The only accurate way to measure bearing clearance is in the true vertical. Bearings are d
Peter Constantine, via carcraft.com: I'm in the beginning stages of my first engine build-nothing fancy, just a mild 355 small-block Chevy to replace the exhausted, nonoriginal small-block in my '69 Z/28. I have a question about bearing clearances. I make my living with precision measurements so I have no problem with the actual measurements. It's the calculation I'm wondering about. Is the bearing clearance radial or diametric? For example, if a recommended clearance is 0.0025 inch, is that 0.0025 inch per side (radial) or total (diametric)? If it's total, then the actual clearance is 0.00125 inch per side. Am I correct?
Jeff Smith: Yes . . . but not always. How's that for an answer? Yes, you are correct that the distance between the bearing insert and the main journal, for example, is the total clearance, which means your above numbers are accurate with the actual clearance on one half of the bearing being 0.00125 inch with a total clearance of 0.0025. Mathematically, that is correct. Now let's take a look at what happens when we put the engine under load.
Oil moves through this clearance, creating what is called a hydrodynamic wedge or hydraulic cushion that keeps the crankshaft journal separated from the engine bearing. In the case of a rod bearing, cylinder pressure pushes down on the top bearing insert. This attempts to push the oil out from under the bearing, but oil pressure and high-pressure lubricants help maintain that wedge. More than likely, however, the clearance at that point is less than half of the total measured clearance.
This Clevite illustration reveals a typical engine bearing eccentricity at the parting lin
Oil viscosity will have an effect on this, and a thicker oil will maintain more clearance. However, as long as the oil can maintain a clearance between the bearing and the journal, it may not be necessary to bolster this clearance with heavier oil that requires more horsepower to pump. Thinner 5W-20 and 5W-30 oils are becoming more popular since this reduced viscosity lowers parasitic pumping losses and improves power and economy.
According to a Clevite technical bulletin, the typical production engine recommendation is between 0.00075 and 0.0010 inch of bearing clearance for each 1.00-inch journal diameter. So for a small-journal small-block Chevy connecting rod of 2.00 inches, that would mean a bearing clearance of between 0.0015 and 0.002 inch. Most performance engine bearing recommendations tend to avoid clearances below 0.002 inch, even for small-journal diameters. Clearances on the tight side will increase bearing load capacity, but this also drastically reduces oil flow, which increases bearing temperature. That's why a slightly wider clearance is acceptable while sacrificing minimal load capacity.
In the case of our Olds 455 engine that uses a monster 3.00-inch main journal, clearances for this application would be acceptable well in the 0.0035-inch range. Conversely, for those Honda rod journal diameters of 1.88 used on more and more race engines, a 0.0020-inch bearing clearance would be acceptable.
Ann Arbor, MI
Iron And Ribs
Here's a peek from the The Rock 'n' Roll Ribs event featuring a cruise night, barbecue, and live music by the host, owner, and Iron Maiden drummer, Nicko McBrain. Our very own Heidi DeRosa got this shot of McBrain Damage.
Back in the early '80s, if your car appeared in Car Craft magazine, we gave you a little window decal to let the world know. They are very rare now. We found this one in John Vermeerch's '61 wagon alongside a '62 NHRA Winternationals decal.
This tight view of aligning the dots on the crank and cam gear merely indicates that the c
All About Timing
Blaine Kuhn, Fremont, CA: I have a '71 small-block Chevy 400. The engine is pretty stock: Edelbrock intake and four-barrel carb. The timing chain needed replacing so I stuck in an Edelbrock timing gear and opted to use the 2-degree-advance feature. Now with no carb changes other than idle speed, the car has zero torque and it takes two-thirds-throttle to get the thing moving. But once it hits about 2,500 rpm, it has much more get-up-and-go. Any help would be really nice, even if I'm not going to like hearing I have to tear it down again and put it to retarded or stock...argh.
