Building the Lynx15

[JimSvarv]

Maybe run it from the crank as waste spark if it would have any advantage.

 

[Vietti]

You've probably noticed the sensor can be removed from the plastic sleeve. It is very small "3/16x3/16" and can be put where needed, pay attention to which side faces magnet. Good luck

 

[Alan's Home Workshop]

Thanks for the helpful suggestions. It hadn't occurred to me that fixing the sensor would prevent adjusting the timing while the engine was running. This may be an advantage of the Nemett rear mounted design as it appears to allow the sensor housing to be rotated. Unfortunately, running from the crank with a lost spark system like the Webster engine isn't possible here as the crank is single sided with no rear protrusion. Also, the valve timing has to be set by rotating the camshaft pulley, so the option of mounting the magnet in the pulley is not on the table in this case. Accepting that I will only be able to statically set the ignition timing, making a cambox lid with integrated sensor mount is looking like the best option. I think it will need to be 3D printed as the instructions urge using an insulated socket, and shaping a tapered socket with a "D" profile with files would be quite tedious. If I do 3D print, I would use PLA-CF filament. This is pretty tough stuff with a softening temperature a bit higher than PLA and the mounting will not be subject to any external bending force.

 

[Eccentric]

The Prefered method is to have a timing ring attached to the Camshaft pulley with a grub screw. This can be made of Aluminum or even 3D Printed higher temp Plastic (PLA-PC polycarbonite or nylon-CF are good choices). A small 3mm round by 2mm deep magnet is bonded into this ring as shown below. The Grub screw allows you to rotate the slip ring and adjust the ignition timing. Marks on both the timing slip ring and the back of the camshaft pulley would help perform timing and insure at a glance that it has not slipped. The PCB has a three pin connector to the ignition module and contains a hall sensor and pullup resistor like the widely available hall sensor boards available for prototyping. As stated above it is important to make cure the correct side of the magnet points outward. The PCB can be any prototyping board cut to size.

Looking good Alan!

 

[Motorman1946]

For me Alan, I would say option 3 is the cleanest, as it also allows adjustments more safely to the pickup. I would also consider fitting the camshaft with a short extension out the back of the cam box and fitting the disc/pickup there.
Chris

 

[Alan's Home Workshop]

 

[Alan's Home Workshop]

 

[JimSvarv]

Thanks for the series, have been fun to watch both the success and failures.
Hope to see a running video soon! But I guess it's up to the postman when it happens.

 

[Alan's Home Workshop]

Thanks for the series, have been fun to watch both the success and failures.
Hope to see a running video soon! But I guess it's up to the postman when it happens.

Thanks Jim.

 

[Alan's Home Workshop]

 

[Eccentric]

Congratulations Alan. You have done an exceptionally thorough job in your build and troubleshooting of the Lynx15. It was great fun seeing the detailed test setups and special tooling you used to build and validate the engine. I especially enjoyed the setups for validating the valve and ignition timing. It's incredibly satisfying to see an engine I designed, built, and successfully run by someone else. You did a great job as the "guinea pig," building to my plans and helping me troubleshoot the design. You provided invaluable feedback, found several errors in the prints, and helped me redesign a couple of parts to improve manufacturability. For example, your tip for easing the alignment of the cylinder to the crankcase was brilliant. There's nothing quite like seeing an engine you've built from scratch in your own workshop, successfully running. And you've done it! Congratulations again.

Greg

 

[JimSvarv]

Congrats on the runner!
Sounds and looks great.

Excited to see what your next project will be.

 

[Alan's Home Workshop]

Congratulations Alan. You have done an exceptionally thorough job in your build and troubleshooting of the Lynx15. It was great fun seeing the detailed test setups and special tooling you used to build and validate the engine. I especially enjoyed the setups for validating the valve and ignition timing. It's incredibly satisfying to see an engine I designed, built, and successfully run by someone else. You did a great job as the "guinea pig," building to my plans and helping me troubleshoot the design. You provided invaluable feedback, found several errors in the prints, and helped me redesign a couple of parts to improve manufacturability. For example, your tip for easing the alignment of the cylinder to the crankcase was brilliant. There's nothing quite like seeing an engine you've built from scratch in your own workshop, successfully running. And you've done it! Congratulations again.

