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Thread: Rebuilding the Q-ship; a 1964 Harley Davidson Sportster

  1. #31
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    Default Part 5 - Pistons; Axtell and Dytch Vintage pistons

    When you flip the piston over, you can see how different the pin bosses look and how the “heat line” is different. In this case, the dark brown is limited to the center of the crown and becomes progressively lighter as we move down towards the oil ring. However, unlike the stock piston, it is clear high temperature oil isn’t just escaping – it is traveling down the skirt and cooling the whole thing. Good. Take a look at the oil holes . . . notice how they are drilled.

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  2. #32
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    Default Part 5 -- Pistons; Dytch and Axtell

    Here’s the fun part; these pistons and their pins weight 492.5 grams. That is almost 10 grams lighter than a stock piston – which is ¼” smaller in diameter! Part of what makes them so light is that they are hollow over the pin bosses. Most Dytch pistons are exactly the same.

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  3. #33
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    Default Part 5 -- Pistons; Vintage Forged Piston sectional

    We’ll jump to the side for a moment and look at early forged stroker pistons. These came in two variety, 2 ring and 3 ring pistons. Three ring pistons were for stock to short strokers and two rings were for long strokes. The major difference as seen in these sections is the compression height. The pin is moved towards the crown to make up for the extra stroke length. This allows you to run minimal or no stroker plates depending on the application and build parameters. These pistons are light and tough – and have been unavailable for some 40 years. However, you can copy them if ordering custom pistons.

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  4. #34
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    Default Part 5 - Pistons; S&S Stroker Pistons

    Next up is the venerable S&S stroker piston. At one time, S&S made these for 900s and 1000s. Today, only 1000s are available and in only one compression height. This particular piston is a TRW forging and when you flip it over, you can again see a very distinctive heat pattern on the crown.

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    Like the stock piston we looked at, it is clear the heat path terminates at the oil ring. When you look at the oil ring land, you’ll see it is slotted, not drilled. Current S&S pistons come drilled to avoid cracking at the end of those slots.

  5. #35
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    Default Part 5 -- Pistons; S&S stroker piston

    When put on a common wrist pin, the difference in compression height becomes clear. These pistons are also quite light. Together with their wrist pin, but without rings, they weigh 446.1 grams – or a whopping 55 grams less than a stock piston. That is a substantial amount of weight savings.

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    Stock 900 Left; S&S Right

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    stock 900 left, Axtell in the middle, S&S on the right

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    S&S foreground, Axtell in the middle, and stock 900 in the back

  6. #36
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    Default Part 5 -- Pistons; JE 900 standard bore stoker piston

    We also happen to have acquired a set of JE stroker pistons for a 900. These are .050 overbores and have a compression height sized for 4-5/8 strokes. These pistons were run for a short period and so there is not a tell-tale heat mark to read. When we examine the total piston, some traits become clear.

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    S&S stroker piston left and JE 900 stroker piston right

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    Stock 900 left; Axtell 3.25 middle left; S&S stroker middle right; and JE 900 stroker right

    This is a 3 ring piston and rather than using a notched pin button to support the oil ring; the JE piston uses short pins held in place with circlips. This means a high quality, flexible oil ring must be used to avoid issues. The oil ring lands are drilled and the top ring land is substantial.

    When placed on a common pin, you can easily see how much “shorter” the piston is compared to stock. In essence, the top ring on the stroker piston is at the same level as the oil ring on a stock piston. These pistons are lovely, but heavy. They weigh in at 481.8 grams with pin, but without rings. This is almost 20 grams lighter than stock – but the weight is almost all in the thick crown. This means the piston will rock quite a bit in the bore and wear rings/ring lands more quickly than a lighter piston. Remember what we said about compromises?

  7. #37
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    Default Part 5 -- Pistons; Venolia Custom

    For comparison, here is a custom Venolia piston for a 3-3/8 bore and what appears to be a 5 inch stroke. These are brand new and never run. Notice how “light” they appear on the underside compared to the JE pistons. They also have drilled oil ring lands and use a captured pin without an oil ring support.

    They feel great in hand because they are well balanced with even weight distribution from crown to skirt. In total, they weigh 509.2 grams with pin, but without rings. This is 8 grams more than our standard piston – despite this Venolia being 3/8th of an inch larger in diameter.

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    Stock 900 left; Venolia Right

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    JE 900 stroker piston left; Venolia Right

  8. #38
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    Default Part 5 -- Pistons; Ring choices

    While we are talking stroker pistons, let’s take a quick second to talk about piston rings. Because of the sheer abuse these pistons will take, we really don’t want to mess around with too many exotic things. Chrome faced rings, moly coated rings, and unusual profiles are not going to buy us anything but a lighter wallet. Instead, we want one of two types of compression rings: Hastings “square” profiled rings – which for all intents and purposes are “stock” rings or total seal rings. Both are plain rings and work very well.

    Oil rings present more choices and challenges. Strokers already pass more oil than a stock bike. If you want a bike that uses no oil, don’t build a stroker. We want flexible oil control rings that can deal with extreme piston rocking, elevated temperatures, and a heavy handed rider.


    HD shipped ironheads with one-piece “ladder” style oil control rings clear into the late 1970s. These rings are next to worthless. They will polish a bore nearly smooth and pass more oil than just about any other style of ring. They also are not terribly flexible and can fracture with heavy piston rock. In short – don’t use them for anything other than decoration.


    Three-piece oil control rings come in a couple of different varieties. While they “look” the same on casual observation, there are subtle differences in the overall thickness of the rings and the style of expander. One style uses relatively thick rings and a rigid expander. The other uses thinner rings with a more flexible expander that utilizes two expander rings. This style ring conforms to the bore better and is more tolerant of flex/rocking. Whenever possible, we want the most flexible style oil rings in a stroker.

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