Month: March 2021

“Run a dingle-ball hone through it, throw in a new set of rings — and you’re ready to go.”

Not long ago, this might have been considered an acceptable practice for a mild street engine. While this may still be the approach for the backyard engine builder, 21st Century internal combustion engines have progressed to the point where attention to detail can pay off with less internal friction, more horsepower and torque, less blow-by, and even superior oil control.

Among all the attention paid to piston rings, far too little has been addressed to the oil rings. But within the trio of the three-ring piston, more friction is generated by the oil ring package than the sum of the other two rings combined. So perhaps we should start with some technical details that may be surprising. One approach to improve power and efficiency on any engine would be to reduce the friction of a typical oil ring while not compromising oil control. Let’s start by addressing what is commonly referred to as standard tension oil rings.

Standard Isn’t So Standard

For street engines, nearly all recommendations call for a “standard” oil ring package and to avoid using “low drag” oil rings because of the risk of allowing too much oil into the combustion chamber.
It turns out that what is termed a “standard” tension oil ring is anything but standardized. We’ve included a chart created using data supplied by Total Seal that offers some interesting information. The force listed in the accompanying chart is expressed in pound-force (lbf).

This is not lb-ft or torque, which is a twisting motion. Pound-force is the radial or outward tension against the cylinder wall created by the oil ring when compressed in the cylinder. These lbf measurements were obtained with a very sophisticated (and expensive — like, $60,000 expensive) tool used by Total Seal to measure this force. These lbf readings do not represent sliding friction, although common sense dictates that higher radial tension will certainly contribute to increased sliding friction.

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(Left) The radial width of an oil ring helps determine its radial tension. Here, we’re measuring a 3.0mm oil ring which comes in a 0.110. (Right) This stack o’ oil rings compares a stock replacement 3/16-inch (bottom), to a 3/16-inch oil ring from a 1/16-inch performance ring package with a different expander (middle), to a 3.0mm oil ring (top) as used in a typical LS 6.0L engine. The top two expanders are the more common flex vent design while the bottom is called an SSU, which is an older configuration similar to the flex vent but turned on its side. Speed says the flex vent is a more efficient design.

A typical performance piston ring combination is a 1/16-inch top, 1/16-inch second, and a 3/16-inch oil ring. A “standard” 3/16-inch (0.187-inch) oil ring package, as listed in the chart, creates a significant 20 lbf radial tension. What’s interesting is the spec for a “standard” late model 3mm (0.117-inch) oil ring package, Total Seal’s radial tension measurement plummets from 20 lbf to 11 lbf – an amazing 45-percent reduction in radial tension.

What’s worth emphasizing is that both of these oil rings are considered “standard” tension. As one example, the lowest radial tension ring — the 3mm ring — is the standard factory oil ring in late-model LS engines. What we’ve learned is that there are many ways to achieve good oil control and still reduce friction when the proper oil ring components are selected.

Less Tension, More Control

Interviews with Total Seal’s Keith Jones and Lake Speed, Jr. offer some tech-savvy insights into how these numbers directly relate to street-driven engines and how a sophisticated and knowledgeable engine builder can create his own custom oil ring package. But before we get into that, let’s look at some details about oil ring construction that will lead us to intelligently create this oil ring package.

Nearly all current oil rings are created using a three-piece construction technique. The expander is the large center piece that is restrained with a pair of oil rings. The expander can be thought of as a spring that is loaded when installed in combination with the upper and lower oil rings. The oil rings’ function is to scrape oil off the cylinder wall and push it inward to oil return holes or slots cut on the inside of the piston’s oil ring groove.

Think of the three-piece oil ring’s job as gross oil control. This is followed by fine control exhibited by the second oil ring. Generally speaking, 80-percent of the second ring’s job is to clean the rest of the oil not removed by the oil ring. The remaining 20-percent of its job is to help seal combustion pressure that has leaked past the top ring.

The first big revelation that Speed offered is that the oil ring’s vertical thickness has nothing to do with overall tension and ring drag. Oil control is created by a combination of the length of the expander and the radial width (as viewed from the top) of the oil rails. Speed says to think of the expander as a spring. If you place an expander inside its intended cylinder, the ends of the expander may not touch. But when the expander is squeezed between the two oil rails, the rails create the load much like adding a spacer under a valve spring to increase its tension on the valve.

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On the left, the arrow points to what Total Seal calls the tab area of the expander. The combination of tab area contact area with oil ring radial depth is what creates the oil ring’s tension. So by using different expanders and oil rings with narrower or wider radial width, Total Seal can create the near exact oil ring tension for a given application. The vertical thickness of the oil control ring is not a variable that controls overall tension. A low tension oil ring can be created with a larger 3/16-inch oil ring just as easily as with a much thinner 2.0mm oil ring (right).

