwards is no match for a starter producing
less than 2 HP. And the result, regardless of
starter make or manufacturer, is very often a
damaged starter and possibly even engine
damage.
To minimize your chances of kickback damage,
have your ignition system inspected and regu-
larly maintained by a qualified aircraft mechanic.
Starter damage resulting from high-torque impact
during start-up is not warrantable. If one should
occur, you should expect the starter to be damaged
and possibly even your engine as well. By install-
ing this (or any other starter), you are assuming all
responsibility for engine and starter damage due to
these impact events.
If you do not wish to be responsible for these dam-
ages, DO NOT INSTALL THE STARTER. Return it
immediately for a full refund from the dealer you
purchased it from.

Matthew_bailey wrote:...
- Both Bendix mags have had their 500 hour inspection within the last 5 hours (I asked them to look for anything that could cause a kick back problem. They said they found a sticky impulse coupler and replaced some parts) ....

Your "sticky" impulse coupler can be the sole reaon fo such problems.

I am not enamored of lightweight starters. They really do "spin" the engine faster during startups. It's not gentle, and I can't help my impression that it abuses the engine. ("spin" might better be described as "kick" or "jolt" in some cases.)

According to the mfr's of the lightweight starters they're not supposed to crank it so fast that the impulse couplers are de-activated, but I wonder about that. Impulse couplers are supposed to operate at/below 500 rpm and I've seen some lightweight starters crank engines at 600 by the tachometer. If that is the actual case, then the impulse couplers will disengage and not retard the spark....so an advanced ignition may occur during start, causing kick-back and possible serious engine damage.

I recommend original starters and overhauls for the same.

Sounds to me like the Sky Tec starter may be turning the engine too fast for the impulse coupling to retard the mag and the result is too much ignition advance for starting.
I had touble with the early Sky Tec starter on my cont. IO-360. It wouldn't release the starter drive and resulted in rxcessive starter drive wear. These starter drives are very expensive to replace. Like $1500.00. After realizing that their starter was a really screwed up piece of crap that the FAA should never have approved, they "gererously" agreed to exchange the defective designed piece of crap for their newly redesigined model for the just about the price of the new model. Needless to say, Sky Tec is high on my s--t list for the foreseeable future.
Perhaps it would be possible to install a resistor in the start circuit to drop the voltage to the sterter to reduce the cranking speed. If the problem is impulse coupling lockout speed, this might solve the problem.

gahorn wrote:

Matthew_bailey wrote:...
- Both Bendix mags have had their 500 hour inspection within the last 5 hours (I asked them to look for anything that could cause a kick back problem. They said they found a sticky impulse coupler and replaced some parts) ....

Your "sticky" impulse coupler can be the sole reaon fo such problems.

I am not enamored of lightweight starters. They really do "spin" the engine faster during startups. It's not gentle, and I can't help my impression that it abuses the engine. ("spin" might better be described as "kick" or "jolt" in some cases.)

According to the mfr's of the lightweight starters they're not supposed to crank it so fast that the impulse couplers are de-activated, but I wonder about that. Impulse couplers are supposed to operate at/below 500 rpm and I've seen some lightweight starters crank engines at 600 by the tachometer. If that is the actual case, then the impulse couplers will disengage and not retard the spark....so an advanced ignition may occur during start, causing kick-back and possible serious engine damage.

I recommend original starters and overhauls for the same.

Of course, once converted (and with the internal stud for the original clutch cut out) it's a major undertaking to return the starter to originality. Please, please, please.... folks..... think long and hard about it before making this conversion. Most problems with original starters are well known and easily, inexpensively repaired, and parts readily available at affordable prices. Neither brand of lightweight starter can be easily or cheaply returned to the good, old, reliable Delco-Remy system if you become dis-enchanted with the lightweight system.

A local FBO, that runs mostly Citabrias, has / had a similar problem of the new lightweight starters spinning too fast.
Their simple fix was fire up the starter, count to three, turn off the starter, back to both.
The engine usually started as the prop slowed down.