Quarter Scale Merlin V-12

[mayhugh1]

The notes accompanying the castings devote more text to discussing issues with the Merlin's cylinder/head construction than with any other single aspect of the build except, possibly, for its unresolved carburetion. The bottom line of the discussion is that the quarter-scale head/cylinder design is very similar to the full-size version, but scaling leaves some unresolved fabrication issues for the builder. In defense of the design the authors mentioned that the full-scale design had suffered a rather rocky evolution.
For illustration I made some not-to-scale sketches showing the installation of a single liner in a portion of the cylinder block. These sketches also show coolant transfer tubes and stud tubes on the same sectional view even though they are really not on the same plane. The studs and head mounting bolts were left out for clarity.
The liner is inserted down through the top of the cylinder block, and a shoulder on the flange that protrudes above the block seals the compression chamber against the face of the head. Both the coolant jacket and the compression chamber are sealed by metal-to-metal contact as there is no head gasket. The bottom end of the coolant jacket is sealed by an o-ring compressed between two metal collars sandwiched between the crankcase and a machined shoulder on the circumference of the liner.
An implementation concern with this design is that the heights of the shoulders on all six liner flanges in a particular bank must be precisely machined to identical heights. These shoulders, though, will be individually machined when the liners are turned; and they must also be free of machining marks. These combustion chamber seals are reminiscent of valve seals and will likely share similar issues. If it weren't for the raised liners the block could be simply machined flat for a conventional head gasket, but it appears there wouldn't be enough material left above the water jacket in order to sink them after the block castings are cleaned up. Anyway, as will be obvious later, the gasket would likely be unwieldy with 70% of its area removed to accommodate some 58 penetrations.
A subtle detail on the cylinder liner drawing, though, may actually be an important but unmentioned part of the design. A fillet is called out for the inside corner of the liner shoulder instead of leaving it sharp. The sharp rim on the aluminum combustion chamber will be deformed against this fillet when the head is torqued down to the block and may be the key to an effective seal. Unfortunately, though, only the first-time assembly will give the very best result. High temperature bearing retainer can probably be used to seal the water jacket at the top of the cylinder.
Assuming the combustion chambers can be effectively sealed, I still have three concerns about the cylinder design. Using the stock bore diameters and their center-to-center distances there will be less than .024" between the edges of the block bores. Although doable, this sounds a little thin to me. More importantly, though, the liners have a wall thickness of only .035". During my Howell V-4 build, I discovered the piston ring sealing was limited by circularity errors in the liners due to their thin wall construction, and the Merlin liners have half the wall thickness of the Howell liners. The Howell liners were made from cast iron which I know from experience can be dimensionally unstable when machined in thin cross-sections. The Merlin liners are intended to be made from 4130 steel; and, admittedly, I have no similar experience with that material. My third concern is with the narrow .040" wide water jackets around the cylinders. This is less than 3/4 teaspoon of coolant surrounding each cylinder, and so the coolant flow rate will be important. I looked ahead in the drawings, and the water pump looks awfully small - only about 30% larger than the pump on the Howell V-4. Overheating was, in fact, a problem with the quarter scale prototype.
The next section will describe the numerous coolant and oil passages that must be provided between the block and the head. - Terry

 

[mayhugh1]

