Halifax W7715 Merlin Engine EP14. Fitting Cams, Magnetos & Timing

Added: 2026-06-03

[00:00:00]Hello and welcome back to this installment of building the Merlin. This time we're going to fit both the cam shaft and rocker mechanism assemblies which are known as CRM. Put both of those on, time them up to the crankshaft, and then we're going to move on to the magnetos. We'll fit those and time those up as well. So before I fit this CRM onto the engine, I'm going to address one of the questions that people quite often ask me, and that is why do the rocker shafts turn? So there's one rocker shaft. You see the rocker on it there. And then there's one on the other side there. And these gears on it. So if I fit this gear like that, put the sleeve in the middle of it. If I turn the cam, you can see these are turning.

[00:00:43]In fact, the rocker shaft isn't turning.

[00:00:44]So these are purely floating on top of the shaft like that. And their purpose is to drive accessories. So you can drive up to two accessories on this bank, two on the other bank. And they spread the accessories around the engine. And it wasn't until much later in the war that they came up with universal power plants where you had a single power takeoff from the supercharger drive which used to drive an auxiliary gearbox and then everything was fitted to that and it would be behind the firewall. The most common accessory you come across is a little single cylinder air compressor like this one. This one's called a Haywood. This actually has an engine oil supply going into it, but there was an earlier BTH compressor which just had a sump. So, it's got a spline inside it. There's a spline on the end of the gear. And then you have a coupling shaft which goes on there like that. That spline engages with the compressor like that. So, I'm almost ready to put this onto the engine. Now, you can see that the rocker arms are hanging down.

[00:01:47]They're going to get in the way. So, what we do is use a piece of wire in this case or a piece of string. This is the simplest way to do it with a loop on the end.

[00:02:01]Hooks over there and it runs diagonally there across each set of rocker arms like that. And you just flip it over.

[00:02:23]Straight on like that.

[00:02:26]Once we make sure that teeth engage there like that, all we do is pull it out, hook it off the end of there. That's it.

[00:02:36]I have seen people online using individual cable ties, plastic cable ties on each of these arms. But to be fair, this is just a very quick way of doing it. And this is how they show you how to do it in the book as well.

[00:02:50]So, we fit the securing nuts and we tighten them down gradually because the cam is actually lifted in certain place.

[00:02:58]It's lifted towards one end actually by the fact that some of the loes are obviously already touching the followers. And as I tighten it down, it'll be pushing those valves open.

[00:03:09]And using this chart again, I'm going to torque these up to 21 pounds feet.

[00:03:22]Then these nuts are going to be moved on to the next castellation and either split pinned or wire locked. Originally they were all split pinned. And if you notice on here, these quarterinch nuts which hold the bearing caps on were also originally split pin, but I'm using these are genuine Packard Nyllock nuts, which is what I use on the ground runners. They never come loose. As I have already fitted and timed the Abank cam shaft assembly, I'm now moving the crankshaft on in its normal direction of rotation towards the B1 inlet opening position, which is visible through the timing aperture in the lower crank case.

[00:03:58]Bit like a large sump plug. This has to be approximately 1/8 of an inch before the timing mark due to backlash in the gear train.

[00:04:07]So before I start using this tap it adjusting tool which has a square and a hexagon I'm going to set this tap it to 17 thou.

[00:04:19]So there we go. Lock it up like that.

[00:04:39]Now, I tend to mark an arrow on these things because it reminds me that the cam goes in that direction. I'm going to turn it until it just nips the three thou fer gauge in there. So, with the engine set on the B1 inlet valve opening position, I need to be able to turn the cam. So, I use this pin spanner here, like that.

[00:05:13]So the car is now in the position where it's just about to start opening the number B1 cylinder inlet valve. Tiny bit clearance in there. So this is a verier coupling shaft here with 19 splines on one end and 21 on the other. And that gives us enough control so that if I just keep turning it eventually it will drop in in one of the positions. There we go. Got it. Then there's this retaining plate with a little tough pad underneath it.

[00:05:43]Goes over the top of there.

[00:05:48]And that's just bolted and tab washed in place.

[00:05:53]Now I'm just going to run along and set each of the valve clearances to 15 thou.

[00:06:07]The final job on the cam shaft is to prelubricate the whole assembly on each side of the engine before fitting the oil feed pipes. I'm using this adapter onto the banjo fitting, which has a 38 BSP fitting on it, which connects to this oil gun that looks a little bit like a vintage bicycle tire pump.

[00:06:30]Once the cam and rocker shafts are full, I need to check for oil flowing from all 48 followers. An electric priming pump will also be used to prime the whole engine before starting it for the first time.

