Quarter Scale Merlin V-12

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mayhugh1

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While procrastinating over the intake manifold drilling I tried to keep the project moving along by working on the valve covers. This project has taught me to spot a problematic casting even from a distance, and my experience tells me the valve covers will be the last ones to require straightening. Besides having a twist along their major axis, their thin half-shell shape had to be spread to fit completely across the heads. Compared with the intake castings they weren't difficult to correct, but they were also about 3/32" too short for my heads which wasn't correctable. I couldn't figure out a way to safely stretch them, and so I settled for an alignment of their fronts with the fronts of the heads since this was the most prominent area of the engine. This decision left a gap at the rear of each head; but, even worse, the threaded holes for the cover's rear mounting bolts almost completely missed the rear mounting flange on the head. This was disappointing, but the defective threads will eventually end up hidden under the valve covers. The increasing front-to-rear mismatch of the cover's mounting hole bosses with those in the heads tells me that maybe the valve cover shrinkage wasn't fully compensated. The surfaces of the valve cover flanges were lapped instead of milled because the castings were too flexible to be safely supported for machining.
I've noticed my head castings seem to be different from those in the photos on Gunnar Sorenson's website as well as those on the Quarter Scale Merlin website. There is a series of holes in the top surfaces of my heads that were probably used for core supports. I hope my heads aren't an early obsolete version, because measurements I made show the required surfacing operations for the camshaft support blocks will leave the top surfaces dangerously thin. I guess it's possible that the mismatch that I encountered between the valve covers and the heads was actually the fault of my heads and not the valve covers.
The valve covers were match-drilled to the heads using 2-56's, and I decided to also use these smaller bolts for the intake manifold instead of continuing with the 3-48's. This gave me a opportunity to experiment with bolt hole clearances, but I eventually ended up again with a .004" diametral clearance which meant that the head mounting holes needed to be drilled and tapped with a positional accuracy of +/-.002". This was one of the reasons I'd been putting off the manifold drilling.
After finishing the valve covers, I finally began the tedious process of drilling the mounting holes for the intake manifold. I match-drilled the side flanges of the assembled intake manifold to the heads using strips of gasket material sandwiched between the two to account for the thicknesses of the intake manifold gaskets. There will eventually be a total of eight manifold gaskets. Six of them will used in the assembly of the manifold itself, and one will be used between each head and the manifold. I purchased a sheet of 1/64" fiber gasket material with an actual measured thickness of .013" to use for the temporary spacers and then, later, for the gaskets themselves. After drilling and tapping all the mounting holes in the 60 degree valley, any other gasket material that deviates more than .002" from this value may no longer work.
Eighteen of the seventy manifold mounting bolts went through the manifold's plenum, and they had to be carefully drilled from both sides of the manifold before being reamed to their final diameters in three steps for the 1-1/4" 2-56 mounting bolts. The reaming was complicated by the rounded interior surfaces of the plenum that continually pushed the reamers off trajectory. All these new long bolts were slightly bent, which isn't at all unusual, and this took up most of the their clearance allowance. After match-drilling and tapping all the manifold mounting holes in the heads, I performed a test to see how critical my hole alignments really were. I increased the effective gasket thickness by .004" by adding a sheet of paper to the strips of temporary gasket material between the manifold and heads. Sure enough, the additional .004" material shifted the manifold holes with respect to the threaded holes in the heads so that only a few of the bolts could be inserted. When the actual cylinder liners and liner collars are machined later, their dimensions will have to closely match the temporary Delrin parts used to fit the manifold.
In total, 180 hole pairs were match-drilled and tapped in order to install the manifold and valve covers onto the heads. I ceremoniously retired the single 2-56 tap that did all the work by grinding its end off so it can someday takes its place as a piece of shafting or a cutting tool in another project. - Terry

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ozzie46

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Amazing!! Your ability to overcome obstacles and press on with this project is truly inspiring.

The finished product will be a testament to your tenacity and skill. Roll On!!!