When a fully machined head is assembled to a fully machined cylinder block, not only must two halves of six combustion chambers come precisely together, but 14 stud tubes and 14 coolant transfer tubes between them must also align. In addition, the two mating parts must also be drilled and tapped for an additional 24 head bolts.
The stud tubes serve a couple functions in addition to acting as conduits for the studs that secure the head and cylinder block to the crankcase. The seven outside tubes double as oil returns for the top-end of the engine. Machined Delrin seals installed between the block and crankcase are compressed to prevent oil leaks when the assembly is bolted together. The outside central stud hole on each block also penetrates the water jacket, and so it must also be sealed with an additional piece of tubing.
The stud tubes are flanged at their tops, and they extend through the head and into a shallow reamed recess in the block. An o-ring around each tube is compressed between the block and head to control oil leaks. The flanges are set in counterbores on the top of the head. Special slotted washers between these flanges and the stud nuts allow top-end oil to drain down along the studs and into the sump under the crankcase.
A significant fabrication issue is that the stud tube holes have already been cast into the heads since they were necessary for core supports. The construction notes warn these cast holes are not likely to be in the correct locations for the stud tubes, and so they will probably have to be slightly moved. Because my particular crankcase casting was undersize, my holes may have to be moved a bit further. Hopefully the cast holes are undersized by more than the distance they will have to be moved.
Because the head and cylinder block are two separate pieces, provisions must be made for coolant to flow between the two. In the Merlin this is accomplished with fourteen sleeved transfer passages. The transfer tubes are short lengths of aluminum tubing 'snugly fitted' into matched reamed recesses in both the head and block. O-rings around each tube are compressed when the assembly is bolted together in order to seal the gaps. Locating all these holes for these 'snug fits' seems unreasonable since the holes on both parts are blind, and there is no way to match drill them. Excess clearance will likely have to be provided for these tubes on at least one side of the interface, and hopefully the o-rings will still be able to handle the sealing. A coolant leak is much more serious than an oil return leak. According to the design notes, early Merlins were sometimes damaged at start-up due to hydrolocked cylinders created by coolant leaks during engine cool-down.
Drilling the rather deep stud holes through the cylinder block so both ends end up in the exactly correct positions for mating with the crankcase seals and the head transfer tubes is going to be difficult. Identical drilling patterns are used on both cylinder blocks, and so time spent developing fixturing will at least apply to two parts. A single casting pattern was used for both blocks, and in the Merlin the left side block is just a right side block turned 180 degrees.
Not shown on the simplified cross-section are the holes for another 24 head bolts used to assemble each head to its block before the paired assembly is bolted to the crankcase. However, since they are only 3-48 SHCS's they may be more cosmetic than functional. - Terry

 

[gbritnell]

Hi Terry,
The issues you are explaining are engineering problems when scaling everything, especially I.C. engines. For the last couple of decades I have been designing and building my own engines. While doing the extensive drawing layouts I try to resolve some of the worst conditions in regard to building and operation. Sometimes concessions have to be made to the design to allow somewhat reasonable operation. These small engines make a lot of heat when running. That being said the only way to run coolant through the head is generally by longitudinal channels drilled through the head and plugged at one end. I have done this on my 302 and inline 6 engines. The flathead that I'm currently working on has it's own unique constraints.
From what you're showing it looks like the author designed the engine to be built and operated mostly in theory and not practicality. It would certainly be a shame to put in mega-hours of building only to find out that you have a beautiful paperweight.
After following your radial build I am confident that you of all people are more than capable of solving some of these issues but my only question is "were any of these casting sets built into running engines?"
gbritnell

 

[mayhugh1]

George,
There's only two examples of running engines using these actual castings that I know of. The first is by the original authors; and the second is by Gunnar Sorensen, a Danish master craftsman:

http://translate.google.com/transla...meside.dk/gunnarsorensen/30857372&sl=da&tl=en

In both cases, though, the running demos were pretty short. The designers of the castings, to the best of my knowledge, have never published any construction photos of their build. The description of the original prototype is so vague that even with the notes accompanying the castings I purchased, I've never been able to figure out just how much of the total design is really functional. The change notices on the drawings span more than ten years, and so a lot of effort was put into the project. Gunnar published some photos of his build and, as far as I can tell, they show him following the stock head design.
I got involved with this project with my eyes wide open, and I have no complaints or regrets. I assumed the supercharger was probably never made truly functional, and I would likely spend a lot of work only to end up with a cool looking diffuser. I also assumed the magneto design was never completed, and I would have to come up with something on my own. It seems that Gunnar did just that. I also assumed I could somehow adapt an RC carb to this engine as I did with my radials. The carb discussion in the notes accompanying the castings propose solutions that do seem to be products of someone's limited experience with actual running models.
I spent a lot of time composing the two previous posts because I think I was using them to clarify in my own mind the thinking behind both designs - the full-scale and quarter scale - and to convince myself I could do the machining needed for the quarter scale. I'm beginning to realize that I really don't like working with castings because options for modifications and improvements are really limited.
My gut tells me the machining is going to be very difficult but not impossible. After all, Gunnar did it. It also tells me the cooling system is most likely inadequate. At this point my plan is to continue with the stock design but to not do any liner construction until I finish the critical head and block machining. If I get through that, I plan to modify the liner design for a thicker wall and wider coolant jacket. This may not entirely solve the overheating problem if one exists, but it should extend the running time a bit. This will mean that the cylinder and piston diameters will have to be reduced, but I can live with that. I should have an option later to design a larger coolant pump since, on the surface, it appears to be a bolt-on. In addition I may have the option to run additional coolant lines since much of the oil and coolant systems on this engine are externally plumbed anyway. - Terry

