Xairflyer

My Feedback: (1)

This is how I went about doing a service on a JetJoe 1400 turbine, which included replacing bearings, cleaning injectors and balancing.

Much has been talked about Jetjoe turbines on other threads, this is thread is about stripping down and rebuilding a 14lb turbine, not about Jetjoe turbines, and will be similar to other makes like wren 54, simjet, PST etc.

Before posting this I waited until I had finished the rebuild which included flying it again, so all stages would be shown.

First I removed the starter housing, then the fuel and gas fittings.
Next you need to remove the glow plug, tailcone and screws securing the case to the front cover. Then the case is slid off.

Important to mark everything as you go, so you know waht way around etc things fit when you put it back together.

Pic 1 shows the complete turbine installed, forgot to take on on the bench before I stripped it.
Pic 2 shows Starter housing removed, fuel and gas fittings, note also restrictor in the bearing lubrication line
Pic 3 8mm thin OS engine spanner used to remove festo fittings
pic 4 Outer case removed showing diffusor at the front (left) combustion chamber in the middle and NGV at the rear

/rebuild

Xairflyer

My Feedback: (1)

Next removing the front spinner nut. Before you do this, if you want to be able to re-assemble without balancing you will need to mark the position of the compressor on the shaft. First mark the spinner nut to compressor position, then after the nut has been removed, mark on the front of the compressor, on the threads and on end of the shaft.

The nut needs a 12mm spanner and has a left hand thread. The serrated/splined nut on the turbine wheel at the back is 8mm ring spanner. The spinner nut should loosen easily enough. Note again left hand thread on aluminium spinner nut.
I had to give the end of the shaft a slight tap to free it from the compressor, you can then withdraw the turbine wheel/shaft assembly.

The NGV then simply pulls out of the end of the combustion chamber and the combustion chamber itself is removed by pushing the ends of the fuel and gas pipes out of the diffuser.
Unscrew the front cover to release the compressor wheel and spacer, Note the spacer and its orientation.

Pic 1 Turbine wheel and shaft removed, also shown is rear bearing on shaft behind turbine wheel
Pic 2 Combustion chamber separated from NGV and Diffuser/shaft tunnel
Pic 3 Front cover separated from diffuser releasing compressor wheel and spacer.

Xairflyer

My Feedback: (1)

With the front cover removed you can now remove the plate and screws holding on the shaft tunnel. When the plate is removed the lubrication pipe is visable, This pipe can be checked for any blockages by connecting up your gas can as detailed below for the fuel ring..

Before taking the bearing out of the shaft tunnel, look at the rear bearing on the shaft and note the arrow marked on it, this is the for correct orientation for the preload, arrow should be pointing out towards the wheel. The front one should be the same.

I carefully pushed the bearing out from the other end of the shaft tunnel with a piece of dowel, Remove also the preload spacer and spring.

Pic 1 shows lubrication tube and front bearing in the middle of the diffuser.
Pic 2 shaft tunnel removed from diffuser
Pic 3 Bearing and preload spacer and spring removed from shaft tunnel

Xairflyer

My Feedback: (1)

Pic below shows a layout of all the main bits, at this stage it is fairly streight forward to put it back together again especially if everything has been marked to aid assembly.

I also want to check the fuel needles so I removed the fuel and gas rings from the combustion chamber.
To do this first mark it all so you know how to put it back together, then the metal tabs have to be bent up to allow the pipes be removed.

I then hooked up my gas can and lit the needles (like a birthday cake ) You should have a similar flame out of each.
As can be seen on mine some are good some poor and two not lit at all.
This could also be seen by looking into the combustion chamber, the ones not lit the vapour tubes are like new so where probably no working for some time.

First job was to get the fuel needles working.
I Found a strand of a piece of multi stranded wire (bowden cable) worked best as it was small but rigid to push into the needles.
At first I thought I was'nt going to get them sorted until I realised that some of the needles were protruding into the collector ring too far (from manuf) and bottoming out, blocking the end, so I gently squeezed the collector ring tube with a pair of pliers, which worked great.

I also checked the three gas needles and the lube tube the same way and they were ok.

pic 1 all the parts
pic 2 combustion chamber and fuel and gas needles
pic 3 shows some needles not working at all
Pic 4 shows all the needles working now with even flame

Xairflyer

My Feedback: (1)

Will post more later tonight

tothemax

Great thread. Thanks for posting.

madmodelman

Excellent Seamus.

