I have a 32 cc engine, converted from a McCulloch chainsaw (eager beaver), and I've just about ran out of ideas on how to eliminate the vibration that keeps rattling it from the mount. The engine has 3 #10x24 bolt holes in the back, and another 1/4 inch bolt going through the bracket coming off the block. I've tried using long metal spacers over 3 inch #10 bolts, on a modified Sullivan mount with isolators,but that only lasted about 2 minutes, at idle, and chewed the rubber isolators up like powder, and rattled loose several times. I then built a "box" type mount, where I ran even longer bolts through the firewall, the box, then into the engine, which lasted alot longer, but came loose in flight on Sunday (see McCulloch chainsaw interferance thread). Will drilling and tapping the #10 holes up to a 1/4 inch by 20 hold better than the #10 holes? Do I need some way to eliminate or isolate the excessive vibration being generated by this engine? The prop (18x10) has been balanced. My neighbor wants to try 2 separate mounts, one for the firewall, with 3 "posts" coming off of it, and another for the engine with the same 3 posts matching the others, then use 1/2 inch hose between the posts to eliminate the vibe. He assures me he can forge this out of aluminum in less than 2 hours, (I've seen him forging and producing parts in his garage), so I'll give it a try and update.....any other ideas would be appreciated......

All this talk about the McCullochs has me wanting to get mine converted so I can see how it does and if it has vibration, etc. I'm not sure why it would vibrate unless it has bad bearings or something. One trick you might try, is to install an un-balanced propellor. Try it with the heavy blade in line with the crank counterweight first, then opposite. When the piston is all the way up, the crank counterweight is all the way down, so install the unbalanced prop with the heavy blade down. If that doesn't help, reverse it and try again.

Ralph, did yours vibrate noticeably more than normal??

Good luck, and keep us posted please,
AV8TOR

Another thought. Are you running electronic ignition or magneto? If you are running magneto, check the balance of the mag flywheel.

AV8TOR

I converted a Mac 28cc and the flywheel was unbalanced to the tune of 5.2 grams on the heavy side. After balancing it has no detectable vibration.

No worse than the other small engines....It just didn't run as well as I thought it should....

Hi all,

One issue I ran into with a 35cc homelite chainsaw convert was had very bad vibes when using a heavy prop (master airscrew). A switch to a wood prop really smartened it up. Both props were balanced- the MA was rechecked and too this day this engine only likes light wood not heavy glass.

The engine was solidly mounted as I gave up trying to get softmounts to work (with the MA). When the wood blade was bolted on the vibe issue went away. When any heavy glass blade was tried the vibes came back.

Has anybody else seen this happen? Anybody with a theory? I have not experienced this with any of my other conversions.

Chris.

Give me some pointers on the flywheel......I have drilled out the 2 flyweights, but all fins are still in tact.....I have a friend with a lathe that can probably take care of the grinding or whatever, but how would I check the balance of the flywheel??? I am using a wooden 18x10 prop solidly mounted (or WAS solidly mounted until Sunday).....I am also using the original coil ignition system which works great....just a vibe issue at this point.....any ideas will be appreciated....

Take the flywheel off and send it to ralph at wackerengines.com for balancing. It only cost 15 dollars and will be the best money you can spend on this problem. RCignitions is ralph and he is one fine gentleman.

That prop you used that viabrated ,could have been drilled on a slight angle....making the tips track to be way off. Best to check props for this tracking. Good luck Capt,n

Motor has standard ignition (coil), a "Top Flite" 18x10 made of wood, and "off balanced" (heavy side opposite of piston), flew yesterday (10-18-04) seemed to be o.k. will know more after a couple of hours flight....replaced #10 diameter bolts with 1/4x20 with some "loc-tite" and torqued pretty tight....we'll see.......

Hi,

Actually, you have more to worry about than the engine falling off. Vibration is hard on the whole airplane, including the all important radio. If it is still vibrating, it is only a matter of time until you have a radio failure, wear your servos out, etc. I would get that flywheel balanced if I were you. Just my two cents worth...

Good luck,
AV8TOR

This link might help.
http://www.rcuniverse.com/forum/Redu...2249704/tm.htm