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Which firewall rivets before hanging engine?

mburch

mburch

Well Known Member
Patron
Hi all,

Since it's too cold in my garage to work on the canopy until summer comes, I'm getting ready for my engine to arrive. The airplane is a -7 QB and the firewall is not really riveted to the fusealge skins anywhere, other than a couple of temporary pop rivets that are still in there from the QB factory. The forward top skin is not riveted on, and I plan to leave it off until late in the game so I can have an easier time with all the under-panel stuff. This also means that the WD-602 upper engine mount brackets aren't riveted to the side skins or longerons either.

What I'm trying to figure out is, do I need to do any additional riveting around the firewall area before I try hanging the engine? From reading ahead to the cowl plans, it looks like I need to refrain from riveting the side and bottom flanges of the firewall to the skins, since that's where the cowl attach hinges will go later on. But does any of that upper stuff need to be stiffened up before I hang the engine? I know plenty of folks bolt on the motor without first riveting on the top skin, so I'm hoping to hear from those who've gone before.

thanks,
mcb
 
No

Matt,
Our 6A QB didn't have any of the upper firewall rivetted but the steel stiffener brackets at all four corners were installed. We hung the engine (0-360) way before we rivetted the top skin and camlok holder strip of .062".

There's plenty of strength between the upper and lower longerons and the steel brackets. You sure don't need to rivet the forward skin on 'til just before flight! :D If I had it to do over again, I'd also cut an access panel in the forward skin to access the radios from the rear. Either that or a removable panel for the flight instruments and another for the radio stack.
Regards,
 
On my -9A, I set the 5 rivets on both sides of center along the bottom firewall edge before I installed the engine mount. These holes do not get hinges riveted to them as this is the rear airbox opening.

Steve
wiring
 
Taildraggers have different engine mounts than nosedraggers...and that's what causes the problem in this area. The lowest 4 or so rivets along the sides are a bithc to rivet since the engine mount for taildraggers has down tubes on the sides.

On my next -7, I'll rivet the side hinges on before installing the engine mount. Imho it's absolutely no big deal to rivet those hinges to the firewall/fuselage early.
 
Thanks Dan - based on your experience, if I rivet the hinges on early with the prescribed 0.020" spacers and leave them a bit long, will be okay later? I figure I can just trim off an extra hinge eye or two if need be.

The thing that still makes me worry a bit is that the WD-602 upper engine mount brackets are riveted to the longeron and the F-695 gusset along the upper surface, but there's still eight 1/8" rivets missing on each side of the aircraft where the side skin, WD-602, and longeron come together. Seems pretty important for supporting the weight of the engine...? I'll have to call Van's later when I get a chance. Now back to work...

mcb
 
1. If memory serves, I didn't use shims on the sides. It wasn't necessary. I don't see any reason to leave the hinges long, either. I'll email you the cowling drawing so you can see the dimensions you need.

2. Almost everybody I know hangs the engine, etc. long before riveting that front deck skin on. I understand your concern about those rivets along the longerons at the front edge, but imho it's not an issue. You'd think things would have potential to move around a bit, but they don't. Those gussets/weldments are riveted everywhere else, and with the engine mount bolts tightly fastening everything up there...well, you get my drift.
 
dan said:
1. If memory serves, I didn't use shims on the sides. It wasn't necessary. I don't see any reason to leave the hinges long, either. I'll email you the cowling drawing so you can see the dimensions you need.
Click to expand...
Thanks, I've got drawing 45 already so I should be all set. The QB firewall flanges are already dimpled... without shims, did you have to dimple or countersink the hinges?

mcb
 
I c-sunk the side hinges. They were pretty thick if memory serves. Just to clarify, I do have shims along the TOP. Just not the sides.

FWIW, on the top, I dimpled the skin & firewall, and then c-sunk the shim/hinge (the shim took 90% of the c-sink and the hinge was relatively untouched).
 
Just shim the upper hinges as Dan recommended. I would get the lower ones all on before the motor mount. They can be driven later, but it is nicer to squeeze them before the mount is in the way. The top ones can be done later, but I got them all on before the mount.

Roberta
 
Thanks guys - I'll press on with the FWF stuff with the goal of having a place to bolt the engine up when it arrives!

mcb
 
No shims here

Hi all.

We've just riveted on the FF-hinges and we didn't have to use ANY shims.
If we had riveted on the hinges (and shims) according to the drawing prior to hanging the engine, we would've had a BIG problem by now!
The the shims would've lowered the FF-hinges to such a level that the cowling and the skin wouldn't be flush.

Maybe the new cowling is thicker than the olds ones, I don't know. (We've the horizontal induction cowling for a IO-360 from Vans)

To set the rivets, we used a modified yoke. We started with the smallest one Avery sells and grinded it down both in thickness and width.
We where able to set all the FF-rivets except two. For those we used cherry-pop rivets.
We'd to tweak a little on some hinge eyelets, but that was easy to fix those afterwards.

In hindsight, I guess we could've clecoed the FF-hinges on the FF before hanging the engine, and checked the thickness of the cowling compared to the FF-hinges.
Then we would've been able to decide if and where to use FF-shims.
Then the FF-hinges could've been riveted on before the engine mount.

Just my 2 cents from Norway.

Regards Alf Olav Frog
RV-7 finishing
 
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Regarding the missing top skin rivets that also attach the upper firewall brackets - remember they are already bolted to the longerons and that the joint is designed to have a big Lycoming hanging on it when it's shake rattle and rolling, not to mention pulling 6g and coping with rough strips and possibly rougher landings! It should be fine quietly pulling 1g in your garage :)
Jim Sharkey
 
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