30cc Inline Twin 4-stroke Engine based on Westbury's Wallaby

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Eccentric

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Valve Train



I have been working on some odds and ends in the valve train.

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This is a rocker arm cut from 1/4" mild steel. I mount it on a mandrel and machine the sides in the lathe.

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The rocker arms are handed, that is the spigot is longer on one side than the other


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Included in the above photo is the rocker arm pivot bracket.

Below are some shots of the fabrication of the Tappet guides cut from bronze.

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Using a tap in the lathe, quicker and easier than cutting threads.

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A threaded fixture used to cut the hex heads on the tappet guides.


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Finished tappet guides, they will thread into the four yet unthreaded holes in the crankcase



Below is the final operation in the fabrication of a valve guide.
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I am using a split bushing to mount the valve guide in the mill vise to prevent marring and deformation while drilling the side hole.

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Completed valve guide.

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The valve guide is test fit into the head, the small 45 degree valve seat is highlighted. This was cut using the cross slide set to 45 degrees in the same setup used to drill and ream the internal holes.
 

Eccentric

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Location
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Wallaby Valve


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This morning I made a valve for my 4-stroke Wallaby.

The valves are machined from 303 stainless steel. I started with a fail. I had too much stick-out when I tried to cut the retaining ring slot.
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I had success with the slot by cutting it with no stick out at all:
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Then I continued machining in a couple of smaller segments
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This works so much better than the last time I made valves, turning the whole length on centers.

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I tested the quality of the seating of the valves using a technique I learned from Terry Mayhugh. My method is much simpler and less scientific. I pull the vacuum through the rear of the valve cage, past the stem of the valve. I seal the side hole and then take time measurements to see how long it takes to bleed down in different configurations. With the valve held slightly open it takes 3 seconds to bleed down--this is my baseline. This measures the leakage between the cage and the valve stem. Lightly holding the valve closed with my thumb the time jumps to 30 seconds to bleed down, this represents the valve spring holding the valve closed. If I do not press on the valve with my thumb and just rely on the vacuum to seal the valve it takes 15 seconds to bleed down.
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Since I pull the vacuum down past the valve stem, the bleed down times do not mean much in themselves and cannot be compared to times others may get. They do indicate that the valve is sealing against the cage and that there is not a misalignment or major flaw in either the seat or the valve. The quality of the seal really can't be determined by this simple method, just that there is a seal.

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I feel confident that I have the techniques down now to build the balance of the valve cages and valves. Back to it. :cool:
 

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