Inspection 2 & Assembly
As soon as you have received and checked all parts back from the machine shop then measured the parts you have purchased you are ready to assemble.
It doesn't matter if you build the head (s) (if the machine shop has not already done that) or the block first. We will cover the head first.
You have looked at the seats in the head to confirm that they were done. (three angle and flat gray seat area or magic marker marks) Insert the valve in the guide at first with no oil and no stem seal, and hold the head of the valve about a half inch open and try to move the valve from side to side. You should feel a little movement but maybe not see much movement. If it moves the thickness of a matchbook cover or more get a professional to look at it. If you can't feel any movement at all also get a professional to look at it (this one is dangerous to the engine)
With the stem lubed. I recommend a 50/50 mix of engine oil and STP. Some use Lubriplate. Don't use bearing grease. Install the stem seal if applicable. Install the spring seat cup or spacer if applicable. Install the spring noting if either end of the spring has closely wound coils. If so look in your manual to see which way the spring goes. If you are using used springs be sure they all were pressure tested. Install the collar (note if the exhaust collars are different than the intakes) (Some Domestics have bearing rotaters). With a spring compressor compress the spring and install either a matched set of keepers or new keepers. (A handy tool to do this with is a thin straight blade screwdriver with a dab of bearing grease on the tip and a little in the hollow of the half keeper. A second thin screwdriver will work as a tool to help place the keeper on the stem correctly. Do the other half the same way. Try to place the two keepers so that there is a gap on both sides and one keeper is not butted up against the other. Release the spring compressor very slowly and watch that the collar does not push a half of the keepers out of place. (You should wear safety glasses as a flying keeper half can put an eye out) If it seated OK, hit the end of the stem with a plastic mallet to seat the keepers. Now with a 6 in. scale or ruler carefully measure the "installed height" of the spring and look in your manual to confirm the specs. If your "Installed height" is too much, you must remove the spring and install a spacer (available from most speed shops and some auto parts stores.) If the "Installed height" is too much, you are in danger of valve float at a lower RPM than it should be and thus you could destroy your engine on a missed gear change or even a mild rev up. If the "Installed height" is not enough you can cause undue cam and valve train ware or in some cases it may even "Coil Bind" the spring and brake something in the valve train as soon as the engine is turned over ONE time. This is very important!! Don't skip this!!!!!
Now with the head together, turn the head up so you can pour some mineral spirts of diesel fuel in the ports and watch for fluid leaking out around the valve head. If it gets damp around the valve head but don't run through, it is OK. If any of the valves leaks fluid by the valve head you need to correct it now. It will not get well by it self.
Examine the block carefully to see that the machine shop installed all of the core plugs (freeze plugs) and oil galley plugs. If the cam is in the block blow compressed air in an oil galley and feel at each cam bearing to see if air is coming through. If you don't have an air compressor turn the block over till an open oil galley is up and pour oil in until you see oil coming out the oil hole in each cam bearing. It will come out one before the others so you may have to put your finger over the hole until it comes out the others. Also check for oil travel to the head if it transfers block to head (s). If it is a cam in the block, be very careful installing the cam as it is easy to scar a bearing with a cam lobe. With the cam installed check to see if it rotates freely. Check with air or oil to see if the oil holes to the crank are open. Install the upper shell of the main bearings in the front and rear main only and double check the crank alignment with a dial indicator. If you don't have one buy one, they are available for as low as $15. You don't need an expensive one unless you plan to build a lot of engines. Install the other bearing shells being careful to align the little tab with the notch in the block and one in each cap also. Remember that NO main cap nor rod cap can be turned around nor switched to any other position than it was made for!!!!!!!!! Before you install any main cap, get some (green) plasti-gauge. Cut a strip off about the width of the bearing shell and lay it across the shell (a little ways away from the hole and turn the crank so the hole in the crank is not lined up with the plasti-gauge) Install that one cap being very careful NOT to move the crank. Torque the bolts or nuts to the manual's specs then remove the cap being careful not to move the crank. check how much crush (with the gauge on the paper