Hi All,
Sorry for the lack of updates on this project. Things have been progressing slowly in the background. Due to a combination of being very busy running my main business and struggling with a few technical challenges progress has been a lot slower than I hoped but I have a small update for you.
We had some issues with the 3D printed cases, dimensionally they seemed to be warped. it's hard to show this but in certain areas, the cases tended to sag. Round features were the worst affected, becoming oval but also flat features like the mounts, were not dimensionally accurate enough adding a lot of additional complications to the case machining. The biggest challenge was that this sagging/warping was not consistent across all the cases we had 3D printed.
In addition, the material was prooving somewhat brittle and liable to cracking in thin areas. There are limited material options when printing aluminum.
Not all was lost though, as I have tried to make clear, we are developing this engine and unless we can make it competitive and reliable we won't bring it to market so we expect these challenges and that there would be iterations and changes as we developed this engine.
The early tests showed some areas that needed some design alterations, I will list them below
1. Additional material for head screws (Pretty self-explanatory, they are only 2.5mm cap heads and we stripped a few so have added some additional material. Additionally, we may look at changing this to something like a UNC thread or something with a courser thread than 2.5mm. (We are about to test some options)
2. We changed the exhaust outlet design. The design we had worked well but meant there was almost no ability to tweak the angle of the exhaust. We soon realised that not everyone has a model designed with a perfectly straight line for the pipe to follow and it's fairly normal to have a couple of degrees of movement. We basically copied the Novarossi design. It's proven and it works well and everyone seems to have Novarossi Exhaust rubbers. (Why reinvent the wheel?) - We did decide to keep the spring clip mounts though as it is by far the best way to secure a pipe/manifold to the engine.
3. Some alterations to the front motor mounts - This was mostly from feedback from some of the tether hydro guys as they direct mount the engine to the sides of the hull. Squaring them off enables a more secure mounting.
4. Some small geometry changes to the internals of the case. This is to smooth out and improve flow to the ports
To solve the issues related to 3D printing we are now using a new process where the mold and core are 3D printed and then the cases are cast in a more conventional way. This is a more expensive process for prototyping but should be more cost-effective when we get to production quantities.
This new process is much more dimensionally accurate and has solved all the warping/sagging issues as far as we can tell. In addition, this has allowed us to use more tried and tested materials for casting. We have opted for a heat-treated LM25 - This is a nice easy machining aluminum but pretty much offers the best in terms of strength and is typically used by companies such as Cosworth for engine case and head castings.
See the pictures below for comparisons. In the future, castings will be sand/glass/bead blasted to give a more uniform matt textured finish. We will see what works best but for the prototypes, we will test them as is
One of the areas that we could really benefit from some help with is advice on low volume crankshaft grinding. We have farmed some out but are getting some very inconsistent results so we are looking to bring it in-house.
I want to avoid doing it on a lathe with a tool post grinder if possible and would be more interested in buying a cylindrical grinder and setting it up for this job specifically. If anyone has any experience of a setup like this I would love some advice.
We have also made some alterations to the induction system but they are all very minor to help smooth the flow path as well as add some additional material where we think we may need it. We have also tweaked things to improve manufacturability that should lead to slightly fast and more cost-effective production
Once we have the crankshaft issues solved we hope to have some engines running - I will post some videos as soon as I can.
Thanks for sticking with us on this journey.
Ricky
