Kawasaki S3 400 Engine & Gearbox

Hi Everybody

This thread is just a bit of fun.

I’m not a complete SketchUp novice as I use it for my work, but this thread is different as I want to document my attempt to create an accurate ‘fully working’’ model of my old motorcycle engine, using just native SketchUp tools and no plugins

I bought a Kawasaki S3-400 when I was 18 back in 1976. I absolutely loved that bike and I still dream about it, and I recently had the idea of modelling and animating its 3-cylinder 2 stroke engine and gearbox assembly using SketchUp which is probably my way of trying to bring it back to life.

I’ve just managed to get hold of the original maintenance manuals which are packed full of photos and drawings, but while I’m waiting for them to arrive I’ve thought of a couple of things I will definitely need to learn which are:

  • The principles of drawing gears accurately.
  • Any ideas for modelling the crank cases.

Any help will be appreciated.



p.s. I still have the original sales brochure plus a photo proving I used to have hair :grinning:


Try searching YouTube with “Drawing gears with Sketchup”.

That’s a hell of a task, especially without extensions!!
I think @DaveR is the most experienced person over here when it comes to threads and gears. Possibly also crankshaft guru!
He hardly ever sleeps and when he does I think he makes sure that @Box is here to answer your calls.
I personally think the animation is the hardest part. All gears, axles and shafts would have to move synced…
Good Luck with this fun project!!
Hope you will show your progress…

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You really should read up the following thread:

Beautyfull piece of modeling!!

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@kevin58 I wish you luck on your project! I have been working on creating a high-fidelity model of a complex mechanical object (an actual historic Mars spacecraft) for many years now, so I can relate to your vision.

I have modeled a number of gears with SketchUp, including a rate-limiting governor assembly with an escapement mechanism coupled to a small gear train. The following reply includes a 1-minute video demonstration of some animation tech that I developed for it a couple of years ago (the first half shows different short views of the gear action):

Drawing conventional gears is fairly simple if you know the gear specifications. If you want to have curved peaks and valleys on the teeth, then the Circle Intersect extension from @slbaumgartner is very handy to make the curves be tangent to the gear tooth faces.


2-stroke * auto-hot *

Sorry, I forgot to mention your project…
Also a beauty!!

One extension that could help for some of your parts is Tax_Engineering @ Sketchucation:


He provides tools for generating chains, suspension springs/pistons and spur gears amongst other things.

Good luck with your project!

@kevin58 says he wants to model it without extensions!

Good point! Missed that when I skimmed it the first time around.

Forget that I suggested anything!

No worries, if I were to model this I would have welcomed your suggestion.

The OP may chain-ge their tune once they get started. :rofl: Some of the curved shapes of the engine case are begging for curviloft.



Thank you very much for your post.

I really enjoyed reading the thread you linked to and I hope to study your project a lot more going forward. I can see that it’s a labour of love for you and the results I have seen of your work are incredible. I used to work on military aircraft in the early 80s and some of your drawings have a similar look and feel to those hand drawn (pre-cad) drawings I worked on. Also, did I read somewhere that you are happy to share your model? If so, I would love to study it in its full detail on my machine.

Thanks again.

@jean_lemire_1 @endlessfix @db11 @SketchUp3D_de @tweenulzeven

Thanks for your responses - in hindsight I may have been a bit naïve thinking I can do this without plugins and I will definitely check out any that are suggested :+1:

I can already see one of the trickiest parts will be animating the connecting rods because they have one end which rotates in a circular motion, and another which goes straight up and down. I’ve been studying the Fredo6 Animator which is fantastic (and it can produce 4K video at 60fps) but it cannot animate that connecting rod movement – but hopefully I may be able to use it in combination with the method described at Muncaster Oscillator - SketchUp / Gallery - SketchUp Community by @DaveR

Anyway – the original maintenance manuals are due to arrive today so I will be studying them with interest. This whole project feels a bit little like I am stripping the real engine down and rebuilding it which is great :grinning:

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Looks like a good project. If I might make a suggestion, my recommendation would be to use meters as the set modeling units whether you are working with inches or millimeters. This will allow you to create the small details you’ll need.That’s my go to method unless I’m modeling one small part for something that otherwise must be modeled with real world dimensions. In that case I use what has become known as “The Dave Method”.


Hi Kevin, yes my work-in-progress model is freely available via this DropBox link. Note that it is about 260MB (in pre-2021 uncompressed format), so it takes a while to load and needs a lot of memory.

Because of the increasing size of the overall model I develop it as separate sub-systems in separate SKP files. I start a new sub-system with a copy of any relevant existing geometry to which the new sub-system will interface (mounting brackets, surface features, etc.) that may already exist in the master model. Then I develop the sub-system in its SKP file built around the interfacing geometry. When the new sub-system is complete, I copy and paste-in-place the subsystem’s components into the master SKP mode file (which is linked above).


You may be surprised what can be accomplished with @Fredo6’s Animator. I’ve used it a lot. The tricky part for complex motion (besides the overall steep learning curve for the plug-in) is to decompose the motion of a part into rotations and translations. These can be combined simultaneously and/or with time skews to make a huge range of motions possible. You might not be able to get it exact, but probably any bindings or collisions between connected parts can be small enough to not be noticeable (if that is acceptable in the animation).

Thanks Dave - I will definitely do that.

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That’s interesting - I studied some tutorials earlier and couldn’t see how Animator could work for the connecting rods. I then spent some time experimenting with the method shown by @DaveR to reproduce the motion of the connecting rods although I used Outliner rather than Tags to hide the multiple instances. Do you think @Fredo6 Animator could achieve this movement?

Connecting Rod Movement

Connecting Rod Movement 2

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I find that method is generally not the best way to do this. It can make file management more difficult especially as your model’s complexity increases.