cover the plasti-gauge came in). One and a half thousandths to two and a half would be normal on most engines but check your manual. What can you get away with? If your manual says 1 to 2 you can run up to 3 but not less than 1. Some race engine builders like a little more clearance to allow more oil to travel through to cool the bearing surface. Too much clearance and you will loose oil pressure and maybe not make oil go to places it needs to. After all the mains are checked and torqued, you need to do the rods the same way except the clearance will probably be a little tighter. like a half to one and a half. How much can you get away with? Several things will determine this. For a street engine that calls for a half to one and a half, I use two as my limit. Some race engine builders use three but use high volume oil pumps. Some thought needs to be put to matching up what you do in clearances. For example, Loose mains and tight rocker arm to rocker arm shaft and a standard oil pump with cold oil will result in low oil supply to the rockers. If your clearances are a little higher than normal you would want to tighten up on the oil pressure regulator spring. This will help keep the oil pressure up to the less accessible parts of the lubrication system. Some race engine builders get all the clearances matched with a little more than normal clearances and run a high volume oil pump. They end up with a large flow of oil for cooling of the bearing and low oil pressure. The low oil pressure helps decrease drag on the engine thus more horse power. A street engine is concerned with a longer life so the added HP is not an important issue.
Back to the "crush" of the Plasti-gauge. Note if it is uniform all the way across the bearing. If it is tapered meaning, a half thou on one end and two on the other end, something is dangerously wrong. If it is a main, either some trash is under a half shell or the journal is tapered. If it is a rod, either the rod is being forced to one side or the journal is tapered. It must not be assembled that way. The crush (thickness) of the plasti-gauge should look uniform across the length of the gauge strip. If the reading is not correct to specs, look under both bearing shells for trash. (a single hair will lock up a crank)
If the engine is an over head cam, you should plasti-gauge the cam bearings also. Some over head cam (OHC) engines have bearing shells like rods and mains and some just run the cam on the aluminum of the caps and head. Either way they need to be checked. Lub the cam bearings with a mix of 50/50 oil and STP and you can use that on the cam lobes or get some cam lub from your auto parts store. Carefully examine the lifter or rocker that contacts the cam for pits and ware. If the machine shop assembled the OHC head, be sure to check valve clearance to the manual's specs. Be careful with any dual OHC heads if the cams are installed. Many dual OHC cams can not be rotated after they are installed if the design is Hemi or Penthouse as you can bend an open valve of the opposite valve by rotating one cam. These types must be assembled "In Time" and must not be rotated until the chain or belt is installed.
Rings and Pistons
Pistons and rings come in an infinite verity and you should know a little about them to make a good decision if you are not putting original equipment (OEM) back in. There are three main materials for pistons as far as an engine builder is concerned. "Cast" which is usually stock (OEM). Cast pistons are OK for a street engine that is not going to be run at high RPM. Cast pistons are usually the weakest of the three. The expansion rate is low so it will stay straight in the bore through a wide temperature range and keep the rings square with the cylinder wall so as to seal better. There are many "After-Market" cast pistons available for most engines and most machine shops have a source. First look at the old original pistons that came out of the engine. Look at the drain back hole in the oil ring grove. If it is a long slot cut into the ring groove, that is the weakest design. A stronger design is drilled holes as drain back holes. Look at the ring lands (area between each ring, especially between the top ring and the second ring down) If that area is thinner than the OEM, it is dangerous. That will be the first thing to collapse if you get any detonation or preignition in the combustion chamber. You want it to be the same as your OEM pistons or wider. Place each ring one at a time in the cylinder bore and square it up with a piston. With your feeler gauge check the end gap and look up the specs. (On a slip of paper that came in the box of pistons or in your manual.) It will probably be about one and a half thou per inch of bore. A little more gap is of little importance But, LESS is very dangerous. If you have a three piece oil ring the thin rails should be checked but, you will usually find the gap to be a little excessive. This is normal, just don't assemble an engine with less gap. I have found factory mistakes where the compression rings were correct but oversized oil rings were in the package. Every