[00:06:42]So, there's one more test to do with these magnetos before I can fit them to the engine. If you watch my earlier video rebuilding one of the magnetos, I was very lucky there because the whole thing went back together and it worked.

[00:06:54]This is the other one. And I've had to replace the coil. So, there's the new coil in there. That's it. Well, I say new out of another magneto. And here's the one that came out of it that didn't work. I mean, it's not surprising to be honest because they were effectively underwater. So, this is on the test rig and then I'm going to start it up and apply 100 PSI of air pressure to it. So, I'll start the mag running at normal atmospheric pressure. Then a couple of seconds after that, I'll put the 100 PSI onto it. And you should actually see the spark getting a bit brighter, unless the mag's faulty, in which case it does stop sparking. But also, it might appear a bit erratic on the video, and that's to do with the frame rate of the camera.

[00:07:45]There we go. That's great. So, the magnetos are timed on when the A6 spark plug is going to fire in the fully advanced position because it's got variable timing, which is this lever here. I know that the rotor goes in this direction. So, I've pulled this all the way back around that way, the points carrier. I also know that this is in the position approximately for the A6 terminal on the distributor block.

[00:08:10]And here we got a thing called the magneto synchronizer. And if I press the button, that red light comes on, which means the points are closed. So for the spark to be firing, I need to turn this rotor until the light goes out while I'm holding the button. Now I've also got this tool here, which I'm going to fit, which has some little teeth machined into it. goes into there and it's slotted so it enables a bit of movement and I can then lock that magneto in that position because at the moment it's not connected to the engine. It's just hanging on the studs because there's no coupling shaft in there. I've got a piece of insulating material in this sliding contact here for the points carrier because the coil itself has a resistance of approximately 1 ohm which makes it very difficult to distinguish between the contact resistance and the coil. So that's completely out of the circuit. So I'm just measuring these opening and closing. So I'm moving the crankshaft onto the A6 EMA mark, which stands for exhaust magneto. And once that mag's been fitted, I'll move on to the inlet magneto. And those two marks are seven degrees apart.

[00:09:17]So if I press the button there, then I very gradually push that clockwise until the light goes out.

[00:09:27]There we go.

[00:09:29]Now I'm going to nip it up in that position there. So I now know that that magneto is in the correct position to be fitted. So, I'm going to remove the synchronizer. Can take this out now as well in case I forget.

[00:09:45]Take that off the engine.

[00:09:48]Now, again, this coupling has a different number of splines in each end and it actually gives you a net 0.9 degree resolution.

[00:10:02]So, now I'm going to fit the coupling onto there, attempt to fit it to the engine. If it doesn't go in, I just turn that around one spline on here. Fit it again until I reach a position where it'll actually go in. There we go. Just whiz one of the nuts on there to make sure it stays put. And obviously remove this tool. Then we're going to move the engine onto the inlet magneto position and do the same on the other side.

[00:10:26]Somebody using a chainsaw out there. I'm sure there's a bylaw somewhere about not using a chainsaw and I'm doing videos on a Sunday. So now we can refit the distributor components and the points cover.

[00:10:39]So the reason these magnetos are timed differently is because they start by firing the exhaust plugs on this side of the block and the mixture there is leaner because it's coming in from the intake side of the cylinder and they want to fire that side first.

[00:10:58]Then the flame takes a finite time to travel across the cylinder once it's ignited. Now it does start to become an issue the bigger you go with the cylinders.

[00:11:10]So Studebaker, the American car manufacturer developed an engine during World War II called the XH9350 and 9350 cubic in 153 L. Now that engine had bore size of about 8 in and the project was finally dropped because of problems with combustion. So they'd really surpassed the maximum efficient size that the cylinder ball could be. The big brother of this engine, which is the Griffin, has a bore of 6 in and that still works. Okay. And so the timing is staggered 7° and on maximum advance you've got 45 degrees of advance on the exhaust plugs and 38 on the inlet plugs.

[00:11:54]I've always thought of it in terms of that is the flame travel time across the cylinder at a given RPM which might be full power or it could be a a high cruising RPM that type of thing. And this shield is another radio screening component.

[00:12:12]And there's the variable ignition timing which just needs to be connected back up to the linkage here. So let's just have a look at one of the design features that gave a certain amount of trouble all the way through the production of the Merlin and the Griffin and the Meteor engine for army tanks and indeed one at least of the Rolls-Royce cars that was in production at that time.

[00:12:32]So these cam followers have a chromeplated rocker pad which is then ground to shape and it's got an oil hole in it which is fed along the rocker shaft as mentioned earlier.

