Honda GX35 Electric Starter

Electric starter for Honda GX35 engine

Uses steel gears, 625 bearings, 5mm steel axles, 5mm bore hex adaptors, an electric motor with a 5 mm shaft (D-shaft preferable), 3D-printed parts, fasteners, and a one-way bearing.

Steel Gears (Modulus 1):

Pinion (19T, 20T, 21T): https://www.amazon.com/dp/B09FGCXPY5?ref=ppx_yo2ov_dt_b_fed_asin_title

Spur (48T x2): https://www.amazon.com/dp/B0FHQF9N1H?ref=ppx_yo2ov_dt_b_fed_asin_title

625 Bearings (any will do):

https://www.amazon.com/dp/B0GCZBYBSD?ref=ppx_yo2ov_dt_b_fed_asin_title

5mm Steel Axles (any will do, at least 100mm):

https://www.amazon.com/dp/B01B27MJC6?ref=ppx_yo2ov_dt_b_fed_asin_title

Hex adaptors:

https://www.amazon.com/dp/B08M379TCT?ref=ppx_yo2ov_dt_b_fed_asin_title

One-way Bearing (any CSK17PP bearing should work): https://www.amazon.com/dp/B07PBQD947?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

Shaft Collars (any will do):

https://www.amazon.com/dp/B0GWKB7WDQ?ref=ppx_yo2ov_dt_b_fed_asin_title

Motor:

I pulled mine off of my old pool vacuum, but any 775 motor or sufficiently fast electric motor with a 5mm shaft (preferably D-shaft) should suffice; you may need to adjust the position of the mounting holes in the base plate (I can remodel it and upload it if you give me the distance of the mounting holes; let me know)

You will also need 400-grit sandpaper and a coarser grit, perhaps 200, a rubber mallet, super glue, and some grease; I used Parktool Polylube 1000 because that's what I had on hand.

Assorted Fasteners:

-1/4in-20 hex nut (3x)

-1/4in-20 x 1.5 hex cap screw (2x)

-M4 x 10mm screw (4x)

-M4 nut (9x)

-M4 x 20mm screw (5x)

-M4 x 25mm (2x)

-M4 washer (x6)

-Short screw that holds on the GX35 recoil starter (2x)

Link to All Part Files: https://www.thingiverse.com/thing:7380921

PLA or stronger (I did mine in PLA and it works fine):

>20% infill, 3 walls

-shell_V2.9.stl (print with hollow inside facing up)

-cover_V2.8.stl (print with hollow inside facing down)

-Base_Plate_V2.4.stl (print with hex inset side facing down)

-Washer_V2.0.stl (2x)

PETG or stronger (I did mine in PETG):

>45% infill, 3 walls

-Hex_adaptor_V1.2.stl

-E_Adaptor.stl (print with hex inset side facing up)

-I_Adaptor.stl

Don't forget to remove the supports!

I put my 5mm steel axles into the chuck of my drill and sanded them down while spinning them so they were even, because they weren't fitting in my bearings. Depending on your bearings and axles, you may need to sand them down a little or a lot. They need to slide into the bearings with little to no wiggle room.

Use a rubber mallet and press two bearings into the base plate and 4 into the shell. They should protrude out around 1mm, so don't worry if a little sticks out; try to get them fully seated and level. Grab two M4 nuts and super glue them into the shell. There should be two hex insets beside the center bearing insets.

Use super glue to stick two M4 nuts into the upper two hex-inset holes in the base plate. We will not be using the two insets in the center. Grab the two M5 bolts that came with the Honda engine; I believe they should be the shortest-sized ones. Screw the screw through the top of the base plate, the top being the side with the bearing insets, which should be facing away from the engine, through the two plastic washers you printed, with their flat sides facing the base plate, and into the two side-by-side mounting holes in the engine. The base plate should be securely held in place, with little wiggle.

Depending on the motor you choose, you may need slightly longer or shorter screws to hold it in place. Grab two M4 washers and two M4 x 10mm screws, and put them in the motor mounting holes at the bottom of the base plate. Screw through the base plate and into the motor to secure it. They should set in nicely and not protrude out of the top of the base plate too much. For reference, the centers of the two mounting holes for my motor were spaced 29mm apart (center-to-center).

