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 !

 

[scale-giant]

Hi All,
long time lurker, first time poster!
Did you ever end up publishing the plans for this engine?
I'd love to purchase them, or if anyone has a set of plans & drawings they can sell, or put me in touch with a site that actually exists with them.
im trying to build one to fit my 1/4 scale aluminium spitfire im building. However it seems the quarterscalemerlin sites all done & dusted, the other ones from Sweden are no longer contactable (original designer has passed and the replacement email bounces back)
I can manufacture with either castings or from solid billet material.

 

[peterl95124]

Hi All,
long time lurker, first time poster!
Did you ever end up publishing the plans for this engine?
I'd love to purchase them, or if anyone has a set of plans & drawings they can sell, or put me in touch with a site that actually exists with them.
im trying to build one to fit my 1/4 scale aluminium spitfire im building. However it seems the quarterscalemerlin sites all done & dusted, the other ones from Sweden are no longer contactable (original designer has passed and the replacement email bounces back)
I can manufacture with either castings or from solid billet material.

what types of IC model engines have you built in the past ?
also have you posted photos of your spitfire anywhere ?

 

[scale-giant]

Hi Peter,
Thank you for the response.
I've started building the forming tools for the tail wing of the spitfire, so not the actual aluminium parts yet. (Start small)
I should explain a little. Im a qualified marine mechanic so my building of IC engines has mainly been more measuring & assembly, however through the covid period and the lack of parts available I've started to manufacture parts for marine engines myself, often just exhaust plates for outboards, raw water pump housings etc for diesels, engine mount plates & adapters, and im currently designing a new 5 axis cnc (similar build size to a Tormach m1100) with an ATC,
Im not the worlds best machinist yet, however im getting much better at cnc work! (Self taught with a cnc router)
I have completed some training at school (20 years ago) on normal machining practices, and I partially completed a hit & miss stationary engine at high school. I hope to be able to locate this and complete it shortly (i believe its at my mothers house) i have built the crank, connecting rod, cylinder blick, cylinder liner, machined the aluminium casting for the base, made the flywheels, the plans were out of an old popular mechanics magazine from the 1960s i think.

 

[peterl95124]

Hi Peter,
Thank you for the response.
I've started building the forming tools for the tail wing of the spitfire, so not the actual aluminium parts yet. (Start small)

you might want to try to acquire a Richard Maheu Quarter Scale Merlin engine or casting kit second hand, mine is scaled for 1" bore so the actual scale factor is 5.4:1, no where near 4:1, its also designed to be rigid rather than light weight (but hopefully you're not planning or even thinking about attempting to fly your model !)

also you should have a couple multi-cylinder IC engines built and running before attempting a V12, especially if you expect it to actually run(!), and I won't say how long it took me to build mine because a) I was designing (and sometimes re-designing) it as I went, and b) "if you have to ask you can't [afford] it" ! (not meant to be discouraging, just my irrepressible and very bad sense of humor !)

since your goal is to build a model engine to go with your model airplane, I don't think anyone would object to your posting photos of your Spitfire progress on this website, especially since IIUC this will be aluminum metal (not balsa wood, or fiber glass, ugh!) I for one would be very interested in seeing a build thread (somewhere?, anywhere!)

 

[peterl95124]

folks thinking about making this Merlin might want to start with the inline-4 version like I did, it was a proof of concept engine to test out bevel gear driven cam shaft and 4-valves-per-cylinder in a 1 inch bore model engine.
here's what scale model Merlin rocker arms look like; jigs, brazing, and machining ops to follow,
(FYI the pieces are not cut to length before brazing even though I show what they look like here below the finished parts)

arms: 3/32 x 1/8 W1 bar stock (MSC carries this wonderful stuff !)
pads: 3/32 x 3/16 W1 bar stock
tubes: 7/32 W1 round stock
bushings: 7/32 bronze
tappets: #1-72 set-screws (cup point ground off and polished semi rounded)
locknuts: 1/8" (IIRC 1-72 nuts were too large, so I used #0-80 and ran a 1-72 tap through them !)
spacers: whatever!