Ron
 

napoleonb

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I seldom post on this forum but you are the main reason of my precense the last years. Your projects are truly inspiring and well documented!
The engine castings for this project are absolutely beautifull and your solutions and plan of operations mindboggling.
 

mayhugh1

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I drilled and tapped yet another 60 hole pairs in the heads for the exhaust tips as well as a pair of coolant outlets at the top front of the engine. Installing the exhaust tips was more interesting than working on the intake manifold or the valve covers since I got to add a new part to the assembly for every four new hole pairs I created. The exhaust tips are beautiful castings and needed only light facing and drilling. They add realistic detail to the engine that would be very difficult to duplicate even with CNC capability.
Only one pair of castings was supplied for the coolant outlet tubes. In the full-size engine, coolant flows between the heads and a header tank located at the front of the engine. The drawings and notes accompanying the castings don't provide any design detail about the tank, nor anything else about the coolant system for that matter, but a riveted sheet metal tank is shown installed on the quarter scale prototype in the original designers' video. A photo on their website shows the outlets installed on the front-end of the heads' manifold flanges, and another photo shows the rears of the manifold flanges drilled and tapped for second set connections to the coolant jacket. Castings for these connections were not supplied, but I also drilled and tapped these holes even though I haven't yet figured out how they'll be used.
The exhaust tips complete my trial assembly of the 30 machined castings forward of the wheel case. My original goal was to get the castings assembled before investing any time or material into the bar-stock components since I had some misgivings about actually getting the castings assembled. I would continue with the foundational machining on the remaining 18 castings and complete the entire exoskeleton of the engine, but the wheel case castings need to be match-machined to bar stock components that I'll have complete first.
A third of the castings and half of the engine's complexity will end up at the rear of the engine behind the wheel case. This is where my understanding becomes a little fuzzy about just how much of the model's development was actually completed. This is also where the notes accompanying the drawings begin to thin out, and comments containing the words 'proposed', 'try', and 'somehow' show up with more frequency.
I included photos of the assembled castings for which nearly all of the machining has been completed. The very last photo shows the 18 un-machined castings that will eventually take their place at the rear of the engine. Although these photos may imply that much of the build is behind me, I've really only scratched its surface as there are probably a thousand parts yet to be machined. (The full-size engine had over 11,000 parts.)
My current plan is to start working on the crankshaft and the bar stock components associated with the overhead cam drive housing. The cam housing is needed so machining on the rest of the castings can continue. I'm including the crankshaft so I can work on a component that doesn't require a bunch of tapped holes.
The Merlin crankshaft is a thing of real beauty, and I'm looking forward to holding it in my hands. It'll be my first attempt at machining a complex multi-throw crank from a single billet. A chunk of 1144 stress proof steel is on its way, and I'm currently studying George Britnell's excellent tutorial on crankshaft fabrication. - Terry

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Swifty

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Every time I see those castings, I'm amazed at the quality.

Paul.
 

gbritnell

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My goodness that is one impressive looking engine! I don't think I would have a problem with the machining aspect of the project but I probably would have quit after finding so many mismatches and warpage. I applaud your tenacity.
gbritnell
 

kvom

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If you had drawings of everything then in theory a bad casting could be drawn and then 3D printed; no warpage and the holes would match up.
 

wirralcnc

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Terry
I might send you my set of castings for you to put all them tapped holes in. :D
 

sbdtasos

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Hi terry
as always extremely perfect ..
i know that project like yours need so much time that you can not imagine
thanks for that you offer
exelent job

ps: all the money that you spend to buy this kit you will spend to buy the bolts for it lol: P: P
 

gus

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We are getting excited and quietly waiting to see the video of this engine roaring away.

You are SuperMachinist/EngineBuilder.
 

barnesrickw

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The size of the blower is amazing. Full scale must be a powerful engine.
 

