Quarter Scale Merlin V-12

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Glad to hear that you got home OK. Take it easy. We are following your work but we have the patience to wait for you to do it no faster than your recovery allows.

Best Wishes.

--ShopShoe
 
Terry, I am so pleased to hear that your procedure went well and you have made it home. The success of all the effort you take, to humbly share your knowledge and skills with others is an inspiration to me. I pray your recovery will continue, free of complications.
 
Terry,
Glad to see everything went well. Take the time to recover, the engine will still be there, if you do something silly you may not, a lot of us are learning more from you being here.

Cheers
Andrew
 
On another issue ...

One of the stents that was put in my heart last April has developed a problem, and I'm soon going into the hospital for open heart surgery that's now required to fix it. While I'm in there, the doctors also plan to replace my aorta which evidently also needs attention. I've been told to expect a long recovery time, but recovery sounds like a good thing. Although the Merlin has recently been a nice diversion from the personal loose ends I'm now scrambling to tie up, there won't be any more posts for a while. I wish everyone a safe and happy holiday. - Terry
Having had an aorta valve replacement 5 years ago, I can tell you that the post recovery period is much longer than the surgeons will tell you. The sternum may heal in 12 weeks but the nerves stay sensitive for up to 2 years. Also, do the post operation physical therapy. You may feel OK but a three month stint in therapy will astound you with the results. If therapy is not prescribed, force the medical team to do so.
Of course, now the cardiologist tells me the next valve emplacement will be just through a small cut in my groin, like when they did the Angiogram.:thumbup:
 
Terry
I do not know if being a member of the zipper club is that great but better than the alternative. Pray all goes well, looking forward to see that little Merlin run.
Nelson
The best of a Christmas Season
 
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Hi Terry,

I had wondered why we hadn't seen you at Rudy's for the past couple of months. Glad to hear everything went well. I hope you have a complete and speedy recovery.

Chuck.
 
Originally, I wasn't going to make any gaskets for this engine other than those made much earlier for the intake manifold. Many of this engine's scaled flanges are tiny with myriads of screw holes, and I thought I would rely on the large number of screws holding the sections together to also seal them. After less than an hour into the final assembly, though, I changed my mind. Much of the Merlin's assembly will be an exercise in patience, and it didn't take long to realize that I didn't want to go through it a second time because of leaks that might have been avoided the first time around. The Merlin's design provides lots of opportunities for leaks - some fifty coolant seals per head.

Final assembly began rather arbitrarily with the forward portion of the wheel case. The already partially assembled case was taken apart and removed from the engine so a gasket, cut from .004" thick linen paper, could be used to seal it to the crankcase. Twenty-three screws hold the wheel case to the crankcase, and six of them are located inside the wheel case behind its multitude of gears. After being stripped down so the internal mounting screws could be added, the wheel case internals were reassembled as far aft as the supercharger flange. The crankshaft was carefully re-checked for binds as each component was added to the wheel case. When the head/block assemblies are installed later, the friction added by the ring'd pistons will likely be too high to detect any binds.

The next sub-assemblies to be completed were the cylinder blocks. An earlier post at
http://www.homemodelenginemachinist.com/showpost.php?p=284553&postcount=419
covered the process and special tools I came up with to install the liners in the cylinder blocks without damage to their o-rings. The final installation was just as difficult as I remembered it being back then when I practiced it several times on one of the liners. Although at this point I couldn't be absolutely certain, I'm reasonably sure all twelve o-rings wound up installed without damage.

