Click on a thumbnail to see the full-size image
Machine Maintenance, Follow The Clues To Avoid The Comeback Blues
If I've said it once, I've said it a thousand times: you can't machine until it's clean. That statement really holds true when it comes to getting the work piece ready for the machining operations ahead
By Dave Monyhan
Even before you start the teardown, you can gather many clues about what needs to be done. Encourage your counter guys to engage in as much conversation with the customer as possible. Just listening to him tell why he is bringing you this engine will yield tons of information that goes a long way toward understanding why the engine has failed.
Of course if the engine could talk it would tell you all about its life. It'd be nice to have one of those little black boxes like airplanes have to record every aspect of the engine's life, but until then, the spent engine components you are about to throw away will provide ample clues as to why it failed. Laying out the critical components for review will tell you a story of that engine's life. It's like looking into the past to prevent a future failure.
So let's get started.
Look at the oil pump pickup screen. Can you see through it or is it clogged from not changing the oil on a regular basis? The oil pan is a real talker if you listen. It's there to act as a reservoir for the oil, not to be a catcher's mitt for an exploding engine. When that engine needs to be rebuilt, take the time to look for any metal particles in the sludge.
You can also cut the oil filter open and inspect the filter paper for metal. A filter-cutting tool works like a can opener and prevents any metal from the opening process from being introduced into the filter. Spread the filter paper out and with a bright light look for metal particles. These metal pieces can give you an indication of which component has failed or is about to fail.
Look at the camshaft and inspect the lobes for abnormal wear. Don't forget to look at the side and the bottom of the lifters. The crankshaft is next. Are there any blue burning marks around the rod or main journals? These blue or black discolorations are an indication of heat. Paint discoloration is also an indicator of overheating. Did the last engine builder install "heat tabs?" Look to see if they are still intact. The center will have melted out if overheating occurred.
Next, look closely at the piston skirt. If you notice scuffing on only one side there is a chance that the engine was started dry, or it could be the use of a sub-standard or improper head gasket.
It's obvious that if you see the impression of a valve on the top of the piston it means just that…the valve was hitting the piston. Well duh! But hold on, the timing may have been off. Now if the piston is broken, a nut or bolt may have accidentally fallen into the carburetor.
Pre-ignition is indicated by a melted and burned appearance of the piston crown cause by extreme heat. Detonation is post-ignition, and rings may be pinched tight in their grooves, also the piston may appear to be broken. A cracked spark plug insulator is also a good indication of detonation. Measuring the bore will tell you how well the last shop bored and honed the block.
Look at the valves. These critters really hold a lot of information concerning the engine's running life. If the valve face is burned or torched, this could be cause by poor seating. Contributing factors include lack of clearance to the valve guide, preignition or a defective cooling system. If you see cupping or tuliping of the valve head it indicates improper air/fuel mixture.
I lost a motor once coming out of the mountains of Colorado. The motor tuliped the valve heads because I started at one extreme altitude and did not stop until several hundred miles later at a considerably lower altitude. I learned that when you come down from 14,000 feet to about 900 feet without stopping something's gonna give. The computer did not have time to re-adjust itself to the lower altitude. Yes, I got a rebuilt engine from a local engine builder and I learned my lesson…take a break when going downhill fully loaded!
Bent valves will generally tell you a timing chain or belt has let go but broken valves are another story. When the head breaks off it is generally caused by over-revving the engine, weak springs, valve float due to over-revving, or sometimes even a stuck valve stem. Yes, it could even be the guide-to-seat alignment. Concentricity is key to any valve job. Breaking off the top or tip by the keeper grooves could be the result of inattention during assembly, worn keeper grooves or excessive valve train clearance.
Look at the rod and main bearings. You can tell if a lack of oil brought you this job. If an oiling problem is inherent in this engine's shortened life then you will need to ensure all oil galleries are cleaned for proper oil flow. Bearing failures occur 45.4 percent of the time due to dirt! Around 11 percent of the time bearing failure is due to lack of lubrication and only 3 percent of the time due to the finish of the crankshaft.
A normal wear pattern on bearings should be centered and cover two-thirds to three-quarters of the bearing surface area. Thrust bearing failure is caused by constant pressure of the crankshaft against the thrust flange of the bearing and can be caused by improper clutch adjustment.
Now that you've examined all of the components and learned everything you can, it's time to start cleaning.
Cleaning the bare heads and blocks in your hot tank or jet washer will get most of the gunk and oily goo off of the outside. There is a really cool tool called the "Super Scraper" that uses a solid carbide flat blade to shave gaskets off. Run it about 30 degrees off the deck surface and this bad boy will remove that gasket fast and without damage to the base material!
Be sure to remove all of the freeze plugs and the gallery plugs. For the block run a long cleaning brush through each and every gallery hole. Extra long brushes of 24? to 40? long are available for this job. Gallery plugs can be a real chore to remove. There are special tools designed for this task. They have a tool steel square end that fits into the gallery plug and are driven by an air impact wrench.
For those real stubborn plugs you can use the old standby: a red bud torch and some beeswax. Heat up the gallery plug, remove the flame and touch the beeswax to the plug. The heat will "wick" the beeswax into the threads and allow you to remove the gallery plug easily.
On overhead cam cylinder heads there are vertical oil galleries that need to be brushed out as well. Crankshafts have oil holes and can trap all kinds of foreign stuff. Run the brush through before and after grinding to insure no contaminants are left behind.
Carbon in the combustion chambers of the cylinder head took a long time to build up, and it's not easy to remove. I have heard of soaking the entire work piece in carburetor cleaner, but the smell is horrible and it's really dangerous. Wire brushes and sanding discs are labor intensive and probably do more damage if used improperly. Instruct your clean-up person never to touch any gasket surface with wire brushes or abrasive discs. Ultrasonic cleaners do a pretty good job, but the old glass bead machine is still the go-to unit for this job.
Before you put the work piece into the glass bead machine, cover the oil holes with some modeling clay or get yourself some "Plug-IT." Just pinch off a piece and knead it between your fingers, then apply it to the head's oil holes and completely cover them.
If you have a thermal oven for cleaning, the oil, grease and carbon are burned off. When you put the work piece into the steel shot machine you will achieve an almost perfectly cleaned component - right down to the bare casting. Aluminum is still cleaned in the glass bead machine or ultrasonic cleaner or you can change to stainless or walnut shells for your airless cleaner to do the aluminum.
Keeping all of the small components like valves, springs, keepers, etc. can be a challenge. There are a number of small parts holders available in the marketplace. Go ahead and invest in these little containers: save your coffee cans for other things. There are a number of plastic (ABS) organizers that really do keep those components from growing feet and walking around your shop, especially when you are working on those multi-valve overhead cam cylinder heads. Some of those applications must have a gazillion parts for you to keep track of. Always label your parts baskets for what job and for which customer. This way when all the components come to the assembly area you don't have to spend valuable time searching throughout the shop.
Prior to assembly, recheck all components to insure all cleaning was properly performed, and the components are machine and ready to go. I still use Tide soap and a large clean nylon brush for final cleaning of the cylinders. Lay everything out in an order that's convenient for assembly. Keep your hands clean, and I know you will have a finished job you and your customers will be proud of.
See ya in the shop!
Dave Monyhan is national sales manager with Goodson Shop Supplies, located in Winona, MN. firstname.lastname@example.org