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miyer2u
Joined: 19 Nov 2009
Posts: 41
Location: Oregon
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 Posted: Wed Mar 02, 2016 1:39 pm Post subject: Rotax 503 - 300 Hour Rebuild - Advice |
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Hello Kolbers,
I have 280 HRS on my 503. I decarbed it, checked the crank, Cleant the piston grooves, rings, dome, put new gaskets and assembled it back. Test ran and alls well.
I DID NOT change the needle bearings and wanted to know if thats an issue.
I have heard the needle bearings can break in the 300 hour range? is that true? Should I go ahead and replace them? Any experience that you could share?
Thanks much!
Mahesh
FS-2
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Sat Mar 05, 2016 7:48 pm Post subject: Re: Rotax 503 - 300 Hour Rebuild - Advice |
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I think no one wants to reply because no one wants to give you bad advice. I currently have 270 hours on my 582, and plan to run it to 450 hours. Given my age, and the number of hours I fly each year, that will probably be sufficient for my aviating future.
BUT
I consistently try and run it at 5,400 rpm, which keeps the centrifugal load on the crank bearings down, and should extend the crank life.
Should. Hmm..
I guess in a another few years I'll find out if that was a good idea.
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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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Jim Baker
Joined: 30 Mar 2006
Posts: 181
Location: Sayre, PA
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| Posted: Sun Mar 06, 2016 6:17 am Post subject: Rotax 503 - 300 Hour Rebuild - Advice |
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Richard brings up a point that drove me to acquiring a Hirth, specifically the old 2704. Max rpm for that model is 5400. I normally fly at 3500 to 3900 rpm, depending on the day and the resultant EGT. Combine that with 624 CC and you get a powerplant that creates its max torque well down the Rev range and is creating much less heat in the cylinder per unit time than the higher revving two stroke.
I, however, run two strokes much differently than others would. The most common ailment heard is burned oil creating coke on the piston crown, ring lands (especially Dykes type, which is the type Rotax uses) and exhaust ports. The oil in the ring lands is cooked and leaves behind the carbon residue from that cooking. Same for crowns and ports.
EGT is, I believe, my key. I don't run an RPM or an airspeed, simply an EGT that is sufficiently high to more completely burn the fuel mixed with the oil. Generally that's in the 1150 to 1200 range. I'll often read an article up to the point that the "expert" says no one should run below 32 or 20:1 ratios. There goes the credibility.
On top of that, more oil is not better. Too much oil will cause roller bearing balls to hydrodynamically skid instead of roll. The amount of lubrication a quality ball bearing or needle bearing needs is vanishingly small. Consider a wheel bearing....packed with grease, initially, after awhile the grease retreats from contact with the balls and ony sporadically comes in contact, usually from some high G load such as a pothole. Re-pack a really old bearing and watch what comes out...congealed chunks of lubicant. The wrist pin needle bearings are the more susceptible to heat damage from lack of lubrication.
So. I run 100:1 oil mix. Doesn't matter which one, I'm not pushing a brand. The less oil there is, the less there is to leave carbon behind. It's a fine balancing act to not use too little that the bearings complain. I think I get away with it because my larger piston surface area more readily sheds heat via cylinder wall contact, less heat per unit time, and the cooling of the underside of the piston by the incoming charge, the oil doesn't have a chance to coke and leave deposits behind. That, and the fact that I don't have a Dykes top ring. Dykes are great at more complete cylinder sealing because of the larger ring/cylinder wall contact area but it also makes them hotter because of that contact.
After 600 hours, no decarbon needed. Plugs have been replaced once, more from curiosity than anything else. They looked just like four stroke plugs, just a light tan and no coking up into the insulator well.
Maybe I'm spouting crap. My Gordon Jennings handbook, the SAE papers I've read have confirmed, at least in my mind, what I've just posted....but as I said, may be crap. Or not.
Jim Baker
405 426 5377
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pipercolt
Joined: 08 Jan 2012
Posts: 46
Location: Randolph New York
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| Posted: Sun Mar 06, 2016 9:49 am Post subject: Rotax 503 - 300 Hour Rebuild - Advice |
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Hi Jim
Thanks for the info. I purchased a recently rebuilt 582 and the previous owner said that the man who rebuilt the engine the first time told him to fun it 100 to 1 and not decarbon it. It was overhauled with about 800 hours on it and was in great condition with minimal parts replaced. Interesting isn't it.
Bob
On Sunday, March 6, 2016 9:12 AM, Jim Baker <jimbaker(at)npacc.net> wrote:
--> Kolb-List message posted by: Jim Baker <jimbaker(at)npacc.net (jimbaker(at)npacc.net)>
Richard brings up a point that drove me to acquiring a Hirth, specifically the old 2704. Max rpm for that model is 5400. I normally fly at 3500 to 3900 rpm, depending on the day and the resultant EGT. Combine that with 624 CC and you get a powerplant that creates its max torque well down the Rev range and is creating much less heat in the cylinder per unit time than the higher revving two stroke.
I, however, run two strokes much differently than others would. The most common ailment heard is burned oil creating coke on the piston crown, ring lands (especially Dykes type, which is the type Rotax uses) and exhaust ports. The oil in the ring lands is cooked and leaves behind the carbon residue from that cooking. Same for crowns and ports.
EGT is, I believe, my key. I don't run an RPM or an airspeed, simply an EGT that is sufficiently high to more completely burn the fuel mixed with the oil. Generally that's in the 1150 to 1200 range. I'll often read an article up to the point that the "expert" says no one should run below 32 or 20:1 ratios. There goes the credibility.
On top of that, more oil is not better. Too much oil will cause roller bearing balls to hydrodynamically skid instead of roll. The amount of lubrication a quality ball bearing or needle bearing needs is vanishingly small. Consider a wheel bearing....packed with grease, initially, after awhile the grease retreats from contact with the balls and ony sporadically comes in contact, usually from some high G load such as a pothole. Re-pack a really old bearing and watch what comes out...congealed chunks of lubicant. The wrist pin needle bearings are the more susceptible to heat damage from lack of lubrication.
So. I run 100:1 oil mix. Doesn't matter which one, I'm not pushing a brand. The less oil there is, the less there is to leave carbon behind. It's a fine balancing act to not use too little that the bearings complain. I think I get away with it because my larger piston surface area more readily sheds heat via cylinder wall contact, less heat per unit time, and the cooling of the underside of the piston by the incoming charge, the oil doesn't have a chance to coke and leave deposits behind. That, and the fact that I don't have a Dykes top ring. Dykes are great at more complete cylinder sealing because of the larger ring/cylinder wall contact area but it also makes them hotter because of that contact.
After 600 hours, no decarbon needed. Plugs have been replaced once, more from curiosity than anything else. They looked just like four stroke plugs, just a light tan and no coking up into the insulator well.
Maybe I'm spouting crap. My Gordon Jennings handbook, the SAE papers I've read have confirmed, at least in my mind, what I've just posted....but as I said, may be crap. Or not.
Jim Baker
405 426 5377
--
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miyer2u
Joined: 19 Nov 2009
Posts: 41
Location: Oregon
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| Posted: Mon Mar 07, 2016 8:18 am Post subject: Re: Rotax 503 - 300 Hour Rebuild - Advice |
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Thank you Richard and Jim for your inputs! Appreciate it.
Mahesh
FS2
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