Starter stall: It's that annoying sound emanating from your motorcycle, and you've heard it before -- you hit the starter button and hear arrrrrra. You think to yourself, is my battery going belly-up? Or maybe it's the starter. You let off the button, and you wait a second to try it again; this time the engine rotates slowly at first, then gets up to speed before firing. You let out a sigh of relief and wonder what you can do to eliminate this problem.
Just what causes starter stall? There are different elements that combine to put serious strain on your starting system. Things like getting the engine components moving quickly and, of course, compression.
Something can be done to help alleviate the last one, compression. That's the reason for the noise you hear as your starter stalls. The engine parts start to rotate, but then slow down as the compression begins to build.
Compression is one of the main items contributing to battery and starter failure; and compounding this problem is the proliferation of high compression, big inch engines.
A compression release (they are installed in pairs, one per head) is a small valve which threads into the head from the outside. At the bottom of its threaded mounting port is a 0.125-inch hole that enters the combustion chamber near the spark plug hole.
Inside the release is a valve and seat arrangement similar to the intake and exhaust valves in your engine. An internal spring in the release is calibrated to close the valve after the initial compression stroke of the piston is completed.
With a cost of around 75 bucks for a set (plus machining, gaskets, and assembly), some serious consideration would be in order when you look at the cost of battery and starter replacement.
While installation is pretty straightforward, it will vary slightly from engine to engine. It would be wise to consult your local shop or dealer before deciding to go ahead.
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Installation of the releases requires removal of the heads, which Eric Bennett of Bennett'
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Here, we got a good look at the compression release in the closed or operating position. W
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When the compression release is open, pressure can flow through the valve. This allows the
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Just as Bennett finished removing the heads, his old pal and chopper builder, Kelly McKern
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Next, Kelly clamped a dial indicator to the mill's spindle. This allowed him to rotate the
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In order from left to right, all the tools needed to make certain the compression release
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McKernan began with a 1/2-inch end mill to create a flat surface for...
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...a center drill to start a hole.
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From there, a 1/8-inch twist drill spinning at 1000 rpm was used to drill a hole approxima
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Next up was a 3/4-inch end mill used to create a smooth surface for the sealing washer to
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A 0.354-inch tap drill is used to drill a 0.650-inch deep hole for introduction of a M10X1
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Before the tap was introduced to the hole, McKernan gently broke the edges at the top of t
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The tap was started from a position in the chuck...
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From there, a T-handle was used to be certain the threads made it all the way down to the
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Before the head was separated from the angle plate, McKernan test fit the compression rele
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This is what the finished head looks like from the top.
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And this is what it looks like from the combustion chamber. As you can see, the hole is sm
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With both heads modified, Bennett wasted no time reassembling the top end.
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Just to prove how much of a difference the compression releases make, we asked Bennett to
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A second reading was taken while the compression release was held open. This time a maximu
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All buttoned up and ready to run. Just depress the cap on the release before you start the