How good of a fit is your NGV on your tunnel ? how good a fit are your bearings in your tunnel ?
My NGV is very tight on the tunnel.

If you look at it from this point of view,
If your shaft is streight, new bearings, your tunnel machined true and the bearings a nice fit, your Diffuser and NGV all machined true, as is the machining of the compressor and turbine wheel, then it has to run true without any contact.

If the shaft is bent, the tunnel worn, the hole in the diffuser, NGV, compressor or turbine wheel not in the centre, all these things will make it run out of true and make contact with the NGV or Intake.

The outer case does play a big part, as it screws to the NGV and can pull it out of line. causing the turbine wheel to touch.
I would like to see the hole in the NGV with a better locating collar about 10mm long this would keep it true on the tunnel. Other designs are the same as this one so maybe there is a reason why it is not made like that.

If you are happy with your bearing fit in the tunnel and the fit of the tunnel to the diffuser and NGV, I would put it together without the case and get it so it is running freely, if it wont then you have a problem with one of the parts listed.
If it does then the problem is the case (more likely).

Slide on the case and look at how the holes line up with the threads, and the gap between the ngv and the case, is it even ?

If you find that that maybe a hole or two is close to the edge, then this will pull the case one way or the other, enlarge the hole ! drill it out slightly bigger, it is not a problem. The threads were bad on one of my case to front cover holes, so I re threaded the 2.5mm out to 3mm.

If you do find that there is a slight gap between the NGV and case on one side, then if you screw it up to the case it will pull the NGV out of line so your turbine wheel will now rub again.
To fix this you either have to try and reform the flange on the case (not easy) buy another case, or allow it to go further forward on the side of the gap, by slotting/enlarging the holes at the front of the case.
You could also drill/tap new ones, either way you are trying to slightly pull the case inline with the NGV not the other way which causes the binding.

Hope you get what I mean

Yes my NGV is also very tight on the tunnel.
I agree with you that the accuracy of the outer case is a important factor when engine assembly. The rear plane of it positions the bore axis of the NGV which shall be line with the shaft. Unfortunately the structure of sheet brings a little error can destroy the concentricity. So I think this is the reason why the gap between turbine blade and NGV is different. Is it true that KJ66 has two thick flanges can ensure a fine plane?

To fit the eight screws in the holes of the case is not very difficult. Also the enlarged holes on the side wall of the case normally can align with the holes on the diffuser.

I replace a new turbine wheel last night and wait to run. Hope it has no vibration problem.

The NGV should not be a real tight on the tunnel a light slip fit is best. If the NGV is too tight it can and will pinch the tunnel and render the preload system inoperable. This will cause the rear bearing to fail.

I think both of the NGV and the tunnel are stationary parts that will not affect the rotor preload operation. The tunnel will not move whatever the NGV is tight or not. It could induce a vibration on the rear shaft if there was a bit of free play on the rear of the tunnel because the NGV is also the rear support of the shaft.
To remain the NGV at the plane is true vertical with the axis of the rotor is a key factor to keep the turbine from contact.
I have an other idea to reduce heat on the rear bearing. Since there is a gap between the platform of turbine and the inner platform of NGV, so hot gas can intrude into the rear bearing area. We can drill some holes on the inner flange of NGV to let cooler air around the CC to push the hot gas back its original path. The cooler air has higher pressure than the gas from the NGV. Any comments about the issue?

That is a question for the guys on www.GTBA.co.uk

What is it with this FRIKKEN RCUNIVERSE SITE???

This is the second time today that I've lost a long reply to a post.

Sorry...I can't be bothered any more.

You can stick your "We are sorry...but your session has timed out" right up your clacker.

At least 5 times today I've had Site Failures. From different log-on's I might add - so it's not my computer.

Get some decent Software! None of the other Sites I Blog on do this...

BJ

If you are typing a long post then every now and then, highlite the txt and right click your mouse and select copy, I do it all the time that way you wont loose anything

What is it on the web page? I can't open it.

http://www.gtba.co.uk/gtba_forums

You need to pay for membership to access the forums. I think it's in the order of 10GBP. If you're interested in turbines it's well worth it IMO. (but I'm biased)

Heat to the rear bearings comes through via the turbine disc and the shaft. The cooling is achieved through the tunnel where fuel is dripped through the front face and travels rearwards.

Sorry I meant the question should be posted at GTBA not the answer !

I normally do - religiously.

But I got kinda absorbed in what I was writing and forgot to. *POOF*... no more post.

Darn, that's bloody annoying...

And it only seems to happen on RC Universe. I often have problems logging in, and/or staying logged it. It often drops me out. Must have some sort of Server issues from time to time.

