Hello guys,

A friend of mine has an old RAM 500 turbine which was involved in a crash some time ago, and ingested some dust. We decided that since this is an old engine, and doesnt cost much, it would make a great candidate for a strip down \ rebuild at home. besides, both him and I enjoy solving problems on our own - its a hobby after all.

We took it completely apart, cleaned everything well, and put it back together. we didnt change the bearings since they looked and felt like they were in good shape.

We didnt rebalance the turbine, but rather marked the parts and put it back together the same way.

The engine was then fired up and seemed to run very well. top RPM was 155K and we did notice a very slight vibration, followed by a light squealing sound only at over 150K. below that everything was smooth.

After some bench test running time (probably 10-20 various starts) we started feeling a constant vibration while the engine was running (regardless of RPM). it comes and goes but this time when its there, it is very evident and very well noticed, so something is definitely wrong.

My questions are:
1. What would you think could be causing this ? as i said, it was mostly very smooth even after the rebuild, and started vibrating all of a sudden. perhaps a bearing is dying ? would this cause vibration such as i described ?
2. How would you recommend checking bearings once taken apart ?
3. How would you recommend balancing the turbine ? what is the simplest (yet still effective) way to do it well at home ?

Overall, we like this tinkering very much, it really is a lot of fun playing with these turbines.

thanks for your help.

Probably the bearings... They usually let you know before they go..

you have to check the compressor and turbine wheel.
if there is a to easy slight fitt , then thats you problem.
its very simple ,if the turbine engine runs at low rpm , everything is alright but at higher revs ,the compressor go's out of the center ,because of the loose fitt.
i dont know if you have this , but i just give you a idea of what can be wrong.
balancing is very simple.
take a roll of tape ,and thats your balancing wheight.
take the engine apart ,and then you only must put the shaft, turbine wheel and spacer, compressor ,and compressor nut in de shaft tunnel, with the bearings offcourse.

then hold the tunnel near the turbine wheel with two fingers ,and spin the wheel with pressed air.
you will feel vibration.
no worries, put a piece of duc tape some where on the wheel ,not the blades.
devide the turbine wheel in 6 marks, mark them with a pen , or what ever , if there are marks ,its oke.
then put the tape each time on another mark ,and you will see ,the vibration will be less .
you have to practice a little ,but its realy good balancing.
if you have found the places of vibration , then slightly grind the spot at the opposite site away on the ring of the wheel.

I use the spinner nut for balancing the compressor.

I you have problems ,just ask me.

good luck.

Martin.

Martin,

How do you use the spinner nut to balance the compressor ?

Hi,
Well... it seems i am that friend that lior (i3dm) is talking about.
as for balancing, i was thinking of using the method described by WREN at their kit manuals - jut put the shaft with the compressor in a specially made cylinder (that holds the bearings) and rock it around on the table's edge...
find the "heavy side" and grind off some weight ... repeat until satisfied.
then redo it all with the turbine wheel.

but yet, the questions remains -
are there any distinct noises or behaviors that indicates the bearings are reaching their end?
if it is a balance issue, what could cause the turbine to "spin out of balance" ?

thanks.
Ravivos.

When I first disassembled my RAM 500 I found the flat washer behind the compressor nut was a very loose fit on the inside dia. It was loose enough that it was detected during the balancing procedure. I replaced it with a washer that i reamed to the exact O.D. of the shaft.

You probably have a different problem but check the washer too.

I used the WREN 54 balancing procedure in the kit instructions. I touched up the balance of the compressor a little bit and my engine is now smoother than from the factory.

Sid Gates

SEND TO CARLOS ( RTI ).

JOSE

that is always the easy answer...

I mean ,i use it for balancing.
I grind a very small amount off the spinner.
with this way you can get a perfect balance of the compressor.
I also use a little piece of tape ,and when i found the right place , i grind a small amount away on the opposite site.


Regards,

Martin.

If you blow the compressor wheel in the engine with pressed air ,and you dont feel vibration , but during running of the engine ,there is vibration, then its the preload.
if the preload is not strong enough ,or the washers are not exact in center of the bearing , then you can have vibration.
you have to know that ,during the run ,the shaft gets longer, because of the temp.
If you dont have the right strenght of washer then there is a bass sound in the engine at full speed.
you also feel vibration ,and the compressor or the turbine can rub ,because of the vibration.
then you think it is unbalance , but it is the preload.
i serviced a simjet 1200 ,and this engine had the same problem.
it was delivered with a preload of 4kg .
i changed it to 6kg , thats a lot more , but the engine still running ,and all the problems are over.
The engine is also more powerfull and lower egt ,because the shaft slides no more ,so with fullpower the compressor keeps the same gap between the blades and the cover.
thats very important for the engine.

Regards,

Martin.

Carlos (RTI) has the means to correctly balance it. Having been in a crash there may be other issues. The bearings being of unknown time should be changed as they are cheap insurance against a bearing failure induced crash.

Roy

Soudns like what we are witnessing. do you suggest spinning the engine with compressed air to check ? if so, to what RPM ?

Oh just forgot something.
if the bearings reach there end ,you engine gets more noisy.
And also there is a second wistle sound when you start ,and shutdown the engine.


you also can feel it when you spin the rotor with your fingers, and on your data terminal you can see the time of running down getting shorter.
very important when you run the engine for the first time to wright down the time of running down the rotor of the engine.

Regards,

Martin.

Yes ,thats about 10.000 rpm.
when you do that , lay two fingers at the backsite of the engine ,and spin it , spin it slowely till you reach 10.000rpm .
there must be a point that you feel vibration .
do the same thing at the compressor site ,and then you know if its the compressor or the turbine.

Regards,
Martin.

I have rebuilt and hand balanced my Wren 54, I thought I was happy with the balance but I have a vibration between 90-100K I suspect preload going by the sound but the compressor wheel is not as tight on the shaft as I would have liked, any ideas?

We will try spinning the engine with compressed air - or perhaps just use the starter up to 10K RPM ?

Can anyone describe (or is there a video of) the sound you get from the preload being too loose ?

What we are witnessing sounds like a single tone whine, it is low pitched, definitely not a high pitch squeal.

And BTW - once apart, how do you tell if the bearings are good for reuse or not ?

You will see wear in the groove of the inner ring (tapered cone), not the balls that wear it is the stainless cage and inner ring

Perhaps you have a picture of one, for reference ?

Best I have

Yes that is defenatly a preload problem.
it sounds like there is a havy bee flying in your engine ,that sound.

if you can find stronger washers ,or a spring , i dont know what you are using, then your problems are over.

yes i have a video off my small engine .
if you listen closely you can hear the bass sound at the end of the video

http://www.youtube.com/watch?v=MBYtt...eature=related

Hi Frema,
It sound something like that...
this bass tone was previously heard, with some vibrations, at maximum throttle (i.e 150K) but lately this tone came more obvious even at lower turbine speeds.
last time we heard it even at start-up ramp at approximately 30K.

another thing, i have a second RAM500 that takes much longer to slow down to a hold.
this might indicate a bearing problem, i guess ill have to take it apart and look.

hi Xairflyer, thanks for the picture, it sure is helpfull.