P-51C Mustang Engine - Oil Relief Valve

So I've realized that when scratchbuilding you have to be willing to fail a few times in order to end up with something that looks good. In the last blog I talked about the oil relief valve and how it would look much better if it was scratchbuilt. This is true, however the process took me a while and I had to check several sources of reference to get a good picture of it. The problem when you do these sorts of projects, especially with older aircraft, is that you will find ten different versions of the same part or component and since most of these aircraft have been restored using more modern parts it is hard sometimes to separate history from modern efficiency. Luckily I have the 1944 release of the Rolls-Royce Merlin V-1650 overhaul manual. I actually found a good picture of the oil relief valve in the back of the manual in a diagram showing how the spare parts bin should be set up. It's odd sometimes where you find information, so don't be afraid to look in weird places for references.

Ok let's get into it. So first I tried to use an image I found online, but I couldn't really see how the relief valve looked. The simpliest way to create a scratchbuilt part like this is to break it down into simple shapes, and with this image, I couldn't see the real shapes. So I went with what I saw. The next couple pictures do not show the final relief valve, but they will give you a good idea of how the beginning of the scratchbuilding process. Start with a base of basic shapes. Details come later. I started with simple plastic rod and strip and started arranging them as I thought I saw in the image.

Now as good as this may look at a start, granted there are no details, this actually isn't how the valve looked. But at least you can get a good idea of how some simple shapes can be formed to make something that looks complex. And had I used this in the model, no one except a Merlin mechanic would be able to tell me that I was wrong. However, anything can be done better and when I found a really good image of the relief valve and could break down the component into simple shapes, I realized I could do it much, much better.

I started with a piece of .030" x .060" and cut and filed it to the proper shape. I left a "tail" on the strip so that it would be easier to handle while assembling. The component will eventully be cut off.


I glued a .040" rod to the bottom and started adding the simple shapes, some half rounds and strips. The rods sticking out the sides will be where the oil lines will eventually connect. I made them intentionally long so its easier to hold while gluing it. This is a trick when scratchbuildling that most people don't see with they look at the finished product. They see all these little parts and wonder what tiny tweezers and magnifiers were used to glue the parts in place. I just used my fingers. Remember, you can always cut and sand them down to the proper length later. A tip: Make sure the glue has dried completely before cutting it or you will definitely ruin your day.


The relief valve was held to the side of the engine with 8 bolts which will be represented by some very thin wire. But first I need the mounts. These were made with .020" rod glued into position. Its hard to see in this image, but they were left long and cut down.


All the rods were cut and filed down to the right length and .010" holes were drilled as close to center as possible. A few details were added to the top with .040" rod and .020" wire.


.008" wire was fed through the holes and epoxied in place. Again, the wires were longer than needed when I installed them. I made sure that the exposed wire on the front of the part were the proper length and allowed the excess to stick out the back. It would be much easier to cut the end that wouldn't be seen. So why make these out of actual wire. Well, this will eventually be painted black like the rest of the engine, but the bolts will be an aluminum color. So once its painted, I'll simply take an X-Acto knife and scrape the paint away from the bolts. This is much easier than trying to paint them afterwards. And I don't have any plastic that thin.

 

So after cutting off the "tail" and adding a few more details, here is the finished oil relief valve.