Another Tamiya Mosquito

[Bstarr3]

As I was working on my Mossie, I was wondering how Tamiya could have left off such a visually prominent feature as the coolant pipes.  Turns out, I was wrong and Tamiya was right.  Seems like their research is as good as their engineering - if something isn't fitting right on a Tamiya kit, you're doing something wrong!

[gwana]

Well, there should still be something connecting the coolant tank to the heads, and the overflow is missing, but they have all the stubs on the tank. The engine sprues are obviously shared amongst other kits. They cast so many other small parts, I'm not sure why they left out the 2 fittings. I'll have to see if I can scratch build something tiny enough that's believable. I think a bit of card and rod will do fine, plus an ignition harness. I'm not going to bother with the ones that are hidden by the exhausts.

[Bstarr3]

I endorse this decision. The outside ignition harnesses are invisible with the exhausts in place, unless you're looking from underneath

[Gerhard]

Here is a clue:

 

[gwana]

Well, yes. I looked at that video and the Eduard instructions for inspiration. But in this case, I think Eduard is incorrect. The engine they model is a representation of a Merlin XX or 21, but it is not visually the same as a 25, or even a 23. The production on these engines was fluid, and I'm not sure many people know or care about the differences. I only got interested because I could see that the pictures I found showed completely different plumbing and I wanted to get to the bottom of it. It's a real rabbit hole since there aren't a whole lot of survivors, and very few pictures of the TOP of a Mosquito engine in situ.

 

Forward the video to 3:03. The pipes being installed on the top of the engine cannot be found on any Merlin 23 or 25 that I can find images of. They are a distinctive feature on the 21 and prior, which was not installed in the MkVI Mosquito. Other kits that depict a MkII or a MkIV may have the Merlin 21. If my production data is correct, it lists every single serial number Mosquito produced, and every MkVI is listed with the 23 or 25.

 

Tamiya's own reference material in the box shows a Merlin 23 or 25 engine in photos of the admittedly over-restored example. I've found examples of period-crashed and under-construction Mossies on the web with engines that do not look like Eduard's example (and some that do, but not MkVI's). That Eduard engine was more common in the Lancaster, Halifax, Beaufighter, and very early spits. I think most of the model producers have a "Merlin" already molded and they just throw it at whatever. The later engine, like the 61, has a completely different supercharger housing and it's obvious, so a later Spitfire kit like a MkIX will have the proper engine and will not have the water pipes, but I think the changes between the 21/23/25 were so esoteric that they just didn't bother. The 25 variant isn't really found in anything else but the Lancaster and the York, and as yet there's nothing in 1/32. So throw what you've got at it. Even if Tamiya comes out with other Mossie variants in the future, they're not likely to model 4-7 different engines to make all the variants correct. Tamiya themselves may have run into the same variable and just decided to model it without the topside plumbing. The kit engine isn't wrong, it's just missing the key features that would differentiate a 21 from a 25. It's generic. Eduard's is not.

 

So, yes, the Eduard engine is A possible Mosquito engine, and a fine model in its own right, but I don't think it's the correct engine for the MkVI of the Tamiya kit. If I'm going to scratchbuild extra detail, it might as well be correct (not to mention the 25 is easier to do). If anyone has a photo of a confirmed Merlin 23 or 25 with the external water pipes on top, I'd love to see it. I think the Eduard engine is a bit more interesting visually, but I just don't think it belongs in this airplane. I have no problem with modelers putting it in there if they want to, I just wanted to satisfy my own curiosity and I couldn't find a definitive answer anywhere.

[Elger]

This flow chart is reproduced in Donald Nijboer's Graphic War and shows how the different Merlin variants are related:

 

 

Unfortunately, the image is just too small to read the print that explains the differences between the sub-series (21, 23, 25, etc). It seems to indicate that the main difference between these sub types is at the bottom of the compressor - but other differences are also indicated.

 

 

I wonder if anyone has a copy of the original?

Edited March 31, 2018 by Elger

[gwana]

Well, I'm still slogging along on this. Having succumbed to detail-itis, I've obtained a set of the Eduard engines from a member here, and I'm beginning my foray into resin. Pretty sure I'm going to try to modify their engines into Merlin 23's. If I don't go blind first. Individual spark plugs... It's like trying to put a leash on an ant.