Rebuilding the Q-ship; a 1964 Harley Davidson Sportster

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Even more cylinder musings

The last set of cylinders we are examining are late Dytch/early Axtell cylinders. Long story made short, Axtell took over Dytch. They continued offering the earlier products, but also introduced even bigger bores. These are also cast in 60,000 psi grey iron by MOCASCO.

Notice however, these cylinders have much thicker cylinder bases than stock, no fire ring, and 3/8 head bolts. These cylinders can be bored/sleeved with relative ease. They are also much longer than stock at 5.490 inches – meaning they can accommodate strokes approaching 5 inches. These are truly life-time buy cylinders and you are likely to outlive them.

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More cylinder musings

In the early 60s, Dytch upped their game and introduced 60,000 psi grey iron cylinders. The overall castings are heavier than stock 900 castings, but not so much so that they are immediately noticeable. These cylinders were also cast by MOCASCO and are easy to spot by the “60” cast on them – and usually because they have thicker fins and cylinder bases. These cylinders were available in 3-3/16 or 3-1/4 with the latter being the most popular option. Many of these cylinders also have 3/8 instead of 7/16 head bolts. This allows for slightly more clamping surface at the head gasket to help prevent blown gaskets.

Cylinder lengths were customizable and it is not unusual to find cylinders that are over-length. This allows the cylinder to be mounted directly without a stroker plate in some applications. These cylinders are also .060 longer than stock at 5.390 inches. This means that we may not need to use stroker plates depending on our stroke length. You can also see the major difference in the fire ring’s outer diameter. This means the cylinder heads must be counter-bored to suit.

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Above: notice the smaller head bolts . . .

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Above: measuring the OD of the fire ring on a brand new cylinder

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Above: measuring the OD of the Dytch big bore cylinder -- notice the difference?

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Above: to accomodate the big bore cylinders; both the heads and the engine cases must be suitably bored. Please ignore the "egging" of the head bolt holes -- we'll be fixing that poor piece of machine work later in the series.

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Above: the "over length" of the cylinder -- this extra length means we should not need stroker plates for the motor Chuck is planning.

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Cylinder Musings

At this point, we’ve decided on our pistons and we have a choice of cylinders from stock to exotic. So, let’s talk briefly about big bore cylinders.

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The photo above is of three different big bore cylinders we are going to look at in this thread. But, before we get there, let's review some information.

Stock cylinders were cast by the Motor Castings Company (MOCASCO) for Harley. This is the triangular mark that looks vaguely like the old AMA logo, found on the cylinder base. They are made from 30,000 psi grey iron and give a very good service life. Currently, brand new cylinders for 900 sportster cost less than $125-150 per cylinder. Most aftermarket cylinders do not carry the MOCASCO mark. For strokes up to 4.5 inches, it is generally not necessary to lower the oil return holes. Stock cylinders measure 5.330 inches from the base gasket to the head gasket surface, though many aftermarket cylinders like the India-cast cylinder pictured below are slightly over-length.

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Dytch was among the very first companies to offer big bore cylinders, starting around 1960. The first Dytch cylinders were cast by MOCASCO and carry many of the same markings as OE (original equipment) cylinders. The challenge is that the cylinders were not “beefed up” and so they were already pretty thin even at 3-3/16. These cylinders are easy to identify by the presence of a “45” cast into the cylinder base – signifying they are 45,000 psi grey iron. They also are generally marked “front” and “rear.” These cylinders will work if in good condition – but they are more fragile and sleeves are more difficult to install

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The "45" is circled in the above picture to make it stand out.

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Well, the Q ship more or less got mocked up last night. Just have to bolt on the handlebars, add the wheels, and figure out my side stand angle. Then, I calculate a few spacer and bushing things . . . and break it all down for paint, powder, plating and parkerizing.

Unusually, almost all the chrome I can clean up -- save the fork sliders. Those need a full replate, which is surprisingly inexpensive. And, other chrome things like the chain guard will be stripped and refinished in black.

Mrs. Chuck was surprised at how fast this one came together. It's often amazing how quickly things assemble when you have the hardware organized and use mostly OEM parts -- not repops.

Now, let's make sure we are honest -- for those of you staring at this bike -- it is NOT 100% factory correct. Big deviations include: repo front fender that isn't quite right, smooth sided rear fender struts, early K model swing arm, a generic, long chain guard, pretty much all the cad plated looking hardware is stainless steel, and there is that generic repo tail lamp/license holder. If you were restoring this bike for judging -- all of this would likely need addressing.

Keep in mind, I am NOT an AMCA judge and my statements should not be taken as even a hint of gospel if you are interested in restoring to that level of detail and skill. Seek those people out if a winners circle award is your goal and follow their advice.

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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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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

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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?

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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

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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.

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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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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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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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Part 5 -- pistons; Axtell/Dytch vintage pistons

Next up is an Axtell 3-1/4 stroker piston. In just looking at the piston, you can tell something is different. The crown is similar to later 1000 pistons and the skirts are very different. These are also cast pistons and intended to move the compression up to 10:1. As such, when put on the same pin as a stock piston you can see they have the same compression height, but the ring lands are at different heights.

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In the last photo; that is our stock 900 piston on the left and the Axtell on the right

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Part 5 - Pistons

Let’s stop for a moment and look at different pistons. Dr. Dick was kind enough to share with us his collection of pistons and piston sectionals. He kept all these because they clearly show different types of solutions to the same problem.

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Let’s start with looking at stock 900 pistons. These are cast aluminum with reinforcing struts and substantial pin bosses. The weight is distributed well between the crown and the skirt, making for a stable piston.

