By Kiyoshi Hamai

It's Just around the block
Part I - The engine block
Over the next few months this series of articles will be discussing basic engine rebuilt techniques. Most of these discussions will be very general in nature with only a few references to Twin Cam, 907, R16 and English Ford engines.

The logic for running such a series is due to the seeming need of many of the members who are novices to the Do-it-Yourself world into which they are often thrown as Lotus owners. Even if they have no interest in becoming a DIYer, basic knowledge will assist in making you into a better consumer. Thus begins this series on engine rebuilds with this month's topic: The Block.

The engine block is the foundation upon which and into which EVERYTHING else goes. Like a building, if the foundation isn't right, then the building ISN'T right. A block is the same; if not correct, you can expect failures.

There are literally dozens of opportunities for block problems including some of the obvious: hairline cracks, tapered cylinders, distorted cylinder bores, improperly finished cylinder walls, damaged cylinder walls, warped deck surfaces, mis-aligned or out of round camshaft (push rod blocks) or crankshaft bearing bores, just to name a few. These are all caused from wear, improper clearance, heat, or some other problem, including improper rebuilding techniques.

So what can you do to save your block from becoming a boat anchor! Two simple things: 1) set everything to the correct tolerances, and 2) Think CLEAN!!!

Let's start with the tear down. You'd think tear down to be unimportant, but quite the contrary. As you tear down any engine watch for telltale signs of problems. This is an autopsy, clean and inspect parts as you remove them from the engine. Wear patterns and component failures will tell you a lot about what's wrong. There's no benefit in replacing a bearing, for example, if the bearing is wearing due to the crank bores being out of line.

After you get the block torn down and over to your machinist, the first thing they'll do is clean it by boiling in a hot tank or bead blasting. Such action destroys the soft parts, such as aluminum cam bearings. Obvious by the above is that aluminum blocks can NOT be boiled in a conventional hot tank, so in most cases high pressure jet washers or cold detergent tanks are used to remove the built up crud. During this cleaning operation the freeze plugs and oil galley plugs are removed. You can request that these be left out if you wish to inspect and replace them yourself.

After the block has been cleaned it is then checked for cracks. Do not fall into the mistake of allowing the machinist to begin boring without checking... it could be $100 worth of boring for naught! Fluorescent dyes, magnetic crack detection equipment (magnafluxing) or pressure testing are used to find those elusive cracks.

If a crack is found it does not necessarily mean that the only future for the block is as an anchor. In some instances a crack can be welded. But, beware of this alternative as welding blocks can be tricky at best, requiring the block to be preheated to relieve stress. The most common fix for cylinder cracks is sleeving. This requires boring the block to accept the sleeve. All of this machine work requires dollars and often it is financially more expedient to get another block, one without a crack.

The block is next checked for wear. Most cylinders wear in a flared fashion, known as taper. Commonly the top is wider than the bottom. Also, normal wear leaves a small ridge or lip at the top rim of each cylinder. This lip must be removed before new rings can be installed. The maximum lip allowable is considered to be 0.003 inch. If the ridge is not removed and new rings are installed the top ring will hit the ridge and crack or pound out the ring groove in the piston or break the ring.

Additionally, cylinders need to be checked for roundness. Both taper and roundness can be checked with a dial indicator bore gauge. Commonly bores should not be any more than 0.003 to 0.010 inch in taper and 0.0014 to 0.005 in out of round.

The finish of the cylinder walls must be inspected for scratching. These scratches can be caused by dirt (running without an air cleaner!) a broken ring or slipped wrist pin. In any case, boring will be necessary to restore the cylinder wall finish. Damage over .030 in depth will probably require a sleeve or new block.

In all cases, boring will require the purchase of an oversized set of pistons and rings. It is recommended that the pistons and rings be handed over to the machinist prior to him boring. Each piston should be numbered and them MATCHED to each cylinder. This means the block is bored according to the size of the piston designated for that hole plus the piston clearance. Pistons DO vary in size, therefore bores can not be assumed to be drilled the same.

