[dougknight]

I just had my 2nd kickback and starter breakage in just 380 hrs TT. At this rate I'm gonna break the bank buying starters.

Here is my set-up

rv-9a
Aerosport rebuilt O-320-D2A lycoming 160 hp @ 2700 rpm
ACS standard starter switch
2 slick mags 4370 and 4371, one impulse (on left) and the other non impulse (on right)
149-LSX skytech flyweight starter
carburated
fixed pitch wood prop, Sensenitch
engine timed @ 25 degrees BTDC (per both nameplate and lyc operators manual)
Lag on impulse coupling = 20 degrees


After the first kickback @ 70 hrs TT I was told the ACS switch could be the culprit as the right mag becomes hot as soon as you let go the key and it spring returns from the "start" position back to the "both" position. If let go at just the most inoppertune time the right mag would/could fire at 25 deg BTDC resulting in the kickback. Made sense to me, so I put the right mag on it's own manual switch so as to keep it grounded and out of the picture during the start sequence. Once the engine started the right mag was then allowed to come on line via the switch. Started just fine the next 300 hrs and approx 500 starts and I thought I had found the cure. Then it happend AGAIN.

The manual switch was checked after this latest incident and confirmed the right mag was grounded and totally out of the picture. So how did it happen? I have to focus on the left mag and its timing.

I'm no expert but a little simple math tells me when the impulse is fireing the engine is still 5 degrees BTDC. I'm supprised I haven't seen more kickbacks actually, if this is true.

Am I seeing this correctly? What can I do to prevent kickbacks in the future?
Can I change the engine timing to 20 degrees BTDC so it matches the lag of the impulse? even tho both nameplate and opperators manual say 25 degrees. Would I lose horsepower? Could it damage the engine somehow?

Can the impulse coupling be changed from 20 degrees to 25 degrees?

Is the wood prop comming into play? Less weight or inertia to carry the crank on through and over the top during the start sequence.


Any insight or help from the community is much appriciated

doug
rv-9a
#625

 

[aerhed]

Don't change your timing. You'll turn it into a dog with big mag drops. Your wood prop isn't helping, but I would look for a new impulse coupling with a bigger lag angle.

 

[Ron Lee]

Caution: questionable advice may follow

When I had my two blade wood prop, I often had issues with it being able to crank through a certain compression area. I do not believe that it was a kickback or how close it may have come to that condition. I switched from an Odyssey 680 to a 925 battery and that seemed to solve that issue.

I changed over to a three blade Catto. Later I also changed to an NL starter.

Now I am back using a 680 battery and it still starts well.

You should get competent advice on whether the starter and/or battery combo may be a factor.

You may be able to get into a NL starter with a rebate on your old starter. Ask.

 

[dougknight]

ron:
I've already talked to the factory and am going to upgrade to the NL series because it has the shear pin and is something I can fix in-house or in the field should it occur again. But I would much rather identify and fix the root problem than put a band-aid on it.

thanks for the insight, keep the ideas comming

doug

 

[humptybump]

The NL started has been reported by others to address a sluggish start.

My airplane had an Aymar Demuth wood prop that weighed all of 11lbs. The builder added an inertia ring to help with starting since the propeller had no real mass to speak of.