[00:12:47]So this is what a good one looks like.

[00:12:51]Now, because of variations in the quality of the chrome and how it aderes to the steel underneath, the process starts by usually getting a little chunk missing up the side of it there, which of course, if nothing else, starts to reduce the surface area. You do get a certain amount of scuffing on the chrome, which you can kind of see on this one. Now, a certain amount of that is normal.

[00:13:20]If it carries on, then more and more of the chrome will pick off like that.

[00:13:29]Again, if you look at the rest of the surface of it, it's actually quite smooth. You know, very, very tiny scuff marks on it, but again, the rest of it normal. You can see the steel underneath. So, that chrome has completely come off. Now you find these flexcks of chrome are very very bright obviously in the scavenge filters if they're big enough to be caught by the mesh which isn't particularly fine I have to say but the return filter to the tank certainly after the scavenge pumps is a bit fine isn't that now it keeps on running this is how they end up you see it's been a bit warm by the color there quite often what happens is the material gets formed over and blocks the oil hole as well just to add insult to injury.

[00:14:19]So that one's completely toast.

[00:14:24]So on certain versions of the Rover MarkV Meteor, and these are primarily really the ones that were sent to Sweden, they developed a roller cam follower system. So because of the amount of room in there, they decided to opt for having a fork trucker arm, which is something you see on the Allison V1710 engines to do two of the valves and then the other two actually have independent rockers like that. And roller cam followers are quite a common thing and it certainly is the right answer. These do have a few problems because occasionally the pin can come out. I believe the rollers can seize occasionally. Don't know if Rover came up with this design or not. It was certainly never implemented on the Marlin, but a bit like the Meteorite V8, that engine wasn't, as many people will tell you on the internet, actually developed by Rover. That was a Rolls-Royce development and it was prototyped by Austin Cars before being on to be built by Rover later on. So, it's not impossible that Rolls-Royce came up with this roller cam system. I'm not sure about that. It could have been designed by Rover, but it's very good.

[00:15:28]Anyway, the first serious attempt at combating the Merlin cam follower problem was invented by Harry Walker of Stratford, Ontario in Canada. He marketed them under the lay Merlin fingers with a double R in Merlin for Rolls-R and they're still used very widely today. The idea is to remove the chrome and then machine a slot through the cam follower. Into that slot, you braze a tungsten carbide insert and then grind it into shape. And the insert still has a hole through the middle for the oil feed. Rous aviation in the states also manufacture an FAA approved roller cam follower system which is supplied with the cam shaft.

[00:16:07]The rocker arms themselves being stainless steel, but I'm not quite sure why that is.

[00:16:13]And finally, here's an interesting conversation piece. This is the roller cam follower rocker system from a DMA Benz DV 605. So this is the engine which powered the message BF 109 in World War II. Now what makes this particularly interesting is that the same cam lobe comes around and operates the exhaust valve and then the inlet. You don't see that on very many engines because nearly always you have a separate lobe for the inlet and the exhaust.

[00:16:43]It does limit the designer's scope a little bit, but at the same time it does actually work. Quite a clever little system. It's very compact as well.

[00:16:52]Obviously being an inverted V12, it would have been that way up on the day of ends.

[00:16:58]So once again, thanks for watching and I hope you enjoyed this video. The only thing remaining to get these ignition systems fully functional on the engine will be to rebuild the harnesses and again put them on test with another magneto. But I think all or virtually all of the flexible conduits and the plug connectors themselves definitely are going to have to be replaced because they're mild steel and they have corroded quite a bit. The engine was upside down so there's a bit of damage on that corner. I think we can deal with that. So there's this center harness and then there are two exhaust harnesses for the plugs on the outsides of the engine.

[00:17:33]I think this might be one of the things I'll do next. We've also got quite a few oil lines on the outside of the engine to do. Some of them were already fitted, particularly back here where we were doing the cams and the magneto. So, they needed to put be put in first. There was some larger oil pipes like these. These are the oil return pipes plus the main one from the pressure pump up to the crank case. They all need to be fitted. A lot of them need to be made again because they're mild steel. Doesn't take much corrosion to put a hole in one of these things.

[00:18:05]These are the parts of the fuel pump.

[00:18:07]That's pretty groy, but I've got it all apart. that needs rebuilding. This is the coolant pump. Goes underneath the engine back there. Again, I don't see that really causing too much of an issue. That's going to need building.

[00:18:20]But I think we'll get on with the ignition system, get that completed before we move on to some of this other stuff. So, tune in next time and see what I've been up to. Cheers. Thanks for watching. Please do subscribe to the channel if you enjoy