 

[mayhugh1]

I decided to do some of the 'easy' machining on the blocks and heads so I could make some progress while thinking more about how I'm going to handle the fixturing for the more demanding drilling and boring operations. Having as many machined surfaces as possible on these parts can only help, and these 'baby steps' should help me get a feel for the kind of precision I can hope to maintain while working with these castings.
The machining of the cylinder block began with facing it's top surface. It turned out that my particular blocks were warped well beyond the limits for which straightening was recommended, but I decided to correct them solely by machining, anyway. There were no cosmetics to be impacted, and with all the deep drilling that's coming up later, I didn't want to deal with hardness variations created by annealing.
I made a fixture to support the blocks by the inside diameters of their two outside cylinders. The complex sides of the blocks made them too difficult to hold with any precision in a vise. This fixture also avoids toe clamps which might disturb the warp I'm trying to remove. It also gave me a reasonable chance of an already cast through-hole coming out normal to the top and bottom machined surfaces. This hole was probably used for a core support, and its location corresponds to that of the outside center stud hole. My naive plan was to use it later as a datum on both surfaces for referencing those drilling and boring operations. Since I'll later be machining features on both the top and bottom surfaces of the blocks it would be really nice if this hole ends up normal to both finished surfaces. A design note mentioned cleaning up this hole up with a 5/32" reamer so a piece of standard size tubing could be used to seal the coolant jacket it penetrates. My holes were quite a bit oversize, and I had to use 7/32" tubing.
The 1/2" thick aluminum baseplate for the fixture was carefully surfaced and squared. Its geometry will become even more important when it's reused later for the drilling and boring operations. I machined this base plate to be as perfect as I possibly could, but after an evening of chasing my tail, the best I could achieve was .0005" flatness over the plate's 12"x4" area, and even that involved some luck. I'm not one to blame my tools, but I think my 20 year old Enco mill was at least part of the problem. Using a less stressed material than 6061-T6 might have also helped. I thought about annealing it, but I was afraid the resulting surface finish might create other problems.
The warped block was installed on the fixture, and its ends were shimmed to equalize the amount of material removed from each end. The two portions of the fixture that actually grasp the block are shop-made expandable Delrin collets. I took light cuts and continually monitored the tightness of the shims on either end to make sure the block didn't shift during machining. After machining the top and bottom surfaces of the first block, surface plate measurements showed a whopping corner-to-corner parallelism error of about .002" between the two surfaces. After an afternoon of experiments and head-scratching I realized the problem was being created by my fixture. The unfinished bores in which the collets were grasping the part were not parallel to each other because of the warped casting. Tightening the Delrin collets bowed the base plate a few thousandths and pulled the block with it - unbelievable! The final solution was a thicker, one inch, baseplate.
After all the effort I put into the first baseplate, I thought the second one would be easier. It was, but I still ended up with the same .0005" flatness over its same area. Re-machining one of the surfaces of the bad block reduced its error to .0005" which is what I'm learning to live with.
After the block surfaces were machined, I drilled the clearance holes for the twenty-four 3-48 head studs. This was as good a time as any since they were located on the centers of now-machined bosses distributed around the top perimeter of the block and were easy to do. Their drilled locations will be later transferred to the heads so the matching threaded holes can be drilled and tapped. A similar technique was used for spotting their locations, i.e. aligning a tube-covered V-drill in the center of the boss, as was done earlier with the oil pan mounting holes.
Final measurements on the reamed hole showed nearly perfect perpendicularity with respect to the long axis of the block and a relatively small, but unacceptable, error along its short axis. The measurement of the hole's offset error was very difficult and inconsistent, and so it became clear it wouldn't be suitable as a reference for the block's top surface machining. When I machined the second block I tried to fixture it so I would machine its first surface normal to this hole, but that became an exercise in futility, and the second one came out with an even larger error than the first.
Setting the blocks down on the crankcase to see how the bores roughly line up around the central stud tubes was a little worrisome. The finished bores in my 'short' crankcase are significantly misaligned with the unfinished block bores which, themselves, seem to be on slightly wider centers than the drawings assume. Hopefully, there's enough excess block material to allow them to be moved over into alignment.
Beginning the head machining required a bit more thought because of the slope of the valve cover mounting surface. For me it was important, for cosmetic reasons, that its thin flange be kept uniform. I decided to clean up the block-mating surface first by removing the minimum amount of material to get it flat. The head was supported in a vise with leather packing against the movable jaw and a machinist jack at one end to adjust for the valve cover slope. After machining, this reference surface was placed against the stationary jaw of the vise so the intake and exhaust flanges could be machined flat. In both cases only the minimum amount of material was removed from the head. The exhaust flange heights are not at all critical, and will be left as machined. The intake flange, though, will be brought to its finished height after the head's face is finish machined and a full trial assembly is made with the intake manifold.
Finally, the valve cover mounting surface was machined. The exact angle of its slope was not important and so it was adjusted to keep its mounting flange uniform in thickness.
So, I'm off to an OK but not a really great start. I'm now confident, after some experimenting though, that mating the stud tubes in the heads with their corresponding holes in the block isn't going to require the precision fits called out in the drawings since the o-rings are capable of absorbing the machining differences I can probably maintain in the non-pressurized oil returns. The pressurized coolant passages are still an lopen question, though. - Terry

