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Old 05-09-2019, 05:21 AM
auj4 auj4 is offline
Join Date: Jun 2018
Location: Sydney, Australia
Posts: 3
Default Firewall foot box and engine mount damage

Hi All,

Iím a virgin poster... So please be gentle with me

Iíve been lurking for a while and started reading at the oldest thread in the RV4 section. Iím currently only about three years behind todayís posts.

Firstly, thank you to everyone who has posted or asked a question. Iíve learned a massive amount from all the posts and continue to learn daily.

So after spending about a year or so of looking for a RV4 to buy Iíve found one that I like. Thanks to what Iíve learned here Iíve been able to ask the right questions.

Iíve also searched here for the problem, but when photo links are broken itís not always easy to get a good understanding of the issues.

So I have some questions. This aircraft has some firewall damage and has the light weight lower longeron firewall-engine mount brackets, creases in the LH footwell and a crack on the weld at the centre engine mount bolt. The current owner/seller is getting the engine mount removed and welded before the sale goes through but the description over the phone of the crease lead me believe it wasnít a big problem. (As the aircraft is ~650NM away Iím doing everything remotely at this stage). Here are photos of the damage.
Firewall longeron brackets:

Firewall crease (LH footwell):

Engine mount weld crack:

So my question for the knowledgeable; If the engine mount is welded/repaired and is straight, is the firewall footwell crease significant enough to be an issue? (Iím buying flying aircraft to have something to fly as my current aeroplane will need restoration soon so Iím less interested if this will mean a lot of work on the 4).

Iíd also like to check whether the consensus on the fuel tank sealant is not slosh? (It doesnít look like slosh but neither does it look like the Proseal Iíve used)
Fuel tank sealant:

Iím sorry about the large images and small text, next thing to learn is to get google photos to resize images.

Thank you,
Flying: Auster J4 (The ĎAeroplaneí above )
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Old 05-09-2019, 05:40 AM
auj4 auj4 is offline
Join Date: Jun 2018
Location: Sydney, Australia
Posts: 3

Still learning. I just found this thread that looks like it deals with a lot of my question above;

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Old 05-09-2019, 05:52 AM
fixnflyguy fixnflyguy is offline
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,034
Default Common on a -4

I have inspected a bunch of -4's and built mine. This, unfortunately is seen to some degree on almost every -4 built. The weldments can be replaced, and would be a best option while the mount is off. The firewall buckle is a pretty bad one, and can be repaired, but isn't really hurting anything. You could stop drill and fill with sealant. -4's built with the new style weldments can still buckle the firewall, but not have additional damages occur. If you do leave the old style longeron weldment in it, make sure they aren't cracked and keep an eye on them. The tank doesn't look sloshed, if your refering to the dark sealant, it may be Flamemaster brand or Proseal. Seems to be a yellowish tint overall, but that may be the lighting.
Bill E.
8A7 / Advance NC
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Old 05-09-2019, 03:04 PM
Sylvester Sylvester is offline
Join Date: Mar 2017
Location: Uk
Posts: 11
Default Firewall

Hey Don. Your firewall looks just like mine did before I rebuilt the front end last year. See Ďfirewall wrinkleí thread. Iíd be cautious with the one youíre looking at, and consider making a bid and getting that front end rebuilt. The bottom internal mount seems to only have 2 bolts through the front angle rather than the 3 or 4 in the drawings, and screws through the lower longeron rather than AN3 bolts. Get someone who knows 4s very well to survey it. Iíd question the build quality.
Not much point just rewelding the mount with the issues that caused the cracking still there.
Just my opinion.......
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Old 05-09-2019, 06:08 PM
Russ McCutcheon's Avatar
Russ McCutcheon Russ McCutcheon is offline
Join Date: Oct 2005
Location: Vancouver, WA USA
Posts: 897

I build these engine mounts for Vanís, I have also repaired a good number of them , the crack you pictured is a somewhat normal stress crack on these mounts so it alone is not a problem re-welding. Make darned sure the mount isnít bent though, this can be a little tricky, if this mount suffered the hit that damaged the firewall it may very likely be bent. If this was mine I would repair the engine mount (whatever that might require) replace the lower firewall and replace the bottom firewall brackets.

I canít see much of your engine mount in the photos but it doesnít look quite right to be one out of my shop but itís hard to say, there are a few home made ones and a few from a previous vendor out there. If itís not off my fixture and itís bent then you better order a new one from Vanís before doing the repair so it all ends up fitting.
Russ McCutcheon
@rv4welder on Facebook
We build many of your RV weldments.
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Old 05-10-2019, 02:50 AM
moosepileit moosepileit is offline
Join Date: Dec 2010
Location: Floyds Knobs, IN
Posts: 508

Off topic, is the use of RTV, "cool" on the left brake cylinder input?
RV-6, bought from builder.
O-320, slider, carb, mags, FP
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Old 05-10-2019, 05:09 AM
auj4 auj4 is offline
Join Date: Jun 2018
Location: Sydney, Australia
Posts: 3


No apparent cracks in the weldments. Long term yes I would fit the newer style. The fuel doesnít look like 100LL. It might be Mogas as we can still get ethanol free Mogas.


That thread is very good. I sent the link to the LAME as it shows a good picture of the new Weldments.


There is an aircraft welder doing the work on the engine mount with reference to some -4 plans. if itís bent, I hope this will be picked up.


The RTV is not cool in my book, even if it is on the reservoir side. Neither is the Bowden cable chafing on the mount bolt or the spacing between the oil cooler lines and the exhaust. The oil and fuel lines are being re-routed away from the exhaust.

Thank you all for your replies and input.
Don H
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