Main Bearings
Using an outside micrometer, carefully measure the crankshaft’s main journal diameters and record the measurements. Set up a bore gauge to this measurement and adjust the gauge dial to the zero mark.
Install the upper and lower main bearings and install the main caps; torque the main cap fasteners to specification. Insert the bore gauge into each installed main bearing.
After a bore gauge is set up to match the crank main journal diameter, the gauge is inserted into the installed main bearing to determine the bearing I.D. relative to the crank main journal.
The difference from the gauge dial’s zero mark indicates how much larger or smaller the main bearing is relative to the crank journal. For instance, if the gauge reads .002 inch greater than the crank journal diameter, you have an oil clearance of .002 inch.
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If a check using standard thickness bearings reveals an inadequate oil clearance, performance bearing makers offer bearings in “X” size, with the “X” indicating that the bearing shell is .001 inch thinner, which provides an additional .001 inch clearance. Builders often mix and match standard with X bearings to obtain the exact oil clearance desired. For instance, if you need to pick up an extra .001 inch, you could use one standard bearing and one X bearing on the same journal. Each bearing half in an X bearing set will provide .001 inch additional clearance. Generally, when mixing thicknesses, the thicker bearing insert is installed as the lower bearing (for example: standard insert as the upper and X insert as the lower). One example is that a standard bearing insert for a small block Chevy measures .095 inch thick, while an X bearing measures .094 inch thick.
An upper H series main bearing insert from MAHLE Clevite. Stamped “STD” to indicate standard thickness. This small block Chevy upper bearing thickness measures .095 inch.
Measure crankshaft main journals with a calibrated micrometer. Make sure that the journal is clean before measuring, with no grease or oils present. Measure each rod journal as well. Make sure that the micrometer anvils are squared up and flush to the journal surfaces.
Rod Bearings
Using an outside micrometer, measure the crankshaft’s rod journal diameters. Record this measurement. Remove the rod’s cap and install the upper and lower rod bearings, and reinstall the rod cap; torque the rod bolts to specification. To stabilize the rod and to protect the rod from damage, place the rod big end into a dedicated rod vise while torquing the rod bolts. Set up a bore gauge to match the rod journal diameter, then zero the gauge dial. Insert the bore gauge into the rod big end bearing and note how the reading differs from
When removing or installing rod caps on the workbench, it’s best to use a dedicated rod vise to secure and protect the rod. These vises feature composite material on the jaws to prevent nicking or gouging the rod big ends.
the rod journal diameter. The difference indicates how much greater or lesser the bearing bore diameter is relative to the rod journal diameter. For instance, if the bearing measurement reads .0024 inch greater than the journal diameter, you have an oil clearance of .0024 inch. When using the bore gauge, gently rock the bore gauge back and forth to obtain an accurate reading. The point at which the gauge needle moves to maximum and then moves to minimum, the minimum point represents the true reading.
When measuring main or rod bearing inside diameters, keep the bore gauge anvil and plunger away from the bearing parting lines, because the area adjacent to the parting lines is slightly tapered to promote oil ramping. Also avoid contacting any oil holes or grooves in the bearings.
Cam Bearings
Generally, in an overhead valve engine, cam bearings are installed and then the camshaft is test fitted. If the cam rotates easily on its bearings, cam to bearing clearance is considered acceptable. However, if you want to know what the oil clearance actually is, use a micrometer to measure the camshaft’s journals. Set up a bore gauge to match the journal diameter, then zero the gauge dial. Insert the bore gauge into the installed cam bearings and observe how the bearing inside diameter differs from the cam journal diameter. For example, if the bearing inside diameter reads .0018 inch greater than the cam journal diameter, you have an oil clearance of .0018 inch. As with main or rod bearings, be
With rod bearings installed and the rod bolts fully tightened to spec, a snap gauge or bore gauge can be used to measure installed bearing I.D.
When test fitting the camshaft, it must rotate freely by hand. If it’s difficult to turn or if you feel resistance in one spot, the cam bearings likely require hand scraping using a sharp cam bearing scraper.
careful to avoid dropping the gauge anvil and plunger into the cam bearing oil hole.
If the camshaft shows resistance to rotating by hand, remove the cam and inspect each cam bearing. You should be able to see slight wear marks on the bearing(s). Using a sharp, dedicated cam bearing scraper tool, the area of the bearing that appears to be tight can be carefully relieved. Reinsert the cam and verify that you have smooth rotation.
Cam Thrust
A flat tappet camshaft features slightly tapered lobes. A slight crown on the face of the flat tappet lifters allows the lifters to rotate to prevent excess wear. The taper profile on the lobes, a slight offset of the lifters’ bores relative to the cam lobes, and the action of the distributor gear all tend to “pull” the cam rearward, so cam endplay isn’t as critical.
