Something VERY interesting and important about Spectra-g's

[rbort]

Some time ago while working on my Spectra-g, I noticed that the engine seemed to wobble when you remove the spark plug and pull it though with the pull starter. People always talked about having a true crank and dial indicating the fan and such, so I sent my engine out to Al at Hanson's to get it tuned up. When it came back and I put everything back in, I had the same problem. That was the week of the MHA FF.

I decided to leave it be and show it to Tim at the FF. We worked on it for a good hour trying different things (he even dial indicated the fan as he thought that was the problem and it was dead nuts straight) and finally the culprit was found to be an out of round clutch delrin ring. This was quite strange but replacing the delrin with a new one cured it.

I am writing this as in the past people had vibration problems with Spectra-g's and this could be your exact issue. While I was at the MHA FF I looked at another guys machine (sorry forgot his name) and he had the same issue (engine wobbled a bit as you pull it through).

If you own a Spectra-g please pull the plug and do this simple test. If you find that the motor is wobbling replace the delrin on the clutch and try again. I went from a "washing machine" fuel tank fuel effect in flight to a fuel tank that resembled my old 1005 gasser in flight (slosh around but nowhere near what it was on the Spectra-g).

I think this is the ticket to cure the vibrations on the Spectra (at least mine and this other guys) and I would definately take a minute to check yours.

-=>Raja.

[DebianDog]

Thanks!

[Peter]

the clutch delrin ring is the uniball ???? One of mine has started to " melt "; all is dialled in , balanced etc , so it may have been/gone out of round too ......
:dontknow :dontknow

[rbort]

the clutch delrin ring is the uniball ???? One of mine has started to " melt "; all is dialled in , balanced etc , so it may have been/gone out of round too ......
:dontknow :dontknow

Couldn't think of the proper name for it. In any case check the engine with the pull start and make sure it spins true with the clutch.

-=>Raja.

[Toadster25]

I checked mine and it looked ok. I have had my ball come loose and drop down onto the nut that holds the fan on the engine but the only reason I found that was because I was taking the heli apart for something else. I think it got knocked loose when I crashed.

[Peter]

I have had my ball come loose and drop down onto the nut .

:roll: :roll: :roll: :roll: Bet that hurt............ :shock: :shock: :shock: :shock:


I've just fitted a new uniball to replace the " melted " one .. all seems smooth with the pull test .. Will see what the flying is like tomorrow..... if it stops raining that is........

[bigrcr]

Toadster hit it. I will bet that your delrin ball was no longer glued onto the driver.

If the glue fails (from vibration, heat, crash or whatever), the uni-ball will melt and drop down so that it gets wedged onto/into the crankshaft nut. This will rapidly cause the uni-ball to become out of round and melted causing a very bad frame vibration.

A lean run or a crash usually causes the uni-ball glue joint to loosen at first and then this failure occurs.

If you have a crash or incident especially one that really loads that frame (very poor auto that slaps the skids down and unloads the blades) expect the glue joint on the uni-ball to fail.

The older 31005 would not do this same thing as the uni-ball was different (driven on the start shaft (as it extends through the clutch) and cannot fall down and get wedged.

You cannot just stick a new ball on and have it to stay as it has to be glued back on with a two-part adhesive (this adhesive is a light Grey/white.)

The following pictures show the uniball damaged (and it caused a huge vibration) and in the first picture no longer glued on. Either of these are not good.

Later,

[rbort]

If you're talking about mine bigrcr, my uniball was glued nice and tight in there. Tim and I had to work on it with a screwdriver to pop it off. It was original on the machine (80 flights old), and somehow out of round or in some way causing the wobble -- probably was like that from day 1. By replacing it with a new one, the problem went away.

The interesting thing I thought was a) strange for that to happen, and b) another fellow at the field had the same exact issue (wobble when pulling engine through).

I've made this post as I'm thinking there may be more people than the two of us having this issue, and, if people are knowlegable to check this, they can eliminate a big source of vibration. In my case before I noticed this the heli looked and flew smooth, the only telltale sign was the washing machine effect on the fuel tank that I was chasing trying to find out where its coming from.

Well, the answer was "from the uniball", that looked absolutely fine when inspected and was still glued up there.

-=>Raja.

[ClayK]

Would this also cause a whine/high pitched noise from around the clutch bell area?
What's the part number for this? I can't find it....

[rbort]

Sometimes that uniball falls and gets chewed up in the fan hole on the fan bolt is what I heard at the MHA ff. Maybe that would cause the whine but I would also check the generator motor and make sure everything is snug and good on the couplers and the motor shaft. You can even take the top plate 4 bolts off and lift the motor out to see if the whine goes.

I never had a whine like this but I say this as electric motors can whine...

-=>Raja.

[paulw1283]

Is there a way to avoid this problem?

[rbort]

Is there a way to avoid this problem?

I think you either have this problem or you don't. A quick way to check is to take the spark plug out and pull the motor through with the starter and look carefully to see if its wobbling. Look at the aircleaner or muffler for signs of that (moving up/down or side to side when you pull). If you see this problem then suspect the delrin as it was in my case. If you don't see this problem then you don't have it and fly on!

To this day I don't understand why I had this problem from the beginning. I think it was a fluke on my part with the delrin as it seems weird it can cause that. Just wanted to post it for all the other Spectra--g flyers out there as something to check -- most probably most of you guys will not have this problem, but better to know about it than to not! Spread the wealth of the knowledge -- that is why we are all here, to learn about our beloved birds!

-=>Raja.

[bigrcr]

MA is using a stronger glue now (have been for a while) to install the uniball on the clutch driver.

Some of the first uniballs for the G did not use this glue. Don't panic if you have one of the first 10 or so models as if the glue bond is still intact it, it will continue to do so. It was not that the original glue was bad or defective, it is just that the new glue is much better and withstands the abuse better.

Later,

[ka6fty]

MA is using a stronger glue now (have been for a while) to install the uniball on the clutch driver.

Some of the first uniballs for the G did not use this glue. Don't panic if you have one of the first 10 or so models as if the glue bond is still intact it, it will continue to do so. It was not that the original glue was bad or defective, it is just that the new glue is much better and withstands the abuse better.

Later,Mine is also loose and falling off - causing excessive vibration. I see the uniball at Rick's p/n 546-3.
Is this the correct part for the Spectra?
What type of adheasive should I use to attach it?
s/n of this machine is 25.

[bigrcr]

The glue is a two part adhesive and is rather expensive as it has to be delivered using a special mixer. The glue sets-up like concrete and nearly cannot be dislodged once it is set by anything. I sent my driver to MA and had the uniball replaced. Call MA for more details.

Later,