Just finished my condition inspection and this was the main finding:
There were 3 hairline cracks in the FAB mounting plate on my carburated -6 which I have highlighted with a Sharpie to see them better. This is after 312 hours in 9? years of flying. I have seen many other RVs with these cracks so this is probably about average. This is probably acceptable wear and tear given the vibration of the significant mass of the FAB, but how to improve?
I did a couple of things that others have done. One, I made a new plate out of .090 instead of the .063 of the original part. Second, I added this brace which I made out of a short piece of 1/4" stainless tube and attached with #6 screws as shown using one of the existing FAB AN3 bolts:
I have no interference with the cowl although it's close and this has been a problem in some cases. I think my cracks are strictly vibration induced. Another solution involves adding about 1/4" spacer between the plate and the carb, which avoids making the cutout in the mounting plate. However, I note that many of the cracks I have observed emanate from the bolt holes, even with plates without the cutouts. In addition, I really didn't think I had enough clearance with the bottom cowl to add the 1/4". So this wasn't really an option for me. I did grind some of the excess casting off of the bottom of the carb that interferes with the mounting plate and this eliminated the majority of the cutout.
Hopefully this will improve on this part's performance over time. We'll see.
There were 3 hairline cracks in the FAB mounting plate on my carburated -6 which I have highlighted with a Sharpie to see them better. This is after 312 hours in 9? years of flying. I have seen many other RVs with these cracks so this is probably about average. This is probably acceptable wear and tear given the vibration of the significant mass of the FAB, but how to improve?
I did a couple of things that others have done. One, I made a new plate out of .090 instead of the .063 of the original part. Second, I added this brace which I made out of a short piece of 1/4" stainless tube and attached with #6 screws as shown using one of the existing FAB AN3 bolts:
I have no interference with the cowl although it's close and this has been a problem in some cases. I think my cracks are strictly vibration induced. Another solution involves adding about 1/4" spacer between the plate and the carb, which avoids making the cutout in the mounting plate. However, I note that many of the cracks I have observed emanate from the bolt holes, even with plates without the cutouts. In addition, I really didn't think I had enough clearance with the bottom cowl to add the 1/4". So this wasn't really an option for me. I did grind some of the excess casting off of the bottom of the carb that interferes with the mounting plate and this eliminated the majority of the cutout.
Hopefully this will improve on this part's performance over time. We'll see.