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When you flip them over, you can see a couple of critical things. First, notice how the underside of the crown is an even, dark brown/black. This is a heat mark. It shows this piston was transferring heat evenly to the top ring and that the oil flung on the underside was clearly stopping at the oil control ring.

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When looking at the oil ring land – you can see it is slotted, not drilled. This is great for a stock bike and works well with a variety of ring packs. However, you can easily compress the piston in a high output application. In terms of weight; this piston is .020 over. With its pin and keepers, but without rings, it weighs 501 grams.

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The Q Ship Saga Part 5: Stroker Piston Choices

The Q ship Saga

Part 5: Stroker Piston Decisions


We finished the last installment by describing how we evaluated and prepared cases to go out for boring. It is important to note this is totally unnecessary for a stock rebuild. Instead, we decided to build a hotrod sportster in a fashion very similar to what would have been done in the late 1960s.

Let’s start with a quick and dirty overview. Ironhead sportsters can be split into two major motor groups: 900s and 1000s. 900s were produced from 1957 to 1971 and have a 3 inch bore. 1000s were made from 1972-1985 and have a 3-3/16 inch bore; though 1972-early 1973 involves some uniqueness. If you are thinking about a stroker, it is far easier to build one on a set of 1000 cases than a 900. This is for a variety of reasons, but today it comes down to one critical factor – pistons.

Put simply, off-the-shelf supplies of 900 stroker pistons dried up decades ago. This leaves us with five options for achieving our goal.

Option One: NOS 900 Stroker Pistons – First, this is a game of luck and patience. These pistons are out there, but they don’t often come up for sale and if they do; it is relatively rare for them to be truly NOS. If you do find a set, they are most likely to be Dytch, Axtell, TRW (S&S), or JE (Jahn’s). They can be in a variety of compression heights and so you have to measure carefully to determine if they will fit your needs. Rings “may” be an issue depending on the oil ring used.
Pros:
they will fit if you did your homework
When broken in properly, they have a long service life
Light weight, in most cases

Cons:
you may only get one set
Replacement may be impossible
Rings maybe difficult to source
May not be the bore size or compression height you need
Ring lands may be too close to top of cylinder

Option Two: Use stroker plates and cut down stock pistons. This is the original way of making a stroker. This works surprisingly well, though you leave displacement on the table as you can only go so big on the stroke.

Pros:inexpensive – you can use readily available pistons and ring packs
Easy to build and live with
No lowering of oil holes in many cases
More piston choices

Cons: Thick stroker plates may cause head to frame fitment issues on the rear
Thick plates may require longer cylinder base studs
Thick plates are easy to spot and “spoil” the motor’s appearance
Depending on cylinder height; manifolds and pushrods could become issues
Leaves power on the table

Option Three: Custom pistons. Over the years, we’ve ordered pistons from JE, Ross, and Venolia for various projects. Service from all three has been excellent and the pistons have been exactly what we ordered. The process is not as complicated as you may think. You simply fill out some forms with your specifications and 8-16 weeks later, pistons arrive.

Pros:Pistons are made to your exact specifications
They will fit – provided you measured correctly!
Can take advantage of tech advances in rings, pins, and forgings
Can have custom dome shapes, etc.
Generally made from higher quality (tougher) materials than stock pistons

Cons: Cost – you generally buy 4 pistons at a time at $150-200 per piston
Generally all 4 of your new custom pistons will be the same size – meaning if you destroy one AND need an over bore – you’re ordering new pistons
Long lead times, often 8-16 weeks for pistons to arrive

Option Four: Adapt the 900 cases to accept 1000 top end components. It is not easy, but it does allow you to take advantage of 1000 stroker pistons which are readily available (at the time of this writing) from S&S.

Pros: cylinders are readily available
Brand new stroker pistons are available from S&S
Simply moving to the 3-3/16 bore nets a 10% displacement increase
Can be combined with a shorter stroke choice to utilize stock pistons

Cons: Requires the most machine work.
You have to buy a lot of new or very good used parts
You have to find a really good machinist if you want the motor to last
Not as “cool” as NOS or custom speed parts

Option Five: Dytch, Axtell or Trock cylinders with matching pistons. This is the deep end of the pool. Most everything becomes “custom” to some extent when going this route – made more difficult by the fact these parts have been out of production for the better part of 40 years. They also were never sold in large quantities and most were bought by guys who blew up more than one motor. As a result, finding survivors in good condition can be challenging. The results, however, are often worth the quest.

Pros: Stronger cylinders that are tough and more wear resistant the OEM.
More bore choices
Sleeving options
Length options
Oil holes are already lowered.
Hard to spot to the casual observer.
3-3/16 and 3-1/4 cylinders can often use S&S 1000 stroker pistons.

Cons: Cost. Finding good cylinders is neither cheap nor easy.
What you find may not fit your needs.
Cases must be bored to fit
Heads must be bored to fit
You may never get a second set


It all comes down to pistons. They are our deciding factor.

After weighing the options, we decided to stick with those solutions that allow us to use S&S stroker pistons. These pistons are sized to work with up to 4-5/8 strokes with either no or very thin stroker plates. This is good because we do not want to stress the cylinder base any more than necessary, nor do we want to disturb the original cylinder studs unless we must.

So, really, why would we bother with all this? It comes down to two words: fun and displacement. The fun comes from the extra horsepower, which is provided by a serious knock upwards in displacement. In this case, we’ll be using a 4-5/8 stroke and 3.25 inch pistons to give 76 inches. This is a whopping 21 inches or 40% more than the stock 900’s 55 inch motor.

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In the above photo, that is a stock 3" 900 piston sitting in a 3.26 axtell bore . . . Just a wee bit of daylight around the edges.