Xairflyer

My Feedback: (1)

Replacing the front bearing is an easy enough job as it is removed during disassembly. Some builders fit a lower spec bearing at the front being cheaper as it is easy to change more often,

The rear bearing replacement requires that you remove the turbine wheel from the shaft.
Again mark the shaft to the turbine wheel position, this will save you having to balance the turbine on rebuild, I will be detailing later how to balance it anyway if needed.

The nut on the end of the shaft will be much tighter than the one on the compressor and this is supposed to be like that. This is so the compressor nut will always loosen first as you may not want or need to remove the turbine wheel ever time.

I found the best way to loosen the nut was to put the shaft in the chuck of my lathe, left hand thread again and a 8mm ring spanner needed. Note the orientation of the spacer behind the turbine wheel as it tapered, the larger diameter goes against the wheel.

After cleaning and inspecting the shaft/wheel a new ceramic D688/602976 GRW bearing can be fitted. The bearings have an arrow stamped on the outer case, (see pic) this is for fitting the correct way around, the arrow points out towards each wheel. The reason for this is the bearing inner race is tapered.
Make sure you line up your mark on your shaft with the one on the turbine wheel and reassemble with the new bearing arrow pointing at wheel and the spacer with the large diam against the turbine wheel.

Put a tiny smear of oil on the nut face (helps getting correct torque) and tighten the 8mm nut (Left hand thread) to 100-105 lb-in, (11.3nm-11.9nm). I used my own experience on how tight to make it, as I did not have a torque figure at the time.
The turbine wheel nut must be tighter than the compressor wheel as it has to stay tight when removing the compressor nut first when dissasembling the turbine.

Xairflyer

My Feedback: (1)

More on the bearings
You need to be careful when sliding the bearing on the shaft as if pushing to hard on the outer race, it can come apart and leave you with balls all over the place.
Bearing needs to be slid on by pushing the inner race if possible, I used a long 1/4 drive socket. the bearing may slide on easy enough and mine was a bit too easy so when I measured the journal of the shaft it was 7.97mm so I decided to fit a new shaft.

The new one was 7.99mm looking at drawings of KJ66 shaft they show journal size to be 8.00 +0.1, my bearing was now a nice snug fit on my shaft so I was happy with it. Journal needs to be measured with a Micrometer and not a vernier caliper.

If the dreaded bearing falls apart happens, then gather up the balls there should be 14.
Note: Good idea to do bearing installation work low over a tray or cloth so if they do fall apart they wont end up on the floor.

Put the balls and the bearing cages into a cup (I use the top of an aerosol can) of white spirit (mineral spirits) and give them a good wash.
Dry your outer cage, smear in the inside of the cage with a thin film of grease, using a pair of tweezers place each ball around the inside of the cage, the grease should hold them in place, put the bearing cage down on the bench (on a clean piece of tissue paper/cloth) with the arrow pointing UP.
Take the inner race with the thin/taper facing down (see pic below) and push into the bearing, it should snap into place.
Wash your bearing out again with clean white spirit, air line also useful for this.

If you are going to temporarily store the bearing, then put a small amount of turbine oil into the bearing, if you are carrying on with assembly then wait to add a some oil to the bearing to just before final assembly, this will minimize and dirt being picked up.

Xairflyer

My Feedback: (1)

Important before re building the turbine that you look over and clean everything, inside the shaft tunnel, so the preload spacer and spring slides freely, there are also two O rings that hold the bearings, these can replaced if worn.
My bearing outer race had a fine ring around it which made me think it had rotated so when I measured up the inner face of the shaft tunnel I decided to fit a new one of those as well.
The tunnel with new O rings would have probably been ok, but a new shaft, with all the spacers and nuts, plus a new tunnel, O rings and preload spacer/spring is only $70 for this turbine so worth doing when you have it all stripped. The higher the tolerances the longer the bearings will last.

Pics below show the old shaft tunnel, O ring inside tunnel and preload spacer/spring

Xairflyer

My Feedback: (1)

Balancing
Debated [sm=confused.gif]whether to add this now or at the end, as it would be done before reassembling I added it now.

I replaced the shaft, so I needed to rebalance. I made loads of enquiry's into how etc, really wanted to try and do it myself with the backup of a very nice guy who suggested if I shipped it to him he would do it for me on his core balancer if I got stuck!

The method I found has been used by many homebuilders of Gas turbines, and on that subject an excellent association to join is the GTBA (Gas turbine builders association) where there is tons of info and help from very knowledgeable people, if you are interested at all in turbines themselves.