 

[petertha]

Timely post Peter, I was just pondering a similar operation. I assume the pads, the contact surface, are machined from annealed W1, then hardened? So how does one silver solder or braze them to the arm without the heat adversely affecting this hardening? Was W1 for the arms chosen for a particular reason over another non-tool steel alloy or was it also hardened for some reason?

 

[peterl95124]

Timely post Peter, I was just pondering a similar operation. I assume the pads, the contact surface, are machined from annealed W1, then hardened? So how does one silver solder or braze them to the arm without the heat adversely affecting this hardening? Was W1 for the arms chosen for a particular reason over another non-tool steel alloy or was it also hardened for some reason?

I did not harden them, AFAIK W1 hardening temperature and 56% silver brazing temperature are about the same (red to orange hot) so you can't harden without melting your braze. I thought about spraying with water right after the silver flowed, but seemed risky and I didn't try it as I've never heard of either good or bad results from quenching silver solder. I probably should have since I used a jig to hold everything in place while brazing. In the mean time I should probably heat a long length of the W1 bar I used up to brazing temp and then after cooling see if it still gives the same impression of strength as it does straight from the supplier, the stuff seems incredibly strong and tough and I really like it for levers, linkages, and such, in model building.

the full size engine uses "stellite" inserts, a cobalt super alloy, which is very available, but also very near impossible to machine, and I wanted a design that was suitable for a hobby machinist. If mine ever wear out I'll probably try A2 "air hardening" tool steel the next time around as it will harden at bright orange heat without needing to be quenched. I've already switched to A2 for camshafts on engines I've started after the Merlin.

so the short answer is I recommend A2, but for the prototype no the W1 cam pads are not hardened, and the 4130 cam shafts themselves aren't as hard as I'd like (I know they're partially hard because I broke one trying to straighten it, but they seemed too easy to grind and polish to be fully hard). The engine seems to be holding up, though it gets very little run time, a couple runs a year at BAEM, GGLS, and Good Guys Autos shows. I do put some 80-120 weight (differential) oil on the cams just to be safe !


let us know what you decide and how it works !

 

[peterl95124]

prepare a tube by drilling about 3/8" into the rod, but don't part off
as we need the length for the brazing jig
if the metal overheats (because you're not using a split point drill) try
not having any stick-out so as to have the chuck act as a heat sink

prepare an arm by notching it with a 15/64 drill, drill a pair at a time,
with some 1/32 brass in between as a spacer, again these are left long for the jig,
the most accurate way to find the center is with a dial-indicator as shown,
this is like an interrupted cut on a lathe, so hard on the drill, which should
be a stub length for rigidity and split point to avoid drift

 

[peterl95124]

now make a jig to hold the arm at 80 degrees across the tube
the jig needs to be symmetrical depth-wise because you need to be
able to make both left and right handed "L" shaped rocker arms so
in the second photo hopefully you can see that the channels for holding
the parts are centered in the jig, and the channel for the arm is 1/4" wide
even though the arm is only 1/8" wide. Also hope you can figure out
where the spring clips came from !

 

[peterl95124]

you can never have too much flux !!!

file the parts clean where you want the silver,
always use white flux so you can see through it once it melts and can observe
the metal heating up to red and where the silver went after its applied, for these
reasonably close fitting parts 56% silver works great (Safety-Silv, cadmium free),
since the parts are so small I used 1/32" diam silver wire. to avoid getting a gigantic
molten ball of silver on the end of the wire, heat from one side and sneak the silver in
from the other side so its shielded from direct flame by the part itself. Propane is
sufficient for these small parts, but since you can't point a propane torch downward
you'll want to hang the part over the edge of the brick and heat from below or from
the side.