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 Post subject: lycoming O-290 timing
PostPosted: Sat Sep 11, 2010 4:21 pm 
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I'am wondering what the timing is for a lycoming o-290 dual mag, but mechanical adjustable rockers is. I know its not a o-290 D2, but I always figured the GPU's had one mag, any way I figured the timing would be around 25 BTDC, but I want to be sure, any help is appreciated.. Thanks

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PostPosted: Sat Sep 11, 2010 5:24 pm 
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25 degrees is correct , depending on the pistons you can advance the timing to 26 or 28 for more power , providing you aren't running D2 pistons.Lower compression = advanced timing for more power.
Twister69z

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PostPosted: Sat Sep 11, 2010 6:54 pm 
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THANKS.

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PostPosted: Sat Sep 11, 2010 8:27 pm 
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If you call Lycoming and give them the serial number , they will tell you when it was manufactured. Yes 25 to 28 degrees is the norm depending on what ya! got inside and you never know with a so called Airboat engine :lol: :lol: I've got my 0-290 apart as we speak, kept hearing a high pitch ping/cling, it ended up being a broken inner exhaust valve spring and one of the push rods, glad I stopped using it and investigated. Damn Aircraft engines aren't to bad to work on if ya! got the wright parts :roll: :roll: :roll:


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PostPosted: Sun Sep 12, 2010 9:46 am 
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I have plenty of parts if you need something. If you broke a pushrod, you may need a cam- the lobe may have been shaved/worn down, did your valve stick, or do you know what happened to break the spring and pushrod? Do you have mechanical or hydraulic tappets?

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PostPosted: Sun Sep 12, 2010 11:40 am 
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twister69z wrote:
25 degrees is correct , depending on the pistons you can advance the timing to 26 or 28 for more power , providing you aren't running D2 pistons.Lower compression = advanced timing for more power.
Twister69z

twister, if lower comp=advanced timing for more power then would it be a good idea to retard the timing a little if the comp has been increased over stock?? i have a lyc 200 with the comp at a legit 10.25 it runs great but it is a little hard to crank espically when its hot the timing is right on 25 always use avgas what do ya think?


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PostPosted: Sun Sep 12, 2010 1:40 pm 
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4 Pistons and a Prop...yes i'm interested in some parts, i will PM you soon :wink:


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PostPosted: Sun Sep 12, 2010 4:54 pm 
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actually there is a bullitan out that calls for timing to be reduced to 18 degrees to save exhaust valve wearing out premature.
it supposed to let the hot gas escape out the head and motor runs cooler. i timed the last one at 22 deg splitting the difference.it run great. next one will be at 18. you can look it up as i remember book stating 25 but them books are 60 years old.

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PostPosted: Sun Sep 12, 2010 6:07 pm 
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jb34974 wrote:
actually there is a bullitan out that calls for timing to be reduced to 18 degrees to save exhaust valve wearing out premature.
it supposed to let the hot gas escape out the head and motor runs cooler. i timed the last one at 22 deg splitting the difference.it run great. next one will be at 18. you can look it up as i remember book stating 25 but them books are 60 years old.

Good Tech Tip :!: :!:

Thank's :thumbright:


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PostPosted: Sun Sep 12, 2010 9:02 pm 
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JB stole my thunder! He is correct.

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PostPosted: Wed Sep 15, 2010 4:00 pm 
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I have mine set at 28d before. I have a friend with a D2 that he says is set at 30d before. 25d befre is stock aircraft but not enough guts for me.
try 25 and then try 28 and you'll be wantin to go to 30


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PostPosted: Wed Sep 15, 2010 8:40 pm 
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Remember when you advance that far detonation and higher temperatures rear their ugly heads.AV gas is a must if you have high compression pistons and a cooling shroud should help cool it.Even in the aviation world cylinder cracking happens even at correct timing settings. O-290's are prone to spark plug cracking.Good Luck!
Twister69z

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