I recently ordered a new 14lb compressor for one of my Wren Engines. I was going to try and statically balance it. Since the engine has been run the bearings are worn so I don't think they would be free running enough to balance with. Would it be possible to balance it with something like the Top Flite magnetic balancer? It can be used to balance wheels and rotors. It has so little resistance I would think it would give you a better balance than using the shaft even with new bearings.

Any help or other suggestions would be appreciated.

Hal

You can do it but it takes a large amount of time and patience by marking the heavy spot with a fine point pin and even when you get it where you think its perfect it still might be just a tick out, you would just have to run it and see, as long as its not to far out, it won't hurt anything. I would suggest to send it to Carlos at RTI unless you have time to do it yourself.

I would think that if you were using bearings to balance it that you should use the current engine bearings and not the new ones unless your current bearings are extremly wore, all experiences I have had with new vs. used bearings is that the used tend to be more free because of the wear and lubrication.

I highly recommend dynamically balancing the compressor and/or turbine wheel. Dynamic balancers use piezos to measure out any un-balance much much more accurate than your static balancer together with your "feel" will ever be able to notice. And never forget the RPMs at which we operate.....a precicely balanced system is a must, for bearing life and safety.
If you do not have access to one of these (rather expensive) balancing machines, send your system to a turbine factory in the vicinity (i know behotec balances systems for homebuilders), or straight back to wren after assembly. They will make fair prices, i paid less than $20 for everything, including shipping back and forth.
Cheers
Miniflyer

Hal,

DON"T TRY TO BALANCE THE NEW COMPRESSOR ! The new compressor was reprofiled and balanced by Garrett before being sent to Wren unlike before. I have one but haven't installed it yet . The tolerances also might be a little tighter and require that you heat up the compressor a little to enable it to slip on the shaft easily. Contact Wren if you want to confirm what I've said.

Marc

I have to agree with Miniflyer.

Has anyone ever taken on of these hand balanced (static) turbines and then run it on a normal balancer? For the life of me I cannot imagine the balance would be that close.

From what I have seen, you can take a perfectly balanced motor, take the compressor off then put it back on and you will blow the balance.

Don't the 44 sized motors have to be factory balanced?

Hi Matt,


You wouldn't think so but it does work ! I have a lot of hours on a hand balanced Wren and it runs great. That was before the compressors came pre balanced so it's even better now. The tolerances have been tightened up as well to make the fit between the shaft and the compressor more exact.

You are correct that the 44 is factory balanced but Hal has the 54.

Marc

Hi Marc,

Don't get me wrong, I am sure they run fine, I am just wondering how one of the hand balance jobs indicates on a $12K balance machine, just curious.

As I said before, on the high performance turbines I have seen, the motor has to be rebalanced after reassembly (just taking the compressor off and putting it back on blows the balance). I mean the WHOLE turbine is up in the balance machine, no way I know of to do that by hand.

Hi Matt,

There's no doubt that you'll get more consistent and accurate results with a balancer . If I'm not mistaken , most of the kits are leaving Wren pre-balanced on their machine . I think the slight interference fit between the shaft and the compressor takes out some of the variability that can happen to the balance when the compressor is removed.

I'm quite certain that Hal will have very good results by just putting the new compressor on and running the motor. In the unlikey event that there are vibes , he can then send it out for machine balancing.

Are you making it out to FJ 2005 ?

Marc

Yeah, I have played with different ways of balancing the unit and seperatly using the hand balencer compared to items from RTI and even though there is no difference is vibes from the engine onto a test stand, wood, etc there is absolutly no difference between the two. Now looking at it upon a digital balencer their has got to be some differences, no matter how good you hand balence it. Im just referring to the outer differences and bearing wear at say 45 / 50 cycles, now in the longer run the may be some horizontal wear in the bearings, etc but in the short term I can not see a difference with one that has been hand balanced correctly.

I also took a hand balanced unit (wheel, compressor, shaft) and broke then down and rotated each one to a different position to check results from that and I still could see/hear/feel any differences. So with all this being said, I too think you will be fine to run it without balencing it first, if there are any balencing marks on the back of the compressor then its more than likly balanced, put it together and spin it up to say around 20K if everything feels okay, then make sure everything is tight and fire it up, you can always shut it down with the FADEC anytime something does not seem right, if its close then its not going to "grenade" like many people fear.

Probabaly not.

At 41 years of age, I finally got my priorities straight and I am enjoying hanging out with a new buddy of mine.

Thanks for the help and advice.

Wren e-mailed me and said you are correct about it being balanced from the factory. I put it in the engine like it was from the factory and got a bad vibration at around 25-30K then the engine stopped. Carlos balanced the turbine wheel originally so I sent the turbine, shaft and compressor back to him to dynamically balance.

Hal

Wow Matt ! Congratulations ! Why don't you bring your new buddy

Marc

Hal,

That seems very odd ! When did the vibes start ? On start or spool down ? There must be something else wrong with the motor . A component would have to be grossly out of balance to cause something like that at such a low RPM . I hope you get it worked out . Please report back with Carlos' findings.

Marc

Marc

I tried to start it several times and it did the same thing each time. It would start to spool up on propane and then it would switch to kero and continue on up and then poof it would quit. I would feel a bad vibration on spooling down.

I assumed it was a balance problem as I don't know what else would cause it to stop or create the vibration.

Hal

It's too bad you have this problem but I'm sure you'll get it worked out. It really is a fine little engine ! Good luck and keep us advised.

Marc