02-01-2010, 04:27 PM
Engine machine work explained
ENGINE MACHINE WORK EXPLAINED (part 1)
I have noticed that many DSM tuners out there are attempting your own engine rebuilds, and many have questions on what machine work to do, how the various types of machining processes differ, and the capabilities of the various machines. This is intended for the laymen so that he/she may better communicate with machine shop staff.
The intent here is to provide information on the various types of machine work available, the types of equipment used, and where appropriate the strengths and limitations of the technology employed.
A good machinist is a must, so many of these operations require skill and a good base knowledge of what is being done and why. A good machinist can do great things with older equipment, but a poor machinist with the best equipment money can buy, will be frustrating and expensive.
There are several types of block cleaning methods. Some of the more popular ones are hot tanking, baking, and heated sprayers. The purpose of this process is to remove oil, grease, and carbon residues from all surfaces of the engine. Additionally corrosion build up and rust may need to be removed as well.
The hot tank method utilizes a heated vat of water with a chemical agent (such as caustic soda). A solution circulator is used on some types of hot tanks. The block is lowered into the vat and allowed to sit there for a period on time. During the time in the vat the chemical solution dissolves the various contaminates. This system works well at removing oils and greases, but may sometimes have difficulty removing heavily sintered carbon deposits. Its effectiveness on corrosion and rust are somewhat dependent on the type of chemical agent used.
Baking is a three or four step process depending on preference. Both employ baking, a heating of the block to a high temperature to bake off or embrittle deposits. The next step is blasting or beading. In this process the block is placed into an enclosure where very small metal shot is circulated at high speeds. As this shot impacts the block it chips off the various baked and embrittled deposits. To finish up the block is placed in a tumbler. This machine has a rubber lined drum in which the block is placed, and tumbled slowly. The purpose of this procedure is to remove captured and entrapped shot from the block. Above I mentioned that this might be a four-step process. The fourth step that some establishments use actually takes place prior to baking the block. Some companies perform a precurery washing of the block to remove basic oil and grease deposits prior to the baking process. Extra care must be taken prior to the assembly process to ensure that all of the shot particles have been removed from the various passages and crevasses in the block. This process usually does an excellent job at cleaning, and generally removes all rust and corrosion. However it does have the potential for shot particles to be left behind. So great care must be taken by the assembler to ensure to removal of all these particles.
The spray wash method uses a solvent similar to that used in the hot tank method. However instead of the block being dipped into a vat, it is placed onto a rotary table that pulls or swings out from the spray cabinet. When this type of machine is cycled it rotates the block while multiple spray nozzles at various angles project the heated solution onto the block at high pressures. Like the hot tank method the types of debris removed by this process is somewhat dependent on the type of chemical agent used. This method does a good job at removing grease, and oil deposits. The high-pressure sprayers help in removing carbon deposits, but it will generally have little effect on rust spots.
Align Boring and Honing
Both of these processes are similar, but are used for different reasons. Align boring uses a carbide type cutter bit to bore the main bearing, and cam bearing housing diameters. This is done to ensure that all of the bearing saddles or housings are on a common plane in all three axis’s. The align boring method is often used in the manufacturing process to initially establish the plane of the bearing housings centerline. This method is also used when a new bearing cap needs to be installed due to previous damage, or if aftermarket bearing caps want to be installed.
For this article I will talk about re-align boring or honing existing housings, as opposed to the manufacturing of a new one. Before the housings can be align bored the housing diameters must first be reduced so that they may be enlarged back to their original size. This is done by cutting the bearing cap on a specialized machine. A small amount of material is removed from the caps surface where it meets its mating surface. This effectively shrinks the housing diameter, although more on one axis than the other. Once the caps have been cut, they are installed and properly torqued. Next the boring machine is set up and a mandrel is precisely aligned to the existing plane of the bearing housings. Then a cutter bit is installed and adjusted for correct size. Next all of the bearing housings are bored without further adjustment to the mandrel; this is done to ensure the integrity of the plane of the bearing housings.
Align honing is generally used to re-align and re-size bearing housings that have not been severally damaged. This process uses a mandrel with many honing stones, and alignment shoes. Like the align boring process the housing diameters must first be reduced to something less than specified. The honing mandrel sort of self aligns to the current bearing housing plane. Then the honing mandrel is rotated and stroked along the bearing housings axis. This process is started, stopped, and size checked several times, until the correct housing diameter is reached. All of the bearing housings are sized simultaneously in this process.
