Replacing the engine mount

[Wheels]

The crack I found in the motor mount grounded me. So I took off the engine and ordered a new mount. As I pulled the engine from the motor mount, the cracked member fell off! It wasn't cracked, it had been broken a long time. Now the fun begins as I re-hose everything, inspect everything and consider changes.
I ordered all new hose from Rotax. The spring type clamps don't work on this engine according to Rotax, so I am back to gear driven clamps. I was told the engine had 68 hours on it before I bought it. I am skeptical now. Are there any tell tale wear spots that can help identify potential age? the cracked motor mount has probably been that way for at least 250 hours, maybe the whole 450 I have flown it. I think it accounts for the bulk of my problems with carb balancing, vibration isolation and general funny behavior that could have been well … not so funny.

[Timberwolf]

Got any pics up close of the welds where it broke? Does it look like fatigue or cold weld?

[Paul Z]

Count your Blessings, if it had broken loose. God was looking after you, if you never lost the engine!

[Wheels]

Here's a close up, its fatigue. This is a known problem with the older engine mounts. It doesn't help that I had an impact during a slide off an ice covered runway the first flight with an instructor. Oh did I say he had never flown a IV in his life. He thought it was just like the Kitfox he had flown before. oops. I paid. I think I'm still paying.
Well, I'll keep you posted.

[Jerrytex]

When I got my partially re-built KF 4 the motor mount was warped and had a crack. I ordered a new one from kit fox and could not believe the difference. The new one was at least twice as heavy and felt much more "meaty" than the original. I say it's worth getting the replacement. One less thing to worry about when flying. On a side note, the DAR that inspected my plane said that he uses a safety cable on every one of his engines. At least if the engine falls off, it will hang there and keep the CG close so you can maintain some control to make an emergency landing otherwise you're falling debris.

[SWeidemann]

Apparently broken engine mounts are common. I am in the midst of replacing my engine mount (Rotax 912 ULS on a Vixen) because of an obvious crack at the top right side just back of a gusset for the top right rubber mount. In my case however I may be able to say it ran a long time before a crack developed, since this engine has run 1600+ hours, presumably with the same engine mount.

Skot

[Wheels]

The crack location is the same as mine. The new engine mount isn't going to crack, its beefy. The problem I have today is that the local machine shop miss drilled the new forward mounting hole. I saw the whole job, I cannot tell you how that occurred. But, never the less, the part is now at a welding shop being TIG welded to fill the miss drill, re drilled and repowder coated. Thats about 1000 for the part and 150 in machining and powder coating. This has been a ground loving summer considering it started out as a boomer with the first flights. Oh well you know what they say. "Never feel sorry for a guy with an airplane."
You need to consider the price of re rubber for your engine. I got a box of hose about 9 feet long and it cost 450.00. Yep its going back to the vendor. A rotax distributer who is usually Johny on the spot for all my rotax needs, but not this time. I could buy a good used dirt bike for the money they want for that hose!
I"ll let you know how it goes, anyway, lots of info and thanks to Roger Lee for the hose information I'm now dealing with.
Happy engine mount changing.

[DesertFox4]

Wheels, my Kitfox kind of looks like yours right now.:eek:



7299

[Wheels]

Why is that going on? Are you doing a rubber replacement or an engine mount?

[DesertFox4]

The mount is fine. Needs new rubber all around. In service now 10 years and time for refresh on rubber mounts and hoses. Probably go with new style fuel pump also. Carbs are off being rebuilt.

[Av8r3400]

Steve, while she's down you should do something about that funny wheel under the engine...:eek:

[DesertFox4]

Well I guess I could remove it but it's gonna be rough on my prop.

[HighWing]

I cannot tell you how that occurred. But, never the less, the part is now at a welding shop being TIG welded to fill the miss drill, re drilled and repowder coated.

This caught my eye. I took an Avid elevator I am modifying for a trim tab to the local Powder coat guy. When he saw it, is first words out of his mouth were, "I thought airplane parts shouldn't be powder coated because it hides cracks". I told him that with home builts we can do pretty much what we want. Yes, occasional reports of cracks in the Model IV engine mount would surface on the lists and forums. A good checklist item for the annual inspection.