As for boring the block, today a deck plate is often needed to keep the block from distorting during boring. This is due to the thinness of the wall of the block. Deck plates are simply thick hunks of metal bolted to the top of the block. The block is then mounted on the boring machine clamp. This positions the block so the boring tool can make straight cuts. The block is bored to a size slightly less than the required size. This allows for about .001 of metal to be removed during honing.

After boring, the surface of the walls are very rough and require honing. The hone is run up and down each cylinder to create a crosshatch finish. The crosshatch pattern is about 450 (or 20 to 30 degrees from horizontal). Hone grit sizes vary between 180 to 220 to leave the proper finish. This finish is slightly rough to help seat the new rings and allow the oil to cling to the surface. Too smooth and you'll have no oil retention on the cylinder walls and rings won't seat. Too rough and you can expect rapid ring wear. The machinist will need to know the type of ring you are using. Different ring materials require different honing finishes.

After boring and honing is completed the block deck is checked for flatness. This surface must be clean and flat in order for the head to seal properly.

The deck is checked for flatness by using a steel straight edge and a feeler gauge. If more than .005 inch of space is found between the deck and the straight edge the deck must be resurfaced. Resurfacing is also required if there are any bad scratches or gouges, these again will not allow the head to seal properly, encouraging head gasket failure.

Decking or resurfacing the block will alter the deck height of the block. This is the distance from the top of the pistons at TDC to the top of the block. This is a critical dimension that affects the compression ratio, valve timing (on overhead cams), and the mating of the intake manifold on V6 and V8 engines. In the worst case, too much milling will allow the valves and pistons to come into contact.

Finally, the camshaft and crankshaft bores must be checked for alignment as well as distortion. If bores are more than .0015 out of round, they should be rebored and oversized bearings installed. To check alignment, an aligning bar about .001 smaller than the inside diameter of the bore is inserted through the bores with the main caps installed and torqued. If the bar doesn't turn easily, the bores are out of alignment and needed to be rebored. An alternate method of checking bores is with a straight edge and feeler gauge. A deviation of more than .0015 calls for align boring.

When you finally get the block home, a good thorough cleaning is needed. You must remove all traces of abrasive and metal particles left from the machine work. Hot soapy water and a stiff bristle brush and rinsing with lots of clean water is the recommended method for cleaning the block with special attention to the bores. After washing, the block should be dried. The cylinders should be wiped clean with a white lint-free rag. If the rag doesn't come out clean, the cylinders are still dirty and need more scrubbing. A light coating of oil should then be wiped on the cylinders to inhibit rust (use some light oil like WD40). If the block is not to be assembled immediately, cover the deck with paper and tape. If stored for a long duration, then it must be oiled heavily prior to storage and scrubbed clean just before assembly.

Remember: DIRT IS YOUR ENEMY!!! There is good reason why engine shops have clean rooms to assemble their engines. Dirt and dust can score bearings, cylinder walls, clog oil passages... keep it clean!

From here on it's a matter of bolting on various parts, checking tolerances, fit, and torquing to specs.

One last word about wet sleeves and aluminum blocks. Both the 907 and R16 aluminum block engines use liners and pistons. Liners usually can not be bored. Therefore, pistons and liners must be purchased and installed as matched sets. Anyway, enough on blocks...

LET'S GET CRANKY
Part II of the Engine Rebuild Series
Last time we spoke of the block and the foundation. This installment we're off to crankshaft land and to get some lessons in crankology.

Next to the block the most important part of the engine is the crank. It's the thing that goes around and around and converts the up and down motion of the pistons and rods into a roundy-round motion. Thus it is subject to incredible loads and constant pounding. The crank is so important to good engine life and power that there are people who specialize in just be cranky.

First off there's disassembly. This is an important step because the old bearings can tell you the whole story about the condition of the crank and rods. So, bust down the engine carefully, keeping bearings and caps in order. Clean them with degreaser and inspect for eveness of wear, scoring, and wear patterns. Now, degrease the crank and check it for wear. Any scoring or gouging means the crank will have to be turned. If the drank has been previously ground the machinist will have usually stamped a 10, 20, or 30 near the journal. Keep this in mind since any further grinding may put the crank under spec, in which case the crank should make yet another good boat anchor.