However, when you’re dealing with a roller camshaft, the lobes are straight, with no taper. The roller lifters need to be maintained on center with the lobes, so you need to avoid excessive cam walk, but you still need a bit of endplay to prevent a too tight fore/aft fit. A retainer plate at the front of the block may be used, or the addition of a roller bearing thrust button may be required to act as a positive stop between the cam nose and timing cover. The thrust button can be shimmed to adjust endplay. Comp Cams, for example, recommends roller cam endplay at .004 to .010 inch. Excessive endplay can cause roller lifters to run at the edges of the lobes, and if the cam features a distributor drive gear, too much endplay can result in premature gear wear and timing fluctuations.
For performance applications, some builders prefer to add a thrust button to reduce cam walk, even to a flat tappet cam, to reduce timing fluctuations.
Piston to Wall Clearance
When reconditioning a block or when prepping a new block, cylinders are bored (if necessary) and final honed to obtain the desired bore diameter and piston to wall clearance. The piston skirt must be measured with a micrometer, at the specific height specified by the piston maker. When piston skirt diameter is known, the cylinders are
If a flat tappet cam is to be used, use a dial indicator to check cam thrust. In this example, you have cam thrust at .004 inch.
Prior to final honing the cylinder bores, measure the piston skirt using a micrometer. Measuring must be performed exactly at the skirt height specified by the piston maker.
With a pair of rods installed to a common crank rod journal, use a feeler gauge to determine rod sideplay.
honed to provide the needed wall clearance. Always refer to the piston maker’s clearance recommendations, which is based not only on the piston design and material but the intended application as well. For instance, a street naturally aspirated application might call for .004 inch clearance, while a forced induction and/or nitrous application may call for slightly greater clearance.
A cylinder bore gauge is carefully adjusted to the measured piston diameter and inserted into the cylinder bore to determine the difference, which indicates piston to wall clearance.
The type and construction of the piston affects the desired piston to wall clearance. For instance, high silica hypereutectic pistons do not expand as much under operating temperature as forged pistons. As a result, hyper pistons usually require a tighter wall clearance when compared to forged pistons.
Generally speaking, a hypereutectic piston may require approximately .0015 to .0025 inch clearance, while a forged piston of the same diameter may require .004 inch or so for a naturally aspirated street application. If the application calls for forced induction or nitrous injection, an additional .001 to .002 inch or so of wall clearance may be required. As I’ve mentioned repeatedly, always refer to the piston maker’s recommendations for wall clearance.
Rod Sideplay
Connecting rod sideplay refers to the distance that each rod big end can move front to rear on its journal. With the crankshaft installed in the block, insert the rod bearings and install the rods to the crank. Make sure that each rod is oriented properly on its journal, with the chamfered side of the big end facing the crank fillet. In an engine that features a pair of rods on a common journal, both rods must be installed to each journal. Using a feeler gauge, push the rod big ends away from each other by hand and insert a feeler gauge between the rod big ends. Refer to the engine specifications for rod sideplay, but it should generally be in the range of .010 to .019 inch.
Lifter Bore
Measure the O.D. of a lifter body. Using a bore gauge, measure the inside diameter of the lifter
Before checking lifter bore clearance, make sure that the lifters are clean and free of any particles. The lifter bores must be clean as well. Measure the lifter body diameter with a micrometer.
Adjust a lifter bore gauge to the lifter diameter and insert into the lifter bore to determine lifter to bore oil clearance.
bore. Always refer to the engine specifications for recommended oil clearance. Generally, lifter to lifter bore clearance is in the .0015 inch or slightly greater range. Regardless
Lifters should drop into their bores easily. Any resistance indicates a too tight lifter bore.
With the block secured upside down on a stand, lay the upper main bearings into their saddles and place the crankshaft. When checking only for crank counterweight clearance to the block, there’s no need to install the main caps.
of the spec, each lifter should easily drop into its bore. If lifter bores must be enlarged, it can be done either by honing or machining with a cutter. In terms of obtaining the best surface finish for oil retention, some lifter makers may recommend honing or cutting.
Crank to Block Clearance
When using a crankshaft that has an extended stroke, you must check crankshaft counterweight clearance to the block, primarily at the lower web and oil pan rail areas. With the block positioned upside down on a stand, install the upper main bearings in the block bearing saddles. Apply a thin coat of oil or lube to the bearing faces. Lay the crankshaft onto the upper bearings. Carefully rotate the crankshaft, noting clearance between the counterweights and the block. To accommodate any dynamic and thermal expansion issues in the running engine, minimum clearance should be approximately .080 inch or more. Examine clearance at each counterweight as you rotate the crank a full 360 degrees. Mark the block with a marker pen at any tight clearance areas. If any clearance issues are found, remove the crank
With the area of interference marked, a die grinder is used to create a relief by the estimated depth, which then must be rechecked with the crank and rod in place.
and the upper bearings, and use a die grinder to relieve material in the appropriate areas. After cleaning the block, install the upper bearings and crankshaft and double-check to verify clearances.
