Jetman007

My Feedback: (6)

OK, so you have $1700+ sunk into this turbine and you can't get it to run.

You should consider getting the recommended ground school instructions.

Contact one of the AMA authorized ground school instrctors for the JPX. Go through the ground school and save yourself alot of aggravation, expense and possible injury to yourself, bystanders or personal property damage.

That's exactly why the AMA requires ground school!

Here's the link to the list of recognized instructors. I suggest you use it!

http://modelaircraft.org/templates/a...-files/518.pdf

Art Gajewski
JetCat Ground School Instructor
AMA Turbine CD

williammillette

ok first off it shouldent take a masters degree to start the engine

i never heard or seen this motor running maybe it wont

the oil is on the top now,and when i reassembled i checked the burners for leaks in water ,

good thing i put cheep bearings in orderd grw bearings for when it starts if it starts

i cant help thinking if im following the manual it must be the turbine

what step can i possibly be leaving out

will dissasemble and look at again

please give any tips on reassembly

Pegasus

To start the JPX you need the needle valve out around 1.5 to 2 mm. Then when you start it, turn on your spark plug and spool it up a few thousand RPM and let off the air and slightly crack the fuel valve. Then hit the air and stay on the air and keep openning up the fuel untill 1.5 bar is reached, do NOT let off the air until 1.5 bar, if you stop giving it air the flame will blow out the rear and you could melt the turbine out due to it not being inconel (they may have changed that in the later versions)
Taking them apart is not a good idea as they are hard make it run smoothly after that. But i guess its top late for that.
The shaft is .400" if memory serves me corectly, you will have a tough time to fine any of these other than JPX, let me know if I am wrong

Instructor

My Feedback: (16)

When you put the fuel needle back in the defusser plate, you must seal the needle to the housing with epoxy. I'm talking about the inside where it meets the tunnel. I was told to keep the air on until you reach 0.6 bar. The total pressure you want on the gauge at full throttle is 1.1 bar. The total travel of the fuel valve at the GRU that you connect the throttle servo to shouldn't be any more that 14mm. Are you using .004 brass shims around the turbine wheel and the NGV in the back? If you don't do this then it will be out of alignment. There will be hot spots between the NGV and the turbine wheel. As soon as the tempature starts to rise, it will slow down and stop. This happens because of more heat on the side that has less clearence. Are you sure there is nothing in the compressor fitting going to the gauge? Good luck....

Larry

williammillette

boy guys all so far ok except for shims

full throtle travel is 11mm idle trim o-3mm

no shims in when i got it

its heating up and not picking up rpm

i never get a flutter on the gauge

i blow as hard as i can and it reads .15 bar

re dissasembled motor and had lots of turbine oil in tunnel

rear bearing overheated again just like the first time

all else ok will put grw bearings in next when arrive

Instructor

My Feedback: (16)

As I read the last reply, you don't get what I'm saying about the shim. You have to put .004 brass shim stock around turbine wheel and the rear gide vane plate when you assembly it. Then you take a long set forcepts and remove the brass shim. This is after you have screwed on the tail cone. This will give you about .008 clearence between the rear gide vane and the turbine wheel. You may have to use RTV silicone sealer between the outer housing and the front inlet assy to get it to seal the compressor.

williammillette

ok i get it !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1


i spent a considerable ammount of time on this your absolutly right


also while i was setting this up i noticed the turbine wheel is out of round!!!!!!!!!!!!!!!!!!!!!!1looking from the rear
from when i first bought it i looked at it with a bright light

this might be my whole problem
no rubbing marks in ngv or wheel

Chrism-RCU

Chicago Bill,

I think your initial set up to run is not quite correct.

Here are a few hints and tips from a long time JPX user.

1) throttle needle, Pust the trhottle needle fully into its housing to indicate fully closed, I put a piece of retract tube about 1.16 in length around the needle, slide this until it touches the needle housing, this will give an indication when the needle is fully closed, then using the clevis attached to the needle, adjust the length so the needle is 1/16th open with the trim up and the throttle fully closed.

allow 14mm of throttle needle movement.

The knurled gas regulating screw should be open 10mm this is measured from the back face of the knurled head to the face of the GRU block, ie where the spring is.

On the T260 gas engine we found best results with the lube system were achieved when we thinned the oil with clean kero on a 75% 25% kero mix, do remember that as the lube is thinner than normal oil you will use a tad more on a run if you thin it.

When you re assemble the engine, pay attention to the position of the series of 1mm holes in the inner liner of the combustion chamber, these are the first holes from the front of the engine, these should be positioned just left or right of centre in relation to the 1mm holes at the front of the shaft tunnel.

