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Kick back question

M

marshmaster pat

Well-known member
Helping work on a Lycoming 0-540. It was giving some kick back as well as running alittle rough. Checked compression and all 6 were bad (lots of hours on it). We did a top end job with some help and fired her up. The magnetos had alot of drop in them, so we stopped the run in process and the mags were rebuilt. Installed them and tried to fire her up. Kicked back hard on the first try, busted in inside gears in one of the new flush mount $tarter$. Ouch.

While it is getting redone, we started at TDC#1 and checked out everything. Timing is all ok and set right. ???

Could a battery with low Amp or volts, have enough juice to turn that Lycoming part way over and then cause kickback?

Ideas anyone. Never had this problem that was not an issue of mags being out of time. Looking for other things to check on while we wait for the starter.

Thanks
 
Pat,

It sounds like it might an impulse problem. I would start there. My son's 540 parallel valve runs 11 to 1 compression with slick start. I have seen the starter fail to get it through but I have not seen a kick back.

It sounds to me like it fired before tdc. I don't know what else could kick back with enough force to break a starter.

I am sure you know that the impulse has to be in the advanced position when timing the engine.


If it has only one impulse, then use that mag only for start.

jim
 
I don't know anything about the 540 but I've seen this before on Lycoming O-360's. It is usually a mag problem. The weak battery may be a indication that one mag is not impulse. Lycomings turn over faster and if you start on Both mags you may never notice the non-impuse firing but if the starter is just slow enough it can cause the kickback. Here is a link that explains it:
http://www.sacskyranch.com/eng2.htm
 
ONA540":2styuj7a said:
WHEN STARTING HOT OR COLD I ALWAYS START TURNING THE MOTOR OVER (MAGS OFF) AND THEN FLIP THE MAGS ON
Click to expand...

sounds like something to be learned here....can you explain the reasoning behind this?
 
Should have clarified that we are running two impulse mags. Only had one mag hot when we tried to fire her up.

Jim - Good to hear from you, your reasoning matches mine.

Will spend some time this weekend working on it. Maybe we can figure something out. Start back at step # 1 in the manuel.

Have an only bracket and bracket mounted high torque starter over here. May try that.

Thanks

pat
 
It is good you have two impulse mags. It still sounds like a bad mag or timing issue. To cause a kickback that will break the starter means the cylinder fired before it got to top dead center. The impulse coupling could have a defective part and is not retarding the spark when it should. Do you have a mag shop that can check it for you and is it the right impulse setting? I assume it is the right mag for the engine.
 
ok I am no mechanical genius but if your spinning the motor over mags off is it possible you are getting to much fuel in the cylinders then when you hit the mag the combustion has that extra strength to make the kick back problem :?:
 
Pat,

I have never tried it, but it looks to me like you could turn it by hand and see where the impulse snaps.

Be careful though and don't get in the way of the prop.

jim
 
i'm no mechanical expert either, but i've seen a handful of starters get busted from turning the motor over with a mag on. i've always been taught to ALWAYS turn it over before turning on the mag. my friend owns a cont 520 and he broke 3 or 4 starters in a years time. once he started turning it over with mags off, he hasn't broken one at all... seems to me that a mag slightly out of time would put a serious strain on any starter damaging it as soon as it got in a bind or kicked back....
 
I wonder if the impulse coupling were changed when the mags were re-built.
Perhaps they are the wrong lag angle couplings if they were.
Just a thought.

I'd pull it throgh watching the timing marks, to see where the couplings snap at, like Jim said.

Should tell ya if it's in the ballpark.
 
The degree of impulse coupling retard is directly proportional to crank speed. Take for example the Lycoming O-235-L2C engine. The original starter cranked the engine too fast. Lycoming Service Instruction 1362 changed the lag angle of the impulse coupling from 15 degrees to 5 degrees to compensate for the fast turning starter and greatly improved starting on this engine. (with the 5 degree lag angle the engine may have a tendency to kick-back during hand propping. Don't hand prop!) The weak battery could also have caused the engine to have turned too slowly for the lag angle set for the mag.

When Lycomings kickback they can break the starter housing. It still sounds like a mag problem with timing, improper impulse lag for that starter, defective impulse coupler or other part that is letting the mag fire too early.
 
recheck your timing. You need to pull the motor past top dead center with the mags off grounded out. be care full until you hear each mag click. This should happen with in 5 to 15 degree after top dead center. Then back the engine up on till points close & bump it forward until they open At the timing mark either 20 or 25 degrees advanced. When you turn forward & the mag with implus coupling clicks before top dead center (mag fires when it clicks) this mag with the implus coupling is either to far advanced, or wrong impluse coupling. if it does not clicks period you have a problem with the coupling or striker post. The newer 6300 series slicks are bad about this.

If you have a non impulse coupling mag IT MUST BE GROUNDED OUT WHEN STARTING. IF not it will fire & give you kick back. If an impulse coupling is not working this will cause the mag to fire early & kick back . The slick mag in the 0540 are bad about this. The bendix is not so bad. Most of the time you can rotate the striker post & clean the coupling & this will fix it. IF you have problems PM me. I have run the 0540 for years
 
duckluv26":232p5lhp said:
i'm no mechanical expert either, but i've seen a handful of starters get busted from turning the motor over with a mag on. i've always been taught to ALWAYS turn it over before turning on the mag. my friend owns a cont 520 and he broke 3 or 4 starters in a years time. once he started turning it over with mags off, he hasn't broken one at all... seems to me that a mag slightly out of time would put a serious strain on any starter damaging it as soon as it got in a bind or kicked back....
Click to expand...

this gets the prop spinning, and the intertia of the prop helps carry it through the ignition point, rather than the poor little starter having to sling a piece of wood and push a 6" piston through a compression stroke.

Sounds like somebody taught you how to fire up a Chrysler starter equipped boat....
 
The started does not carry it Thur the ignition point if the mags are working wright. The wright coupling function to to delay the spark until after top dead center- no kick back -kick forward-start. When it trips it spins the mag fast to get a hot spark. If only one impluse coupling is used the other mag must be grounded out & not runed on until the motor is running or it will kick back & blow the starter
 
Too many cooks apparently ruined the soup they say. Well that might be true with me and my help.

Three of us make believe mechanics were working on her. Somehow ??? we never tightened the rear starter nuts or the nut in the front by the crank. :shock: We ruined the inside gears alright, but also cracked the aluminum frame of the starter. That thing produced some great torque apparently on the kick back. Also had a battery that was only pushing about 650 amps. Jumped it up to a 800 cranking amps battery and another starter. Ran like a top through the break ins.

Glad we had someone that knew what they were doing when we changed all 6 jugs.

Thing is that no one remembers who supposedly tightened up the starter nuts. :oops:

P.S. - rechecked all the timing and things were set as they were supposed to be. Even pulled it through by hand and both magnetos click at almost the exact time. Thanks for the advice everyone.
 
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