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Rod to Block Clearance
As with potential crankshaft to block issues, if you’re using a stroker crank, you must check rod big end to block clearances. With the block upside down on a stand, install the upper main bearings and apply a thin coat of lube to the bearing faces. Install the crankshaft, install the lower main bearings to the main caps, lube the lower bearings, and install the main caps. Assuming the cylinder bores have already been bored and honed to size for your pistons, assemble rods to pistons and arrange the rods/pistons on a clean workbench. There’s no need to install piston rings at this time. Remove the rod caps from each rod, keeping all rods and their caps organized. Install upper and lower rod bearings to the
During test fitting of this engine, the rod big ends contacted the inner edge of the oil pan rails. Areas of concern were marked for grinding.
rods and caps and apply a thin coat of lube to the exposed bearing faces. Apply a thin coat of oil to the cylinder walls.
Perform this check one cylinder at a time. Cylinder by cylinder, starting with cylinder number 1, install a rod and piston assembly. Snug the rod bolts so that the cap is fully seated. There’s no need to fully torque the rod bolts to spec at this time.
Carefully and slowly rotate the crank a full 360 degrees, closely watching the rod big end for clearance at the block webs and pan rails. If you find an obstruction or inadequate clearance, mark the block with a pen.
Remove that rod and piston and continue the process with remaining bore locations, marking any clearance issues as you go.
Minimum rod big end to the block should be at least .080 inch or more. If clearancing is required, disassemble to a bare block, grind clearance as needed, wash the block, and reinstall the crank and rods to verify your clearances.
Aftermarket performance blocks commonly provide a rod clearance notch to accommodate common stroke increases. Depending on the stroke of the crank, this may or may not clear your combination.
During test fitting, the rod bolts interfered with the block pan rail inboard area.
After grinding a relief, the fit was again checked to verify adequate rod bolt clearance.
When using an increased stroke crankshaft, check for possible rod big end clearance issues with the camshaft. This shot shows a rod shoulder that seems close to the cam tunnel, but further checking verified that clearance was not an issue. This is the reason that many aftermarket block makers offer block versions with raised cam tunnels.
Piston Ring Gap
After the cylinders have been final honed to size, check the piston ring end gaps in each cylinder. In some cases, you may be using file to fit rings. Organize the rings on a clean workbench, grouping all top rings and second rings.
When checking installed ring end gap, the ring must be squared in the bore at an equal depth along the entire circumference of the ring. A ring-squaring tool such as the one shown here makes this easy. Simply insert the ring, place the tool into the bore, and press down until the tool base is flush to the deck. This type of squaring tool is adjustable for bore diameter.
If top and second piston rings must be filed to fit the cylinder bore, a small, flat, fine file may be used. A bench-mounted ring filer makes the job eas¬ier and quicker. Gen¬tly apply pressure to force the ring end into the diamond wheel, keeping the ring flat on the tool base and the end square to the abrasive wheel. File the same amount from each end of the ring’s gap in small increments, checking installed gap as you go. Until you become accustomed to how much material is removed per stroke of the filer, plan on performing this task several times to creep up on the desired gap. After the ring has been filed to fit, use a small, flat, fine file to deburr the filed edges.
With the cylinder walls clean, carefully insert a top ring into the cylinder by hand. Using a ring squaring tool, push the ring down into the cylinder. The ring must be “squared,” meaning that it must be placed at the same depth around the entire circumference of the ring. The ring should be placed approximately 1/2 to 1 inch below deck.
Using a feeler gauge, measure the ring end gap. Refer to your piston spec sheet for recommended gap for top and second rings. If the ring has no gap, it must be filed to fit. Remove the ring and, using a fine file or a dedicated ring filer, file an equal amount from each end of the gap, clean the ring, and reinsert into the cylinder and measure the gap. Perform this in gradual steps to avoid removing too much ring material. After the ring is properly gapped, use a fine file to carefully remove any sharp edges and burrs from the filed ends. Clean the ring and place it on a clean workbench, marked for the specific cylinder where the check was performed. Continue this for all remaining top
With the ring squared in the bore, use a feeler gauge to measure the ring end gap.
With the dial indicator mounted rigidly, the gauge plunger is set with a slight preload of about .050 inch. The crank is pushed fully in one direction, and the dial is adjusted to the zero mark. As the crank is pushed in the opposite direction, the amount of endplay is revealed on the gauge. Repeat this check several times to verify an accurate measurement.