I dont know what air pressure you are using to do the start but it should be about 130psi, we always set the idle on the engine to give .2barg, this can be adjusted on the throttle needle clevis.

I will have a dig around and see if I have anymore info, if so I will mail it to you.

BRG,
Chris.

wsmalley

My Feedback: (6)

Been following this thread with interest, having just bought a 'new' 260P. Haven't run it yet as I'm still gathering the peripherals, but have built a couple of Schrecklings-so somewhat familiar with the turbine. The question with the bearings, is it not possible to ream a 10mm bearing inner race to the 10.175mm-or whatever it is-rather than modify shaft? I was under the impression the bearings were ceramics (original). I seem to remember the GBTA guys talking about buying the balls separately and replacing the metal balls. I think this was back when the ceramics were just coming on the scene. I guess the underlying issue is: are you guys modifying the shafts to accept 10mm and/or, what is the life expectancy under normal circumstances for turbine bearings?

F9F Texan

Does this look like what you need?

williammillette

thanks chrism

the info on the liner and gru is priceless ive been looking for a good starting point.

bearings cannot be resized that would have been my first choice

jpx manual is useless it might as well tell me how to use my credit card

any info on why my turbin is not perfectly round looking from the rear when you spin it it shows to be out of round

williammillette

hey i just thought of something the filler propane tank has no regulator to the airborne tank when it gets filled is that possibly pressurizing the turbine to much and smokeing it

the filler just has can adapter,filter,valve and fuelline
is a regulator needed when filling

orderd grw bearings next day will assemble turbine tommarrow and ready for retest on fri any other assemblie tips or starting prosedures

also i quite dont understand chrism

full trim should be set for only 1/16"travel to start and not like the
manual states 2-3mm or1/4" please state clearer for this may be my demise

Instructor

My Feedback: (16)

chicagobill,

I think you have already burned your turbine wheel with it being out of alignment. That was the reason for the brass shims.
Like I said, too close on one side will create hotspots and burn the turbine wheel. One more thing to look for. Next time you run it, leave the air hose hooked to the start fitting and see if you get
any reading on the gauge. If you get a reading with it hooked up, you might have a problem with the check ball in the start fitting. If that ball doesn't seat right, it will let compressor pressure bleed by. Good luck.....

Larry

williammillette

NO CHECK BALL SEALING DENNIS SAYS TURBIN WHEEL IS NORMAL WHEN I FIRST GOT IT I INSPECTED IT AND THATS HOW IT WAS THEN ALSO GAUGE NEVER EVEN FLUTTERS BUT TESTS OK

AIR HOSE WAS NEVER DISCONNECTED AND AIR WAS ON ALL THE WAY THROUGH ALL THE STARTING ATTEMPTS

MADE SHIM FOR REBUILD TOMARROW

Chrism-RCU

Hi Chicago Bill and all,

OK to clarify, do set the piece of tube on the needle as it is the only reference you have to see how far out the needle is from fully shut, I checked my 260p manual and it says 1/16 inch open for start, you can always increase this by using a little throttle stick movement.

Somthing to remember is that the JPX on start up is very air hungry, and you will use a lot of air, make sure you have at least 130 psi and a good continuse flow.

Depending on the ambient air temps the idle setting on the engine will change, so be prepared to adjust it, first by using the throttle,stick, and take note of the marker tube on the needle, then once established at idle, use the clevis to adjust to this setting.

From what you have described on the aborted starts, it seems that you are not using enough air and keeping it on long enough, do not relate the start of this engine to any of the kero fired engines, it is very different, in that you must ramp the engine way above idle on start up by using the air, then allow the engine to come down to idle and be ready to set the idle using the throttle stick on the first start.

The adjuster screw on the GRU is used for setting max rpm or case pressure, and is basicaly a metering valve, as I said 10mm open is the recomended start point, unless this valve is screwed in to far it should not effect the start of the engine, only the top end rpm of the engine.

If you are worried about the turbine wheels possibly being out of true, them take the whole shaft assembly to a turbo workshop and have them balance it to Garret T3 specifications, try to achieve a balance of less than 0.05 in both axis on this program.

Refering back to the holes on the shaft tunnel and inner combustion chamber I refered to yesterday, these are critical to the running of the engine, and if out of alignment will cause the engine not to start or run very hot. it really is trial and error getting the relationship between these hole correct.