Jeff Smith: We're not always the bearers of good tidings, Blaine. It sounds like when you installed the timing set, the marks between the crank and cam gears were not precisely aligned. This places the camshaft one tooth off, which can either be advanced or retarded. The amount the cam timing is off depends on the number of teeth on the cam gear. For example, I think the Edelbrock gear for the small-block Chevy has 44 teeth, while the crank gear has 22, which means the cam spins at half crankshaft speed. If we divide 360 degrees in a circle by 44, we get 8.18 degrees. If the cam gear had 40 teeth, then one tooth would be equal to 9 degrees. That is why adjustable cam gears rarely offer more than 8 degrees of retard or advance. If you needed more than 8 degrees (and why would you?), just move the cam gear one tooth.
You mentioned your engine is very sluggish until about 2,500 rpm. With all other things like ignition timing and carburetion set properly, your description sounds like you accidentally retarded the cam gear by one tooth, which would retard the cam timing by roughly 9 degrees and easily make your engine run the way you described. You will have to remove the water pump, harmonic balancer, and timing cover again, which also means loosening and dropping the oil pan-a real pain on the original small-block Chevys. This might be a good time to consider a one-piece oil pan gasket (sold by Fel-Pro). That could save you a lot of grief.
The best way to determine if everything is installed properly is to degree the camshaft. Y
Before you remove the cam gear, remove all the spark plugs and slowly turn the engine over until the little mark on the cam gear is at its lowest point. For the cam to be timed properly, the dot on the cam gear should line up perfectly with the dot on the tooth on the crank gear (as in our photo of a small-block Chevy cam installation). More than likely, your cam gear dot is not lined up with the crank gear and is retarded by one tooth.
Of course, the best way to double-check your work is to degree the camshaft. If the numbers are off by 9 degrees or more, then you know you have a problem. For the record, aligning the dots does not constitute degreeing the camshaft. That term is often misused. To degree the cam requires special tools and a little bit more effort. Finally, if it's any consolation, it's an easy thing to miss the alignment of these dots when the engine is in the car. I've done it.
At the same all-GM show, we ran across this absolutely gorgeous Pontiac Bonneville convertible with a Tri-power 421ci motor and couldn't resist it. This just oozes cool.
Weight transfer is a big reason adjustable brake proportioning valves should be used to fi
Gil Acheson, Denver, CO: I've read Car Craft from cover to cover since its inception, and I race a SuperFormance Cobra with Wilwood brakes. Now that I've established my "street creds," let me ask a question: On page 44 of the "What's Your Problem" column in the Mar. '10 issue, you are discussing proportioning valves, front and rear adjustments, and so on. You state that a "taller tire requires less brake pressure than a shorter tire." Please help me understand this, because my intuition would tell me the opposite would be true due to the higher leverage or turning moment of the taller tire exceeding that for the shorter tire, therefore requiring more pressure to equal the braking power.
Jeff Smith: My first editor, Rick Voegelin, used to tell me, "Doctors bury their mistakes; we publish ours." Both of you are very much correct. Let's get into why this is, and then I'll explain where my statement originated and how my experience set me up.
In the HP Books Brake Handbook by Fed Puhn, which is now out of print, there is a section on brake system design that lists a formula:
New pedal effort = old pedal effort x (new tire radius/old tire radius)
The values for this formula include pedal effort in pounds, and tire radius in inches. But to be completely accurate, these tire numbers must be the loaded tire radius. We'll look at the difference between the tire diameter of 26 inches and the new tire diameter of 28 inches.
New pedal effort = 100 pounds x (14 inches/13 inches)
New pedal effort = 100 pounds x 1.077
New pedal effort = 107.7 pounds
This means that a taller tire requires greater pedal effort to generate the same brake torque. Conversely, a shorter tire will require less pedal effort to achieve the same brake torque. So you are correct, Gil, in your assumption that the taller tire creates greater leverage. This is true for front or rear brakes.