Here a dial indicator is set up to check crank endplay. If the block is aluminum, placing the magnetic base to the front of the main cap suffices.
rings, then repeat the process for all second rings. Keep all rings organized on a per cylinder location basis.
Crank Thrust
Install the upper main bearings and apply a thin coat of lube to the bearing faces. Make sure that the crank is clean, with any residue or shipping surface grease cleaned from all journals. Install the crankshaft to the upper bearings. Install the lower main bearings to the main caps, apply lube to the bearing faces and install the main caps, fully tightening all main cap fasteners to specification. As you tighten the main caps in steps, start by tightening to about 10 to 15 ft lbs, then rotate the crank and gently knock it forward and rearward with a plastic or rubber mallet. Continue tightening to about 30 to 35 ft lbs and rotate again. Continue until all main caps are fully torqued to specification. Place a magnetic base dial indicator
If the block is cast iron, the dial indicator’s magnetic base may be placed against any convenient flat surface. Make sure that the magnetic base is rigid and does not rock or wiggle.
stand onto the face of the block, or to the face of the front main cap if you’re dealing with an aluminum block. Adjust the stand so that the dial indicator gauge plunger contacts the front of the crank, at either the end of the snout or at the front of the first counterweight.
Using a clean pry tool such as a long straight end screwdriver, pry the crank fully rearward, placing the pry tool between a counterweight and a cap; be careful not to contact any journal surface. With the crank moved fully rearward, adjust the dial indicator to place about .050 inch or so preload against the crank, then zero the gauge.
Thrust bearings feature front and rear bearing shoulders to provide a bearing buffer that locates the crank’s fore/aft clearance. If crank thrust is too tight, the thrust faces may be slightly relieved by laying the thrust surface against a clean sheet of emery cloth on a perfectly flat hard surface and rubbing the thrust surface against the abrasive.
Next, carefully pry the crank fully forward, and note how far the crank has moved on the dial indicator gauge. Repeat this measurement several times to make sure that you’re obtaining an accurate and repeatable measurement. This movement distance represents the crank’s endplay, or thrust movement. Refer to your engine’s crank endplay specification. Generally, crank endplay should be in the range of .005 to .008 inch, but don’t assume. Always refer to the specs. Depending on thrust bearing style, if endplay is too tight, you may be able to shave a bit of material from the thrust bearing thrust faces by laying a new sheet of emery cloth onto a flat, hard surface
Applying clay to the piston requires cleaning the piston dome so that it’s completely dry for the clay to stick. The valve faces need to be lightly oiled to prevent the clay from sticking to the valves.
such as glass or granite and rubbing the thrust face against the emery cloth. If you do need to shave the thrust faces, measure the existing thrust face width with a caliper or micrometer and record the measurement. Constantly remeasure as you remove material to avoid removing too much. If crank endplay is excessive, again depending on the thrust bearing style, you may be able to order a thrust bearing with a thicker thrust wall.
Valve to Piston Clearance
As I discussed in Chapter 8, valve to piston clearance must be checked in both the vertical and radial
The clay is sectioned with a razor and measured for thickness. Using clay is helpful but may not be extremely accurate, considering potential springback of the compressed clay, but it gets you in the ballpark.
planes. In the vertical plane, you’re checking for the clearance between the valve face and the valve pocket. In the radial plane, you’re checking for the radial clearance of the valve head to the radius of the valve pocket in the piston dome. Refer to Chapter 8 for the procedure in checking these clearances. One method involves clay checking, where modeling clay is applied to the piston dome and the crank is rotated to allow the cam, lifters, pushrods, rockers, and valves to run through a complete cycle, providing witness impressions that allow you to measure valve clearance by cutting a cross-section of the clay and measuring its thickness. Another method involves using a dial indicator to measure valve movement relative to the piston dome.
A rule of thumb is to obtain approximately .080 to .090 inch of vertical intake valve to piston clearance and about .100 to .110 inch of vertical clearance for exhaust valves. A forced induction application generally calls for greater clearance, in the range of .125 inch for intake valves and .175 inch for exhaust valves. Valve radial clearance should be in the range of .085 to .100 inch.
To create a witness mark onto the piston that indicates the valve’s centerline, a spare valvestem tip is ground to a point.
The valve head is measured for diameter.
The radius measured from the valve’s center point.
A point machined spare valve is inserted to place a reference center mark onto the piston.
Here an exhaust valve to piston clearance is being checked. With a light checking valvespring installed, and with the piston moved to 10 degrees BTDC, where the valve should be closest to the piston, position a dial indicator contacting the top of the retainer. Preload the gauge by about .150 to .200 inch and zero the gauge.
By pushing the retainer down until the valve touches the piston, note the sweep movement of the gauge needle. In this example, you note an exhaust valve clearance of .113 inch.
Written by Scott Parker and republished with permission of CarTech Inc
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