I caused a crack in my engine mount of my ARF when I redrilled holes so I can move the engine forward. I tried to move the engine after I got it screwed in and it does not move at all. I was wondering if this would cause any problems or should it be ok??

If the crack is behind any engine bolt then replace it. It's dangerous and not worth the risk. If the crack is at least 1/8" in front of the forward bolt then it should be ok.

CafeenMan is all over this one with very good advise. If ever in doubt, for safety sake, replace it.

Just remember, the vibration levels from a running engine can do far more damage than you can "feel" with your hand. I don't know about you, but I can't back out screws with my fingers, but my engine sure is good at it if I don't use locktite

Great advice from CafeenMan.

(oh, disclaimer time, I have acutally flown with cracked mounts, but as CafeenMan indicated, the crack was small, and in a location such that even if it failed, I'd lot have the engine come off. And it was on a plane that gets a lot of pre-flight attention and maintenance anyway).

It may be tight now, but it will crack more when you start the engine. As stated, if the crack is not quite a ways in front of the front bolt, replace it. No use wrecking a plane because you didn't want to spend $4 on an engine mount. Take the time to do it right. It takes a lot less time than rebuilding a plane.

Or healing

HI JACKSON JRS! MY original reply to your question I deleted because I read your question wrong. A weak mount can only get worse, and $4 can fix the problem the right way. Vibration can disintegrate servo gears, cause lean runs, and fracture solder joints on printed circuit cards.

I would replace the mount.

Crack in an engine mount?! Replace it asap nomatter where the crack is located and how it "looks" like!

Thanks for the advice guys. I will be ordering a new mount soon (I have about 4 months until the weather will break.) I do have another question though. The plane came with the mount already on the firewall. Its a wood mount so there aren't any screws that are holding the mount on. When I put the new (plastic) mount on what should I use to secure the mount to the fire wall. Keep in mind I might not be able to reach the back of the fire wall due to a brace blocking it. So a long screw with a bolt is prolly out of the question. Will regular wood screws hold it tight enough??

I can post pics if that helps any

NO NO NO NO NO NO NO

on most of my combat planes .25 or smaller,the engines are mounted to the fire wall with sheet metal screws,any thing else up to g26 or similar is mounted to the firewall with blind nuts and bolts,any thing larger is mounted with bolts ,washers,and locknuts.If you have an engine size from .30 to 180 then I would use blindnuts and bolts.

HI JACKSON JR! Depends whether or not your firewall is made out of aircraft ply or cheap ARF junk. If it is good wood, then wood screws will work on your smaller [.25 and under] engines. the threads that you form in the wood should be hardened with thin CA glue. If you aren't sure about the wood, you can "fish" blind nuts into drilled holes by sliding a long wire into the fuselage through the firewall, slide the blind nut over the wire, then bend the end of the wire into a tight T. then yank the wire to seat the blind nut. You should start a bolt into the nut carefully, and tighten it to fully seat the nut.

jackson,
Your last post may make a difference in the answers here.

Is this "mount" two wooden rails that are actually a part of the fuselage construction? Do they go through the firewall? (It sounds like it.)

If this is the case, then I would apply epoxy to the "Crack", and maybe wrap it tightly with nylon thread while the epoxy is still wet.

Wooden rail type mounts that go through the "firewall" generally mean that there isn't any substantial firewall, just a forward former; and that won't take the stresses induced by a motor mounted to it.

I think we need more information, and a picture sure would help.
Dennis-