So, you think the crank is okay! No, no yet, you haven't mic-ed the journals. Break out the micrometer and let's measure'em and see what's what. First there's taper wear; that's where one end of a journal is worn more than the other end. Next, there's "Hour-glass"; that's where the center is worn more than the ends. The opposite of Hourglass is "Barrel" wear; yes, the outer ends are worn more than the center. Finally, you need to check for out-of-roundness and overall size. Missing any of these and just slapping in a new set of bearings is a guarantee for failure. As a rule of thumb, the maximum amount of allowable out-of-roundness for cranks with journals less than 3" in diameter is 0.0002 to 0.0005 inches. Some folks seem to think that it's okay to go to as much as 0.001 inch, but I'm a skeptic and certainly for race engines the lower limit of 0.0002 should be used.

As for Taper wear across a rod journal the limit is 0.0003 to 0.0005 inches (2" or greater diameter). Again use the lower limit for highly stressed engines (race).

As you inspect the crank you can usually tell if the crank has been re-ground by finding those machinist's markings. Now, as for getting the crank ground, here's a few things to check. First, the journals should be within 0.001 inches of the size you wanted. Most machinists are extremely precise, but they're human, so check the dimensions, this is easy and good preventative medicine. Secondly, check to see if the journals have a properly machined fillet. This is the radius between a journal and the adjacent counterweight. If the radius between a journal and the adjacent counterweight is too large it could cause interference with the bearing. If the radius is too small or absent, the sharp corner can create a stress point which may cause the crank to break.

Thirdly, the oil holes should be gently blended or chamfered. This slight smoothing of these holes promotes good oil flow to the bearings. Finally, the journals should have a relatively smooth finish, no rougher than 10 to 15 micro-inches. If you have questions about the condition, then ask the machinist to check it out.

There are basically two types of cranks: Forged and Cast. The forged crank is pressed out of forged steel while the cast crank is molded from cast iron. Obviously, forged cranks are costly, but are considerably stronger. The Kent based Fords as used in the Lotus Twin Cam all used cast cranks as stock. The 907 Lotus engine uses a forged crank except for in some early Jensen Healeys where a cast crank was used.

To differentiate between the two is not easy, but crucial. Typically, forged cranks have a wide separation line where the flashings produced by forging have been ground off. Whereas a cast crank will have a fine line where the casting mold parted.

A forged crank can be straightened. A cast crank will snap under a press. Therefore, a forged crank should be checked for straightness. Usually the bearings in the center will be worn more than the outer ones. And, then the crank itself can be checked for trueness by rotating it on V-blocks while checking for wobble with a dial indicator. If any runout is found and is greater than spec in a forged crank it can be straightened. However, if runout is found in a cast crank it is JUNK.

Speaking of bent cranks, beware that it is possible to BEND a crank by not properly storing it. NEVER, EVER, lay a crank on its side. It may seem safer but cranks are KNOWN to bend under their own weight when set prone. STAND CRANKS ON THEIR ENDS!

Also, prior to any machining, be sure to have the crank checked for cracks be it done with dyes or magnafluxing. It's silly to do dollars of machine work on what turns out to be a two pieced boat anchor.

Now, when you get the crank home and you're thinking about installing it, the first thing you do is give the crank a bath. That's right, a bath. A hot soapy one, with bubbles. Scrub it with a soft sponge (new or very clean) and dry it thoroughly. This will remove any tiny metal particles from the machining.

Next, NEVER assume the machinist ground things correctly. Double check bearing clearances with Plasti-gauge (do every bearing!!). You don't need to find out a bearing is too loose by wondering why you haven't any oil pressure, or wondering why that bearing seized. Double check the end float with a dial indicator, and make sure you've installed the thrust washers in the correct orientation.