Take five M4 nuts and press them into the "E Adaptor" part you printed earlier. Then take one of the 48T steel gears and place it onto the plastic piece, having the side with the five round holes fit into the cavity in the gear. Screws five M4 x 20mm screws through the steel gear and into the plastic part until everything is very solid. Then take your one-way bearing and press it into the cavity in the plastic part, being sure to align the keyway so it's locked in place. Orientation matters here. The housing, with the steel gear side facing you, will rotate clockwise and spin the engine, so you can put your fingers into the center of the bearing and rotate the outside clockwise. If the inside locks up and spins with the outside, that is the correct orientation. You can test this by pushing the "I Adaptor" into the center of the adaptor and placing it on the crankshaft nut. Try gripping the outside of the bearing and rotating it clockwise. The engine's flywheel should rotate, too. If so, leave the bearing on the engine and push the steel gear and adaptor assembly onto it, which is the correct orientation. Don't forget to seat the bearing fully. It will protrude slightly and seat the plastic piece inside the bearing, too, but not too tightly.

Place one of the hex adaptors onto the motor shaft and tighten the two set screws (tighten them, but don't strip them). Attach another hex adaptor onto one of the axles and tighten both set screws. Use the hex adaptor you printed earlier and connect the hex adaptors, essentially extending the motor's axle. If it's a tight fit, you can remove the hex adaptors and pound them into the plastic part while on a stable surface, then reattach the assembly to the motor and bare axle afterwards.

Place the remaining two axles into the bearings in the base plate, and slide two shaft collars onto them. Push the axles in until they bottom out, hitting the plastic of the base plate behind the bearings. Then, back them out slightly, slide the shaft collar until it touches the base plate's bearing, and tighten. This ensures that the axles are far in, but not rubbing against the plastic, which could cause friction and the plastic to melt.

Slide the 19mm gear onto the axle attached to the motor. Slide it all the way down and secure it. Then slide on a 1/4in-20 hex nut until it touches the gear and superglue it in place so it doesn't spin. The nut will act as a spacer because my shaft collars were slightly too wide and caused the shell to bulge when screwed on. Ideally, you could 3d print a washer or something similar.

The 19T gear goes on axle 1, the motor axle, as mentioned earlier. Axle 2, the axle above axle 1, will have a 21T gear as an idler gear. This gear should line up with the 19T gear on axle 1. Axle 3 will have a 20T pinion gear and the other 48T spur gear. The 20T gear meshes with the 48T gear on axle 4; make sure you push axle 4 firmly when aligning axle 3's 20T gear, since it tends to sag currently without support. The 48T gear on axle 3 will mesh with the other two gears on axles 1 and 2. Make sure to properly tighten the set screws, as we don't want the gears to slide around on the axles.

This is slightly tricky. Slide a shaft collar onto axles 2, 3, and 4 after the gears have been aligned and secured. You will want to line their outer edge up with axle 1's nut to start. The goal is to have a microscopic amount of wiggle room after the shell has been placed on; that way, there is minimal friction from the bearings sandwiching the axles. It will take some trial and error, but I find it helpful to push in the two 1/4in-20 x 1.5 hex cap screws into the shell until they are fully set in and use them to line up the shell with the base plate when testing the shaft collars' placement for added accuracy.

Feel free to test out the gears and see how they spin. With the shell on the base plate and the two bolts pressed into their insets at the bottom of the shell, try rotating axle 1 CCW to see if the gears spin smoothly. If you get a strong enough grip, you might be able to rotate it CW and see the flywheel move, too. After you have confirmed the shaft collar placement and fit of the gears and parts, apply grease onto all the teeth of the gears. Try not to overgrease, but it shouldn't be an issue since the entire system is enclosed.

Grab two M4 washers and both M4 x 25mm screws and place them into the two holes at the top of the shell. Gently screw them in so as not to push out the inset hex nuts before the threads grab onto them. Tighten until snug, then about a 1/2 turn more. Use a wrench to tighten the two 1/4in-20 hex nuts onto the bolts from the back of the base plate. The whole system should be feeling sturdy.

The last step, after wiring up the motor and testing the system, will be to cut the axles nearly flush with the front of the shell, leaving about 1-2 mm protruding. You don't need to worry about cleaning up the cuts, since they will not interfere with the system. Take your remaining two M4 washers and two M4 x 10mm screws and screw the cover onto the front of the shell, enclosing the whole system.

I haven't gotten around to cutting my axles yet, so I don't have any images other than the render attached, but I plan to use an angle grinder to cut off the extra sections of the steel axles.

If the engine is spinning too fast, you can use a motor controller to decrease the speed of your motor, although I doubt that will be an issue. Please contact me with any suggestions or feedback, as I am actively revising and improving the system!