Lawrence Merlin V12

[peterl95124]

in DiegoVV's thread "Olsryd Merlin - Feasible?" I posted a picture of my model Merlin,
but I think it would be better to fork off since I didn't start with Oslryd's plans or castings.

DiegoVV asks

I fully agree, If I put the effort it takes, I would make it as closer as the real Merlin as my capabilities allow me. Where did you get this picture? Is it a modified Olsryd? Is there any available plans?

this is my own engine, designed from scratch and built from bar stock, based on cross section drawings in "The Merlin in Perspective" published by the Rolls-Royce Heritage Society which I xerox-enlarged to 1" cylinder bore and then took all measurements from so its as scale accurate as I could make it.

Steve Hazelton made a youtube video of it running at a BAEM-Club meeting, search for "first pop merlin v12".

I would very much like to make the plans available, but currently they are all pencil on paper, so I have a tremendous amount of work to make them readable and reproducible, and many of them only make sense to me (X-ray-vision drawings where things at different Z depths show up in the same drawing, a big no-no in classical drafting but that's how I do it anyway).

In the best of all worlds I'd author a book like Kozo's "Pennsylvania A-3 Switcher" which I have and greatly admire, more realistically maybe something along the lines of Bruce Satra's plans and construction notes for his O-440 engine, but don't think I have the energy or inclination to do that either, so maybe a plans and construction article sequence in Mike Rhemus' Model Engine Builder, but he would have to CAD my drawings and do much of the writing and I don't know if he still has the energy to do that, we're at least talking about a presentation article as he wants to take a cover-photo of it.

needless to say this is not a beginner project, and some parts are so complicated (intake manifolds, supercharger) that I'm considering getting a CNC mill and making those for folks that see them as too challenging, and that would depend on how much interest there was (as otherwise I have no desire for CNC). And I built my own cam shaft grinder so I'd offer those as well. The parts that are manufactured are screws, gears, ball bearings, and springs, everything else if made from bar stock. it does take a lot of determination and motivation to for example make 48 valves and rocker arms, 24 spark plugs, 36 piston rings, and 12 pistons, conrods and cylinder liners, but as the saying goes "a journey of a thousand parts starts with a single cut".

I must also add that if you are familiar with Barry Hares' model Merlin engine, this isn't anywhere near that detailed, and I'm not anywhere near that capable, my aim was to make something that an ordinary home shop machinist could do (and some will argue with whether I succeeded), I'd call this "stand off scale", it has all the correct proportions but I simplified things for manual machining, for example you won't see any casting artifacts that are on real full size engines (that Barry Hares did duplicate).

anyway, those are some of my thoughts, my goal is to get this design out there for other folks but still don't know how that will happen.

 

[petertha]

Beautiful work, Peter
I've linked the YouTube video you referenced.

 

[peterl95124]

here is the design detail that made the model practical, where it went from pipe dream to possible reality, the so called wheel case (wheel is British for gear), this houses the gears that power the cams, oil water and fuel pumps, magnetos, and finally the supercharger. I really didn't want to use timing belt drive for the cams like so many other models do since that isn't scale and just doesn't look right, I wanted bevel gears to the cams like the full size, but...

in the full-size engine the cams are driven by an awkward series of bevel gears, first a vertical shaft, then a split into two separate shafts one for each cam. that combination of bevel gears have weird angles and would have to be custom made, something I didn't want to do, also the two cam drive shafts aren't at the same 60-deg angle as the cylinder blocks so the cams themselves can only be located where those axies intersect which dictates the height of the cam shafts above the head, and as power increased during and after the war it became obvious that larger diameter sturdier cam shafts were necessary but impractical as it would require totally new tooling to make bevel gears for a slightly different angle, so impractical in fact that they never did it.

while I was pondering these issues I wondered if I could get rid of the intermediate (custom angle) bevel gears and go directly from the crankshaft to the camshaft, and it turns out that for 2:1 bevel gears things do fit AOK, using off-the-shelf 48-DP bevel gears (from sdp-si.com). with that I knew it was all clear full steam ahead (so to speak) to finish the design and it would look scale the way I wanted it to.

this is the one part that from the outside doesn't quite resemble the full size and why I call this a stand-off scale model, but its sandwiched between the crankcase and supercharger and hidden behind magnetos and intake piping so its really hard to notice unless you're specifically looking for it, and you'd have to be an expert at R.R. Merlins to know the difference.

here's a picture showing the wheel case (sorry for the blur, but for now I'm not going to disassemble the engine to take a better one) you can see the two cam drive shafts coming out at the top at 60-deg to match the cylinder banks, and their bevel gears in the center are close but don't interfere with each other. (pump drives out the bottom, and magneto drive on the side).

