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#1
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Ahhh...what about the engines
For how many years should you operate an engine which has not reached TBO without a full overhaul?
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#2
06-19-02, 11:32 AM
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Well....... it depends
That is kinda like saying how long will a light bulb last.... smile...
The two reasons that you want to overhaul your engines are these.... First we have worn out the parts ... yep this usually never happens unless you are using your plane on a daily basis... and have reached the manufactures time limit on RECOMENDED overhaul... Now if you are using your plane in the states under part 91... and the engine is still making its rated power you can contenue to use it... as the power output is the deciding factor... well kinda..... see we have these bearings and valves that start to go away... and if they (the bearings) get too far gone the soft parts (lead/babbett) are not their anymore... and the next harder backing part (copper)start working on the crank ... which will score it and wear it out... so doing a overhaul will replace the soft part of the bearing... and will save you from having to buy more expensive parts... like cranks.. etc... just to start off... Now the second reason we overhaul the engines.... is because of RUSTED parts and the time limit on such things as the rubber gaskets... which are under the cyc bases... rocker arm tubes... and the missing seal (silk thread) that makes up the crankcase seal...(no to use other things is not best...)... So here we have a engine that sits.. never got to see any time in the air... and so it develops condensation and the steel parts start to rust and pit... and yes they do... Cyc that are pitted are big users of oil because as the rings go up the holes or cavities fill with oil... as the rings go down... they pass over these grand canyons' and allow the oil to be exposed to the heat of combustion... and burns off... but..... that is not all... we have gears and shafts like the accessory shaft that rust and lock the gears on... pit the hardness on the teeth and cause failures... So to answer your question about how long... the manufacture has specs in the shop manual... and their he says that you should overhaul the engine every so often.. 5 years but, realisticly we see them about every 10years... but again it depends on a lot of things... useage... storage.. and maintance... so all of these are variables that can determine exactly when... Hoses and flex parts are supposed to be replaced every 5 years ... again that is in the service manual... you do have one... someone else want to go over what manuals one should have for him... thanks... Hope this helps.. GMAs
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#3
06-20-02, 03:41 PM
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George, thanks for your reply but you got me thinking when you posted "ahhh... what about the props??? " I have been making plans for a trip to Aruba and the island of Margarita in Venezuela and since my engines have 16 years since they were overhauled I started asking questions. Mine is a 74 G and normall aspiration engines with about 1050 hours on both, oil comsumption is around 1 quart for every 8 hours on both engines and there has been no variation in the oil pressure and oil temperature in many many years. I fly the aircraft at least one hour a week because of the high humidity in my country, would that be enough for a healthy engine? I have been told that oil temperature under normal operations should be no less than 180 degrees to get rid of the humidity, my engines under normal conditions have an indication of around 140 degrees and yes every 5 years I change all hoses and flexibles on all of the aircraft. Please take into consideration that my knowledge about mechanics is nil, thanks again
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#4
06-20-02, 05:50 PM
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Oil temp... is not what you see... its what is happening
As to the subject of the oil temp... lets first look at how its is controlled... first it has a heater... yep the back sides of the pistons... so what you see on the temp guage is not necessarly what the real inside temp is... it is usually much higher... and that is where the moisture is driven out of the oil... in the forms of crank case exhausting...
Second we have the cooler... yep their is a device that causes the oil to cool off... its the oil cooler located on the engine... its job is to cool the oil... but.... we don't want big variations in oil temp so they put a cooler by pass on it ... sort of ....the thermostat in the oil line is like a cars is in line with the radiator.... execpt that this one doesn't block until it get warm... so it maintains the temp of the oil... till it starts getting too hot then the varitherm blocks off the bypass and the oil is routed thru the oil cooler... which then tries to bring it back down.... simple huh... Now if your oil temp is truly runing cold... i.e you have checked the gauge and other parts and they are correct... then you need to go look at the varitherm... and make sure its not stuck closed... yep closed... they do that... and then the oil temp gets too cold.... all the time... not good for the engine.... as other parts are dependent on the temp being about right..... for constant expansion and cycling... Check the oil temp... and then if off check the varitherm... As to the props... you get a lot of gunk mixed with moisture in oil... and it really fills up the piston area in the prop...making the thing slugish and not work right... you may want to have them checked... its not too expensive and like insurance... better to have than not... Good luck.. GMAs...