 

[makila]

Terry,
This is a fantastic build.
I think that your solution of reducing the bore to rectify the thin cylinder wall and increasing the water capacity adjacent to the cylinder is a excellent idea. Not knowing what the dimension of the cylinder bore is, if it was reduced by .100" for example, this could be used to increase cylinder strength and have a outside waisted portion at the water jacket to allow more cooling water to surround the cylinder. The cylinder external dimensions at the top and bottom would be the same as the drawings so as not to have any affect on the castings, but you would have a .025" increase in water capacity/flow each side and .025" increase in wall thickness at the mid point of the cylinder giving a bit more structural stability to the component.
Of course, I do not know if this modification would have an impact on valve clearance at the top of the cylinder, hopefully not. There may be a need to provide cut outs for connecting rod clearance at the base of the cylinders. Also, I am not sure how this modification would affect performance, but at least the whole modification would be reversible (with x 12 new cylinders) and may solve possible over heating and cylinder integrity at elevated temperatures.
As George mentions, concessions are sometimes needed.
Steve.

 

[mayhugh1]

Makila,
Yep, that's just what I was thinking, er... hoping. - Terry

 

[petertha]

Terry I was Amazon surfing & happened to see this. Its dated Mar-15-2015, not sure if that means its a new release or reprint date. Anyway just a FYI.

http://www.amazon.ca/dp/0857337580/?tag=skimlinks_replacement-20

 

[Charles Lamont]

I machined this base plate to be as perfect as I possibly could, but after an evening of chasing my tail, the best I could achieve was .0005" flatness over the plate's 12"x4" area, and even that involved some luck.

I would say that was pretty good going. To get any better I would expect
to have to scrape it, (something I don't think I have tried with light alloy).