ring must be checked. Note that all rings can be pushed into it's groove further than the outer surface of the piston. Look closely at the top and bottom of each ring close to it's ends for any marking. The marking can be an oversize, "STD", or just a dot. If there is a mark, the mark MUST face upward. This is an indication the ring is a "Scraper" ring meaning it scrapes oil off of the cylinder wall and allows the oil ring to scrape it into the drain back slot or holes. If any of the compression rings have a bevel on the inside edge. That bevel must face upward. Another piston type is "Forged". These pistons are much stronger than "Cast" and are mainly used in high performance engines. The piston manufacture determines the skirt clearance not the engine manufacture. On "Forged" pistons you will probably find much higher clearances. This makes the piston rock back and forth and makes the rings not seal well on the cylinder wall at least until the piston heats up and expands. These pistons can stand the strain of higher RPM and I have noted they are usually more prone to withstand some detonation. Some piston manufactures don't keep a close tolerance on matched sizes of a set of pistons so a machine shop will bore a cylinder to match each piston. If they do that, they will number each piston as to which bore it must go in. Look at the top of the piston for any marking as to which is "front". Some pistons must only go one way.
As far as the piston is concerned in a "Balanced" engine, it just means all the pistons have had their weight matched. Many pistons have some excess metal just under the piston pin boss. This can be machined off to get a piston down to match the lightest piston. Then, that weight will be figured in to a weight added to each rod journal when a crank balancer sets up a crank to be balanced. On a single cylinder engine that is expected to be turned at 8,000 RPM, 66 % of the weight of the piston, pin, rings, pin clips and little end of the rod are added to the weight of the large end of the rod w/bearings and that added to the rod journal of the crank and that balanced. A different figure is used for different engines. Balancing a crank is a little expensive for a street engine but weight balancing the pistons and rods is something an amateur engine builder can do himself with a accurate gram scale and a little work. I have found that most engines will benefit from this even if you don't have the crank balanced. The % a crank balancer uses will effect a certain RPM range more than others. Reciprocating weight (things that move up and down) can not be in balance with things that rotate so a happy medium is looked for. Some engine manufactures have had some success in counteracting this out of balance condition by adding rotating counter weights and an aux shaft in the crankcase.
Some rods have an extra lug on the center of the rod cap or on the sides of the rod so you can machine some off so as to match the lightest rod. If you decide to weight match each rod, don't forget the total weight of the rod must match but also each end of each rod must match too. In older engines you could improve the strength of a rod by polishing the face of each rod. This would help prevent fatigue fractures as the rod flexed under the strain of high RPM. However, rod manufactures use other methods to improve the strength of a rod and grinding and polishing a rod may weaken it if you don't know what a manufacture has done. There are several brands of racing rods available now, so you can just buy a set that is weight matched and high strength. Even some stock rods are OK for high performance but the only way to find out is to talk to those racing that engine. Some engine manufactures advise you to replace rod bolts on an overhaul. Others quote a max. rod length or stretch. What ever you do NEVER use a conventional bolt on a rod. The strain on a rod to stop a piston at TDC at high RPM is measured in tons so a conventional bolt will not stand that strain. Also, the torque of a rod bolt is critical, probably the most critical of any bolt in the engine. Don't gamble on rod bolts.
Chain / Belt Tensioner
Check the chain or belt tensioner. Note that some chain tensioners are spring and oil pressure operated. Cam timing is very critical, so follow the manual very closely. Some engines don't have an effective method to accurately set cam timing if a head is surfaced or the top of the block has been decked. In this case one tooth off to either side will not make the timing mark line up. Most engines will run a little better if you put it so the cam is advanced that half tooth rather than on the retard side. Several late model engines use a variable cam timing on one cam. You should refer to your manual for this. If it is a belt drive, look at the belt to see if there is an arrow marked on it and if the belt has marks on it for cam timing. Even some chains have marks for cam timing. These will usually be shinny or different colored links. If there is a master link be sure that the clip on the master link has it's open end pointed away from the direction of travel.
