There are some fittings related to the cooling and oiling systems that probably should completed before further assembly makes their locations less accessible. The castings seem to contain a number of undocumented provisions for plumbing coolant through the engine. Some of these may have been the result of a continually evolving Quarter Scale cooling system, and some may be cosmetic and never intended to be functional. Some are probably my misunderstanding of by-products of the casting process and totally unrelated to the operation of the cooling system.
At the beginning of the build, I was thoroughly confused about coolant flow through the engine because many of the passages in the heads and cylinder blocks weren't continuous. As I probed my way through them, nothing seemed to make sense until I realized the passages were blocked by investment left behind by the casting process. After clearing the blockages, I was able to develop a plan for the coolant loops for which I can now machine the final fittings and block-offs.
The first of these fittings is associated with the cylinder blocks. The dual output pump will pump coolant into the engine through the outside of each cylinder block so it can flow around the liners on its way up into the heads. The coolant will enter the blocks through inlet logs that were previously assembled from aluminum tubing and machined fittings that were supplied as castings. I turned stainless barb adapters to attach flexible hoses between the pump and these assemblies. The o.d.'s of the adapters were limited by their close proximities to the rear engine mounts. For maximum flow, the i.d.'s of the cast fittings were partially threaded for the largest UNF thread that wouldn't break through their walls, and the threads were sealed with JB Weld. An aluminum plug was turned and pressed/Loctited into the final opening in the block's coolant passage located just below each inlet log.
Based on recommendations received earlier on this forum, I purchased two sealants: Hylomar M and Permatex Aviation Grade Sealer. Neither of these were available locally, but both were easily found online. The Permatex aviation sealer is thinner but otherwise very similar to the Permatex No. 2 non-hardening sealer that I've used for decades in automotive applications. Its squeeze out is much easier to clean up than the sticky mess typically left behind by the No. 2 sealant, though.
The blue-colored Hylomar M is quite different from any sealer that I've used before. There are a number of Youtube videos that demonstrate its use much better than I can describe with words.
[ame]https://m.youtube.com/watch?v=6gKbg8ah0c4[/ame]
After painting it on the mating faces of the two parts to be sealed, the solvent is allowed to evaporate for several minutes, and this leaves the sealant adhered to each surface. When the two parts are placed against each other, the interface between the layers of sealant forms an effective seal against most engine fluids. The two parts may be easily separated any number of times, but the same seal will be recreated each time they are reassembled. Some testing that I did showed that using minimally thin layers of Hylomar on a pair of metal surfaces will add a minimum of .006" between them. My first use of this sealant was on the three pipe flanges of each inlet log assembly. Its squeeze-out is also easily cleaned up. My first use of the aviation grade Permatex was to seal the aluminum tubes inside the cast fittings.
Coolant from the cylinder blocks will flow up into the heads through a number of o-ring'd transfer passages between the two. These passages as well as their transfer tubes were machined earlier during the head machining. The o-rings will be added when the heads are finally assembled to the blocks. Each head has a major coolant exit at its front and rear. The castings included only a single elbow fitting for each head, and so they will be used to direct the coolant flow out of the heads and toward the front of the engine as was done in the Merlin's aero applications. Stainless steel barbs were also turned and JB Welded to these fittings. A reservoir, wrapped around the front end of the full-size Merlin just behind its prop, collected coolant from these outlets before returning it to the pump. This reservoir had a unique and very complex shape and would have been an excellent candidate for casting, but it was evidently never part of the Quarter Scale design. I'll likely fabricate one from scratch even though I currently plan to also include a small radiator hidden under engine and cooled with a 12V fan.
In the full-size engine, a second pair of major coolant exits at the rear of the heads was used for a number of purposes including the plane's cabin heating system, but they were likely used also for other purposes. I created block-off plates for these, although I think the cooling system might benefit from making them functional along with the front exits. There is a second pair of smaller coolant ports at the front and rear of each head located just below the main exits. The drawing for the head specified these to be tapped 10-32, but there were no further references to them in any documentation. I temporarily plugged these with modified 10-32 button head cap screws. These ports may be used for coolant temperature sensors later on.
In order to create a sketch for the block-off plates, I gathered up the manifold gaskets that I fabricated last year:
http://www.homemodelenginemachinist.com/showthread.php?p=273966&highlight=Merlin+gaskets#post273966
To my dismay, they no longer fit the heads nor the metal templates used to drill their mounting holes. The ten inch long gaskets had all shrunk about 3/16", and only a tiny fraction of the some fifty mounting holes still aligned with those in the engine. Hoping that the automotive paper gasket material just needed some moisture to return the gaskets to their original size, I used my wife's steam iron to make a few passes over one of the spare gaskets as a test. This caused it to over expand a bit, and so when I'm actually ready to install them I'll need to be more careful.
The only oil fitting that really needs to be machined and installed at this time is a tiny injector that will lubricate the prop reduction gear set at the front of the engine. This was one of those parts that my clumsy hands and poor eyesight would rather not deal with. The body of the injector was threaded 10-40 to match a previously tapped hole for it in the gear case cover. A banjo fitting and locknut were machined to complete the tiny assembly. Drilling the pair of cross-intersecting .020" holes in a 3-48 stainless SHCS required for the banjo fitting turned out to be less of a hassle than I had expected. The threading of the injector body was done manually on a lathe by turning the spindle by hand with the half-nuts left engaged until all the passes were completed. After the injector was installed, the front cover was finally sealed to the crankcase with a gasket cut from .004" thick linen paper. An oil line which will be part of an externally plumbed oil distribution system will be soldered to the banjo after the engine's final assembly.
I was never able to determine the purpose of yet another mysterious crankcase port located just behind the gear case, and so it was lined it with Tygon tubing and stoppered with a turned aluminum plug. In a wet sump engine this would have been an ideal candidate for a crankcase vent, but I found the crankcases in my two dry sump radials never required venting. In fact, the crankcase pressure pulses in those engines actually tended to assist the scavenger pump in moving oil out of the engine and into the collection/separation tank. The collection tank will require venting, however. - Terry
