Section 3. 

Machine Work

& Inspection 2

Machine work is a very important part of building an engine. Yet most mechanics don't have the equipment nor the know-how to do the machine work. So it is "Subletted" to a machine shop. Most rely on the reputation of their machine shop to do the job needed on each component. Today, very few mechanics rebuild engines. They either buy a "short block" and send the head (heads) to a machine shop and thus the only work the mechanic does is "R&R" (remove and replace) the engine and head (s) and outer sheet metal and components. Or just install a "Crate" engine. Unfortunately, many of the causes for the engine going bad to start with was caused by something outside of the engine and that does not get corrected when the mechanic installs the new engine.

In this section we are just concerned with the actual machine work. Over the years, I have used many machine shops and learned very early to closely inspect ALL machine work returned from the machine shop. Even the best machine shop in the world can make a mistake and that little mistake can cost the mechanic and the shop he is in, lots of time and money.

Early on, I was forced to purchase a set of micrometers to measure each and every crankshaft that I had a machine shop regrind. It is not necessary to purchase block bore gauges as there is a way to check the bore size of a cylinder without any type of bore gauges. All you need is a set of feeler gauges that go down to at least one thousandth of an inch and preferably have half thousandths above that for a few thousandths. A tool truck will usually have individual feeler gauges available that are longer than normal. these are much easier to work with and you only need a few. 

The procedure should be as follows, After tear down, take each piston with it still on the rod (rod makes a good handle) insert the cleaned piston without rings into each bore upside down and with the smallest feeler gauge on the full face of the skirt and extending up on the ring lands. This makes it easier to get the piston and feeler gauge into the bore. If the machine shop has put a number on each piston you should only check each piston in it's respective bore as they probably found a small or large difference in the size of each piston. If they did not number them you must check each piston in one bore to see if there is any difference in the size of any of the pistons. If they all check out the same use one to check all the bores. You will note that as you use a larger feeler gauge it has more drag to slide the piston up and down. The amount of drag can increase to a point that it is difficult to insert the piston into the bore. You should back up to a smaller feeler gauge at this point. It becomes a matter of feel as to how much drag is correct. A rough way to get it close is to insert the piston with the feeler gauge and pull the feeler gauge out with just two fingers. If it is difficult to pull out with two fingers than go down one size. 

Go to your manual and look up "Piston skirt clearance". If it is a cast piston (most street car pistons are "cast") it will probably be one to two thousandths. If it is a "forged" piston it can be as much as three to six thousandths skirt clearance. If the pistons are not from the engine manufacture, the piston manufacture sets the skirt clearance. So there should be a slip of paper in the piston box stating the skirt clearance. 

A crankshaft that has been reground needs to be measured on every journal and closely inspected for nicks and smoothness. Also you should look at the radiuses to see they are smooth and no sharp edges. Now measure each journal in two places 90 degrees to each other. This checks roundness. You should find NO out of round condition. Check your manual for crank journal and main journal sizes. Rod journals must be within one half thousandths of specs. The mains must be within one thousandths of specs. A good machine shop can stay within one quarter of a thousandths on either a rod or main. You should detect no taper to any main or rod journal. See if they polished up the rear seal journal. If you have a dial indicator (only about $15. at discount tool companies) you can check crank alignment. Put the bearing shells in the front and rear mains and oil them and set the crank in place. No need for main caps. Set up the dial indicator on the center main journal and hand rotate the crank. Any bend in the crank will show up on the dial indicator.

If you see any pits in the lifter faces you should replace them and examine the cam loabs for ware. If the machine shop reground the valves you need to check them even if they look good. You don't need much in the way of tools to do it. The tools needed are, a piece of 5/16 fuel hose about 8 to 10 inches long, a black magic marker and a little oil on the stem.

Mark the valve face with the marker across the face about every 1/4 to 1/2 inch all the way around the valve, then do the valve seats the same way. Oil the stem and guide and insert the valve and force the hose on to the end of the stem. Now, with the hose between your flattened hands, rotate and as you rotate back and forth be sure to pull on the hose. After you have done this for a minute or so, remove the hose and valve and look at the marks. Ideally they all should be smeared. If they are not all smeared clean the marks off and repeat the test. If you get the same results, you need to return the head and valves to the machine shop. Show the test results to them and ask them to do the same test to be sure the test was done correctly. A few good machine shops use valve lapping compound to check their grinding. If this were done the valve face and seats in the head will have a dull gray finish not a bright shinny ground finish. A three angle seat in the head with the center of the three faces a dull gray finish usually means they do very good work. Some machine shops do a good job and check it with magic marker marks and don't do the valve lapping. If you see a wide seat surface on the exhaust valves and a narrow seat surface on the intake valve seats in the head, that is OK. The reason for the wide seat on the exhaust is to get better heat transfer from the valve to the head. The intake is cooled by the fuel/air charge so it is not necessary to have a lot of transfer of heat from the valve to the head.