My statement originated from an experience many years ago testing a friend's Chevelle in which we had tested his brakes with several aggressive stops and set the brake balance with an adjustable proportioning valve. Then he installed a set of taller drag tires on the rear of the car, and on his first aggressive stop, the rear tires locked up and the car spun. Luckily, he didn't hit anything, but it was plenty scary. I assumed the taller tires required less brake pressure. The reality was that the combination of a more aggressive use of the brakes combined with more weight transfer that was partially due to the taller tires (that created a greater static rake that moved weight to the front) all contributed to a greater transfer of dynamic weight onto the front wheels and off of the rear wheels. With reduced load on the rear tires but the same hydraulic pressure to the rear, the rear brakes locked up prematurely. To fix the problem, we reduced the rear brake pressure with the adjustable proportioning valve and the car stopped fine with no drama after that. While I thought that reducing the pressure was because of the taller tire, it really was because of the greater weight transfer. It's a small point, but it led me to an incorrect assumption.
As an interesting aside, there was also a formula in the book for calculating the equivalent amount of horsepower it takes to stop a vehicle of a given weight at a given speed and deceleration rate. For fun, I used a 3,500-pound car decelerating at 1 g from 60 to 0 mph and the formula says it would take the equivalent of 563 hp to pull it off. This gives you an idea of how much power it takes to stop a heavy muscle car from even a relatively mild 60 mph.
ARP recently invited us to its open house. Among the 50-plus cars that showed up were this tribute Penske Camaro and the Poteet and Main streamliner that has already run 436 mph. They're shooting for 500! Also worth noting: This is ARP's main production shop and the floor is this clean all the time, not just for the show.
When looking for a suitable engine to rebuild, a good indication of decent wear is the amo
Chris Jackson, Maple Grove, MN: Do you have any recommendations for a good first-time engine to build? I'm not looking to do any modifications and I don't need any big power numbers-just a good practice engine to cut my teeth on. I'd like to tear down the engine, clean it up, replace any parts that need to be replaced, and build it back up. My goal will be to make it run like new or slightly better.
It doesn't really matter how many cylinders the engine has or what vehicle it comes from. I just want a good engine to practice on that will help me learn the fundamentals.
Jeff Smith: There are lots of ways to go, Chris, so we'll toss out a couple of ideas. First, as much as the boo-birds will snivel, it's hard to beat the small-block Chevy as a first-time engine project. The reasons for this are simple: There are more Gen I small-block Chevys out there in the world than any other domestic V-8, and because of that, the replacement parts for these engines are incredibly inexpensive based on the immense volume. This means that a typical rebuild kit for a small-block Chevy will be less money than a V-6 Chevy or oftentimes even less than comparable kits for a four-cylinder engine. Even the venerable small-block Ford 302 comparable kit is more expensive than a small-block Chevy. But keep in mind we're talking about a 350 small-block here. A 305 can cost more because these engines are not nearly as popular as the 350, even though most of the parts are exactly the same between the two kits. For a bunch of tips on building the engine, refer to the budget engine buildup we did in the May '10 issue ("How To Build a Cheap, Street, $650 Small-Block," pg. 22).
So the first thing is to begin looking for an engine to rebuild, but one thing to consider is what your plan is for the engine once it is rebuilt, as you could then sell it and recoup the investment. There are several ways to go here. You could probably find a rusty old hulk engine that you could get for next to nothing, and that's OK, but you might want to consider an engine with a decent history that's in good shape. Then purchase a kit that would allow you to completely rebuild the engine, including new pistons, rings, bearings (including cam bearings), oil pump, gasket set, and maybe some assembly lube. You will then need to take the block to a reputable machine shop to be bored and honed for the new pistons. If the crank is serviceable, you might be able to get away with not grinding the rods and mains 0.010 inch undersize. Most of this you won't know until you dismantle the engine. That's why it's a good idea to obtain the engine first, disassemble it, and determine what parts-like the crank and rods-can be reused. That will determine the kit level you purchase.