As for the connecting rods, as with cranks, rods are usually either forged or cast (there's also aluminum, steel, titanium, etc.). Again, forged rods are stronger and can be repaired. Common rod problems are cracks (rendering the rod junk), worn piston pin bushings (can be re-bushed), out-of-round bearing bores (bores can be re-machinied), bent rods (more junk, replace), and twisted rods (often due to taper wear on crank) that can often be straightened. There is some controversy about straightening even twisted rods. Many claim that rods should be considered junk if found twisted. When in doubt, replace it!

Finally some tips..:. Use Anti-seize for the rod bolts and main cap bolts. Be sure the bolts are clean and properly torqued. Assembly lube is a must, whether it be some straight motor oil or some specialized stuff on the market. USE IT. Don't use white grease, it doesn't mix with oil (if you do, make sure you do an oil change soon). And, don't forget to change the pilot bearing/bushing in the flywheel end of the crank.

RING AROUND THE ROSEY
Part III of the Basic Engine Rebuild
In the last parts we covered the basics of crank and rod technique, and prior to that was a discussion on the fundamentals of the block. This month we get into the pistons, rings, wrist pins and a comment or two about balance.

The pistons and rings are subjected to incredible loads as they are accelerated by a massive explosion that produces rapidly expanding gasses and tremendous amounts of heat and tons of friction as they scrape down and up the sides of the cylinder bores. How much loading! Let's take a typical Twin Cam, stroke is 2.864 inches. Say at 4000 rpm we take a look at what's happening. The piston would be traveling a total of 1909 feet per minute (21.696 mph). Consider at both TDC and BDC the piston stops traveling up or down and reverses direction, therefore it is accelerated from 0 ft/sec. to 1909 ft/min. Quickly, then this acceleration can be put in the terms of "g's". Any guesses! How about...131.769 Gs! This means if a typical TC piston weighs about 1.25 pounds (with pin and rings), the force it produces is about 165 pounds (about the weight of an average guy standing on your stomach...). Consider that loading and unloading is taking place 8000 times per minute at 4000 rpm, and you begin to realize the pounding things take, and wonder how it all holds together. Let's not forget that the argument above DID NOT take into consideration the additional loads created by the explosion of air and fuel, nor the load of compression.

There are basically two types of pistons; forged and cast. Most street engines use cast, and like cranks and rods, forged pistons are stronger and more costly. A cast piston can be identified by looking at its underside, there you will find the casting mold seams. Forged pistons have no seams and usually have a swirl-like pattern on the surface where the metal flowed during forging.

All pistons are not, however, round. They are, in fact, oval, being wider 90° to the wrist pin. Thus when measuring the diameter of the piston a caliper should be taken across this width. Rebuild spec will include a spec for the clearance between the piston and the bore, this is the difference between piston OD and cylinder bore ID. Please note that forged pistons expand to a greater extent than cast and therefore require more clearance. This is important if using forged pistons on the street where the forged piston may never, (in a short run), come up to full temperature (and therefore full expansion). The forged piston in those circumstances may have problems with oil control and piston slap. Hence, often it is not a great idea for that hot street motor to drop in a set of forged pistons.

A new casting technique has been recently developed called Press Molding. Simply put, the metal is compressed as it is cast. The resulting piston is nearly as strong as a forged unit but much less expensive and usually lighter than cast.

Also, manufacturers of pistons have recently gone into coating pistons with various substances including tin, teflon, iron and graphite. In the future, expect to see more in the way of ceramics.

Now the rings. Most standard rings are constructed of nodular cast iron. Others may be chrome-plated, coated or filled with molybdenum, ceramic or other materials that will add to life and wear. The rule here to remember is, "The harder the ring, the longer the life...but the longer it will require to take a seat". Obviously, as mentioned previously, the finish on the cylinder bores will greatly affect the wear and seating of the rings.

The top ring is referred to as the Compression Ring, the second (middle) is the Intermediate Compression Ring, and the bottom most is the Oil Ring. The design of rings is all over the map, with claims of better sealing, better oil control, etc. Each has its advantages. The best advice is to follow the ring manufacturers recommendations.