Generally speaking align boring is more expensive than align honing, this is because there is more set-up time involved in the align boring process. If you need to have a bearing cap replaced you will most likely need to use the align boring method. If there is just an alignment or slight size issue, you may be able to use the align honing method. There are several problems or concerns that may arise when using either of these processes. First there can be a squareness issue when the bearing caps are cut. Meaning that when the cap was cut to reduce the housing diameter it was not cut parallel with the housing bore, or its original face. This can be a problem if one or more of the caps have additional machining perpendicular to the axis of the housing diameter for a thrust bearing. Basically this can cause the thrust bearing on the cap side to sit differently than it does on the block or head side. Second since both of these processes alter the bearing plane, the distance from the bearings centerline to the deck surface will change. Additionally the squareness of the bearing centerline to the deck surface and cylinders can also be affected.
Re-surfacing of the block deck, or cylinder head. There are several types of block and head resurfacing machines, there is also deck and head resurfacing, deck and head straighting, deck squaring, and angle milling.
Types of machines
Rolling belt surfaces. These machines are similar to a large belt sander. Basically there is a large abrasive belt that revolves, and the cylinder head is pressed against the belt removing material from the head surface. This type of surfacing generally leaves
fairly rough surface finishes, and does a less than average job at controlling how much material is removed, and retaining surface squareness.
Grinding head surfaces. These machines use single or multiple stones to remove material from the cylinder head or block surface. Surface finish with these machines varies depending of type of stone used, cutter speed and feed rates. The stones must be dressed to provide good consistent results. Most of these types of machines allow the operator to set up and dial in the part, so they do a reasonably good job of removing a specified amount of material. Additionally many of them are capable of correcting alignment and uneven surface wear.
Multiple carbide cutters. These machines have an indexable cutter wheel, in which many carbide inserts are held. Most have a provision for positioning the block or head and are capable of adjusting the part to be machined on three axis’s. Also many of these machines have variable cutter speeds and feed rates, as well as different carbide inserts for varying tasks. Some of the higher end machines are capable of surfacing a head or block back to its original plane, (this is not the same as just surfacing something).
Most machine shops will surface a part for you by indicating in on four corners, and then removing as much material as necessary to clean it up. Although there are limits as to how much material can be removed, and it varies with type, and manufacturer. One of the problems with this method is that unless the part being surfaced has equal wear on all corners or its only imperfections are not near one of the surface corners, then equal amounts of material may not be remove form each end of the part. On a cylinder head this can lead to uneven combustion chamber volumes. On over head cam heads it can also lead to camshaft centerline parallelism problems, causing undue cam thrust loads, and/or timing belt or chain run-out troubles. On blocks it can cause varying deck heights in relation to the crankshaft centerline. This is not usually major concern since typical cylinder head warpage is most often found between the combustion chambers. However if you suspect that the part has seen excessive heat, has been machined before , or want more than the typical rebuild, then you may want to enquire with your machinist prior to having them do any work.
Angle milling is typically used on wedge shaped combustion chamber engines. It is a resurfacing process that tips the cylinder head prior to resurfacing it so that more material is removed from the deep combustion chamber side of the head, than the shallow side. This process requires that the intake manifold surface of a V-8 type cylinder head be machined also to correct the “V” angle that was slightly altered in the previous process.
Boring and Honing
Boring is a process used to establish or re-size a cylinder to accept a given piston diameter or oversize. Boring is a machining process and must be followed up with honing to achieve to correct surface finish.
Boring Bars (like the Kwik-way FW) are semi portable machines that most often mount to the block via an attachment anchored in the adjacent cylinder to the one being bored. These machines are very accurate, and can last decades. These machines most often incorporate a self centering device that quickly allows the operator to center the boring head within the cylinder. A setting tool (micrometer) is used to position the carbide cutter to a specific diameter. The machine then automatically feeds vertically to bore the cylinder to the size set. The machine is then moved from cylinder to cylinder until all have been bored to the correct size.
This is one of those machines where the operator can make a big difference. Centering high in the cylinder (where the most wear is) will allow for the smallest oversize piston to be used. This is because this centers the boring head to the area of greatest wear, which most often is not concentric with the bores centerline. So yes this will reposition the cylinder by several thousands of an inch. Conversely centering low in the cylinder will best pick up the factory original bore spacing, but may require a +.030, or .060 overbore to clean up the entire cylinder. Since boring requires the secondary operation of honing a specific amount of material must be left after the boring process. Too much material left can result in cylinder taper, out of roundness, and baler shaped cylinders. Too little material can lead too excessive piston to wall clearance. Too little can also lead to microscopic imperfections being left in the cylinder walls from the boring process. Boring is a cutting process, therefore some tearing of the material take place. To adequately remove these imperfections there are minimum material removal requirements for cylinder honing. Leaving these imperfections can lead to piston ring sealing problems as well as piston skirt problem.