 

[mayhugh1]

Thanks, Peter. I just ordered a copy. - Terry

 

[mayhugh1]

I started the more demanding machining on the blocks by mounting the first one upside down on the heavy baseplate I made earlier. It was secured to the baseplate with Delrin disks screwed down inside the two outside cylinder bores. These disks clamp the top lips of the two bores against the baseplate so the long axis of the block can be held securely in alignment with mill's x-axis. A gage plug fitted in the single reamed stud tube hole was used as a reference to ensure alignment of it and the bottom-side block machining with the already-machined crankcase.
Because of the hold-down disks inside the outer cylinders, only the four central cylinders were initially bored. Once these bores were completed, a second pair of disks were screwed down inside the inner cylinders before the outer disks were removed. An inconspicuous dimple spotted on the far end of the block before machining began was targeted with a spindle microscope to verify the block hadn't shifted during boring or the disk change-out. A high rake triangular carbide insert fitted to a boring bar and driven by a boring head was used to bore the cylinders.
The boring was done in four passes: three passes of .010" radial doc and a finish pass of .005". Just after the first pass of the first cylinder in the second block I noticed a dark spot on the interior wall of the cylinder. The cast i.d. of this particular cylinder had always looked a little suspicious compared with the others because of a slightly sunken-in pea-size area. At first I thought I was looking at was a shadow, but when I touched it with my finger I felt a sickening pang in my stomach. This pea-size area was now a thin layer of foil covering what was evidently a void just below the surface. Succeeding passes peeled the foil away to reveal a small cavity. After boring the adjacent cylinder I was left with an irregularly shaped hole between the two cylinders. Although it'll eventually be hidden by the liners, and it isn't fatal since it basically connects the water jackets of two adjacent cylinders, it's the only thing I see when looking over the last several weeks of work. If it were a bar stock part I'd scrap it without a second thought. I eventually filed the hole into a rectangular shape so it wouldn't look like so much like a defect.
Curiously, the block is the only casting for which drawings were supplied for a bar stock equivalent. The reason for their existence isn't mentioned anywhere in the documentation which leads me to wonder if there were yield problems with the block castings, and billet replacements were plan B. The issue with using them, however, is that they contain no provision for coolant flow which makes them impractical for use in a functional multi-cylinder engine.
The holes for the studs were referenced to each bore before being spotted, drilled, and counterbored. Because of concern about the holes not coming out in the exact same locations on the other side of the 2" thick block, they were drilled to only half depth using a slightly undersized Guhring drill. Once the holes are similarly drilled from the top side they will be reamed to their finished diameters. The counterbores on the bottom surface of the block match those previously machined in the top surface of the crankcase. The counterbores were drilled using a very long 4-flute end mill extended out from a 'special' collet with a known TIR problem so i could get the over-size diameter I needed. Oil seals will eventually be inserted into these counterbores to contain the drain-back oil from the engine's top end.
As mentioned in an earlier post, my particular crankcase was cast slightly undersize which necessitated altering its machined bore spacing from that of the drawings. Because the blocks which were properly cast on-size, the machined cylinder bores and stud holes in them had to be relocated to match those in the crankcase. If you look closely at the block photos you may notice the stud holes are not in the exact centers of their bosses. Since all machining was referenced to the center of the block, the resulting errors progressively increase toward the two ends. The cylinder wall thicknesses around the machined bores are reasonably uniform, though not identical, due to a slight lateral warp in the castings.
Other than my little gas bubble, the undersize crankcase, and all the warped parts, I still remain impressed with the castings. Next up is to flip the heads over for the top side machining and to decide how to deal with the center stud tube holes which were not cast vertically through the block. - Terry

 

[digiex-chris]

Is that an optical alignment tool held in your mill spindle?

 

[mayhugh1]

Yes, it is. I calibrated it by drilling a tiny spot on a piece of metal and then replacing the spotting tool with the scope. There is an adjustment on the scope to zero the spot under its cross hairs. It works especially well on my Tormach because it can be re-inserted into same position in the spindle due to the spindle lock in their mill. Once calibrated it doesn't have to be messed with. I believe I bought it from Enco. It's one of those items that often goes on sale. - Terry

 

[petertha]

I was left with an irregularly shaped hole between the two cylinders. Although it'll eventually be hidden by the liners, and it isn't fatal since it basically connects the water jackets of two adjacent cylinders, it's the only thing I see when looking over the last several weeks of work.

Dang. If it doesn't adversely affect cooling or performance, I guess the biggest challenge is just mentally forgetting its there once its all buttoned up. Tough for a perfectionist, but maybe the best solution of few available options. I don't know what to suggest for fear of making matters worse.