You will need a few specific tools to assemble the engine. Start buying tools like microme
For example, several years ago my friend Ed Taylor bought a used 350 truck engine from a friend for $100 that we intended to put into my son's '65 El Camino. After teardown, we discovered the cylinders did not exhibit much taper at the top, and the crank was in great shape, so we decided to reuse the stock cast pistons and add new rings, bearings, and gaskets. Federal-Mogul makes a specific kit for this type of rebuild that costs $127.69 for a small-block 350 from Summit Racing. We merely hit the cylinders with a bottle brush hone then cleaned the block, reused the original cam bearings, and carefully reassembled the engine with the original pistons and new rings and bearings. The crank was serviceable, so we verified the rod and main bearing clearances, endplay, and rod side clearance before reassembling the short-block. If you plan on keeping this engine or using it in a car, finding an engine like this is a good plan.
More than likely, however, the engine you find will be in worse shape, meaning the cylinders will have significant bore taper-which you can easily spot with the heads off-as well as a worn crank. These are generally the two places that will exhibit the most wear and therefore will need the most machine work. Again, assuming you will want to keep your first engine, you will need a more substantial engine kit. Federal-Mogul, for example, offers a complete economy rebuild kit that includes a set of 0.030-over cast pistons, rings, bearings, cam bearings, an oil pump, freeze plugs, and all the gaskets you'll need for the ridiculously low price of $219.95 from Summit Racing. Think about that-you'll have most of the parts you will need to rebuild the short-block for a little more than $200.
Of course, we must consider that it will cost a few bucks to have the block cleaned, bored/honed, new cam bearings installed, and the rods resized. Let's estimate this labor at $400. Now you've got more than $600 invested in this engine. You'll still need a camshaft to complete the short-block, and then we must consider cylinder heads. We'd suggest going with any one of several replacement iron heads like the GM Performance Parts Vortec iron heads only because they are brand-new, offer great performance, and will cost much less than having the stock castings rebuilt. You can buy these heads right now from Scoggin-Dickey for $309.95 each (less than $620 for the pair). These heads are complete and ready to run. If you choose a camshaft with less than 0.450-inch lift, you don't have to do anything except bolt them on. These heads do require a center bolt-style valve cover, but most late-model small-blocks after 1987 use these same valve covers.
Another important thing to point out is that you will need to pay attention to the style of used small-block you purchase. The late-model small-block Chevys built after 1987 all use a one-piece rear main seal. This is a different cylinder block and crank configuration compared with small-blocks built from 1955 through 1986. It will probably be easier to find one of these later one-piece rear main seal engines than an earlier motor. Plus, the one-piece rear main seal and one-piece pan gasket are much less likely to leak than the earlier engines and are easier to assemble. Also, these later small-blocks were designed to be used with a hydraulic roller camshaft, and the parts are easy to obtain and not that expensive. Enjoy your buildup!
Also at the GM show we attended was this very cool Corvair Corsa. Did you know the very first Yenko performance cars were not Camaros but Don Yenko Stinger Corvairs built in 1966? This Corsa sported the typical flat-six with four carburetors.
Jon Thomas, via carcraft.com: Do automotive fluids in factory-sealed containers have a limited shelf life? For example, I have a bottle of brake fluid that's about five years old. The plastic container has become misshapen, like a vacuum is forming inside (yes, unlikely, I know.) But is it still good? How about motor oil?
On another subject, when do you lube fasteners? What do you use, and where-on bolt threads and under bolt heads? This might make a good article.
Jeff Smith: Jon, any brake fluid has a shelf life that can be directly attributed first to the type of container used. For example, the plastic container that you mention is not as good as metal cans with a pressed-in seal and a screw cap. The fact that the bottle is misshapen probably has more to do with pressure changes than anything else. I have several plastic bottles that have done the same thing that are only about six months old. I spoke with Amsoil and the company says that in its sealed plastic container, the brake fluid is good for two years, stored in a cool, dry location away from sunlight. The company also says the paneling or changes in shape of the bottle are merely cosmetic and have no relation to the quality of the fluid inside. I also spoke with Wilwood brakes and the company representative says that purchasing the smaller brake fluid containers minimizes the loss. So the key here would be to buy brake fluid in small quantities so there's not a larger container sitting around. Also keep the fluid container tightly closed to help with shelf life.
