New carb socket fits loose

Kelsie,

The key word is 'temporary" (not a modification) as in temporarily remove the suspect (RV) parts. Refit socket & carburettor. (no starting engine/flying involved) If carb now fits socket, you have found the problem - RV parts  need to be fixed/changed/ditched.  If socket :carb still a problem then check aluminium inlet manifold for distortion. You  can now act/move forward accordingly. 

Sean Griffin wrote:

Kelsie,

The key word is 'temporary" (not a modification) as in temporarily remove the suspect (RV) parts. Refit socket & carburettor. (no starting engine/flying involved) If carb now fits socket, you have found the problem - RV parts  need to be fixed/changed/ditched.  If socket :carb still a problem then check aluminium inlet manifold for distortion. You  can now act/move forward accordingly. 

Sure, that last reply saying no modifications was directed at the comment telling me to shave down the spacer on the clamp. Your suggestion to remove the tray from the equation to check the fit makes sense to me.

Kelsie Kerchmar wrote:

Jim Isaacs wrote:

Thanks that clears it up for me. Setup similar to the Rotax drip tray only using sealant instead of the Rotax gasket (why not try the Rotax gasket?) But I can’t figure out how some irregular sealant thickness behind the rubber flange would prevent you from tightening down the carb- that flange is rigid back there behind the socket and your sealant and doubler. Have you tried removing the rubber flange clamp spacer and temporarily substituting something 1-2mm shorter, then tightening the clamp against the shorter spacer with the carb installed?

Modifications like that are not legal, this is an SLSA. It is necessary to find the root cause of this problem.

The irregular sealant thickness can be causing the rubber socket to flex open, if say there is a thicker sealant in the middle versus the edges. This would make sense because the edges are where I had the clamps when I applied the doubler with the sealant.

Kelsie,

I assumed using the word “temporarily” in my message would be understood by you as not a permanent solution.  I wonder why Vans did not just use the Rotax drip tray? Anyway, as you have a SLSA aircraft, once you discover the cause of the problem and a potential fix, then you must gain approval from Vans to implement the fix, with documentation as well, am I correct on that?

Jim Isaacs wrote:

Kelsie Kerchmar wrote:

Jim Isaacs wrote:

Thanks that clears it up for me. Setup similar to the Rotax drip tray only using sealant instead of the Rotax gasket (why not try the Rotax gasket?) But I can’t figure out how some irregular sealant thickness behind the rubber flange would prevent you from tightening down the carb- that flange is rigid back there behind the socket and your sealant and doubler. Have you tried removing the rubber flange clamp spacer and temporarily substituting something 1-2mm shorter, then tightening the clamp against the shorter spacer with the carb installed?

Modifications like that are not legal, this is an SLSA. It is necessary to find the root cause of this problem.

The irregular sealant thickness can be causing the rubber socket to flex open, if say there is a thicker sealant in the middle versus the edges. This would make sense because the edges are where I had the clamps when I applied the doubler with the sealant.

Kelsie,

I assumed using the word “temporarily” in my message would be understood by you as not a permanent solution.  I wonder why Vans did not just use the Rotax drip tray? Anyway, as you have a SLSA aircraft, once you discover the cause of the problem and a potential fix, then you must gain approval from Vans to implement the fix, with documentation as well, am I correct on that?

I guess I misread, didn't realize you said temporary. What would I gain by doing it temporarily? It might end up tight, but is there a conclusion I can draw from that?

I am not sure why Vans did it this way, but I have wondered the same.

I do not need specific approval from Vans to do this part replacement because the maintenance manual grants broad authorization to do part replacements that conform to the kit assembly instructions, with only a few restrictions. There's no issue in this case as long as what I do is by the book.

I have made progress today on this issue that I want to share.

I removed the 2/4 socket to see if the drip tray might be a contributing factor. The socket continued to be loose off the airplane attached to only the carb. I then made a decision that I have been hesitant to do- I removed the socket from the 1/3 side that was tighter because I wanted to try that socket on the 2/4 carb. It was indeed tighter, but still not actually as tight as the 1/3 carb in that socket on the airplane. I decided to start over and question all of my previous tests.

I noticed a couple of things. Two of my sockets fit tighter with no clamp than another two of my sockets. I decided to continue further tests with only the tighter of the sockets. But it is clear at this point that the sockets themselves are just not all equally tight. Maybe this does or maybe this does not matter, once the clamps are on, but it is noticeable.

At this point, I noticed that the old clamps from before I replaced the carb sockets at all, that I had not intended to reuse, fit significantly tighter than any of the new ones. I hadn't tried the old clamps before. I started to investigate why this is, and it appears that the spacer is wedging into the welded nut side a little bit in a way that none of the new ones are. I'm not sure if this is intentional, but it is making a significant difference in the overall tightness. See the attached pictures for what I mean. The side-by-side clamps are the new ones, and you can see the spacers relatively flush and not wedging into the sides at all. In the pictures with the individual clamps, you can see that the spacers are both wedging into the one side a bit. Those are the older clamps.

With the older clamps and the tighter pair of the sockets i have on hand, I find the final tightness acceptable. I do not feel that the wedging that is occurring is intended, it feels like a worn part doing something unintended, and just happening to work out okay.

I have attempted to get the spacers to seat in the new clamps in the way that the old ones are, and no matter what I've tried, I have not been able to accomplish getting them to seat in the manner that they effortlessly seat on the old clamps.

After identifying this difference in the clamps, I also observed that the orientation of the clamp (fastening on top vs fastening on bottom) has an effect on how the spacer seats when things are tightened down. One of the newer clamps is VERY slightly allowing a bit of this wedging to occur, much less visibly than the original clamps, and it only occurs if the fastening of the clamp is on the bottom. None of the other new clamps are behaving this way at all. If you rotate the fastener it to the top, the spacer rests in a different manner before tightening, and then it doesn't end up with any wedging. In order to access the fastener, Vans has you orient one of the clamps such that the fastener is on the bottom of the socket (for the 1/3 side) and the other side on the top of the socket (for the 2/4 side), so that the machine screw head is always facing outward and is accessible. Thus, when I put the clamp from the "tight" side on the "loose" side, it ended up actually being looser on that side.

In order to move forward right now, using the old clamps seems a viable option, but I am still not particularly satisfied that it is necessary for the spacer to wedge itself in before I can get a proper tightness. This still doesn't seem right to me.