[Wheels]

I ordered hose for my rubber replacement and almost had a heart attack at the 460.00 bill and the tiny box of assorted hoses. They added up to a little over 10 feet of hose. So I'm sending it back. There wasn't enough hose in the box to actually do the whole job. My rubber isn't actually due yet and I thought I would just add some life while the engine was off but not for that kind of money.

So I'm researching hoses and I have a list from CPS I got from Roger Lee on the Rotax forum. the price is coming down. significantly. There are a few specialty items that you just HAVE to have like the 90 degree bend hose on the coolant tank etc. Pricey but mandatory. I am considering buying the special tools for squeezing on clamps and getting rid of the gear driven ones. Rotax said the spring type are not working well on some of the aircraft . any druthers on that tool and part choice? Well, Happy hose replacement, anyone with a list or sources for quality hose and clamps feel free to jump in.

[Wheels]

Here is a pic of the new dyna-focal mount for a model IV and the old one side by side. The black one is the old one. No tube thickness change, but the extra gusset welded to the extra support will change the strength tremendously.
I measured the tube thickness and they are the same, so unless the material has changed, the beefiness is confined to the gusset and the extra member.

I have a serious p-factor to the left and need to stand on the right rudder enough at cruise that its annoying. Was playing with the idea of shims now that the engine is off. A mechanic friend of mine asked me if I thought the shims would have an adverse affect on the equal dampening of the dyna-focal engineering. Damn I hate it when someone else is smarter than me, so I hate it a lot. Any comments?

[jrevens]

...
I have a serious p-factor to the left and need to stand on the right rudder enough at cruise that its annoying. Was playing with the idea of shims now that the engine is off. A mechanic friend of mine asked me if I thought the shims would have an adverse affect on the equal dampening of the dyna-focal engineering. Damn I hate it when someone else is smarter than me, so I hate it a lot. Any comments?
Wheels,
I doubt that a little shimming of the mount would make any descernable difference with vibration. I've seen it done frequently with Lycoming engines - mostly to correct slight misalignment with the cowl. However, it sounds like you need a rudder trim tab.

[jrevens]

This caught my eye. I took an Avid elevator I am modifying for a trim tab to the local Powder coat guy. When he saw it, is first words out of his mouth were, "I thought airplane parts shouldn't be powder coated because it hides cracks". I told him that with home builts we can do pretty much what we want. Yes, occasional reports of cracks in the Model IV engine mount would surface on the lists and forums. A good checklist item for the annual inspection.
I know painters who hate powder coating - it is generally thick & flexible enough that it can hide cracks. It also can hide corrosion if not applied correctly, to a properly cleaned & prepared surface. I saw an example of a piece of 4130 tubing that had corroded badly underneath the powder-coating. The outer surface of the powder coat looked beautiful. I had some serious doubts about whether I wanted to order my Kitfox parts with powder coating, but I did it anyway.
On my "other" airplane, I painted my engine mount black, but that is generally considered a no-no by some, as it makes it a little harder to spot any developing cracks. White is better in that regard.

[Esser]

Drill a hole at every intersection of pipe and then add a spot to thread in a gauge and a place to add air. Every year see if the mount holds air…if it doesn't you have a crack. No worries if you powder coat it.

[mr bill]

Cessna and Piper both paint their engine mounts black. Personally, I prefer white for aesthetic reasons. If shimming, it might be better to shim at the firewall, rather that at the dynafocal end of the mount. Shimming will cause the crankshaft to move relative to the cowl. Sometimes there is no easy way.