 

[Shopgeezer]

Wow. Impressive work. I hope you succeed in getting the plans out. What did you do for the ignition? You mention making spark plugs.

 

[peterl95124]

Wow. Impressive work. I hope you succeed in getting the plans out. What did you do for the ignition? You mention making spark plugs.

yes, my spark plugs are made, 8-40 threads, you might be able to get away with 10-40 for a slightly thicker insulator, I might try if I had to do it over again, but things are really tight in the heads, larger plugs will interfere with the intake and exhaust components

while Barry Hares succeeded in making working scale magnetos that's way too impossible for me, I made my magnetos empty shells for scale looks, my actual coils and distributors are large enough to be practical to build and deliver a strong spark without worry of flash over between distributor parts, they are mounted behind the firewall of the display mount, here's a view from the rear, Sage-Geddy electronic ignition, moped coils, and 2" distributors (clear acrylic aids in setting timing!), one system per cylinder bank. real aircraft engines always have two spark plugs per cylinder, and mine does to be scale, but I only fire one per cylinder as that allows 6 outputs per distributor whereas 12 puts the parts too close together and I suspect flash over would be inevitable (I might make a 12 output 2" dist just to prove/disprove that some day)

 

[Shopgeezer]

Your close up of the gear box showing the cam drive also shows a gear you label as the magneto drive. Is this how you are driving the distributers? You must have Hall sensors on a shaft somewhere.

 

[peterl95124]

Your close up of the gear box showing the cam drive also shows a gear you label as the magneto drive. Is this how you are driving the distributers? You must have Hall sensors on a shaft somewhere.

that magneto gear in the wheel case is for the scale but non-functional magnetos

the actual working distributors are behind the firewall, driven from the cam shafts, and the actual working hall sensors are in the working distributors.

while I was still thinking I could at least use the scale magnetos as distributors (with coils mounted elsewhere) I had designed gears in the wheel case for them, and made rotors for the magneto/distributors, but the downfall of this effort (for me at least, I'm no Barry Hares!) was all the pickups around the rotor, they're too close together, and I never found a satisfactory way to install them (was also making clear acrylic magneto tops, which allowed me to see how poorly my pickups were located)

its possible I gave up too soon, but had already made lots of trial parts, and even if I eventually had succeeded it probably wouldn't be something the average model engine builder could duplicate which was and still is my goal, so in the end I went with remote and large enough to be easy distributors / coils / circuits.

 

[awake]

Marvelous work. Congratulations!

 

[mayhugh1]

Peter,
I just came upon this thread and must say its a marvelous piece of work. If you have any construction photos I'm sure we'd all be interested in seeing more of your process you'd be willing to share. This would have made a wonderful build thread being one of those projects that many talk about starting but never quite get going. I wonder how long have you been working on it? You've accomplished an miraculous 'off-air' result. Congratulations! - Terry

 

[peterl95124]

Peter,
I just came upon this thread and must say its a marvelous piece of work. If you have any construction photos I'm sure we'd all be interested in seeing more of your process you'd be willing to share. This would have made a wonderful build thread being one of those projects that many talk about starting but never quite get going. I wonder how long have you been working on it? You've accomplished an miraculous 'off-air' result. Congratulations! - Terry

Terry,
I'm pretty sure HMEM didn't exist when I started this project, back in Dec 2007.
I don't have as many photos as I'd like, and it will take a while to dig them up, but I would like to start posting some. Its not really "off-air", there are lots of photos and progress reports in the back issues of BAEMClub-dot-com newsletter, a few from scattered years are

Sep 2008 --- cylinder blocks on crankcase
Oct 2008 --- supercharger and wheelcase
Nov 2008 --- crankshaft and bearings in crankcase

Nov 2017 --- engine mount silver soldered together
Dec 2017 --- oil pan with oil pumps and filters, oil pressure regulator
Jan 2018 --- another engine mount and oilpan photo
May 2018 --- clear acrylic magneto tops
Jul 2018 --- all parts disassembled
Sep 2018 --- cam grinder

Feb 2022 --- issues with camshafts
Mar 2022 --- continuing issues with camshafts, really good closeup photo
May 2022 --- valves aren't sealing, Argh !
Jun 2022 --- FIRST POP, YEAH !!!
http://www.baemclub.com/crkcallarchive/jun22nl.pdf

don't know why there aren't any photos of the heads in 2008, that's what I started on first, experimenting with fitting four valves and four rocker arms per cylinder with only 1" bore, probably still feeling too shy at the meetings back then

for my New Years Resolution in 2022 I decided that the only way I was going to finish the Merlin was if I stopped all other work on all other projects and focused all my energy on just the Merlin, was hoping for something by the end of the year, things came together faster than that, retirement has its benefits !