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Starter case broke at start

RVG8tor

Well Known Member
IO-360 739 (hobbs) Hours in 9 years.
Sky-Tec 149-NL, I never had any start issues.

Plane sat for 5 months while I traveled this summer. Returned, flew once which revealed a brake problem. solved that and yesterday when I went to start, prop moved then stops. I am not sure if it even made a full revolution. Got out and tried to hand turn the prop, it moved but heard loose items, so I stopped there to look under the cowling. After taking the cowling off I found the starter case broken, one part sitting on top of the air box.

Prop rotates through fine and fells like good compression on all cylinders.

In April I did not notice any cracking in the starter case or any issues with fly wheel or starter teeth. Currently the flywheel looks fine, no broken teeth.

The shear pin did not break so I am fairly certain this was not a kickback issue.

I am at a loss as to how this could happen since I have had no indications that the starter was having any issues.

So aside from a new starter, I am sure the warranty is long passed, what other inspections should I perform?

Is it worth sending the starter to Sky-Tec for rebuild to have a spare on the shelf?

Thank for advice.


https://drive.google.com/file/d/1N6Gs8FLSTCvVtTGo1FX377y1XY-_bbVm/view?usp=sharing

https://drive.google.com/file/d/1xwuaWJ-UMu8naMnxLaw1w--CdfISAQUX/view?usp=sharing

https://drive.google.com/file/d/1sapNmPtESylNGzMY-lEPPgmOQr5HKj27/view?usp=sharing
 
In the first pic, there are significantly large gouges in the internal ring gear teeth. Assuming that is a steel gear, so it couldn't have been damaged by the aluminum case during it's destruction. Seems that something came loose inside and caused that gear to jam. Once that gear was jammed/siezed (force is now outward/leverred and not rotational), the only way to relieve the torque from the motor was for the case to crack and let the gear out.

Not a positive diagnosis, but an idea. It does not seem likely this was caused by an engine issue. In that case, the shear pin would either be broken or deformed.

Larry
 
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I suspect a fatigue crack grew from the bolt hole threaded area. you probably had this crack for awhile and this just happened to be when it had grown large enough to fail. starters work harder on a cold engine.
 
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Looks like the gear teeth internal to the starter are not chewed up, just picked up lots of case material.

The one drive gear tooth at 3 O'Clock that engages the flywheel ring sure has a dinger in its edge.

Is that normal or do any other drive gear teeth look similar? Was the starter dropped? How is the ring gear in the flywheel?
 
I have seen a number of the NL series starters with loose thru bolts which hold the assy together, if they get loose enough I imagine this could be the end result.
 
Fly any aerobatics?
Some of the Cole Hersee starter contactors can engage in flight at around 5G+.
That would do exactly that kind of damage. Someone on the forum had this happen before.

Some builders mount the starter contactor sideways so that can't happen, but it's better to just get a proper one with a stronger spring.

In search of a better one I cut apart a Lamar contactor and weighed the plunger on it. Calculated it to engage at 14G.
 
Contact Hartzell

Hartzell bought Sky-tec. I had a failure similar but not as dramatic as yours and Hartzell replaced the unit at no charge though six years old at the time. They knew of a latent problem but I never got specifics.

John Siebold
Now building #6 'cause there's nothin' on TV
 
I have seen a number of the NL series starters with loose thru bolts which hold the assy together, if they get loose enough I imagine this could be the end result.

The 149NL starters tend to stretch the through bolts over time, needing a retightening at roughly 150 hours or thereabouts. At 900 hours I've tightened mine at least 3 times and replaced the starter once.

It's a good starter - just lightweight and therefor subject to wear. I use it specifically for the low weight, and accept the accelerated wear.
 
The 149NL starters tend to stretch the through bolts over time, needing a retightening at roughly 150 hours or thereabouts. At 900 hours I've tightened mine at least 3 times and replaced the starter once.

Same experience - bolts stretched, tightened once, lost once (presumably loosened again vs broken). So far the replacement is holding well. I second the recommendation to check the starter routinely - like every time the cowl is off!
 