I can visualize a patch made from HT aluminum filled epoxy or urethane casting putties using a male release plug in the opposing cylinder, but would that even hold up under service? Any kind of braze like those zinc? alloy wonder sticks is asking for trouble. I've seen pictures where people Loctite a plug & re-machine, but the cavity is such a thin, irregular feature as an add-on & only 'grip area' is the small periphery of the open window.

Don't let my armchair ramblings influence you. I'd feel real bad if a repair attempt went sideways. Trying to be helpful, but way out of my league.

 

[mayhugh1]

Peter,
I gave some thought to repairing it, but in every case the repair had more long term uncertainty associated with it than the hole itself. The section is just too thin for a cold patch, and the heat required for a hot patch is too risky for a number of reasons. It stings now, but my long term memory isn't what it used to be, and I'm sure I'll have a lot of more serious issues to deal with before this project is over. - Terry

 

[Scott_M]

Hi Terry
Bummer about the gas hole. But like you said, any repair will likely introduce more issues than the hole itself. And If you have to have a void somewhere, that is not a bad place.
Awesome work, following along closely

Scott

 

[digiex-chris]

You could cut a hole through all cylinders like that, and call it a little extra coolant flow...

 

[mayhugh1]

Next, the blocks were flipped over on the baseplate for their top-side machining. Since the necks of the bores are no longer against the baseplate the bores couldn't be clamped down with disks, and so I made another pair of expandable Delrin collets to grip the i.d.'s of the newly finished bores. As before, these collets were used in the two outside cylinders to hold the blocks down against the baseplate. It was important to keep the heads tightly against the baseplate and to align the axes of their already finished bores with the mill. These next operations will impact the seals of the combustion chambers as well as the seals of some 28 oil and coolant transfer tubes between each block and head. I was prepared to spend a lot of time shimming the baseplate-mounted block into alignment with the mill but was pleasantly surprised to find both block centerlines were aligned to within .003" before shimming.
The first operation was to bore the cylinder necks to their finished i.d. The shoulders of the liners will be lightly pressed into these bores in order to seal the water jackets at the tops of the blocks. Each liner will be supported at top of the block by its shoulder and at the bottom by a sealing ring that forms a joint with the crankcase, and so the neck bores need to be accurately centered over the cylinder bores. Both should have been machined in the same set-up, but I couldn't come up with a fixture that would have allowed me to measure both i.d.'s during machining.
I used a DTI in the mill spindle to find the center of each bore. Each of these indicated centers were used for the corresponding neck boring operation as well as the second half drilling and counterboring operations on their associated stud holes. Because the two cast central stud tube holes were too far off vertical to be corrected during the previous facing operations, they were not where they were supposed to be on the top surfaces. In fact, the hole in the right-side block was off by a whopping .020". These holes will have to be specially treated later when the matching operations are performed on the heads. As far as I could tell, the topside half-depth stud holes appeared to match up with the bottom-side half-depth holes previously drilled. I could feel no detectable intersections when they were reamed through.
I machined the diameters of the 14 stud hole counterbores .005" larger than the diameters of the head stud tubes that will be inserted into them. I used a long stick-out end mill in a spindle chuck with a poor TIR to get the counterbore diameter I wanted. These tubes will have to be pressed into the heads since they penetrate the head coolant jackets. The holes for these tubes are those holes mentioned earlier that were pre-cast in the heads in the wrong locations, and so they will all have to be 'moved.' The .005" clearance assumes I can match the hole placements in the blocks and heads to better than .0025" each which doesn't seem reasonable, but it's twice the clearance called out in the drawings. I really wonder what the placement accuracy was for all these holes in the full-size engine back in the 40's. O-rings will be inserted on these stud tubes and compressed between the head and block to help seal the intersections against oil leaks. I won't be surprised, though, if I have to come back later and manually increase these clearances in order to be able to assemble the heads to the blocks.
The last top surface operation was drilling and counterboring the 14 holes for the coolant transfer tubes that carry pressurized coolant from the blocks to the heads. The same .005" over-size counterbores were applied to these holes. I haven't yet decided if the coolant tubes will be a tight fit in the heads or whether the heads will also receive the same counterbore clearances. I need to do some assembly experiments on some dummy parts before I decide. Compressed o-rings will also be used around these tubes.