mayhugh1

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I came across two online references to help me with machining the Merlin crankshaft. The first is a thread by a Belgium builder 'Zapjack' who fabricated this exact part with some 200 hours of work over a period of two months nearly three years ago. It's located at
http://www.homemodelenginemachinist.com/showthread.php?t=18747
He first published his build on a French forum and then cross-posted its highlights on HMEM in 2012. The original non-English forum where he posted his realtime build as well as an additional two year's work on his Merlin is located at:
http://www.usinages.com/threads/rolls-royce-merlin-v12-echelle-1-4.42350/
Unfortunately, his posts faded away in 2014 after completing the crankshaft, prop shaft, and cylinder liners as well as the crankcase and some of the cylinder block machining.
The second reference is George Brittnel's crankshaft tutorial inside his V-8 flathead build thread starting at:
http://www.modelenginemaker.com/index.php?topic=3846.210
Since I have some limited four axis CNC capability, my hope is to combine the information in the two threads and take advantage of my Tormach's fourth axis. I don't if my particular CAM software can be convinced to continuously machine the offset throws from billet, but it's worth several days of experimenting to see just what it can do. Hopefully, I can at least come up with g-code for some of the tedious roughing.
Work started on the crankshaft by sawing off a 10-1/2" length of 2-3/4" diameter 1144 steel. I've not used this particular alloy before, but it comes highly recommended for crankshafts by George. I bought a piece long enough for two parts just in case my learning curve takes an ugly turn. I purchased the metal from an online supplier who advertises it as 1144 Stressproof or 'equivalent'. The 'equivalent' sounded ominous, but their price was nearly half that of the other online supplier that I've used used in the past for material not available in my scrap collection. Since Stressproof is a brand name, I'm not sure it's legal to use it to advertise a generic equivalent.
Anyway, after facing and center drilling one end, I turned the o.d. down to 2-1/2" over as much of the length as I could before flipping it around, facing and center-drilling the opposite end and then turning the rest of the o.d. After cutting through the black outside layer I was relieved to find the material turns pretty similarly to mild steel. The chips resemble those from free machining steel, and the surface finish is similar. An amazing thing I noticed was the material's consistent o.d.. The run-out at the end of the 10.5" long un-machined round was only .002" after being chucked in my lathe's 3-jaw without tailstock support. The material I purchased was their low-end cold-roll, but it is also available as precision ground and polished.
After studying the crankshaft drawing I realized just how complex this part is. The webs are not identical, and there are many machining features associated with them. Another wrinkle is that each bearing and crank pin is bored-through in order to reduce weight. In addition, both ends of each of these bores must be counterbored for end plugs since internal oil passages supply pressurized oil from the mains to the crank pins. The workpiece I'm starting with weighs 18 pounds, and the weight of the finished part will be only 1-1/2 pounds. A lot of metal has to be removed from some very difficult to reach locations.
The first and probably most important decision to make is how the workpiece will be held for offset turning. George's offset end blocks looked good to me as they positively grip both ends of the heavy eccentrically rotating load. When I tried to adapt his technique to my crank I realized the four-sided headstock block he used for his 90 degree throws would not work with my crank and its 120 degree throws. I looked at using a hexagonal end block but I wasn't happy with two of the four jaws gripping on the corners of the block. A 12-sided polygon would work, but it wouldn't have long enough sides to handle the crank's 1-1/2" stroke in my 4-jaw.
Zapjack center-drilled the ends of his workpiece for center-turning on each of the three offset axes. I don't have much experience with center-turning, but supporting the weight of this workpiece between two centers concerned me. None of Zapjack's photos showed his headstock drive, but I can't imagine it was merely a conventional drive dog.
I decided to both center-drill and mill reference flats on both ends of the workpiece. Currently my plan is to use the center-spots to locate the workpiece between centers while finish turning the crankshaft. However, I will also add a head support block similar to George's to secure the crankshaft to my lathe's faceplate. The tailstock end will just be supported in an offset center-drilled spot by either a live or dead center. Most of the material will be initially roughed out on the mill and probably with the workpiece held horizontally in a vise. If I run into problems and have to come up with a plan B, at least I'll still have the flats and center-drill references to work with.
A first pair of reference flats was milled into each end of the workpiece while it was held horizontally in a vise. The workpiece was then stood vertically in the mill and clamped against an indicated reference plate using a ground block between the flat and the plate. I was relieved that this rather dicey set-up was actually able to hold the workpiece truly vertical and was rigid enough to mill the additional flats. Zapjack actually removed the table from his mill so he could perform a similar operation. The 120 degree center-drills were then drilled, and the remaining two flats were milled on the perimeter. Both ends of the workpiece were similarly machined but an additional nine holes were added to the front-end. These will eventually be tapped and used to secure a driveshaft to the front of the finished crankshaft.
Because of its complexity and the need to modify its dimensions to fit my 'short' crankcase, I modeled the crankshaft in SolidWorks so I could better understand what I will be up against. This crankshaft looks like a part that can be easily ruined by lapse of attention. It also looks like it will be the most complex part I've ever attempted to machine. It wasn't too long ago, when I was intimidated by what now looks like a pretty simple crankshaft in my 18 cylinder radial. - Terry

