B

britt fincher

Member
I understand it is fairly common to see some crinkle on the firewall sheet metal at lower engine mount. Maybe from a hard landing. Is this a major concern? Any way to tell if it is cosmetic vs structural? Also is there any negative to having an 0 320 B2C former helicopter eng. in an RV 4?

Thanks for any advice.
 
firewall

Mine has a wrinkle from a previous life... still bugs me since the previous owner did not disclose it and the EAA member from Meadow Lake, Colorado that did the paid inspection did not pick it up.
Had the a/c for almost 5 years now and no issues have developed.
It is probably more important to check out the 4 weldments on the corners of the firewall inside the aircraft and also the engine mount for integrity... no cracks.
 
Rv4

The one comment on the lower engine mounts, is the best advise. Make sure they are the "upgrade" bigger ones, I've changed them out before, not that big of a deal, but needs to be done. I think Vans gave them away, if you returned the old ones? The chopper engine, maybe a conical mount, plus the mags use retarded points and a vibrator box, but they do start right now!
You can't prop start one very easily.
Depends on the price, but keep in mind resale when dealing with odd engines or problems with airframes. Good luck with your search.
 
Crinkle

britt fincher said:
I understand it is fairly common to see some crinkle on the firewall sheet metal at lower engine mount. Maybe from a hard landing. Is this a major concern? Any way to tell if it is cosmetic vs structural? Also is there any negative to having an 0 320 B2C former helicopter eng. in an RV 4?

Thanks for any advice.
Click to expand...

The keelbeem structure does not sit flush in relation to the lower gear mounts in the bottom corners. On mine the 2 keelbeams "inner gear mounts" were 0.200" aft, 0.150" in another RV4. I installed internal doublers between the keelbeam and my new firewall. If you go to Vans Mobile site, look in RV-4, and I'm BARRON. U will see what i did. The krinkles WILL crack with time, as did mine. For sure if your in and out of grass strips. The doublers were made 0.500" larger than the keelbeam for better stress distibution,and from 0.250"T6. alodine,prime,paint. Installed with titanium Hi-Loks."IMPORTANT" the steel keelbeam structure and aluminum touching will corode like no tomorow. Must protect. Titanium interfierence fit fasteners to replace the original screws stops any problems with indifferent material and shifting. I went 050 thicker than necessary to snug stuff up. Turned out verry nice. Next.... Cockpit.
 
Crinkle

britt fincher said:
I understand it is fairly common to see some crinkle on the firewall sheet metal at lower engine mount. Maybe from a hard landing. Is this a major concern? Any way to tell if it is cosmetic vs structural? Also is there any negative to having an 0 320 B2C former helicopter eng. in an RV 4?

Thanks for any advice.
Click to expand...

The keelbeem structure does not sit flush in relation to the lower gear mounts in the bottom corners. On mine the 2 keelbeams "inner gear mounts" were 0.200" aft, 0.150" in another RV4. I installed internal doublers between the keelbeam and my new firewall. If you go to Vans Mobile site, look in RV-4, and I'm BARRON. U will see what i did. The krinkles WILL crack with time, as did mine. For sure if your in and out of grass strips. The doublers were made 0.500" larger than the keelbeam for better stress distibution,and from 0.250"T6. alodine,prime,paint. Installed with titanium Hi-Loks."IMPORTANT" the steel keelbeam structure and aluminum touching will corode like no tomorow. Must protect. Titanium interfierence fit fasteners to replace the original screws stops any problems with indifferent material and shifting. I went 050 thicker than necessary to snug stuff up. Turned out verry nice. Next.... Cockpit.
 
Link to photos?

BARRON - I'd love to look at your photos as I'm a bit confused what you are describing. Do you have a link to your photos? I'm not familiar with the "Vans Mobile Site".....so your post is making me feel a bit like this: :confused:

:D Thanks.
 
Not only do the shims Barron describe help if you replace or repair the lower firewall, it's also beneficial to insert a bolt, nut and washers to compress the lower corners of the firewall prior to drilling, and riveting. The firewall is non-structural stainless and is harder and less flexible than the surrounding structure, thus prone to fatigue cracking over time (or wrinkling in the event of a hard landing). Fatigue cracking is common in the corners, even on low time airplanes, depending on how the corners were assembled. Generally, you can't see cracks unless the engine mount is removed. Stop drilling existing cracks and sealing with silicone or other appropriate sealant is acceptable in most cases.

The lower gear/engine mount sockets and surrounding structure should be inspected regularly for signs of fatigue damage, especially for aircraft operated off of grass.

Cheers,

Vac
 
Last edited:
You must log in or register to reply here.