The method used is the "rocking method" I have posted how I done it on anther RCU thread and have reprinted it below, rather than a link, as it keeps everything related to this turbine together for future use.

Balancing compressor and turbine wheel assembly.
This is a simple method for the DIY guy but you do have to be patient and take your time.
You first need a bearing housing similar to a shaft tunnel with the correct dimensions etc to suit your bearing spacings on your shaft. (easy enough to make your own from 20mm round stock if you have a lathe or a suitable piece of tubing) What I done was turn down the flange of my old shaft tunnel.

Also I bought a pair of standard bearings to use for the balancing tool but the ones I got were only 5mm think and the turbine ones are 6mm, so if getting some make sure they are 6mm, std 688 bearings are 5mm.

So I cleaned out the old bearings with white spirit and blew them out with the airline, the bearings need to be very free, when you spin them by hand they should run on for long time, white spirit is great for cleaning. You can use your new turbine ones but I wanted to keep them clean.

I used a piece of glass I keep in the workshop (handy for lots of things) on the bed of my CNC router so I knew everything was flat and level, I done the compressor wheel first, I fitted it on the shaft with the bearing spacer and nut and made sure the nut was as tight as it would be if installed on the turbine, then marked everything with a permanent marker, nut position on compressor wheel, compressor to spacer and shaft. (I had fitted a new shaft so had no previous marks.)
Fit the assembly in your tunnel with the other bearing at the opposite end of the shaft, you don’t need to secure it in place.

Spin your wheel to make sure it is free and spin it up with an airline if you have one, as it will help free it up especially if using new bearings. This should be done often as the less friction the better the method works.

Place the alum tunnel on the flat surface with the wheel over the edge and rock the tunnel back and forth with your fingers, mark the wheel at the bottom and do it again, spin the wheel a few times and do the rocking again and again and again, until you can be fairly certain that the mark or a new mark you may have made is staying at the bottom.
Turn the mark to the top and rock it again it should always end up at the bottom, if so then this is your heavy part.

I used a round shaped grinding wheel in my dremel and ground off a bit of the back off the wheel, and rubbed it over with a scotch brite pad when done. Before you do any grinding wrap a paper towel around the bearing to prevent and dust and make sure to clean it all off again before proceeding.

Fit back in your tunnel and start again, it can get frustrating[sm=72_72.gif] as you might see no difference, I was surprised how much I needed to grind off the compressor wheel.
If you are having a problem deciding where the heavy part is then you are getting there, it should either stay anywhere you put it or will just keep changing to random places when balanced.
If at the start you are having problems establishing a heavy part then you may be fairly well balanced already. You can also stick a small piece of blu tak or something similar to add some weight so to artificially create a heavy part to see the method working.

I then removed the spinner nut, and marked the shaft threads to compressor position, making sure the compressor was still at the same position on the shaft (should be as the compressor is usually a tight fit on the shaft).

I removed the compressor wheel and spacer and then fitted the bearing, spacer and turbine wheel to the other end and done the same process. The turbine wheel normally has sacrificial ring to grind for balancing.

You want to use the new bearing here so it will not need to come apart again, you have to be very careful with preventling any grinding dust getting near the bearing. I was not certain at the time the method would work, so used the old bearing being happy to take it apart again. When I refitted the new bearing I checked the balance again and it was still ok.

When rebuilding the turbine you line your compressor up with the marks on your shaft and tighten your nut which again should tighten to the marks you made earlier.
This way you are giving everything the best chance of remaining in balance.
Remember even the compressor nut has a magnet so its position can effect the balance.

You could take this one step further and refit your compressor wheel to the shaft and balance as a complete dumbbell unit. To do this you would need to make a level rocking table to fit between your wheels, I have not tried it, and don't see any real benefit as it still has to be taken apart again to rebuild the turbine, and which wheel would you then grind?

Also I have noted on some other turbines, the shaft itself has been balanced, I tried it on my twin disk prop balancer but could not see any difference or find a reliable way of doing it so did'nt bother.

Jumping forward to after the rebuild
I spun my rebuilt turbine up first with compressed air, and done the finger nail test, by putting my finger nail on the casing, no vibration was felt. I then re installed and started the turbine and no vibration was felt at idle, so I opened it up to 85K and again seemed ok, also then to full power at 160K.

So all I can say is this rocking method seems to work, [sm=thumbup.gif]no doubt core balancing of a assembled turbine would make it even better, time will tell how it is after a few hours.

Pis show back of the wheels where the grinding was done, some of this had been done when new (at factory) and seemed to use a milling cutter which was probably not the best was of doing it, as it leaves sharp edges.