Modifying a stock engine
Over the years, many of my customers have asked, "What can we do on this overhaul to pep up the power a little?" Unless it is an older car you have an emissions test to meet so other than "Off the shelf" modifications, you are dead in the water. However, on older cars you can make a few changes and still meet any state or federal specs. Keep in mind that it is progressive that the more power you make, the shorter the life span of the engine. For example, a dragster owner is hopping for a few seconds of engine. While a stock car owner is hopping for 500 miles of engine running. And a Grand Prix racer is hopping for 24 hours of engine.
If you have an engine that is a little low on compression ratio you can boost power by just raising the compression ratio. Any change you make to an engine changes the required ignition timing, changes the advance curve and changes the necessary fuel mixture. Also as you make changes that makes it necessary to change other things. We will start with raising compression. Now you need to use a higher octane fuel. OK, you switched to the higher octane fuel and reset ignition timing to match and you changed fuel mixture in a carb or injection system. But the manufacture designed the exhaust system to keep the exhaust note quiet, but you are forcing a lot more exhaust out in a shorter time frame so you now have "back pressure" which causes all kinds of problems. Now you have to get a more free flow exhaust system. Oh! I forgot to tell you the same thing happens at the other end, the air filter may now hold you back with the more air volume you a pulling through. We have not even mentioned that now the engine will turn a higher RPM much quicker. As long as "Lead Foot" don't drive it you may still be OK. The objective is to make it a match set of modifications. For example, you just want a little more "Umph" taking off from a light or climbing a hill. In this case it is probably no necessary to go to the expense of forged pistons, high dollar rods etc., etc. When you are going to turn a high RPM is when you need to get the expensive rods, forged pistons, stronger valve springs and on and on.
The most common engine killer is, "Detonation/ Preignition". or "Abnormal Combustion" wrongly called "Valve Rattle". If you have any experience with engines at all, you have heard it. It sounds like a tin can full of marbles being shaken. Usually on a quick throttle opening from idle or a heavy load on the engine in a high gear. Unfortuneately there is "Abnormal Combustion" that can't be heard at high RPM too. Or heard with a loud exhaust. If you plan to improve the performance of your engine, you should consider the MSD unit called "Knock Alert" part number 8964, that gives you a visual display in LED lights of engine noise. I don't work for MSD nor get anything from them but I do think it is a good item to any engine "hop up". Keep in mind that the maximum horse power in any engine is just before "Detonation".
In 1960, I raced a 250cc Honda motorcycle at Daytona. I didn't have equipment like the MSD unit or a dyno but I knew that horse power dropped off at the point of detonation. I had made several engine modifications and was in the process of establishing what ignition timing and fuel mixture was needed to match my mods. Since this was only a 250cc bike I used it's top speed as a dyno. I don't recommend this to anyone today.
To first establish a power curve. I made full throttle runs and kept gearing higher a little at a time. That happened to be 9,500 RPM on each run until I noted a drop in RPM meaning I reached the peek of the power curve of this engine. With it geared to only turn 9K, I advanced the ignition timing and noted it would turn 9.5 K again. Gearing higher so it would only turn 9 K, I again advanced to regain 9.5 K. I continued this process of gearing higher and advancing the timing until I noted a sharp drop to 8 K. This I knew was just at or close to detonation. I backed off 5 degrees and regained my 9.5 K which during time trials at Daytona netted me the 4th fastest time of about 150 bikes at 105 MPH. This was a good speed for a 250cc bike back then. The end result on this engine was 60 degrees advance. This also told me I could have jacked the compression ratio a little higher. The carb had to be rejetted several times to stay a little on the rich side of 1.1.
Today you have many options to work with, like most major cities have one or more dynos you can put an engine on to determine what ignition timing to use and what fuel mixture to run. Dyno time is very expensive but you can also look at tools like the MSD unit to watch for detonation and there are accelerometers available to measure power with.