Rings, too, must be checked for size. Ring gap must be at spec. This is the gap that remains between the two ends of the ring when it is installed in the cylinder bore. It also must be the correct thickness. This means with the use of a feeler gauge measure the gap between the ring and the piston when the ring is fitted into the piston's ring land (groove). Excessive clearance here is usually caused by wear, (in the case of reusing an old piston with worn ring land), or by the incorrect ring size. In the former case, a new piston is in order. In the latter, get the correct ring. Too much clearance between the ring and the piston ring land will allow the ring to be pounded up and down in the land and will eventually cause ring failure.

When installing new rings always use a ring expander tool, it will prevent the accidental bending or twisting of a new ring. The rings must be rotated so that the ring gaps are at least 600 apart, 1800 is better. Be sure to install the rings with right side up. Most rings are marked with a dot or symbol to indicate the top. And, if reusing an old piston, be sure the ring lands are thoroughly clean. Lastly, little or NO lubrication is needed on the piston and rings.

Piston installation is straight forward. Inspect the wrist pins, replace the wrist pin bushes in the rods, and install with new cir-clip retaining rings. If you find any looseness between rod and pin and/or piston and pin, find out its cause and rectify. Be sure to orient the rod front with the piston front, then install into the block with the front facing the front ... sounds simple, but I've seen and heard of too many times when an engine failed due to the piston and/or rod being installed backward.

Lightly coat the cylinder walls with motor oil and install the piston using a ring compressor. DO NOT oil the ring and pistons, doing so simply causes the rings to take much longer to seat and you take the chance of having the oil coke (burn) and collect in the ring lands. A number of engine builders do not recommend WD40... DO use assembly lube between the wrist pin and piston and rod (at all bearing surfaces).

A word on balancing. Highly recommend, balancing ALL Lotus engines. It is worth the expense. This means taking your crank, harmonic pulley, flywheel, flywheel bolts, pressure plate, rods, rod bolts, rod bearing caps, wrist pins, pistons, rings, etc., into a good machinist. Remember at the opening of this article spoke about the forces involved, well with a balanced engine all those reciprocating parts are equal in weight. The result is a smoother, longer, better rev'ing, engine.

IT'S ALL IN YOUR HEAD
This is the 4th of the engine series and this month as the title suggests we will be investigating cylinder heads and valves.

Again we start with disassembly. This is an important as it is the best time to inspect parts as they come off. Check for wear patterns, cracks, pitting, etc. Once the head is stripped check for warpage and cracks. This is especially true with aluminum heads. A cracked head is usually considered terminal, even with cast iron. Although there are cases when cracked heads can be welded and rebuilt.

Warped heads are another matter, as the normal fix for a warped head is to mill (deck) the head. To check for warpage, lay a straight edge across the head both along the length and across the head in a few places. Any daylight indicates a degree of warpage. Ignoring warpage is a guarantee for a blown head gasket.

Some care should be taken in simply decking the head to get it straight. Firstly, consider that it will raise the compression ratio. Secondly, it will bring the valves in closer proximity to the pistons and may cause interference. Thirdly, on overhead cam engines, it will alter the cam drive geometry, altering the timing. Lastly, and perhaps most overlooked is that fact that if a head is warped, and warped badly enough it may cause the cam bearings to be out of alignment. This means that the cam bearing journals should be line bored. Not doing this may either cause premature cam bearing failure or the cam to break!

Warped aluminum heads can often be straightened by heating and clamping in an oven. This may save a head. Also, after you've gotten all those hundred of dollars of head work done don't store the head flat (prone), like the crank the head will warp. Stand the head on its end for storage, next best is to lay it on a flat straight surface.

Let's talk valves. Valves are subjected to heat, friction, abrasion and metal fatigue. Consider that in a typical Twin Cam Europa that at 60 MPH the engine is turning about 3000 RPM. This means in an hour's time the valves have opened and slammed closed 90,000 times!

