Kiwi piston dimensions

Mike Ginn · Mar 20, 2023

Guys. I have completed the machining of the piston for the Kiwi MK2 from solid. All is well and I have left the length as 1 1/8inch which is longer than needed.

My question is "how far from the top of the cylinder should the top of the piston be". This obviously affects the compression and Westbury makes a reference to this for the cylinder machining. The engine is only intended for occasional use and will not be used to drive anything.

I would appreciate any guidance

Many thanks

Mike

Vietti · Mar 20, 2023

If it were me I'd leave it full height and shorten if need be. Leave ring grooves lower on the piston in case it needs lowering. I tend to think slightly higher compression ratios are good in a model as they seem to make idling lower and more consistent, there are limits of course.

Mike Ginn · Mar 20, 2023

Thanks for that reply. As an update I found I had the GA which shows the top of the piston flush with the cylinder liner top so I guess that is what I will do.

I cut up my drawings and scan each part and print on A4 (letter) size. During this process I "lost" the GA but now found!

Thanks

Mike

jrslogs52 · Mar 20, 2023

Hello Mike,
My drawings are in inch and the piston top is flush with the top of cylinder liner.
Hope this helps,
John

Mike Ginn · Sep 7, 2024

Guys
Some advice please. I have finished (well almost) my KIWI and need to get it running. Using an electric drill it will fire but it is not sustained. I am using Coleman fuel. I have removed the float and valve and am using the float chamber as the fuel tank (I have blocked the normal fuel inlet at the base). I notice that the engine usually fires when the fuel is about level with the outlet to the carb and that maybe is a clue. I could rig up a fuel tank and set-up the float to keep the fuel level with the outlet if that is the solution.
I have a general lack of experience of running this type of engine so any thoughts would be appreciated.
Many thanks
Mike

Mike Ginn · Wednesday at 9:10 AM

Hi Guys
I have finished the Kiwi and mounted it on a base. A few things to note. The round device under the carb is the flywheel extractor - the flywheel has a taper sleeve and the extractor screws into the flywheel with a central screw to extract. The contacts design was taken from the Wyvern, also a Westbury model. The head, crank case and back end of the crank has "O" ring seals. O rings are also used in the carb to give a smooth lever motion. All fixings are BA with reduced heads.
I still have to get it to run. I think I will need to use a vapour system since the float chamber doesn't work very well.
Many thanks to those who have offered help over the past year.
Now for the next model!
Mike

Vietti · Wednesday at 11:25 AM

Mike,

Early on I made a Wall 30 which is very similar to your ETW designed engine. It was my first engine. Anyway, I never got it to run properly on three different home made carbs of various designs. I finally fitted an OS model airplane carb and never looked back. I think the only thing harder in building a model IC engine than getting the valves to seat is making a carb that works properly.

Mike Ginn · Wednesday at 12:20 PM

Yes I agree. My main aim (and its up for debate) was to make a presentable model to a good standard and if it didn't run I could live with that! Maybe controversial to the purest I guess. I would need to strip the model down and check everything especially the timing and this would likely damage the finish. A commercial carb would make a difference but look completely out of place. Maybe after I have finished admiring my work (!) I might investigate the various alternatives but for now it will sit on my study shelf with the other models.
Mike

Vietti · Wednesday at 4:58 PM

Static models are more common than you might think! You could try a commercial carb and narrow down the reasons why it doesn't run. Also I fitted mine with a one way breather where the drain plug goes. The air and oil travel to a vented reservoir and the oil is fed back into the engine-works very well.

Mike Ginn · Wednesday at 5:38 PM

The timing is not correct and it seems to be too stiff. I am using rings which are correctly sized and gapped on a good smooth parallel cylinder. I know the big end bearing is free running and the crank bearings are in-line. So something is not correct which will require a complete strip-down. I pinned the 2 halfs of the crank case and the cylinder/crank case surface was machined using a through drill rod on V blocks and I can't measure any miss alignment error.
I think I will return to the Kiwi after the Christmas festivities and in the mean time start on another engine.
Mike

Kiwi piston dimensions

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