The combustion chamber seals created when the heads are finally assembled onto the cylinder blocks was detailed at
http://www.homemodelenginemachinist.com/showpost.php?p=284308&postcount=414 .
Each head/block pair includes fourteen o-ring'd coolant transfer tubes running between them as well as another fourteen o-ring coolant seals around the bottoms of the stud tubes. An additional fourteen coolant seals are used on the tops of the stud tubes of each head. Before attempting these sub-assemblies, I wanted to double check the integrities of the valve and spark plug seals to reduce any chance of having to separate them again later. Each valve seal had previously been verified by pulling a vacuum behind it through its port and then measuring its resulting leak-down time:
http://www.homemodelenginemachinist.com/showpost.php?p=273401&postcount=233 .
These tests, however, didn't include possible valve spring effects since I held the valves closed with my fingers during the tests, nor did they include possible leaks at the Viper plugs' tiny sealing flanges. A last minute valve sealing issue can sometimes unexpectedly arise from a non-square spring failing to hold its valve uniformly on an otherwise perfectly formed seat.

I made a simple fixture that would allow me to pressurize each individual combustion chamber with both valves held closed by their springs and a spark plug screwed into its port. An -026 o-ring just happened to fit the corner recess in the combustion chamber intended to receive the top end of the cylinder liner, and so I only had to turn a piece of Delrin with the correct o.d. to hold the o-ring in place. Each combustion chamber was pressurized to 30 psi and then allowed to leak down to 10 psi after switching off the air supply. The individual leak-down times combine like paralleled resistors, and the final results for each cylinder were very close to what I expected from my previous individual valve measurments.

Waste oil from the heads returns to the sump by flowing down and around the enclosed stud bolts. Stud tubes inserted in the tops of the heads surround the upper portions of the studs. Holes drilled around the upper peripheries of these tubes allow oil to enter them on its way to the sump. Since the stud tubes pass through the coolant jackets in the heads, they must be sealed to the heads at both their tops and bottoms. Twenty-five percent compressed Viton o-rings seal the bottom ends of the tubes. My original plan for the top seals was to use a gasket sealer, but since I've had a lot of time on my hands recently, I thought I would, instead, make a set of gaskets. The gaskets were cut from a new US dollar bill which is made from high quality .004" thick linen paper. (I've had a sample of this paper sitting in motor oil for over a year with no sign of deterioration.) The gaskets are simple washers with a .312" o.d. and a .210" i.d., and in this application it's very important the i.d.'s be concentric with the o.d.'s.

I first punched the gasket i.d. using a piece of brass tubing sharpened into a punch with a small 45 degree countersink. The punched stock was then moved to a gasket punch/die set where the washer was punched out. The gasket's i.d. was held concentric to the punch's o.d. using a centering spacer temporarily shoved up through the gasket's i.d. from the bottom of the die. The process was slow, but it created accurate washers with crisp edges. A pair of these washers were stacked to create a .008" thick gasket under the head of each stud tube. In all, 56 washers plus some spares were required, but I was able to cut them all from a single dollar bill.

After installing the fourteen o-ring'd coolant transfer tubes in the top of the cylinder block, the fourteen gasket'd stud tubes were inserted into the head, and Viton o-rings were slipped over the bottoms of the tubes sticking through the bottom surface of the head. The head was then carefully set down on top of the block so all 28 tubes aligned and sealed along with the six liner flanges. The pair was then bolted together with the twenty-eight 3-48 auxiliary head bolts whose holes were drilled and tapped earlier during the head machining. Miraculously, all 62 features aligned perfectly. The resulting gap between the head and block measured .052" indicating that the auxiliary head bolts were not sufficient on their own to draw the tops of the liners into the combustion chambers the additional .002" needed to crush the corners and complete the seals. This wasn't totally unexpected since the real purpose of the auxiliary head bolts is for convenience while assembling the head/block pair to the crankcase. The fourteen 8-32 studs that will later draw each head/block assembly down to the crankcase will exert the force required to completely close these seals. - Terry

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Terry
as always your work is magnificent
ps if you have leakage problems with dollar you can use the 20 euro :) :):)
 
Who'd a'thought the Dollar was cheaper than gasket paper.

Really good quality linen paper - nice lateral thinking.

Glad to see you are up and functional - mentally as well - after your op.

Regards,
Ken
 
Heh, he could still take it to the bank and get a new dollar bill.
 