Greg

Thanks Greg. I knew nothing about camshafts when I started this project, but with your patient support I was able to successfully make and test one for the Lynx. Your drawings are clear, well laid out and quite comprehensive. I am a self taught amateur and whilst some of the machining required a bit thought, it was all achievable with a good work sequence.
Not sure whether I'll build another engine, but I wouldn't hesitate to recommend your Lynx15 to other builders looking for an interesting project.
Cheers.

 

[Alan's Home Workshop]

Congrats on the runner!
Sounds and looks great.

Excited to see what your next project will be.

Thanks Jim.

 

[Motorman1946]

Nice work Alan - must be all very satisfying and rewarding for you, especially when you got it to run.

And do build another engine.......!!!!

Chris

 

[Wp356]

Enjoyed the video Alan. Hopefully this will serve as inspiration to others to make a 4 stroke. And yes, you always find the part you lost after a new one is made! And you can not believe the missing part traveled that far from the bench. Looking forward to you next project.
Wes

 

[Alan's Home Workshop]

Quick update on the Lynx15. Compression has gone up as the valves bed in and the engine is now a bit hard to start.
Not complaining though - its a nice problem to have

 

[Eccentric]

Alan,
Now you need to machine an electric starter for your Lynx15.
Greg

 

[petertha]

Congrats Alan! @Alan's Home Workshop In the YouTube part-13 where you build the hall effect housing

- can you confirm the magnet disc is made from aluminum? I always assumed it needed to be steel, but maybe that pertains to multi-cylinder engines which have topside 'distributer' components (rotor, contactor, wires...) & steel helps block magnetic forces getting up in there? ie. where as you have a single ignition wire coming from the module to the plug

- I think you mentioned 1/8" diameter magnet? What was the thickness? Was that in your S/S kit or you just sourced?

- what is the distance between magnet & sensor and can you elaborate on the black bit holding the sensor/wire assembly in place. is that glued into the aluminum housing side tube?

Maybe I missed it but
- what carb are you using
- what fuel were you running
- are those 'regular' (assume RCEXL 1/4-32) type plugs or the Iridium ones?

 

[Alan's Home Workshop]

Thanks @petertha.

Timing disk is made from aluminium 20mm ϕ x 5 thick.
Magnet is 1/8"ϕ x 1/8" long and 2 were included with the kit. I reamed a 1/8" hole in the disk and pushed the magnet in from the sensor side to just below the surface. Then I staked that edge of the hole and filled the hole on reverse side with epoxy cement.
Clearance between front face of timing disk and the reading face of the sensor is ~1mm.

The black bit (far right) is a moulded sleeve supplied with the sensor. The actual sensor is slid into this sleeve and locked in with a wedging piece. Second from right is a 3d printed adapter with an internal taper and an indexing flat. These features combine to firmly hold the sensor in correct alignment. Third from right is an aluminium socket that is a light press fit into the aluminium timing disk cover. The 3d printed adapter is permanently fixed into this aluminium socket with superglue.

Carbie is a Traxxas Pro.15

I started with 25:1 95 (Aus) octane unleaded and two stroke oil. Over several sessions, changed to 50:1 with no apparent issues. Added a couple of squirts of oil to the crankcase and noticed some oil mist coming up the breather. I assumed this indicated that oil was being splashed up under the piston and this gave me confidence to try running with no oil added to the fuel - which seems to be fine. The engine runs surprisingly cool considering there is no fan - possibly the mixture should be leaned out more.

There is nothing special about the 1/4" 32tpi plug - it was just the cheapest one I could find.

Hopefully that covers all your questions.
Cheers.