More info

Fly any aerobatics?
Some of the Cole Hersee starter contactors can engage in flight at around 5G+.
That would do exactly that kind of damage. Someone on the forum had this happen before.

Some builders mount the starter contactor sideways so that can't happen, but it's better to just get a proper one with a stronger spring.

In search of a better one I cut apart a Lamar contactor and weighed the plunger on it. Calculated it to engage at 14G.

I have done a fair amount of aerobatics, I mounted my start relay upside down for the reason you mention. I don't see any signs the starter has been engaging during flight. I also have a light to warn if the starter is engaged.

The 149NL starters tend to stretch the through bolts over time, needing a retightening at roughly 150 hours or thereabouts. At 900 hours I've tightened mine at least 3 times and replaced the starter once.

It's a good starter - just lightweight and therefor subject to wear. I use it specifically for the low weight, and accept the accelerated wear.

I will keep this in mind, I have never and done this, You are talking about the bolts that go the length of the starter?


More pictures as I spent some time looking at the parts. The internal gear was not damaged, the photo in the original post showed grease on the teeth that made it look like damage.

The gear that engages the fly wheel has normal ware and not missing teeth.

The shaft that goes into a slip gear broke entirely when things failed. I guess that is a result of failure or maybe the cause.

I pulled the drive gear clear so you can see the point where it broke, then a photo of the other half still in the main body of the starter. The main body half rotates smoothly. The front drive part rotates but is not smooth.

Hopefully today, I will get some info from Hartzel as to what they can help me with warranty wise.

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view
 
I have done a fair amount of aerobatics, I mounted my start relay upside down for the reason you mention. I don't see any signs the starter has been engaging during flight. I also have a light to warn if the starter is engaged.



I will keep this in mind, I have never and done this, You are talking about the bolts that go the length of the starter?


More pictures as I spent some time looking at the parts. The internal gear was not damaged, the photo in the original post showed grease on the teeth that made it look like damage.

The gear that engages the fly wheel has normal ware and not missing teeth.

The shaft that goes into a slip gear broke entirely when things failed. I guess that is a result of failure or maybe the cause.

I pulled the drive gear clear so you can see the point where it broke, then a photo of the other half still in the main body of the starter. The main body half rotates smoothly. The front drive part rotates but is not smooth.

Hopefully today, I will get some info from Hartzel as to what they can help me with warranty wise.

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view

I have had the long bolts loosen as well. However, they only hold the motor assy to the main gear assembly. The do not go through the main assy that cracked in your case, so don't see how they could have caused this damage. Any chance a loose item fell and got jammed between the bendix gear and the flywheel gear? The geometry of the crack looks like pressure was applied downward on the bendix gear.

Larry
 
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Sounds like the old Chevy starter problems. Bolts get loose, or no/wrong shims, and the housings would break every time.
Tom
 
New Starter on the way :)

Quick response from Sky-Tec Aero (Harzell), they are sending a new starter.

The person I spoke with said that my starter was old enough that it might have some issue as others in that year range and that I should just get online and make a warranty claim. Within an hour they responded.

The warranty person did say that I might have had a kick-back but I am not sure but glad for the warning. I have Dual P-Mags with the firmware that was supposed to help prevent kickback issues.

I will double check the timing before I attempt the first start with the new starter.

Very please with the customer support!

Cheers
 
Flywheel Damage

So the flywheel has some damage to the teeth but there are non missing. Only one section is gouged up and looks like it would need some dressing up.

Anyone with experience, is dressing the teeth up a good course of action or should the flywheel be replaced?

Pictures of the teeth

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Cheers
 
Dressing removes material, so that would not be the conventional wisdom.
I have seen ring gears in worse shape on operating airplanes, but every deformed tooth is an opportunity for a misengagement leading to another broken starter.
For about $120, and a few hours of your time, you can pull the flywheel, (ring gear support in Lycon lexicon) and install a new ring gear. Multiple threads here about doing it. Involves cutting the old ring gear off, heating the new gear to 450F in the oven, and dropping it in place.
Saves trashing a new starter.
 
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