The rails are also an important part of the equation. Changing the radial width of the oil ring will alter the load created by the expander. A thinner radial width oil ring will reduce the load created by the expander. We’ve created a chart where we measured the radial width of three different oil rings. Notice the major change in oil ring radial width between the 3/16-inch oil ring rails and the 3mm rails. There’s nearly a 50-percent change. Compare these numbers to the radial tension chart and there is a direct correlation between the radial width of the oil rails and reduced tension.

Beyond Standard: Even Less Ring Tension

Using this information, Speed offered that Total Seal can create nearly any desired tension for any oil ring package. Working with the example that a 3mm oil ring offers a radial tension of 10 pounds of force, a similar radial tension could be created using a larger 3/16-inch ring by combining a custom expander and oil rings. Speed said that perhaps half of Total Seal’s business is building custom ring packages that are not necessarily listed in the Total Seal catalog.

Speed offered that just within the 4.030-inch bore diameter for a 3/16-inch oil ring that Total Seal offers several different radial widths for the oil rings that can be combined with a given length of expander to create the intended overall oil ring tension spec. As an example, Speed says Total Seal could create a 10 lbf (or just as easily a 16 lbf) oil ring package for a 3/16-inch oil ring piston that would reduce friction and still control oil on a street engine.

But there’s more to the story. In order to be successful, a “low tension” oil ring should be combined with a Napier-style second ring. The Napier ring is a tapered scraper style ring that includes a hook or recessed area behind the tapered lower face of the ring that enhances the ring’s ability to remove oil from the cylinder wall. Speed emphasized that the combination of the Napier second ring with the custom 3/16-inch oil ring would improve oil control while also offering the opportunity to reduce friction which would result in more horsepower over a “standard” tension oil ring of the same size.

Speed further mentioned that the engine’s intended usage is an important factor in creating an oil ring package. A drag race engine that does not create high oil temperature could benefit from a different oil ring package compared to an engine that is raced in autocross where oil temperature could escalate beyond 250 degrees-Fahrenheit. So oil ring combinations should include the oil viscosity as part of the oil ring equation.

A purely drag race engine could get by with a much thinner oil viscosity such as a 0w20 while the autocross or road race engine might need a slightly higher viscosity oil like 10w30 or 10w40. If the engine in question will use a high viscosity 20w50 oil, then a higher tension oil ring will be required to more efficiently scrape the thicker oil off the cylinder wall.

A typical retort to all this is that the reduced load exerted by the oil ring will only result in poor oil control and increased oil usage. But, that does not account for the fact that GM research has chosen to employ a 3.0mm oil ring package in a 6.2L LS engine that does not have an oil control problem. One reason for this performance is that this smaller ring package and lower tension allows the oil ring to more accurately follow the distortions in the bore which means more oil is removed from the cylinder wall by both the oil and second rings.

Talk Is Cheap, Proof Is Priceless

A further example of how a custom oil ring package can perform is the 383ci small-block Chevy used as Shaver Specialties Racing Engines’ mule engine that has survived thousands of dyno pulls. It is currently equipped with a set of Total Seal 0.7mm top, 0.7mm Napier second, and an 8 lbf, 2mm oil ring package. We personally witnessed one of these pistons slide down the bore by itself (merely from the force of gravity) because of the reduced radial tension exerted by the ring package.

While this sounds like the engine should be challenged when it comes to oil control, Shavers’ dyno operator “Dyno Don” MacAskill reports that the engine has no oil control problems, the chambers stay very dry, and the blow-by is quite low. Further, this engine does not employ any special windage control measures. In other words, the oil pan is devoid of screens, trays, or other control devices.

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(Left) If an oil support rail is required because the oil ring groove intrudes into the wrist pin hole, always place the support rail with the small dimple facing down. The dimple contacts the piston and prevents the support rail from moving. (Right) When installing the oil ring, make sure to Install the expander first and make sure the ends of the expander do not overlap. Then gently install the top oil rail followed by the lower rail.

As for a practical street engine application for all this acquired knowledge, let’s stick with a typical 1/16-, 1/16-, 3/16-inch ring package engine. The consideration would be to use a lower tension oil ring package with a custom expander nested with thinner radial width oil rings combined with a Napier second ring. This would measurably reduce friction while still minimizing oil consumption.

Armed with this new information, you might want to consider the advantages of building your next engine with more attention paid to the lowly oil ring. It might just pay off with a little less friction and a touch more horsepower.