[jrevens]

Drill a hole at every intersection of pipe and then add a spot to thread in a gauge and a place to add air. Every year see if the mount holds air…if it doesn't you have a crack. No worries if you powder coat it.
I'm not sure if you're joking or not, Esser. I've heard that idea before, and pressurizing a sealed structure & monitoring the pressure with certain very highly stressed and critical structures has been done. It's interesting, but it wouldn't necessarily be of any use as a crack was forming, or corrosion was forming on the surfaces of the tubing of a Kitfox. As I said, most painted pieces will show a developing crack before a powder coated one will, & hidden corrosion has been known to form under powder coating, as opposed to a properly primed & painted surface. Cracks do not necessarily occur all at once, penetrating the full depth of the structure. They can & do start at the surface, frequently the outer surface of a tube, & gradually increase in length & depth until failure of a structure. I'm not trying to infer that powder coating is necessarily bad - again, I chose the powder coating option for my Kitfox. For a builder to decide which way to go, having knowledge of the pros and cons should be part of the equation.

[Wheels]

trim tab sounds doable and pretty fool proof. Thanks.

[HighWing]

I have a serious p-factor to the left and need to stand on the right rudder enough at cruise that its annoying.... Any comments?

My first Model IV had the left turn tendency - as does my new one. I sort of expected it as when I was laying out my engine mount - home brew - I found that the kitfox engine mount has no thrust offset, vertically or horizontally. Not being the engineer, I did as Kitfox did and built it with no offset.

While flying my first airplane, I often imagined a rudder trim that would warp the ribs in the rudder modifying the airfoil shape from symmetrical to asymmetrical by degree to give some "lift" to the right side. I did the deed and it works well and in my experience, it doesn't take a lot to trim the rudder to reduce that constant right foot pressure. Most guys who have added trim have riveted a blade tab to the trailing edge of the rudder.

What I did on the first Model IV

[Wheels]

thank you Highwing. I think that looks like something I can use. I assume you took off the fabric to do all the work, but the drawing looks like maybe it was externally mounted without a fabric patch, am I crazy? Well, am i crazier than you first thought I was?

[HighWing]

Painted and riveted externally. I did start the bend with the a sheet metal brake.

[Wheels]

thanks again sir. Ok, one more item. I had a bracket on the old engine mount that was part of the original air box for carb heat. The new mount doesn't have it so I have no where to attach my CDI for security on the left side. I guess I"ll just make a bracket and screw it into one of the two holes at the engine lift point, but do you have any other ideas?

[kitfox5v]

Don't care too much for the white ground wire in the bottom photo. too much tension and angle.

[HighWing]

The picture shows the ignition modules mounted to the builder fabricated brackets that were in the original builders manual rather than the airbox mount. Due to vibration issues and the non Tefzel wire in the modules resulting in frequent broken wires, most guys moved the modules to the firewall side of the engine mount. Since the runs will be longer you can get by by shuffling the existing wires. You will likely only have to buy a couple of feet or so of new ignition wire to make the swap.

[mr bill]

I mounted the ignition modules per the pictures, directly to the engine mount, using rubber vibration isolators, simple and very secure. This is on a model lV.

[Wheels]

I like the module movement to the upper mount position. I havn't done much electrical so it appears a little out of my league but up until last March, everything else was too.
Ok back to the plane. The white ground wire was a test wire to see if I could back up the ground strap/bracket that broke in flight. I posted about that non event. It isn't staying on the plane but a real ground strap will be going there as well as the bracket.
I'm getting all new hose and all new clamps with the "clamp it" tool and then the fun really begins. So much for flying by next friday.

[Wheels]

Haven't changed the module location yet but I did get the Lord mounts on the engine mount and the mount is on the engine. I am pretty sure the guy who invented the lord mount was in fact an atheist.

[Peteohms]

I ordered hose for my rubber replacement and almost had a heart attack at the 460.00 bill and the tiny box of assorted hoses. They added up to a little over 10 feet of hose.....


All hoses on my plane came from auto parts or truck parts stores. Couldn't have cost more than $150-$200. I'd be tempted to skip the expensive stuff unless you are making a show plane.

[Peteohms]

Painted and riveted externally. I did start the bend with the a sheet metal brake.


I used exterior double sided foam tape to attach my sheet metal trim tabs. 4 years and still attached.

[mcomeaux53]

requires replacement of Service Bulletetin SB #54 A
Bushings And shortened tubes. Anyone have a source we
can purchase these items? Regards Mike

[Av8r3400]

You can buy them from Kitfox or you can just shorten the ones you have with a bench grinder or even an angle grinder.