The jpx engine is very finnicky to set up after a rebuild, good luck

BRG,
Chris.

williammillette

ok how far off on the inner liner just side by side

on start im still not getting it
i adj throtle trim to full witch gets 1/16"open
i add air 130 psi full trigger,wait till sharp,start spark,open propane,pop and burn starts,rpm picks up then i should or shouldent add throtle,and if so how much,

will the turbine start at 1/16" and sustain without adding throtle

S_Ellzey

Remembering back to my JPX T260P days. I would set the throttle trim to achieve about 1/16” of throttle, which was about 1/3 of the trim, I would apply air ( I used a welding type regulator set at 150 psi) and after a few seconds start to slowly open the shut-off valve, as soon as my wife saw fuel movement she would hit the igniter, as soon as I heard light-off I quickly finished opening the shut-off valve and quickly pushed the throttle trim all the way open. As soon as the pressure rose above .15 I watched the temperature and discontinued air a few seconds after the temperature started to drop, maybe 5-10 seconds after light-off. The pressure would be .22-.25 at the end of the start sequence.

My engine ate its rear bearing after a couple of years, but even with the bearing gone bad the engine brought my Bandit back home, for that reason alone I have a warm spot for JPX. I ended up re-engining with a different engine.

I tried to get the engine back up and going a couple of years ago. A Sophia tech took on the challenge. The first problem was getting the right bearings. The originals where made by SNFA, and when we contacted them they told us we did not have any of their bearings since they where only sold to military contractors. This seemed a bit odd since I still have a set of them. I then contacted JPX and got a set of bearings from them, however they where a different brand (NSK I think) and the ID was ever so slightly larger. These were sent to the Tech who put every thing back together. When I started the engine on the bench the rear bearing went out in about 30 seconds. As best we could figure the fit to the shaft was too lose and the shaft whipped around over loading the bearing. The bottom line; the bearings have to be right. I know that this is not much help, but may give you an ideal of what you are up against.

Steven Ellzey

williammillette

re assembleing now as we speak
grw bearings are amazing
there cageless!and spin forever!

the fit to the shaft is tight! but rite

the turbin wheel after fine inspection revield a bent vain witch i was able to straighten

well post more as i assemble

williammillette

ok shes built


lubed bearings and air tested

this will be my last attempt to light the fires !!!!!!!!!!!!!!!!!!!!!!

the attempt will be tommarrow at noon all bets post at 9am.

next thread either ( allright!!!!!!!!!!!) or ( jpx parts for sale)

maverick

My Feedback: (12)

At least you still have a sense of humor!

Instructor

My Feedback: (16)

Dear Bill,

Glad to hear that you have it back together. I still think you need to keep the air going untill you can get it to half throttle. If you don't see any reading on the gauge, you still have air goinng in and it won't get real hot. If there is any reading on the gauge at half throttle, srew in the screw on the GRU untill you get 0.6 bars on the gauge. Then you can release the air and advance it to full throttle. At full throttle, you should show 1.1 bar on the gauge. If it is just shy of 1.1, screw in the gru screw untill it shows 1.1 on the gauge. At that time you can reduce the throttle
to idle. Use the trim bring it down to 0.15 bar, which is the idle setting. Good luck......

Larry

williammillette

got it

after it lights add throtle and wait til gauge reads if i can get to this point ill be ok

if i add throtle too fast or to much how will that act.

witch is worse too fast or to much

and only add like a 1/4"?

williammillette

also on past starts i think air bubbles were in the fuel line all connections were tight whei i opened and watched the line

fuel tank was full though.

if it runs can i let it run dry as long as oil is left and when it stops can i just let it cool.

Instructor

My Feedback: (16)

What yo want to do is add throttle very slowly. Did you take the go-slow away from the throttle servo? You want to take at least 6 seconds to get to high throttle. Do you have a leaf blower? You can run it to high throttle but not for long. Since the engine is on a test stand, you don't have a lot of air going around it to keep it cool, like you would inside the airplane. During flight, air is sucked around the engine. 80% of the air going in through the inlets are used by the engine. The other20% is used to cool it down. When you decide to shut it down, bring it to idle for about 1 minute, then up to half throttle for 20 seconds. Then shut the fuel off and let it spool down. Take the leaf blower and blow air through the inlet for about 1 to 2 minutes or untill the tail pipe feels cool.

Larry

Johnny Woods

C-Bill,
May be I can clarify something. Separate starting and
running. The 1/6 setting that Jonh C gave will alow
the engine to start and sustain itself around .2 bar.
You do not have to mess with the throttle during
start. Once the engine has started then you can
move the throttle. Do not let the engine deplete the
gas and slow to a stop unless you are monitoring
the temp and it does not rise above normal. It is
best to advance the throttle, for cooling, then
shut down and apply start air to remove the heat.

Johnny