BJ

Finally got around to getting JJ-3000 Turbine #2 all set up on the new 'dual' test-bench (ok...so I drilled a few more holes in the 900 x 600 7-ply sheet and offset everything to centralise the two Turbines...but you get the gist)

And what a pearler she is - fired up first time, straight from the box ex-China. Didn't miss a beat. What a joy it was.

Then I cracked it for the big-one - well in my book anyways. Did my fist Dual Start...

Man, to hear the two of them belting it out in unison was truly awesome...

JJ's *RAWK*.

BJ

Well.... another lesson well learnt, and before it happened in an Aircraft.

I was a bit short on the proper Jet fuel hose, so I used a few lengths of 'Nitro' hose seeing as none of the local LHS's stock the right stuff.

In a word - don't use it. Kero makes it bloat and go soggy and kinda slimy. From there, the hose becomes compromised and can balloon and/or rupture.

Here's what happened when I was running the 'Twins': http://www.youtube.com/watch?v=ZUli0n2KhME

I'd already gently nudged the throttle a couple of times and thought I'd give it a bit more of a decent stab. That's when the hose on T1 (port side) let go - at about 3/4 throttle. Probably pretty lucky that I didn't have a fire, but I caught it pretty much straight away. And I had the fire extinguisher, watering can and hose nearby anyways.

T2's substitute hoses didn't suffer the same failure purely because they were new and hadn't had Kero through them the week before.

We live and we learn.

Thought it might pay to share my folly so that others might perhaps not make the same mistake.

Had this happened inside an Airframe, the plane would most probably have been lost - by the time a Pilot would have realised what had happened, she'd have had a belly fuel of fuel and some nice hot Turbines to set it off.

Still, that's why I'm on a test-bench - still plenty to learn and do yet.

BJ

How much was the torque when tighten the turbine nut and compressor nut? My turbine nut was loose after the first start of rebuild. The start was unsuccessful and RPM can not go up.

I never found out a true torque setting for the turbine wheel, just used my own judgement. The turbine wheel nut must be tighter than the compressor wheel nut which is just nipped up.

If anyone finds an official torque figure the please post it here.

Hi Guys,

The 1200/1400 turbine nut torque should be 100-105 lb-in, (11.3nm-11.9nm), use a small amount of oil on the thread and face of the nut to aid in correct torque reading. I use a pair of specially made clamp tools in a vice to hold the shaft during the torque procedure. The torque on the turbine nut is very important, too little and the consequences are obvious, too much and the shaft will be too highly stressed and "may" fail at high rpm/temp situations.

The compressor/impeller nut torque should be 85-90lb-in, (9.6nm-10.2nm). Be sure to put a "very small" amount of thread locker on the impeller nut threads to help prevent it working loose over time, just for a little bit of insurance....also a small amount of oil on the face of the nut to help prevent the aluminium fretting during the torquing process. It's highly unlikely it will come loose... but anything is possible.

If possible, be sure to use a "T" bar and socket rather than wrenches/spanners, this will prevent any possibility of the shaft flexing/bending in an undesireable manner causing undue stress on the shaft.

Xairflyer is correct in saying the compressor nut should have slightly less torque than the turbine nut, makes it easier during dis-assembly, it's a pain in the backside when the turbine nut comes undone first during teardown.

Cheers,
Smithy.

Thanks Smithy I should have asked you before, I knew you would know!

Did you look at my stripdown/rebuild thread ? how many mistakes did I make ? or anything you think I should add/edit

No, I don't think I have seen it, do you have a link?

Cheers,
Smithy.

http://www.rcuniverse.com/forum/m_94...tm.htm#9458885

Thanks for your useful information.
I did tighten the turbine nut at higher torque value by one hand holding the turbine blades cloth covered. Additionally I put a film of pure nickel antiseize compound on the thread of shaft when installing of the nut to prevent high temperature seize.

The failed start was due to high EGT and slow acceleration. The rotor RPM decreased after starter disengaged whenas the rotor RPM should go up quickly. This was the first time I met. When engine striped, the turbine nut can easily loose (usually the compressor nut loose first). So I suspect my mistake during change the turbine wheel.
These information may be useful for anybody.

Hey Seamus,

I had a good read of your strip/re-build thread.....pretty damn good IMHO, you're not doing anything wrong as far as I can tell...well done Sir..!!

Cheers,
Smithy.

Glad to know what I have done looks ok, I wanted to post something that may be of use to others as I could not find anything similar myself.
May open up one big secret in this turbine world

<font size="4">Hey Pips

Im currently building a KJ66 style combustion chamber , does anybody know where I can get Inconel vaporizer tubes ?

AlsowhichGrade inconel is best for this purpous, 718 or 625 ??</font>

You can get them from Wren

Thanks  I completely forgot they did it !
Does anybody else sell it ?