When building or performing maintenance on the engine in your hot rod, checking your engine’s bearing clearances is a great practice while you are “knuckles deep.” Not only is it advisable to check the visible condition of your main and rod bearings, but it is also a good practice to see how the tolerances are holding up.

Reasonably Priced Tool

For big horsepower applications, generally defined at 800-horsepower and above, working with your bottom-end bearing clearances suggests using highly accurate micrometers and dial bore gauges to ensure proper clearances. While these tools can be great for an engine builder, they are not typically considered “average” tools every enthusiast has in the arsenal.

MAHLE Aftermarket Incorporated recently took over the United States production of Plastigage, and Dan Begle from MAHLE provided his take on its practical applications with performance engines.

“In reference to your 800-horsepower fundamentals for Plastigage, that’s probably a good number,” says Begle. “I’m not sure if horsepower levels are a huge issue; it depends on the engine builder or machine shop you trust. If you talk to someone who builds a considerable number of performance engines, they’re probably using precision gauges.”

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With our engine dismantled down to the short block, we are visually checking the condition of all rod bearings and main bearings for wear or damage. With no visible problems, we can comfortably use Plastigage to confirm our bearing clearances without the use of micrometers and dial bore gauges.

Begle continues, “If you’re looking at performing checks and balances on your engine, this is the ticket. It is not quite as accurate as a dial bore gauge, but if you’re conservative and not building something totally crazy, you’re probably good.”

For approximately ten-bucks, the home engine builder can utilize Plastigage to get the job done, especially when combined with a proper visual inspection of your bearing surfaces. Currently, I have the 489 big-block Chevy out of our bracket racing Camaro, and this is a prime opportunity to carefully check out the engine that came with our unfamiliar turn-key purchase a while back.

 

The typical rule of thumb for an OE or mild-performance application is .001-inch bearing clearance for every 1-inch of crankshaft or rod journal diameter. With a big block Chevy using a 2.75-inch main journal diameter, our tolerance is calculated to .0027-inch. A similar calculation for the rod journal indicates a necessary .002-inch clearance.

These tolerances can vary depending on engine design, horsepower levels, intended oil viscosity to be used, and many more variables. In fact, I called the original engine builder, who cited that a bracket racing engine like this is constructed at his shop with clearances slightly tighter than the previously mentioned standard. Make sure to do your research before scrutinizing your dimensions.

“I am also kind of old school on the .00075- to.001-inch of clearance per inch of journal rule, but you also need to consider the oil viscosity you are using,” comments Begle. “With a light viscosity and/or synthetic oil, I would certainly lean to the lower side of that clearance spectrum. In equal consideration, if you’re running a higher viscosity oil, definitely lean to the higher side of your clearances.”

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The first step in checking your engine’s bottom end is to carefully inspect all bearings for damage or uneven wear. Only then can you measure bearing tolerances. It is also critical to test with the Plastigage when the engine steel is at a minimum of 65 to 70 degrees for proper metal expansion. While extreme cold will make the Plastigage somewhat brittle and heat will soften the material, Plastigage remains usable and accurate through all normal variations of air temperature and humidity.

Each package of Plastigage comes with one 12-inch piece of color-matched, formulated plastic. These pieces are usually referred to as “threads” since they are equivalent in size to a piece of sewing thread in an uncompressed state. With a standard V8 engine, this will test all rod and main bearings with a little to spare. The extra is handy because, if you ever drop a small section of this thread, it is my experience that you will never find it again.

Plastigage is offered in three tolerance ranges for typical automotive use. The sizes range from green: .001- to .003-inch (.025- to .076-mm), red: .002- to .006-inch (.051- to .152-mm), and blue: .004- to .009-inch (.102- to .229-mm).

I first inspected each bearing for any signs of damage. If damage is evident, measuring tolerance is a moot point until you have the crankshaft checked and possibly polished or machined for future use. If you install new bearings, the use of Plastigage at this point would be a good step during reassembly.

When I purchased the Camaro, the seller told me the engine had no more than 25-passes on it since built new. This bearing inspection indicated that to be true with no damage or heavy wear indicators.

I began testing the bearing tolerances one bearing cap at a time. Removing one rod cap at a time to install the Plastigage test seems like a reasonable precaution to avoid any switch-ups. Make sure not to place the test thread near any oiling holes as tolerances may differ around that area of the crank journal.

Remove, Retorque, and Repeat

With the recommended bearing clearance from the engine builder noted, I used the green Plastigage. To gauge the results, use the printed ruler-type measurements marked on the thread wrapper. The wider the thread is when compressed, the tighter the bearing clearance.