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Scott_M

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Wow Terry, that is gonna be a lot of work. And as you said a little distraction could ruin a bunch of work. Best of luck, I'll be watching.

Scott
 

petertha

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None of Zapjack's photos showed his headstock drive, but I can't imagine it was merely a conventional drive dog. Terry
I might be way off base but between the pics & posts it almost looks like the jig plate he used on the milling operation somehow served double duty in the lathe setup? I see some sort of thickish pin, but not sure if that's what's engaged to a faceplate slot?

I know this is a few miles down the road, but what are your thoughts on the journals final sizing/finishing - compound mounted grinding attachment or...?

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Mattsta

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You're a very brave man Terry! LOL!

It's going to be a treat to see how you manage this insane challenge!
 

gbritnell

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Hi Terry,
Another suggestion I could make which would help in the crank pin turning operation is this but it depends on the tooling you have available. When starting out in this hobby I had limited tools, a lathe with a milling attachment, so it took some creativeness to machine certain parts. The one thing that I did have was a face plate for the lathe. I don't mean a driving face plate but a true face plate. Depending on the size of the lathe a face plate can have holes or slots in it, or both. I don't have one for my Logan lathe and have been looking for quite some time. It's not that it would get used a lot but they sure are handy for jobs such as this.
If you do have one I would make the fixture block and securely mount it to the face plate with the required offset. Another nice feature of a face plate is you can bolt opposing weight to the plate to somewhat counterbalance the working weight. For the tailstock end you could still use the center drilled holes in the stock.
 

mayhugh1

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George,
Thanks for the advice. I do have a facplate for my lathe and will likely follow your advice when I get to the crankpins. I'm currently experimenting with cutters for the various operations I expect to have to do. The one I'm having trouble with (no surprise) is the deep grooving cutter for the crankpin turning. I admit I haven't yet tried to duplicate your 1/2" bifircated HSS cutter. I've been trying to use carbide grooving inserts that I have on hand. I have one in particular that will do a nice job, but the deep blade holder I need doesn't commercially exist, and it looks like a useable shop-made equivalent may not be practical. I may be gravitating to something similar to your cutter. If it isn't too much trouble could you post some profile photos showing the rake and relief angles? I've been wondering why you didn't start with a 1/2" HSS blade in a toolholder instead of grinding your tool from a full 1/2" square blank? I'm seeing a lot of side flex on the 1.7" long 3/32" wide 1/2" HSS blade cutter that I've been running some quick and dirty tests with. And that is just with plunge cutting. I'm not sure the toolholder is causing this, but I might be wrong and thought I would ask for your opinion in case you had already been down this road. -Terry
 
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gbritnell

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Hi Terry,
I have in the past used high speed cutoff blades. The problem I had was not with the plunging but rather when moving from side to side to clean up the journal the tool would flex. On a crank with no counterweights the tool can be shorter and therefore is more rigid.
This is why I ground my own. I will admit it was a tedious job but once finished it did a wonderful job. The width of the tip is a little less than half the journal width so that when moved from cheek to cheek it will overlap at the center with the radius on the corner. It has no top clearance. It's just flat like a cutoff tool. The sides and front have about 2 degrees on them. Once I had the blade ground parallel I went back and removed about .020 from each side leaving about .200 of full width at the tip. This would allow me quite a few sharpenings if needed. To split the tip I used a thin abrasive disc to rough it and then used a tapered diamond burr to give some clearance to the inside edges. I will take some pictures tomorrow morning and post them for you.
gbritnell
 

Charles Lamont

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A potential problem, especially with a broad faced tool, will be chatter.
For the far less complicated Seagull crankshaft I finished the pins in bottom back-gear. That is 25 rpm.
 
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