Terry
Is great that everything worked out. I guess it give us better sense of how fragile our bodies can be.
A Happy Healthy New Year
Nelson Collar
 
The next step in the Merlin's final assembly was a major one - the assembly of the cylinder heads and blocks to the crankcase. Because of the modifications made to my liners, the only way this could be done was to slide the pre-assembled head/block pairs down over the pre-installed studs and ring'd pistons in the same way the full-size engines were assembled. The purpose of the previously installed auxiliary head bolts is to hold the head/block pairs tightly together while this particular step is performed.

The Quarter Scale's unmodified stock rods and liners, on the other hand, would have allowed the rods to pass completely through the liners permitting a more piecemeal assembly. In this case, the blocks would be first installed on the crankcase so the rods and pistons can be slipped down through the tops of the blocks to be bolted onto the rod journals. The heads may then be finally installed on the blocks. This assembly method does away with any real need for the auxiliary head bolts which may be why the Quarter Scale's head drawing refers to them as optional.

In my case, assembly began by installing the studs on the decks of the crankcase. Delrin oil seals were then pressed into the bottoms of the blocks using a simple shop-made insertion tool. These oil seals prevent the oil flowing down and around the studs on its way to the sump from leaking out the sides of the engine. After installing the pistons on the connecting rods, the head/block assemblies were lowered down into position over the studs. The tapers turned into the bottoms of the liners were invaluable for guiding the ring'd pistons into their cylinders. Without these tapers, a pair of piston installation tools operated by an extra set of hands would probably have been needed. This assembly method also greatly benefits from the studs being turned down a bit between their threaded ends so there is some 'wiggle room' available to the assemblies while they are being inched down into position. I've included a photo of a full-size engine rebuild going through this very same assembly step.

Tightening down the flange nuts on the tops of the studs not only secured the head/block pairs to the crankcase, but the head/block pairs were pulled together another .002". This crush height collapse was an indication that the liners had been pulled into the heads to complete the combustion chamber seals. The auxiliary head bolts could then be finally torqued. These particular assemblies are probably the most critical in the entire build, and hopefully they won't have to come apart during my lifetime. In a full-size engine rebuild they're separated using an overhead hoist to pull the head/block pair against the weight of a fully loaded crankcase. A similar operation might be performed on the Quarter Scale, but great care would have to be taken to reduce risk of damage to its castings.

After assembly, the friction added by the piston rings increased the rotational torque requirements on the crankshaft to the point where it became very difficult to manually turn the crank using the prop shaft. Of course, this isn't totally fair since the prop shaft's gear reduction nearly doubles the torque required through the prop shaft. At this point, the starter shaft sticking out from the wheel case is the most convenient way to turn the crankshaft, and its operation was verified using an adapter mounted in a battery-powered drill. The crankshaft torque requirement will increase again once the timing chain is installed, and the overhead cams are being driven. When the engine is timed and compression is added, the crank will become very difficult to manually turn. All this is adding to my misgivings about the engine's seemingly fragile starting system. On a more positive note, the connecting rods ended up nicely centered in their pistons, and so the numerous dimension changes that had to be made to accommodate my short crankcase casting seem to have come out OK.

With the cylinder head/block assemblies in place, the intake manifold could be finally installed. Hylomar was used during pre-assembly to seal the manifold's three components together. These components were drilled/tapped almost twenty months ago using fixtures to simulate the engine's final deck heights and angles.

http://www.homemodelenginemachinist.com/showpost.php?p=266334&postcount=81

The manifold gaskets made at the same time to seal the intake manifold to the heads had, over those twenty months, shrunk nearly 5/16" and would no longer fit the heads. Spritzing the gaskets with water and carefully heating them with my wife's laundry iron re-hydrated the material and brought the gaskets back to their original size. A total of 128 SHCS's are used to secure the manifold subassembly to the heads. I was a bit concerned about all these previously match-drilled holes actually lining up during final assembly, especially after my unexpected gasket problem which also changed its thickness. Fortunately, every screw went back into place with no issues.