The depths of the stud tube counterbores are slightly deeper than the depths of the coolant tube counterbores. This was done so the pressed-in stud tubes that will extend down from the head can be made a bit longer than the coolant transfer tubes. When the head is assembled to the block the hope is that the 14 stud tubes will engage the head first and act as guides for the 14 coolant tubes and five liner spigots following closely behind. I really have trouble describing this critical assembly step without laughing hysterically.
A confusing, at least to me, issue involved determining the asymmetrically placed locations for the coolant tubes. They, too, had to modified from the locations called out for them in the drawings in order to accommodate the changes created by the short crankcase. For simplicity, the same drilling pattern is specified for both the left and right blocks since both are machined from the same casting. The left block is just the right block turned 180 degrees, but since the hole patterns are not symmetrical across the long axis centerline of the block, some algebra and a lot of mental gymnastics were needed to calculate their new locations. If I were starting over, I would just allow the rods to run a bit offset in their pistons rather than correct for the crankcase casting error which seems to be propagating with no end in sight throughout the engine.
The final block operation included surfacing the coolant tube flanges on the outboard side of each block. A pair of external coolant feed tubes are affixed to the outside of each block using three small, but highly detailed, cast tube fittings. I believe these tubes are the coolant inputs for the engine. There's no explanation of the cooling system in any of the documentation I received, and so I'll need to do some research on the full-size engine when I get to that point. I was disappointed to discover there was no casting supplied for the coolant reservoir which is a prominent component on the top front of the engine. It's shape is very complex, and it will have to be hammer-formed from sheet metal or CNC'd from billet.
I decided to machine the cast tube fittings at this time, as well, so each block could be match-drilled for them while still on its baseplate. It was very difficult to fixture these parts for machining, and after a few unsuccessful attempts that left their flanges considerably thinner than intended, I decided to hand file them. It's important that the flanges on these tube fittings be flat and normal to their mounting surfaces on the block since they connect a pair of tightly-fit rigid tubes between them, and provide at least seven opportunities for coolant leaks. A couple long, small diameter bosses that had to be through-drilled for mounting screws kept the filing even more interesting. I think the intention was to use 2-56 SHCS to mount them, but I settled on 1-72's because of a lack of excess stock. I Loctited short, thin-wall tubes into the block flanges to help locate the fittings for transfer drilling their mounting holes to the block. These tubes will also make it a bit easier to seal the flanges.
I received the Haynes 'Workshop' manual for the Merlin. It'll be interesting reading, but it's mostly an historical accounting of the engine's development with very little workshop content. I did find a warning about about the necessity of monitoring the oil level in the Merlin as it was known to leak quite a bit of oil, probably from the numerous seals I've been encountering. It reminded me of a joke that I heard long ago from a mechanic friend who incessantly teased a Jaguar owner whose car spent more time in his repair shop than it did on the street: "Why is it that the British don't manufacture televisions?" Answer: "They've never figured out how to make them leak oil." - Terry

 

[petertha]

Impressive positioning & finicky machining operations.
Can you elaborate on your Delrin ID clamping collets. I see the slits & assume a tightening nut on top? So is there a steel cone under the nut that yields the radial expansion? How is the shaft fixed in the base plate? What is a typical collet OD vs Bore ID dimension?

 

[mayhugh1]

Peter,
The collets are threaded for shoulder bolts that are inserted up through the bottom of the baseplate. I turned the collets for .003" smaller diameter than the bores. There is a 60 degree counter sink bore in the end of the collet and a 60 degree conical piece that is forced down into the countersink to spread the collet. I tightened the nuts that forced the conical sections into the countersinks while the the center of the assembly was lightly clamped in a vise. When done, I tried to pull the block up from the baseplate while checking with a .001" piece of shimstock as well as for any light between the block and the baseplate. During machining, I also watched for any hydrodynamic pumping of the coolant that collected around the bottom periphery of the intersection of the block and baseplate. I saw none and assumed all went well. - Terry