When a valve slams shut the face of the valve is pulled tightly against the valve seat, thus sealing the combustion chamber. During this brief interlude of intimate contact some of the valve's heat is transferred away through the seat into the head. This assists in cooling the valve. Second, there is a microscopic welding process that occurs. A few tiny particles of valve and seat will stick together and will be torn loose when the valve is opened. They remain on the surface and act like hard abrasives when the valve slams shut atop them. This gradually wears both the valve and the seat until the seal is lost. This process is called valve recession. Consider that an exhaust valve is exposed to the greatest amount of heat, the intake valve gets a cool blast of air/fuel mixture when it opens, the exhaust valve only gets a hot blast of burning gasses when it is opened, therefore it stands to reason that the exhaust valves fail first.

Valve wear can be, accelerated by excessive engine temperatures (lean mixtures, or cooling system probIems), running an·engine at high rpm, insufficient valve Iash, dirt contamination (from lack of an air filter), and use· of unleaded fuels with heads that require leaded petrol.

Lead assists in prolonging valve life by reducing the microscopic welding that occurs. The lead thus acts as lubricant between the valve and the seat. The only permanent solution to the problem is to change the valves to harder material (such as those found in newer engines) and new harder valve seats. There are chemical substitutes for lead that are sold as after market gas additives, but these should be considered temporary until the ultimate solution can be installed.

Good machine work is a must. For example, if the valve seat is too narrow there will not be enough contact surface for good heat transfer. Conversely, if there is too much contact between valve and seat a good seal may not be had since,·there may not be enough pressure from the spring when the force is spread over a larger surface area.

The clearance between the valve stem and valve guide is absolutely critical. Insufficient clearance leads to scuffing and rapid stem and guide wear. This may even Iead to sticking which can put the face of the valve·through the top of the·piston. Too much clearance will allow a steady flow of oil down the guide. The oil in turn cokes and becomes an abrassive, further wearing the exhaust or intake valve.

To check for worn guides, simply lift the valve about an inch off its seat and check for wobble. If it does, it's loose. Loose, guides can be repaired either by out right replacement or, if minor clearance problems are·found, the·guide may be knurled.

Many engines use valve seals (but not Twin Cams). There are positive seals, these are seals made of Mitrile rubber, Polyacrylic, Vitron or Teflon. Nitrile is good to about 250°F, Polyacrylic to 350°F, and Vitron to 440°F. The cost of the better seals is worth the expense. The other type of seal is deflector or splash type. These deflect the oil away from the guide.

All valves must be checked for straightness. New exhaust vaIves are·often needed due to the heat to which they are exposed. If valves are to be reused, the tip of the stem must be ground if the valve face is ground. This must be done to retain the proper valve stem length. Valve height is extremely critical. If a valve rides too high, it can over heat. Too low, and it can interfere with the eignine's ability to breathe, reduce the effective spring pressure of the springs and possibly upset the valve train geometry.

Valve springs require attention too. Again, they too are subject to heat, heat which accelerates their fatique They lose tension and often break. It is a good idea to place shims under the springs. This increases the·spring tension and helps to insulate the spring from heat.

So, get your head on straight, get your valves right and your engine will perform as it should.

IS IT TIME YET
This is the fifth in the basic engine rebuild series In the previous 4 installments of this series on basic engine rebuilding we covered the overt items that require attention in the basic engine rebuild. This month we will discuss something that is more often overlooked and usually taken totally for granted, that being cam timing.

Why cam timing! Because more often than not cam timing is not correct and therefore a major cause of power loss. The question here is why should you go through all the trouble and expense of doing costly machine work only to not get the maximum horsepower due to improperly timed cams.

How important is cam timing! Try 3-5 BHP for every 1 degree of crank rotation in a typical Twin Cam motor. In real life this means as much as 15 BHP for 5 degrees of inaccuracy.

What is cam timing! When the engineer designs a powerplant he indicates a specific point at which the intake and exhaust valves open and close. This is specified to insure that the power, torque and fuel consumption will be as intended. Therefore cams should be timed when the engine is assembled.

How does one time the cams! It is not unlike ignition timing, where one compares the opening with the crank revolution. The equipment required to time cams is a short list which includes; dial indicator, stiff piece of wire, degree wheel (usually can be found at a hot rod shop, like one from Mr. Gasket), and either a clamp or mag mount for the dial indicator.