An area I see where a lot of mistakes are made is valve to guide clearance. Called stem clearance, it is often overlooked and even when it is checked it is done as a black art. (by feel)  It is time consuming to measure a valve guide (after it is installed) and measure each stem.

I once worked for a production engine rebuilder as a "warranty claims processor" (big mistake) The person in charge of checking stem clearance was well experienced, however from my office I was able to see that he was not the one checking these much of the time. In my job I seen the end result of this. I requested that they either set up a simple air pressure system to check clearance or make "go/no go" gauges to at least check the guide inside diameter. This was rejected and things went "status quoe". I was continually pressured to blame the customer even when I knew it was the rebuilder's problem on many failures.

You have to keep in mind that it is far better to check everything before assembly and not assume any of the machine work or even a factory part is correct before you install it. A set of micrometers, feeler gauges, a compression gauge and an oil pressure gauge should be considered as part of the cost of building an engine.

A difficult one to check after a machine shop has installed them is a set of cam bearings in a block. The only thing you can easily check is that it spins free. If it does not spin free by hand, send the cam and the block back to machine shop. They will have to check to see if the cam is true and check the inside diameter of each cam bearing and see that the oil holes line up if necessary and that the line bore is true. In that rebuilder's shop I seen a man driving a cam into a block with a large hammer. I quized one of the shop foreman about it, I was told he had been doing that for a year that they knew about it and they had learned the hard way to keep their mouth shut. 

I also have learned over the years (sometimes the hard way) not to let anything wrong go by without correcting it (or attempting to correct it in the case of my job) (yes, it I did make several enemies and yes, it finally got me fired) In building an engine You Can NOT let Anything Wrong Slip By You. There are NO shortcuts in building an engine!!!!!

If the piston pins are "press fit" and you do not feel comfortable doing it, have the machine shop do it. You will find that most "Press Fit" pins are press in the rod. But there are some engines that press fit in the piston. It can be done with a torch or even a propane torch but only do it yourself if you can get guidance from someone who has done it before. The combination of a torch, hammer and drift can result in a bent rod or destroyed piston. A "Rod Eye Heater" will get the rod to the correct temperature so the pin can be easily installed with little to no force. If it is a "free float" pin you can easily check clearance by installing the pin and check for any free play or any rocking movement. This should be checked without any oil on the parts. It it checks OK then oil all the components and BE SURE TO INSTALL THE CLIPS. Then DOUBLE CHECK THE SEATING OF THE CLIPS. A clip left out or not seated correctly can totally destroy an engine very quickly.

Many shops now just have the machine shop do the valve work and assemble the head so the only way you can look at the work is to disassemble the head. However, that is a lot of extra work and you paid to have it assembled. Here you can look at the stem seals to see if they are installed if necessary. (some engines don't use stem seals and others only install seals on the intake side, check your manual) Note that new springs were used. look closely at the keepers to see that new keepers were installed. If you don't get an itemized list of parts from the machine shop, ASK ABOUT THE KEEPERS. This is very important and must not be overlooked. THE ONLY WAY THE OLD KEEPERS CAN BE REUSED IS TO HAVE KEPT THEM IN PAIRS AS THEY WERE REMOVED!!!!!!!

I set up the warranty department and the procedures for WorldParts Corp. and was the claims specialist for several large corporations and a production engine rebuilder (big mistake) and I seen first hand the reasons why you can not mix up used sets of keepers.

If everything looks good, new keepers, stem seals where needed and new springs. You can check the end result very easily. Turn the head up so the ports are up. (Intake or exhaust or both) and pour in some diesel fuel or kerosene or mineral spirits into each port. A valve head may get damp around the edges but fluid must not run freely through.

Check every port this way. If any fail this test you need to either send it back to the machine shop or remove that valve and see if it passes the magic marker test outlined earlier.

If you have the machine shop clean your block (advised) even if it don't need reboring don't forget to ask that the oil galleys be cleaned and new core plugs (wrongly known as freeze plugs) be installed.

On to section 4

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