On the up side boring bars allow for the cylinders to be resized square to the crankshaft centerline and perpendicular to the deck surface, this is especially important if you have had your block align honed or bored, and the block decked, which can both lead to misalignment of the cylinders in terms of their position relative to the crank centerline and deck surface.
Vertical boring machines are similar to boring bars, but would not be considered portable, and instead of mounting the boring bar on the block, the block is placed in the machine. Some of the higher end machines allow positioning of the block based on crankshaft centerline, and allow precise V angle rotation to maintain square-ness. Many of these machines allow the block to be dialed in position wise, so again a lot comes down to the operator. Vertical boring machines are more expensive than boring bars, but are also much more ridged, and have more options for the machinist.
Vertical honing machines (like the Sunnen CV616) are very popular due to their ease of use, and high production rate. These machines do not use carbide cutters; they hone the material out from start to finish, using variable grit stones. They do not precisely center the honing mandrel in the cylinder, nor do they usually hone based on crank centerline, or deck square-ness. The honing process simply removes material from a given hole position. These machines will not correct cylinder position, nor will they correct for square-ness. However these are very tried and true machines, and in most cases the possible problems listed above, and their impact on the final product will be small. These machines exert much more pressure then one could use a hand held hone, thereby helping to ensure a very clean surface finish.
Some high end or race shops will use either a boring bar or vertical boring machine to ensure correct cylinder position, and then finish the process with a vertical honing machine, getting the best from both worlds. This is a little longer process, and is typically more expensive.
Real hand honing is back breaking work (trust me here) and no I am not talking about the little dingle ball or flexi-flier hone you did your last job with from Auto-zone. These types of de-glazing tools are not worth mentioning further. A good ridged hone uses the same type of stones and guide shoes as the CV-616 mentioned above. They also include a mechanism for expanding and applying force to the stones on the cylinder walls. These hand hones are several hindered dollars (stones & shoes sold separately) are typically driven by a ˝” or ľ” electric drill motor. If you have access to one or want to try it I would suggest locking the block down somehow, and make sure your feet are well planted, as to do this correctly you will need to apply enough force to load down your drill motor. Like most things in life the result you get is directly proportional to the effort you put in. Even though this is a mostly outdated process, there are still many high end race shops that only trust the very final honing step to this process, and only then on their motors for the best of the best.
Cylinder head work:
Degreasing and cleaning of cylinder heads is not much different from the processes and machines used for block cleaning mentioned above.
Valve re-facing & valve seat machining
The term valve grind is in actuality several machine processes. For example if you drop your head off at a machine shop and ask for a valve grind several operations will occur, like cleaning, valve facing, seat cutting, assembly, and if applicable valve clearance adjustment.
The actual grinding or cutting of the valve face is intended to establish a new sealing surface on the valve head that is concentric with the valve stem. There are three basic parts to most valve facing machines, the first part holds and rotates the valve so that the face or sealing surface can be evenly machined. On many machines this part also pivots in relation to the grinding wheel or cutter allowing a change to the face angle machined on the valve. There are two basic types on valve holding methods employed centering and center-less valve holding.
The second part of the machine is either a grinding wheel powered by an electric motor or a carbide/diamond cutter bit; both are used to machine the valve face. Grinding wheel machines require that the grinding stone to be dressed/trued every so often due to the fact that grinding also removes material from the grinding wheel as well as the valve during the facing process. Carbide or diamond bits are simply replaced when required.
Third is a mechanism for facing the tip of the valve stem, this is needed to correct the stem height of the valve when installed in the cylinder head. This is typically a rotating stone and pivoting valve holding mechanism with a micrometer adjustment wheel. This adjustment wheel allows very specific amounts of material to be removed from the valve stem. This is a very important step, when the valve face is cut it moves the valve toward the cam, rocker, or lifter depending on the engine type. Machining the valve seat has the same effect. Therefore if .015 is removed from the valve, and .020 is removed from the seat .035 must be removed from the valve stem tip. In order to maintain the correct hydraulic lifter preload, or to maintain a specified valve lash setting. Failure to do so will result in incorrect valve lash setting, too much or too little lifter preload.
