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Engine Mount – Cracked Tube at Lower Left Engine Bolt

Piper J3

Well Known Member
I’m just starting Annual Condition Inspection at 633TT and began by looking at engine mount standoff for cracks per SB-00023. Standoff looks good; however, further inspection of the main engine mount found a cracked tube at the lower left engine bolt. Two tubes are welded in a cluster at this location and upper tube is severed in half – lower tube looks fine. I suspect the failure is induced stress from welding. Perhaps the normalizing process wasn’t sufficient to equalize strain in the two tubes that form this joint.

So, even though the standoff passes inspection I will replace it as long as I have everything apart. I’m also going to do 5-year rubber hoses with High Performance Silicone Heater Hose, install new rubber engine mount isolators, and remove the fiberglass cooling shroud.

Good thing the US Congress is passing the COVID relief bill, it looks like my stimulus check should just about cover the cost of parts.

The photos below are my airplane and one in Australia with a crack recently discovered. The Australian RV-12 has crack in lower right main tube near the oil tank. Both failures have been reported to Van’s…
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How many hours, now, on the Hobbs meter? 633TT

Are those cracks showing on the extension side or compression side of the weld joint from the the load of the engine's inertia from gravity when landing? I'm guessing extension

Mostly grass field landings? Yes, grass

Did you also show cracks on the outboard main gear landing attachment points, and what was Van's solution to that? I incorporated a fix that was designed locally. I believe Van's is working on problem. In my opinion, the SB for aluminum channel gear carry-thru is insufficient.
 
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Buddy with N120RV next row of hangars over had to replace his lower engine mount

I don't follow... Engine mount PN WD-1220 with large ring tube on back is a single weldment. Can't replace "lower engine mount" unless someone is cutting/splicing.

Van's responded today to my email request for information. Engine mount has been redesigned for added strength. New PN is WD-1220-1.
 
I don't follow... Engine mount PN WD-1220 with large ring tube on back is a single weldment. Can't replace "lower engine mount" unless someone is cutting/splicing.

Van's responded today to my email request for information. Engine mount has been redesigned for added strength. New PN is WD-1220-1.

Did Van’s mention an upcoming SB to deal with this?.
 
why is this not getting more press , this is a pretty big deal.

Brad Stiefvater
124BJ
Salem SD
 
typically a commercial airliner landing over 4G should have the engine mounts inspected. I don't know the typical limits for small piston aircraft.
 
I have a new twist on my problem… Van’s tells me today that engine mounts are not in stock and expected delivery is May 3.

So, a couple of possibilities:

Does anyone either have a spare engine mount, or perhaps building now and don’t need engine mount for a month or two and be willing to send to me for brand new engine mount I have on order?

Second choice would be to repair existing engine mount. See photo below. I can send mount to be welded and would like to use a reputable service. Any suggestions appreciated.
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It took two guys a total of eight hours to remove engine mount. As stated above, Van’s won’t receive mounts from their supplier until May 3.

I have located a welding shop that specializes in TIG. We will make a jig to hold 189mm vertical spacing between mounting pads per Rotax Engine Installation Manual. Crack will be chamfered with a carbide burr for good weld penetration. Tubing will be preheated to around 800F, TIG welded, and cooled slowly. A Chromoly 4130 split over-sleave will be welded in place to complete the repair. Lucky thing (if you want to call it that) the crack is in the straight upper tube and not the curved lower tube. I will find somebody locally to strip and powder-coat.

Brilliant white color is good for showing cracks, as I’m finding out first hand…
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Jim, can you share some pics of the crack close up and distant showing the relationship to the overall mount.
 
Now that the mount is no longer bolted to the engine the crack has closed up and vertical spacing between mounting pads is less than 189mm. When we jig the mount for 189MM vertical spacing between mounting pads the crack will separate just like when it was bolted to the engine. So, when welded, the mounting pads will line up with the engine bolt holes.
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Is this the correct location?


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Now that the mount is no longer bolted to the engine the crack has closed up and vertical spacing between mounting pads is less than 189mm. When we jig the mount for 189MM vertical spacing between mounting pads the crack will separate just like when it was bolted to the engine. So, when welded, the mounting pads will line up with the engine bolt holes.
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Man, that looks to be completely broken.. Is there still part of the tube on the other side not broken, or is it a clean break? I only have 189 on the Hobbs meter and don’t see any breaks in mine yet, but you definitely made me decide to pull the cowling and check last night. Thanks for the info.. I see another SB coming out soon... Wonder how much a new and improved engine mount is going to cost? $$$$...
 
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Bite your tongue, David!��

Agreed! I didn't build my plane, but feel like I'm slowly rebuilding it one SB at a time :)

Actually, it hasn't been that bad. But I do have to do the gear leg and engine mount standoff in next couple weeks (I have the parts). Time and a helper are all I need.

Still an excellent aircraft. And experience tells me ALL aircrafts break and have/should have a litany of SBs on them.
 
Weld repair is complete. Chromoly 4130 split over-sleave is TIG welded into tubing cluster.

Third photo shows weld fixture to hold 189mm vertical centerline distance for engine mounting pads.

On closer inspection… on the left side of the mount (broken side) I see heavy internal thread markings in both the top and bottom engine mounting pads. See photos below. I think this engine mount was made incorrectly from the get-go. My guess is the 189mm vertical centerline distance was compromised during initial fabrication, and when assembled to the engine, it caused tension and stress in the lower tube.

Engine mounting pads on the right side of mount look pristine. Now that mounting pad centerline dimension is corrected with this repair, everything should be hunky-dory.
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It's too bad Van's didn't have one they could exchange and bring yours in for extensive testing and analysis.

Just curious with that time - had you had the carbs rebuilt and do you balance them often or at least annually?

Also - prop balance? Recent or at the initial stages like most of the rest of us did?

Really think the key to long life on this plane is getting those vibrations out and keeping them out.
 
I rebuilt carbs last year and synch checked annually.

This year I will balance prop for first time. I will be interested to see balance improvement. Engine runs extremely smooth at cruise and off-idle.

Reinstalling repaired engine mount - where do all these hoses go???
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I have added a third photo to my post #1 above. I am in contact a RV-12 builder/owner in Australia. He has now discovered a second crack in the main circular back mounting ring after disassembling cabin heater control cable. He is in process of installing new engine mount after discovering crack on lower right side near oil tank. I would think main circular back mounting ring is very robust and that cracks would appear in thin tubing where engine attaches, like in my instance.

Just a heads-up when doing next condition inspection…
 
Another victim - -

I found my standoff mount was cracked more than half the way around on the cross tube. I have no idea what the fix is from Van's, but I ordered it. 1,450 hours. I have balanced prop I think 3 times, and sync carbs every year. I decided not to weld it, but did consider it. Not sure it won't break beyond the weld fix area. Engine torque I assume causes this problem. Hopefully the factory fix will last a long time.
 
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