[Loman]

I am following the revised FAB instructions for the O-320 in my RV-9 but finding them a little scarce on detail, particularly the drawings. For instance, no drawing (or text for that matter) shows the orientation of the flush rivets through the carb heat door assembly. Is it countersink head up or down?

I know I am supposed to be a big boy now that I have reached FWF but it seems I still need my training wheels a little bit longer. The only justification I can think of for countersunk rivets here is for smooth airflow across the underside of the carb heat door. However, that’s hardly important when the forward edge of the door presents a step at least 1/16th thick and causes turbulent airflow there in any case.

I would prefer AN470-AD3 as used to rivet the bowl edge to the top plate. They seem to me to be stronger, especially when the instructions call for the shop head to be under-set.

Any thoughts?

 

[Kyle Boatright]

I am following the revised FAB instructions for the O-320 in my RV-9 but finding them a little scarce on detail, particularly the drawings. For instance, no drawing (or text for that matter) shows the orientation of the flush rivets through the carb heat door assembly. Is it countersink head up or down?

I know I am supposed to be a big boy now that I have reached FWF but it seems I still need my training wheels a little bit longer. The only justification I can think of for countersunk rivets here is for smooth airflow across the underside of the carb heat door. However, that’s hardly important when the forward edge of the door presents a step at least 1/16th thick and causes turbulent airflow there in any case.

I would prefer AN470-AD3 as used to rivet the bowl edge to the top plate. They seem to me to be stronger, especially when the instructions call for the shop head to be under-set.

Any thoughts?

On my 0-320, the flush side on the countersunk rivets is "up". On riveting the airbox to the top plate, I used the AN470AD3's.

It's worked well for 23 years.

 

[71459]

I could swear the FAB kit came specifying the carb heat door uses flush rivets on the inside of the duct, facing the air flow. It makes no sense putting them in the other way. And, the bowl edge to top plate uses 470-AD3's (exactly as you are preferring).

 

[Ralph Inkster]

The door/hinge assy must fit flush inside the top FAB plate. Use 426 rivets where the door & top plate overlap to achieve this flush fit. 470 rivets could be used to hold on the hinge & lever in those locations that don’t conflict with the top plate.
Some use 426 rivets (factory head up) mounting the forward hinge half/spacer to the top plate to facilitate a smooth surface to attach the inlet baffle material to the FAB housing.