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#5
06-20-02, 06:05 PM
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Gmas, could the valve stay open and in by-pass mode and not go thru oil coller, would this then show a high oil temp. Running 210 at cruise and 216 at slow climb 150 MPH, to keep cool. Open and close cowl flaps, a few degrees of change. New engine on rear of 73 P-337-G
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#6
06-20-02, 06:20 PM
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GMAs, I do overhaul every five years to the propellers. IŽll check the oil temperature. Thanks, Chachi
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#7
06-20-02, 06:54 PM
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Oil coolers, varitherms and general engine temp control...
Yes it can stick open.. and their have been cases that we have seen... it results in high oil temp without much cooling once airborne... you might check and see if it is... it screws into the back of the engine oil cooler adapter... its that big silver looking thing with a nut on it... about 1 inch in dia and 1 inch long... it treads out and the guts that are inside... come with it... of the cooler adapter... it has a safety wire on it...
One way of testing it is to put it in a pan of water.. on the stove... and use a candy theromoter... should start to change at about 160 deg f. and be almost all the way at about 180... or so.. they can change the temps on them with different ones ...just like your car theromostat... they make all kinds of temps... but, stick with the original... Now a couple of more thing... to check also...you might want to remove it real careful... and make sure its not full of junk... as that too will not let it seat on the boss... thus keeping it in bypass mode.... Oil coolers... send it to pacific oil coolers... to get overhauled... they can make it like new... and yes they do plug up with carbon that just won't flush out.... we have found and toured the shop their... get ahold of Mr. Sourman... and let him know that your with the skymasters group... he said he would give us a discount... they will return it to you better than new... and its fairly inexpensive too... we send ours out every 5 years and have them done... they have the equipment for it as well as the experteese... and will pick them up over at El Monte field if you make arangements... prior... we have found they do excellent work and are reasonable... if you need the no... let me know... I will put you in contact with them... and I think they are on the web now... too.. so you might check it out... Last but, not least.. the baffeling and seals around the engine... here we just can't say enough.. and seems to be a major problem in aircraft that are not maintained correctly... so check it out too... My money is on the varitherm... and oil cooler if you haven't had them checked in a while... Of course when you start pyleing on accessories like AC and larger items.. things are going to get hotter... so watch the loading too... Hope this helps.. GMAs...
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#9
06-20-02, 07:07 PM
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ahhhh and a few more tricks of cooling..
I guess I forgot about the last thing I was going to say... seeings how they use a crush gasket... if you use a new one or don't crush it ... or do crush it down flat... you can change the temp of the oil about 10-30 deg.. because the plug is either going over sooner with the gasket crushed or later with the gasket not crushed... so we have found a way to vari it just slightly by either over tightning or not real tight... some have used two gaskets to bring the temp up even more... on the racers...
I found Pacfic oil coolers... want the address... http://www.oilcoolers.com/ oil coolers are the most overlooked item when it comes to running too cold or too hot that their is... check out the site and they take you thru their checklist as well as some of these sites also have lots of good info on them about the item... care and maintance and cleaning... Good hunting... GMAs...
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#10
06-20-02, 07:14 PM
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12 years is too long... it should be....
if you wait 12 years I can garentee you that the oil cooler will be full of carbon... if you use it or not... sure it will still be working but, not much in the way of effecency....
if your using it part 135 your placing more than 1400 hrs on it every 5 years... else its just sitting around all the time building carbon up and plugging the cooler... again we use 5 years to clean them out... its not that expensive and like insurance ... good to know ... however, some people place more bets on their attry than the insurance... but, then again they get to change planes and start over every so often.. smile... Again 12 years or 1400 hrs... that is the suggested max time allowed... how many of you are runing around with ones that are 20 years old and never been serviced... Hmmmmm GMAs...
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#12
06-20-02, 07:54 PM
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No the oil cooler is really a accessory
Sometimes they do and sometimes they don't... most of the time they just flush them out and slap them back on... with the old saying ... looks good to me... now if its a factory reman... they usually come complete but, you have to check as some come just as basic blocks... and you put yours back on... GMAs
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#13
06-20-02, 08:06 PM
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I agree with Gmas that there has to be many airplanes being flown with probably more than 20 years since OH on the engines.
If TBO is 1400 hours you should fly 117 hours per year to make it 12 years, if I fly mine 52 hours a year, that is one hour a week, it will be 27 years before I reach the 1400 hours. The question is that if I have high oil preassure and low oil temperature plus oil conpsumtion is low (1 quarts per 8 hours) should I worry about the engines being 16 years since last overhaul? Last edited by Eustacio-Chachi : 06-20-02 at 10:54 PM.
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#15
06-20-02, 10:51 PM
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Sorry, I meant 1 quart for every 8 hours
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