Im putting together a VQ .42 Hawker Hurricane. I went to put the fuel tank in and found the pre-drilled hole in the firewall was drilled off set. (see pic) would it be ok if i cut the hole larger or could I risk messing up where engine mounts? The yellow hole is around where the fuel tank sits.

As long as you don't have a problem with that missing wood part of the firewall,
to put the engine mount template over the firewall & mark the area for the x4 holes that keep the mount in place
there is no problem installing your fuel tank as you should,
even if the fuel lines make a Z-bend/travel to rich your carb/needle valve!

That's the thing I hate about ARF aircraft, but that's another topic that has been beaten to death before.

What I would do sailor is I would make my marks, make a templete of the original hole and trace it on a equal sized piece of ply. Cut out the tracing with a scroll saw or do it by hand until you can make the piece fit. Once you have a snug fit, epoxy it in place.

Once everything is fully cured, re-drill or Dremel the hole to size. I would drill the hole with a regular drill and then make the hole large enough so I can use the sanding drum bit on the Dremel- to finish making the hole.

When everything is done, sand everything smooth and re-paint or epoxy the firewall so it will be fuel proof. Making the hole larger you risk weakening the firewall. JMHO

I'm wondering by studying the picture that the design is for the engine to be mounted horizontally? I've seen ARF aircraft with funky firewalls like that and I suspect it was made like that so the cylinder of the engine won't protrude so much out the side of the fuse.

But if you want to change the angle of the engine, then I would do what I suggested to be safe.

If you think that firewall is funky, you should see the firewall on my Discontinued .60 Great Planes Fokker Dr1. Now that's Funky!


Pete

The firewall is tilted to the right to give a little Right Hand thrust to counteract the torque of the prop.

The engine is offset to the Left Hand side of the firewall so the prop will come through the center of the cowl.

If the tank doesn't line up with the hole, there's nothing wrong with elongating the hole so the tanl will poke through as long as it doesn't interfere with the mounting holes.

I agree. Everything is moved to the left, so the FRONT of your engine winds up in the middle of the cowl, as a result of the' thrust angle'. The ARF manufacture got it right. Once a guy figures out WHY certain things are done the way they are, it will help him to know what to do in the future if he gets a plane that is NOT engineered properly. This is a good thing, and a good question to ask and understand. I love the Hurricane. Landing gear is a little close, but wish you well with it.