Question, I was out flying my Avistar yesterday, and I noticed that the engine was vibrating quite a bit, I am sure it was much more than it has in the past. I thought the glow starter was going to fall off when I started it, it was rattling so hard at the end. I took it home and the prop and spinner looked alright, the mounts were tight to the firewall (although I tried to tighten it more and broke the screw off, so I took a couple steps backwards) the only other thing I can think of is I had mounted the engine to the mount with threaded screws, rather than a screw, washer, nut. (I am changing that). Could that have caused such vibration? Also, since I haven't spent a lot of time around other planes, do you guys get much vibration in the engine, when it is mounted properly? Or is it real smooth?

Also, I still get mixed responses to quality and age of fuel. Could some of the roughness be due to using old fuel? Seems some guys say it stays good a long time, and others say trash it at the end of the season. I have about a quarter gallon of some fuel left that I bought late last fall. It sat out in the garage all winter in Wisconsin, too.

Thanks in advance for your thoughts!!

try balancing your prop before any major surgery. that's really the only thing i can think of off hand. cheers.

Please tell us what size and brand engine, and type pf fuel your using.

It's an OS 46 LA, and the fuel is 5%/20%, I honestly don't know the brand, I just grabbed it at a local Hobbytown. Is there much difference in brand, or were you more concerned about the nitro/oil mixes?

Thanks again!

(I also cleaned the engine, it was a little dirty from taking off from a dirt strip. I imagine that may have contributed)

Live twice,

I too have a 46 la and had it on my kadet. I had loud vibration problems in certain rpm ranges (not all). at about 1/8 to 1/4 throttle it was pretty loud, but when I put it at low idle it would quit and go to full throttle it would quit. Some guys at the club indicated that this is an annoying property of the la motors and I can't understand why yours just started doing it (mine always did it), unless yours is getting broken in and that's affecting it. How many tanks have you run through it?

BTW, I no longer have the la on my plane, my instructor sold me a 46 fx he had for a really good price. Haven't flown it yet, but man it runs much smoother/quieter and I can definitely hear that it has much more on the top end. We didn't do the engine swap for the vibration, we were having issues with multiple dead stick landings and couldn't figure out why (and seeing that I'm learning myself, I didn't want to spend what precious little time I have with my instructor to debug my engine). Maybe as I get more experience with the hobby I'll get the LA back down and goof with it.

Wayne

P.S. I was running a 10% synthetic (ritch's brew) through it and tried someone else's cool power 15% and got the same thing.

Check the play up n down (grab the prop) and see if the bushings in the engine are sloppy. Ive heard that was a problem with that particular engine. Just a thought.

IN most cases the Vibration is due to the fasterners not tight enough or the exhaust being loose .

The vibration woudl effect the servos as the screws begin to get loose and cause the servos to get out of alignment .

U woudl have to undo the screws on the servo and applu epoxy on the previous holes & then insert the screws in them .

Check if the engine mounts are fastened , also the screws on the firewalls & teh muffler .

These are the only causes of vibration on the engine .

The fuel has no basis for the vibration .

Thanks for the replies, it is definitely running better now, although there still is some, probably more acceptable, vibration. I think changing the bolts on the engine mount helped.
Groundforce, I am interested to learn, what did you mean by the bushings being sloppy? If the prop is horizontal, and I grab both ends and lift it vertically, are you saying there might be some play that shouldn't be there? thanks for the clarification. I don't know much about engines, but am trying to learn.
Thanks again!

Turn the prop straight up and down, then gently "pull and push" against the prop. should be very little , if any, movement.
If I remember correctly, that engine is a bushing rather than a ball bearing type engine, I could be mistakin though, maybe others have some input here as well.

Yes, it definitely has some play 'in and out' so to speak. enough that I thought it was normal. The prop shaft doesn't really feel like it is loose on the axis it is spinning on, but it does move in and out. I assumed with the prop creating thrust, it just pulled the shaft tight out, or away, from the engine. What does that mean for the engine now?? ( I'm not talking about a quarter inch or anything, maybe 1/16 to 1/8 inch max of movement)
Thanks

I was talking "up and down" play. The in and out ive not heard of, not sure if thats really a problem as all engines will have some movement that way.