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I use some heavy white cardstock paper to cut each piece of thread carefully. With Plastigage sections cut narrower than the journal width, we also use a narrower piece of cardstock to place the tread onto the journal face. This avoids accidentally crushing the thread if you try to pick it up and place it.

Thoroughly cleaning the bearing surface and the journal face before testing is absolutely necessary. Plastigage is intended to be used in a dry condition. Any oil or residue on the surfaces can throw off the compression results. Once installed, torqued to specifications, and then loosened, carefully remove the caps directly outward from the crankshaft face, as not to damage the compressed thread. Sometimes the compressed Plastigage will affix to the crankshaft journal or the bearing face.

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If your engine uses a main girdle or internal oil pump, make sure to perform the proper install, torque, and removal process to ensure any changes to bearing clearance measurements. We carefully clean all bearings and journals with brake cleaner as Plastigage is intended for use on oil free surfaces.

Trust, But Verify If Necessary

Once the bearing cap was removed, I matched our compressed thread with the width ruler on the thread wrapper. The thread compressed to just slightly wider than the .002-inch indicator. This measurement indicates the bearing clearance at just slightly more than .002 clearance or near our goal of .0020- to .0025-inch.

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To gauge the Plastigage results, compare the crushed Plasigage to the thread wrapper markings. The wider the thread is compressed, the tighter the bearing clearance. When you carefully remove the bearing caps following the crush process, it may adhere to the bearing or the journal.

The bottom line is, Plastigage is a “trust, but verify” device for me. Many engine builders highly downplay the accuracy of the plastic thread. In contrast, many home builders swear by its use for the task, such as those I performed on our bracket engine.

With some friends watching my Plastigage work within my own shop, one buddy asked me if coated bearings play any role with clearances. I passed the question along to Begle. He responded, “Clearance is clearance, no matter what the bearing type. Though coated bearings in a performance application is an entirely different subject, I would still set up my clearances the same, coated or uncoated.”

If you have the talent to tear down, build, and rebuild an engine in your shop, Plastigage is an excellent tool to help you verify “red flags” along the way. If bearings do not pass a visual inspection or you find they have fallen out of tolerance, it is time to visit your favorite engine machine shop.

When shopping for new automotive components, it never fails that we are bombarded with tricky sounding terms and acronyms. Many times, we are casually familiar with these acronyms and we may know what they stand for, but don’t actually know what it does. Take CFM for example. Most people can correctly state that CFM stands for Cubic Feet per Minute and it is a measurement of airflow. But, what does it really mean to car enthusiasts?

It is not uncommon to hear salesmen quote CFM numbers when explaining cooling fans. From time to time, you may also hear one representative explain how company X’s CFM numbers are not as accurate as company Y’s. So we approached the specialists at SPAL USA to explain CFM to us.

“One of the most common questions we hear from customers is ‘What is the CFM rating?’ of a particular fan,” said Thom Balistrieri, director of aftermarket sales for SPAL USA. “This is a tricky question, as it’s very important to understand how CFM ratings are determined as well as how much CFM an application actually requires.”

According to Balistrieri, CFM ratings should be looked at subjectively because there is not an accepted standalone method of measure when it comes to determining CFM ratings.

“Think of it like wheel horsepower. Different dynamometers [dynos] will give different wheel horsepower ratings,” Balistrieri explained. “Sometimes, there is a ‘correction factor’ from one dyno manufacturer to another. This is the same situation, where measuring on a machine with different certifications could give different data.”

Tabular Data

SPAL uses a broader spectrum of CFM data for consumers to understand a fan’s ratings. “We provide tabular airflow data to our customers,” Balistrieri added. “This tabular data allows our customers to see how the fans perform across the entire static-pressure range.  This is critical information when selecting the correct fan for the job, and often, the most misunderstood aspect of fan selection,” he said.  “When customers don’t consider the static pressure drop of the radiator, it’s easy to get a fan that is underpowered for the task.” 

Balistrieri’s advice is to not get misled by trying to standardize and compare all the different methods of CFM measurement in the industry. He says there is an easier approach. “One way to determine if CFM ratings make sense is to look at the current draw of the fan.”

This approach states the current draw (in amps) is proportional to overall fan performance. “Motor-current draw is directly related to motor torque and the amount of pressure the fan can generate to overcome the restriction of the radiator,” he said. To put it even more simply: Increased amperage typically equates to increased airflow.

“We have a fan to solve nearly any circumstance you can imagine,” added Balistrieri. We actually put together an article about fan selection, and you can find that information by clicking here. According to Balistrieri,  “just call (800) 345-0327 to talk to an experienced technician and determine which SPAL fan is best for you.” Or visit them online at www.spalusa.com.