In your case, the problem with even a still-sealed new bottle that is five years old is that the plastic bottle is still slightly porous. Brake fluid is hygroscopic, meaning that it attracts water and will absorb moisture right out of the air. I'm not sure where you live, but let's just say that if you live anywhere that is humid (which is just about everywhere except maybe the desert Southwest or Denver), that the brake fluid in your can is probably contaminated with water. The problem with water in brake fluid should be obvious. Not only does water create rust and corrosion in the brake system, which can lock up wheel cylinders, but water also turns to steam when subjected to temperatures above 212 degrees F-something a wheel cylinder or caliper can easily achieve. Once the water turns to steam, it creates air in the system, which creates a very spongy pedal-something else you don't want. Brake fluid is rated by its dry boiling point. There are several grades of brake fluid: DOT 3, 4, 5, and 5.1. The above chart (courtesy of AfcoRacing.com) illustrates the differences in boiling points at degrees F. Also note the drastic change in boiling points when the fluid is mixed with as little as 3 percent water. With DOT 4 fluid, this small amount of water creates a massive drop in boiling point of 30 percent. This is why it's so important when taking any car to a road course track day where the brakes will be severely heat tested to always completely change and bleed the hydraulic system with new, high-quality brake fluid. DOT 5 brake fluid is silicone based, which is not recommended for any performance application. The only advantage to silicone might be with museum-stored cars that are rarely driven in which the fluid might delay hydraulic circuit moisture damage.
I contacted oil engineer Mark Ferner at Quaker State and he says that when stored inside in a cool, dry place, engine oil has a shelf life of about four years in its original, sealed container. Exposure to sunlight and/or higher temperatures can significantly shorten this time period. Longer than the noted shelf life, additives may tend to fall out of suspension, although higher-quality oils will probably do a better job of maintaining integrity than inexpensive brands. Moisture is also a detractor, which is why it's best to keep the oil in its original sealed container. Also consider that as oil classifications change, oil more than four years old could possibly not be adequate for newer vehicle applications.
Your question about what lubricant to use with fasteners is a highly debated subject. The abbreviated answer is that engine oil is the standard by which all factory fastener torque values are based, but there are numerous variables that affect this torque. Basically, if you coat a bolt with engine oil and then subject it to a sequence of torque and release, the actual clamp load on the fastener will change each time the bolt is retightened, despite the fact that bolt is tightened to the same torque. This is because engine oil will not respond consistently under these high-pressure conditions. ARP just recently introduced a new thread lubricant called ARP Ultra-Torque that is designed to be consistent through numerous torque applications. At least for ARP fasteners like head bolts, this would be the lubricant that we would recommend and what ARP's torque specs will likely indicate. Keep in mind that when you use a torque wrench, a majority of the torque applied to the fastener is used to overcome friction. For a head bolt, for example, friction between the underside of the bolt head and the washer, between the washer and the head, and then between the bolt threads and the block requires some kind of lubricant. Because of the variation in torque readings that occurs during this procedure, many manufacturers are now using what is called torque-angle measurements. This is where the bolt is pretightened to a given spec like 20 ft-lb and then the fastener is turned a given number of degrees-say 90. The pretorque and the angle are established through very specific testing to establish the proper clamp load. This is more accurate because the torque-angle method is not affected by resistance due to friction that affects all torque wrench readings. If there is enough reader interest in this subject, we could do a complete story on how torque angle is a much better way to load certain engine fasteners like head bolts.
Brake Fluid / Dry Boiling / Wet Boiling
DOT 3 / 401 / 284
DOT 4 / 446 / 311
DOT 5 / 500 / 356
DOT 5.1 / 518 / 375
All temperatures are in degrees Fahrenheit. Wet boiling point is brake fluid containing 3 percent water by volume.
Automotive Racing Products (ARP)
We made a quick pass through the all-GM car show at Woodley Park in California's San Fernando Valley and ran across this super-sleeper '62 Buick Special quadra-door. The drivetrain is a 350ci small-block Chevy, 700-R4 automatic and a Ford 8-inch. The owner says it runs 14s at 100 mph.