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Ruh-roh: firewall flange to bottom skin rivets

Draker

Well Known Member
Here's something I probably should have done before I mounted my engine. The firewall-to-skin rivets just behind and beneath the gear attach bolts on the "new tricycle gear" engine mount are going to be impossible to buck. The other ones along the bottom between the bolts are going to be difficult but probably not impossible. Looks like at least a couple of these will have to be pop rivets. Any other ideas that don't involve removing the engine and engine mount?



 
I don't know if there are cherry max or equivalent in 3/32. If so then i would just use these. You can try to fit a thin and long piece of steel between the tube and the rivet as bucking bar. That should work too.
 
Yep, just went through this myself. Another OH S...T moment. I was able to get all of the AN426AD3 rivets set with a shallow no hole yoke on my rivet squeezer except two of the rivets. But it was a tight squeeze if you'll pardon the pun. In a couple of cases I had to pre-squeeze the rivets, just enough so they would still go through the hole and just enough to give me a bit more head room below the engine mount. For the last two rivets I used the MK-319-BS rivets left over from the (sliding) canopy. These are POP/Avdel nickel copper alloy rivets with a steel mandrill and countersunk head. The rivet body is 7/64" diameter, just 1/64" larger than the AN426AD3 rivets. I think the smallest Cherrymax is 1/8".

I did have to remove the nose gear leg before I could set these rivets but this was a minor inconvenience. Especially as I had just bought an automotive type engine hoist to lift the fuselage to install the main gear legs. Cost per usage of the hoist dropped a bit with the additional use.:)
 
Heh... yeah, I remember those. I actually forgot to put rivets in the center 8 or so holes, guess I was leaving them open for some reason later. Made it all the way through DAR inspection and Phase 1, and caught it on my first annual.
 
I wouldn't go so far as to try to put a cherry max in it. Yeah, some of those you won't buck. I would put a pulled rivet in there, maybe a MSP?, and move on unless you really want to set the "impossible" solid rivet. That is fun sometimes too :). I have a few of those. They make fun conversation pieces with other RV builders years later.
 
Thanks everyone.. Looks like the consensus is use a pull rivet for the impossible ones. I'll probably just do that.

But bear with me, and maybe talk me out of this one: I only need an inch. Support the engine+mount with the engine hoist, support the tail, remove the six engine mount to fuselage bolts, move the whole shebang forward an inch, buck the rivets, and then bolt the engine mount back on to the fuselage. Sounds like a lot of work when I already have the pull rivet solution. Not worth the effort?
 
But bear with me, and maybe talk me out of this one: I only need an inch. Support the engine+mount with the engine hoist, support the tail, remove the six engine mount to fuselage bolts, move the whole shebang forward an inch, buck the rivets, and then bolt the engine mount back on to the fuselage. Sounds like a lot of work when I already have the pull rivet solution. Not worth the effort?

Well, for a day or two you will probably feel "good" if you put in the extra effort to do it right with the solid rivets, or "bad" if you "cheat" and use the pulled rivets. But... in time it will all be forgotten and it is in an out of the way place that will never be seen. So the pragmatic approach is to use the pulled rivets and spend your precious time on something else! :p
 
Thanks everyone.. Looks like the consensus is use a pull rivet for the impossible ones. I'll probably just do that.

But bear with me, and maybe talk me out of this one: I only need an inch. Support the engine+mount with the engine hoist, support the tail, remove the six engine mount to fuselage bolts, move the whole shebang forward an inch, buck the rivets, and then bolt the engine mount back on to the fuselage. Sounds like a lot of work when I already have the pull rivet solution. Not worth the effort?

The engine mount to fuselage bolts are among the most critical bolts in the whole airplane. You have installed them, torqued them, and they are happy where they are. If you remove the nuts, I'd recommend using new ones. If you scrape the plating off the bolts moving the engine mount forward, I'd recommend using new ones. For six or eight rivets???
 
Ryan,

I have a thin tungsten bucking bar which might fit in there. You are welcome to borrow it if you think it might work.
 
I think this is a very common issue. I too missed the middle 8 rivets. Ended up putting in pop rivets. Might have even been after I was already flying.
 
Ryan, don't do any strange things with your engine mount! That part is really critical. You are a human and not a computer, so oops moments just happen and for these kind of moments the lord (or aircraft industry) gave us blind rivets. Just use good ones and they will last forever. Move on, you will love your RV no matter what.
 
Thanks everyone, I'm convinced. Chalk this one up as a "plans gotcha" and build on. Hopefully someone else coming behind me doesn't make the mistake. Look at the cowl plans and figure out what parts of the flange get attach hinge later and what parts can be riveted before fitting the cowl.
 
I ran into a similar issue with my RV9A with the new gear and Skybolt cowl fasteners. I finally bit the bullet and took the bolts out of the firewall/mount/engine and squeezed the rivets. Removed it as a complete assembly and only moved it a couple inches from the firewall and immediately slid it back on. Biggest issue was getting my wife under the panel to hold the bolts. Didn't take as long as I expected. Glad I did it as it now has all driven AN rivets. But I am a bit OCD :)
 
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Thanks a bunch

Thanks everyone, I'm convinced. Chalk this one up as a "plans gotcha" and build on. Hopefully someone else coming behind me doesn't make the mistake. Look at the cowl plans and figure out what parts of the flange get attach hinge later and what parts can be riveted before fitting the cowl.

Thanks for posting. I am going to do exactly as you suggest and look at plans and put those rivets in before I install engine mount. Your posr really helped me and I thank you.

Moving forward in small steps.
 
Happy ending. I had to temporarily remove the front gear leg but set 8/10 solid rivets and used CCR-264SS-3-2 rivets for the impossible ones. No remorse.
 
Happy ending. I had to temporarily remove the front gear leg but set 8/10 solid rivets and used CCR-264SS-3-2 rivets for the impossible ones. No remorse.

Perfect! That is the experience of this process. You ARE an airplane builder.
 
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