First, you'll need to mount the degree wheel to the front harmonic pulley. Do this in such a manner that the degree wheel will not easily be disturbed (bolts or hard fasteners are the best). If you have a spare harmonic pulley you can hard mount the degree wheel permanently. Now you're ready to find Top Dead Center (TDC). Now afix a short piece of stiff wire to the block such that it can be used as a pointer for the degree wheel.

Next, place the dial indicator (one with 1" of travel) such that the plunger reaches through the #1 spark plug hole. True TDC can now be found. Put the engine near TDC, note the reading of the dial indicator and degree wheel using the wire indicator. Now run the crank through TDC and beyond until the dial indicator reaches the same reading, note the reading on the degree wheel again. TDC is exactly half way between the two degree wheel readings. Set the degree wheel such that TDC on the degree wheel is pointed at the indicator. You have now set and found TDC. Be VERY careful not to accidentally alter the degree wheel setting.

Next locate the dial indicator at one of the valves of the #1 cylinder. Place it carefully next to the cam lobe, being careful that it doesn't foul with the cam. On push rod engines, the dial indicator plunger can be placed on the valve keeper. Slowly rotate the engine in the proper direction, noting the maximum lift (this is not a true lift reading, since usually the dial indicator is at a slight angle, thus showing more lift than actual).

Locating the actual valve opening and closing angles is not simply using the dial indicator to show when the valve opens and closes. The problem here lies in the fact that the cam lobes are ramped to prevent the valves from slamming violently closed. Hence, if one were to attempt to find when the valve opened, one would find a variance of 5 degrees or more. Therefore, the most accurate means of setting cams is by finding the cam lobe center. This is the number of degrees of crankshaft rotation at which it reaches maximum lift. To determine the lobe centers the following formulas are used. Use specs from given cam specifications.

Intake Lobe Center = [IOIBTDC + 180 + ICIABDC - IOIBTDC] / 2

Exhaust Lobe Center = [EOIBBDC + 180 + ECIATDC - ECIATDC] / 2

IOIBTDC = Intake opens before top dead center
ICIABDC = Intake closes after bottom dead center
EOIBBDC = Exhaust opens before bottom dead center
ECIATDC = Exhaust closes after top dead center

For example, a Twin Cam engine's specs call for the intakes to open at 26 degrees BTDC and close at 66 degrees ABDC. Thus ((26+180+66)/2)-26=110. The lobe center is 110 degrees. For the exhaust it's ((66+180+26)/2)-26 = 110.

Now, to find the actual lobe center of the engine rotate the engine near the maximum left, noting the measurement on the dial indicator. Note the degrees on the degree wheel. Rotate the engine through cam lobe center until reaching the same measurement on the dial indicator. Note the number of the degrees indicated by the degree wheel. The actual engine lobe center is halfway between the two measurements. Compare this to your calculated lobe center from the specs. In all probability they will not be the same and will require the cam timing to be altered. For DOHC engine duplicate this procedure for the exhaust cam.

To alter the cam timing you must either rotate the cam or the sprocket the number of degrees in error you found. Remember cam timing is altered 10 degrees for every tooth on the sprocket. For lesser adjustments offset sprocket pins can be used. These pins come in a range from 1 to 9 degrees.

To install offset dowels for degree changes you must first remove the camshaft (it can be done without removing the cams, but extreme care must be taken as usually the pins are too tight and need to be driven out) and exchange the pin for the new one. If installing a new chain, allow 1-2 degrees for chain stretch. Reassemble and check cam timing, being sure to install the offset pin in the opposite rotational-sense from what you've calculated.

Finally, you might consider marking your sprockets for the new orientation of your cams. Check the ignition timing and carburetion to max out your new found power.

TO OPEN OR CLOSE THAT IS...
This is the last installment of this 6 part series on basic engine rebuilding techniques. We will be covering the cam and lifters. Because of the various configurations of valve trains now used this discussion will concentrate on push rod and the overhead cam with bucket tappets as used in the Lotus Twin Cam and 907 engines.