After the intake manifold was installed, the mounting flanges of the coolant block-off plates and exit fittings were sealed with Permatex Aviation grade sealer. The entire coolant jacket in each head assembly, including its nearly fifty internal o-rings and gaskets, was then leak-checked. Each head jacket was pressurized to 10 psi by injecting compressed air into its coolant entrance fitting while its exit fitting was temporarily plugged. Unfortunately, both head assemblies quickly leaked down. Using a piece of plastic hose as a stethoscope to locate the source of the leaks, I discovered that some of the tapped holes in the lower row of mounting holes for the exhaust tips had broken into the coolant jackets. When the holes were originally drilled, I vaguely recall flagging this as a potential issue during final assembly, but I evidently forgot to record a warning for myself in my notes.

I hadn't planned on installing the exhaust tips until after the spark plug wiring was completed and tested, but I chose to install them now so the leak checks could be completed. A bit of non-hardening thread sealant applied to the ends of all the screws in the lower row of exhaust tip mounting holes in both heads easily sealed those leaks. However, I then discovered a pinhole defect on the outside of the starboard head casting that was evidently deep enough to also penetrate the coolant jacket. My makeshift stethoscope worked much better than I had expected. Although the pinhole was barely visible, the whoosh of air that streamed from it during the test was very pronounced and easily located. I enlarged the pinhole with a small drill and backfilled it with JB Weld. A Mity-Vac was used to pull a vacuum on the coolant jacket to help draw the epoxy down into the defect before it was allowed to cure.

I continued using the stethoscope to probe inside the spark plug ports looking for possible liner leaks inside the combustion chambers. I also probed in and around the gaps between the head/block pairs as well as around all the intake mounting screws for any signs of leaks. Fortunately, I found none. After repairing the pinhole in the starboard casting, the leak down times of both heads had increased to nearly a minute which was essentially the noise floor of my cobbled-up tester.

One piece of advice that I might offer to anyone who gets a chance to build this engine is to plan for a good rotisserie engine stand early in the build. Over time, mine has evolved from being a nice-to-have convenience to a must-have necessity. At this point in the build, the engine weight is some twenty-five pounds, and I continually find myself rotating the engine on its stand to just the right angle so I can best install the next screw. There's no safe bottom nor sides for this engine to rest on without risking damage to some machined part or irreplaceable casting. The only practical way to support this engine is by its motor mounts which are integral to the crankcase casting. Bolting these to an engine stand allows total access to the entire engine during construction. - Terry.

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Terry:

Looks liked you're getting real close to the point where you can quit making the engine noises and let the Merlin speak for itself.

It's been a Helluva ride so far, but I'm pretty sure that the light you've been seeing at the end of the tunnel is not another train. I've no doubt that the Merlin will be purring for you soon, maybe snarling depending on the throttle setting.

Don
 
Looking SO good, Terry.
Re that hylomar, when you paint the opposing part surfaces & it 'flashes off'. Does that mean its essentially bonded/cured? Or there is a specific time to mate the parts? ie. could you paint each, leave that way overnight & do the bolt-up next day for example & still have the removal/re-seal capability?
 
Peter,
My understanding is that there is just a minimum flash-over time. You should be able to paint the two surfaces and then assemble them a day later - Terry
 
Re that hylomar, when you paint the opposing part surfaces & it 'flashes off'. Does that mean its essentially bonded/cured? Or there is a specific time to mate the parts? ie. could you paint each, leave that way overnight & do the bolt-up next day for example & still have the removal/re-seal capability?
As I understand it, there is no question of a cure or bond. Hylomar comes out of the tube fairly soft to allow it to be applied, and all that happens is that a solvent evaporates leaving the sealant stiff and gummy. It is supposed to remain in that state indefinitely. The instructions say (I am not going out to the shop to look) something like 'torque down, leave an hour or two and torque again' as it will continue to squeeze out for a while.
 
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