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06-23-2014, 10:01 PM
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Join Date: Jan 2010
Location: Mission Viejo, CA
Posts: 130
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Unhappy Result on First Engine Start
I?ll get right to the sad punch line: I had a kickback and broke six teeth on the flywheel ring gear on my engine last weekend during the first start attempt.
Here are the details:
- Aero Sport Power IO-360-B2B
- 8.5:1 compression
- Dual PMags with jumper installed to operate on the A curve. I set the timing on the PMags right at TDC, or as close as my eyeball could align the flywheel mark to the hole in the starter case.
- Catto 3-blade prop
- Skytec 149 NL starter
- Andair fuel pump
- Airflow Performance fuel injection
I used the cold start procedure recommended by AFP for the fuel injection.
a) Purge Valve out (at ICO position)
b) Mixture ? Full Rich
c) Throttle open 1/2
d) Fuel Boost Pump ? ON for 30 to 45 seconds
e) Prime: Purge Valve to RUN position for 5 seconds then back to ICO
f) Throttle to 1/8
g) Propeller Area -- CLEAR
h) Crank engine until it fires then reduce throttle to idle
i) Purge Valve to RUN position On the first try the engine fired after about two revolutions and ran for about 3 seconds then died before I could get the purge valve to the run position. I primed again and it did the same thing. I tried several more times with the same result. It really seemed like it was trying to start but was starved of fuel. On the sixth try I heard a clunk and the prop stuttered about a second after I pressed the starter button. Six teeth missing from the ring gear. The starter looks fine with no visible damage and the shear pin seems to be intact.
Obviously I need a new ring gear but the most important thing is trying to understand why this happened and prevent it from happening again. I thought the Skytec NL starter shear pin was supposed to protect the ring gear from damage.
I would like to hear comments on possible causes of this incident. The tooth damage was in several different areas. The photo shows it pretty well (yes, I already pulled the flywheel off). What can I do to make sure this is the last time this happens?

__________________
John Harrell
RV-7A Tip-up, Aero Sport Power IO-360, Dual PMags, AFP FI, Catto 3-blade, Dual Dynon Skyviews
Flying since August 2014
Mission Viejo, CA
http://www.johnsrv7a.wordpress.com
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06-23-2014, 10:17 PM
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Join Date: Aug 2009
Location: Redding,Ca
Posts: 633
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Kickback
This sounds like it's not timed correctly, possibly you have the ignition leads plumbed to the wrong cylinders? The two wires closest to the vacuum fitting go the the cylinders closest to the prop, see the manual. It's a wasted spark system so it doesn't matter if you time it to the wrong stroke, as long as you had TDC.
Cheer up though, the ring gear is probably cheaper than the starter, but I would have hoped the shear pin in the starter would let go first.
Good luck.
Tim
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06-23-2014, 10:34 PM
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ring gear
I agree timing probably off. Ring gears are pretty easy to replace.
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06-23-2014, 10:50 PM
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Join Date: Aug 2006
Location: santa barbara, CA
Posts: 1,682
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It is certainly possible to suffer a kickback with pmags even if correctly timed, especially when using a lightweight prop. Ask me how i know...
Assuming you have the leads attached correctly and were able to identify TDC correctly, there are a few additional things that will minimize the chances for reoccurrence. First, retard the timing slightly by rotating the ring gear teeth past TDC by several teeth. Second, if the engine doesn't start on first attempt, on subsequent attempts, (master still on) set your switches to ground the p-leads, hit and hold the start button to let the prop gain momentum for a few seconds, then unground the p leads while continuing to hold the start button. Harder to write than do.
Info from brad at emagair. Works for me.
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06-23-2014, 11:04 PM
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Join Date: Dec 2005
Posts: 976
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Ensure your Ring Gear marks are designed to align with the starter mark and not the top of the crankcase centreline. Ask me how I know  albeit got away without any damage.
Diagnosed by someone with better knowledge than me reverting to first principles and establishing TDC with a plug out and checking piston #1 TDC.
I have also had both P-Mags re-time themselves once preventing start - I can only think some unusual voltage patterns? So check timing again.
No idea about the AFP procedure, but seems somewhat complex? I had an RV-8 with AFP, albeit purge valve not fitted. Started fine using standard cold FI procedures i.e. Mix Rich 1/2 throttle, prime for 3-5s (until you get FP), then ICO + 1/8 throttle and start.
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06-24-2014, 04:16 AM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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The P-mags fire at TDC when below 200 RPM's. If your timing is off a little, you can get a kickback.
How many teeth is your starter ring? If it has 122 teeth then regarding it one tooth is equal to 2.9 degrees. (360 divided by 122)
One other thing, when my engine doesn't catch on the first try, I usually cycle the power to the P-mags. No real reason other than I am comfortable doing that and my P-mags are wired in a non-standard fashion so I can do that independent of the master switch.
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
Last edited by N941WR : 06-24-2014 at 04:18 AM.
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06-24-2014, 05:10 AM
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Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,219
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With a lightweight prop, I engage the starter for a couple of prop revolutions and turn on the ignition system while the engine is already spinning.
__________________
Kyle Boatright
Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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06-24-2014, 06:55 AM
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Join Date: Feb 2005
Location: Bridgewater, MA - KPYM
Posts: 458
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What Andy said......been there, done that. On my ring gear there are timing marks both on the front *and* the back of the ring gear. It's very easy to use the wrong mark when aligning the TDC mark with the case seam.
It is also a good idea to confirm that the ring gear has been installed correctly.
A good reference: Lycoming documentation on Engine Timing Marks
__________________
Mike Draper
RV-8 N468RV
First Flight 11/13/2011
TMX0360, Pmags, CS
Bridgewater, MA
KPYM
Last edited by drill_and_buck : 06-24-2014 at 01:18 PM.
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06-24-2014, 07:19 AM
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Join Date: Mar 2007
Location: Gold Coast - Australia
Posts: 137
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149 teeth
[quote=N941WR;891284]The P-mags fire at TDC when below 200 RPM's. If your timing is off a little, you can get a kickback.
How many teeth is your starter ring? If it has 122 teeth then regarding it one tooth is equal to 2.9 degrees. (360 divided by 122)
John did mention he is using a Skytech 149 NL starter hence it is 149 teeth = 2.4 degrees
__________________
Peter Vernon
Eagle Heights, Queensland, Australia
RV8, QB Wings, Standard Build Fuse (85% @ April 12)
email: pve95448@bigpond.net.au
Paid dues ... pleased to support DR
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06-24-2014, 07:44 AM
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Join Date: Aug 2005
Location: Pasadena CA
Posts: 2,484
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I'm generally critical of 'recommended' start procedures on FI Lycomings, and this is no different. Cranking at 1/2 throttle seems like a very bad idea, no way you can move all the controls quick enough to follow that procedure without having the engine >1000rpm with essentially no oil pressure.
My general flow:
Mixture rich (In your case, purge valve RUN as well)
Fuel pump 3-7 seconds, looking for fuel pressure to show on the gauge generally.
throttle cracked, just off the idle stop
Crank until it fires, and then release immediately, let it either run or die. As soon as it fires, the starter is just weighing it down.
That cold start procedure works in every airplane I've tried it in. Leaving the throttle up halfway seems a recipe for disaster.
__________________
Stephen Samuelian, CFII, A&P IA, CTO
RV4 wing in Jig @ KPOC
RV7 emp built
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