Xairflyer

My Feedback: (1)

Putting it back together
Before I refitted the fuel and gas rings into the combustion chamber I got a friend to add a spot of tig weld to my glow plug collar as it looked like it could come loose if overtightened, I see wren fit two strips of metal down each side to re enforce it which is a good idea.

The fuel ring is held in place by metal tabs that are just bent around it, the needles are all bent near the ends so the spray hits the sides of the vapour tubes and increases the vaporization process if that is the correct term
Gas needles are fitted first then the fuel ring which is meant to sit proud of the combustion chamber something to do with airflow into the vapour tubes.
The position of the gas and fuel pipes was marked on the outside of the combustion chamber before removal, these line up with the holes in the diffuser.

Xairflyer

My Feedback: (1)

I forgot to take some pics during rebuild so some used are from another source but the same turbine.

New GRW bearing fitted into the end of the shaft tunnel with again arrow pointing out/at the wheel, Tunnel is fitted into diffuser and should be a nice push fit. It is secured with countersunk screws after first fitting the oil lube pipe cover plate. Add some turbine oil to the front bearing before fitting the cover plate.
Note important to use threadlock on these screws as you don't want one backing out. I forgot and It happened to me which is another story detailed later[sm=crying.gif]

Xairflyer

My Feedback: (1)

Next I fitted the combustion chamber over the tunnel and fed the fuel/gas pipes through the diffuser. The festo fittings shown were only temp screwed on to help pull them pipe through.

The front cover is a one piece unit on the JetJoe, some other turbines this is in two parts and requires shimming the intake around the compressor wheel. This is not needed which I suppose shows how good the machining is, as it would be CNC I suppose is not difficult to get right.

There is a Top hat type spacer that is fitted between the bearing and the compressor wheel, the rim or large diam of the spacer, fits against the back of the compressor. Shaft is shown just to show positions of the parts in picture, and not installed at this stage..

Spacer and Compressor wheel are just placed between the diffuser and the front cover and the front cover is screwed onto the diffuser with the cap head screws. Dont fully tighten them for now as you will probably have to remove two again when you refit the rpm sensor pcb. Pull through the fuel&gas pipes, and you can fit the festo fittings temp for now.

Jetbono

Hey Xairflyer , What plane did you have your jj1400 fitted on ?
Did you have any flame out during flight or taxy ?

basimpsn

My Feedback: (5)

Why did you replace the Shaft ??.

Xairflyer

My Feedback: (1)

Put a little smear of turbine oil into the tunnel and on the outside of the preload spacer, drop in the Preload spring into the tunnel, followed by the spacer, if the O ring is new this may require some further lube to help slide the spacer in.

Fit the NGV onto the end of the tunnel, you may need to temp slide on and off the case to see how far on the NGV needs to go. Make sure it is the correct way around, the NGV should also locate on the combustion chamber.

Slide on the case and secure with a few screws, make sure the glow plug hole lines up with the combustion chamber, if not remove the cover again and twist/push/pull the combustion chamber so it lines up better.
One of the things I don't like about the design, a more positive securing of the combustion chamber would be better, but once the glow plug is fitted it is then ok.

Make sure you have a mark for the compressor position on the END of the shaft and the front of the compressor as you wont be able to see any marks on the back of the compressor wheel/shaft now.
Add some turbine oil to your rear bearing and feed the shaft/turbine wheel assembly into the tunnel, hold some pressure against the compressor, so you wont push out the middle of the bearing if the shaft is not aligned properly.

It may be a bit of a fiddle to feed through front bearing/spacer and compressor, you also have the preload spring pushing against you.
Once through line up mark on shaft with mark on compressor and push on as far as you can, which will now be spring loaded due to the preload spring, and tight as the compressor is press fit on the shaft. Temp fit the spinner nut.

Turn the turbine wheel/compressor to see if everything is free, if not then the ngv is probably not aligned properly and I found it was a matter of getting the case on fully with all the screw in place as the case is what finally locates the NGV.
I did'nt realise how critical this was and goes to show that any damage to the case of a turbine means a replacement, not just for cosmetics.

Once you are happy you can tighten the compressor nut adding a slight smear of oil on the face to prevent fretting (alum to alum) tighten to 85-90lb-in, (9.6nm-10.2nm) checking and double checking the compressor/shaft alignment is still correct and all your marks line up.
I found I had to offset the compressor on the shaft and the final tighten of the spinner nut lined everything up.
Note it has been recomended that a T handle driver be used to tighten nuts to help prevent any shaft bending or flexing.