02-01-2010, 04:28 PM
Valve seat machining
Many types of machines are available for machining the valve seats. Powered and un-powered, grinding or cutting, and wet or dry machining. Basically grinding type machines use stones which can be dressed or cut to a specific angle; these stones are then attached to a mandrel with a specific pilot diameter and bearing assembly. A guide arbor is used to accurately machine the valve seat relative to the valve guide. The guide arbor has two ends one which employs either a short or long taper and its median diameter is specified in one thousandth of an inch increment. Specific arbor diameters are selected based on the diameter of the valve guide. The other end of the guide arbor is usually a specific diameter that is proprietary to the type of stone mandrel being used. The stone and mandrel are aligned to the valve seat based on the valve guide centerline. The stone is then rotated usually with an electric motor to machine a fresh angle on the valve seat concentric with the valve guide and at a specific angle. This process can be repeated with as many different angles as required. Most of you have herd of a 3 or 5 angle valve job before, this refers specifically to the number of angles machined on and around the valve seat. Most valve seats use a 45 degree sealing surface; the other two or four angles can be referred to as entry and exit angles. For example a 3 angle valve job with a 45 degree seat would also machine a 30 degree exit angle just below the valve seat on an intake port (this would be considered an entry angle on an exhaust port), and a 60 degree entry angle just above the seat on an intake port (& vice versa). A 5 angle valve job typically adds 15 and 75 degree cuts to the ones mentioned above. This process is intended to create a funnel leading into, past and out from around the valve itself.
Valve seat machining with carbide or diamond cutters is a newer method than grinding, and some do not require a powered drive motor, they are simply turned by hand. These systems use the same types of locating equipment to correctly position the seat, entry or exit angles. An advantage with this type of system is that the carbide or diamond cutters do not wear very quickly, thereby creating a more precise set of angled diameters. Stones wear and require dressing often to maintain the correct angle and cut to cleanly.
Some systems employ a coolant bath during the machining process, this clears removed material, helps dissipate heat during the cutting process, and helps maintain cutter life.
An additional item to the 3 and 5 angle valve jobs mentioned above is actually a process with the valve itself. It is called back-cutting and is done with the valve facing machines mentioned above. This process relieves the un-used portion of the valve face an additional 15 or 20 degrees. A typical exhaust valve when re-faced at 45 degrees could have a .175 wide face angle, the valve seat in the head maybe .100 wide so we need only provide roughly a .110 wide face angle.
A good quality valve job will remove enough material from all the valves to adequately clean them up, and remove the same amount from all intake and exhaust valves. Basically the valve that requires the most amount of material removed is determined first, and then the other valves are machined to match. The same is done with the valve seats, except that they all need to be machined to the same depth. This depth is usually measured from a good reference point like the deck surface. This process ensures that all valves are like distances from other moving things like pistons. If this process is not used you should plan on checking every valve for piston to valve clearance, because they will all be different. Additionally this process allows the machinist to determine the amount of material to remove from the valve stem tip in order to maintain lifter pre-load, or valve lash, as mentioned above.
I will try to write more as time permits. There are many other operations and machine types to address.
Connecting rod re-conditioning
Valve seat and guide work
Lifter bore re-alignment
I hope some of you find this helpful.
I did not write this article, I found it on DSM Tuners
I give credit to DSM Tuner Wiseman Big Woo for this write up.
I find it a well written, and did receive permission from the author to post it on other forums.
I have added to it, and will add more as time allows me to bring it more into date.
Surfacing-equipment used by Machine Shops
The common ways to surface a head, have changed with how and what engines are built out of
In the day of Cast Iron Heads and cast iron blocks, table stone surfacers were used, think of something about the size of a large end table, with a 14 inch stone spinning in the center of it, the machinist would grab the head and hold it, working the head in a circular motion ageist rotation of the stone. Till it was flat? Not a very good way of surfacing a head. I have still seen this style of surfacer in use in shops to this day.
Next is the "master head surfacer" some are wet, others are Dry, very common in shops, they are cheap to buy and quick to use. Its nothing more than a big belt sander. These machines are not at all accurate, the head is flat, but not square or level, they tend to grind more off the leading edge of the head. On this machine the machinist holds the head and works it across the belt, assuming he has a clue of how that machine cuts. Most do not.
Rotary Broach is another common machine, found as single speed or dual speed, the head is held ridged in a hold down fixture, then a wheel with 10 carbide inserts pass under the head. its a decent machine, but the finish depends allot in how well indexed the carbide inserts are to one another, .001 makes a big difference, it can take hours to set the blades up. Works great on cast iron heads, and some alum, BUT it depends on what kind of Alum the head is made of.
Another machine is the surface grinder, not a bad machine, it keeps the head leveled and indexed, it uses segmented stones. The surface finish is not smooth enough most of the time for MLS gaskets, The finish is dependent on what stones, how well dressed they are, spindle speed and table speed. Still very common in shops
The new boy on the block is a High speed Milling machine, these use a .500 (1/2) inch insert, CBN for cast Iron and CBN for alum. for the most part, as far I as know, have been around about 10 years. smaller shops are slow on getting them due to there cost, But without a doubt give the best surface finish. Some machines, like the comec I use, have variable rate spindle speed and variable rate table feed rates. This will allow for different surface finishes for different gaskets
|cam, centerline, decking, dsm, effect, engine, facing, head, hot, kwik, machine, machining, overhead, superspeed, tank, valve
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