Xairflyer

My Feedback: (1)

It was first fitted for a few flights in a AMD Hawk I then fitted it into a Nitro planes/planenutz bobcat which it had been flown in for a year and a half or so before I stripped the turbine back in the summer.
It has never flamed out, if your set up/installation is correct it should'nt happen.

Xairflyer

My Feedback: (1)

I mentioned it somewhere further up the posts, I was not happy with the journal size at 7.97mm.

Jetbono

Did you fit a UAT in your AMD Hawk and Nitro planes/planenutz bobcat  ?

Xairflyer

My Feedback: (1)

Before going any further you could blow the compressor with an airline and spin it up fairly fast and see if any vibration, if you think it seems ok then you can remove your screws at the back and fit your tailcone, also properly install your festo fittings not forgetting the fibre washers. Again as mentioned during disassembly a thin 8mm spanner is needed here.

Check also the preload by pushing against the turbine wheel/nut you should feel it move slightly and spring back., if nothing can be felt you may have to strip it again and investigate.

Also note the correct location of the RPM pickup, a pic like below is useful for reassembly.

The lube line should have a restrictor as shown. This is my layout but others may be different.

If any vibration is noted then slightly offsetting the compressor on the shaft either way may cure it, or you are back to stripping it and re balancing, or sending it off to someone else [sm=sad_smile.gif]

Final stage of assembly is refitting your starter housing and plumbing.

Fed up typing for now, later I will go through my first startups and first test flight since rebuild.

Xairflyer

My Feedback: (1)

No myself and all the guys I fly jets with use a centre pickup header tank system and no one has had any problems in the three years or so we have been flying turbines. I think I have it detailed somewhere in the Bobcat or AMD Hawk forum. Cheap and works.

jason

My Feedback: (1)

Tell you what, them JetJoe parts look just like Wren's!..

Very well put together thread by the way.

Jason

Xairflyer

My Feedback: (1)

First Runs
It fired up as usual once the fuel reached the turbine as I prefer to let it take it's time rather than priming, I always think you can prime to much. Ramp up was good, fair bit of pops and bangs and some nice hot blue flames till it settled around idle.
Egt's at idle were higher (580°c) than before (500°c) and was expected with all the 12 injectors now working, but higher than I liked, no vibration was felt, which looked good.
Turbine was taken up to 90K which is normally the coolest and EGT's were at 580°c before was 400°c, still no vibration, up to max at 160K still no vibration, so very pleased there, but my EGT's were now 750°c never seen them before above 640°c so I shut it down.

I had in the past replaced the original two piece tailcone with a single piece which increase the thrust, as quite possibly not all my injectors were working as well as they are now. So I re-fitted the two piece cone and my EGT's were much better and got better with each run as the ecu was learning the new setup.

On one of the runs I noticed a funny squeal when throttling down, []after it had cooled down and sat for an hour I noted that the turbine wheel was sticky, similar to when bearings are at the end of their life, and you give it a spin and it is ok again.
Also I had no preload movement. So I decided to take it out and strip it again to investigate, [sm=confused.gif]

Once I had removed the front cover/intake and the compressor wheel I discovered one of the countersunk screws holding the diffuser to the tunnel had backed out, I had forgot to threadlock them as I mentioned in an earlier post [:@]

This Explained the squeal, no preload movement and sticky turbine.
Back of the compressor wheel had been scored, luckily any alum dust had went out with the airflow and a light smear was on the inside of the case, could’nt see anywhere else, but I washed out the bearings again just in case. Could have wrecked my new bearings !
Put the compressor wheel on the old shaft and cleaned it up on the lathe, not much needed and only in the middle where there is plenty of metal, then polished it up with scotch brite.

Snag was I had to balance it again !

Put it all back together, fitted in the model and fired it up, first start a bit hot again but no vibration (getting good at this balancing) and after a few runs, it was starting smooth and EGT’s were looking much better through the range.

Bobcat was charged up and after a further ground run she was back in the air again.
I downloaded all the data from the ECU and the max EGT seen for the flight was 636°c at 160k and around 460°c at idle 45k.
The data was showing the EGT’s getting better and better after each run as again the ECU was learning the parameters.

So very satisfying to have it flying again after a DIY strip and Balance, made a silly mistake forgetting to threadlock the screws, but learned a lot. Proves also that with a bit of time the rocking method of balance works and hope to get some more flights clocked up in the next few days.

chrigui

Check the right bearing assembly...(the inner cone bearing must to be in center shaft direction)