Compact Diesel Engines

By Dwayne Dugas

A license to steal

Compact diesel engines can be a very profitable part of the engine rebuilding market.  Many shops have been afraid to get into this segment of the market for many different reasons.  Many shops say they do not want to work on them because parts are too hard to acquire.  It has also been said that these engines are too small for their shop equipment.  Many shops are afraid they cannot source information to rebuild these engines.  Some shops are not seeing these engines in their shop because of not having realized where all these engines are used and where the potential customers can be found.   After reading this article, I hope to give you many of the tools you need to find these customers and establish profitable customers with these compact diesel engines.  Once your tool box is full with the tools, you will have a “license to steal”.


Where are these engines?

The first objective is to find these compact diesel engines to rebuild.  These engines are used in a wide variety of applications.  Several original equipment manufacturers have been using other manufacturers’ engines in their equipment for more than thirty years.  As an example John Deere uses Yanmar engines, Ford small tractors use Shibaura engines, Bobcat uses Kubota engines and we have even done several Case small tractor engines that were Nissan engines.   At our shop, we began seeing these engines years ago from a nearby salt mine.  They use recreational type vehicles like the John Deere Gator in the bottom of the mine as personnel carriers.  They have to be diesel powered below ground surface.  One salt mine customer we deal with has about 60 of these units below ground to travel around the mine all day.  These units operate in harsh conditions and are in use 24 hours a day, 7 days a week.  Rebuilding their first engine was a starting point for us to enter this market.

Small diesel engines are also used on portable welding machines.  Look around at rental services and see if they rent welding machines.  If they do, they’re a great potential customer.  While looking at rental companies, if they have small tractors or skid steers, most of those also have small diesels in them.  Some other uses for these engines are on generators, light plants, stump grinders and lawn and garden equipment.  Great places to visit with huge lawns include golf courses and cemeteries.  And, if you play golf, next time you are at the course early, look at all the equipment they use to maintain the course.  Many of these units have small diesels on them.  These small diesel engines have a wide variety of uses and if you remain observant you will find potential customers every day.


Have the engine – Where to start?

The first step I recommend is to identify the engine and purchase a service manual.  This is one of the most important steps you will do in working on these engines.  The next step is to make sure you purchased the manual.  I cannot say that enough, even though some may be a little costly, purchasing and then using the manual for the engine will save you money in the long run. Most of these engine manuals have to be obtained from the equipment dealer.  If you have an established relationship with the OEM (Original Equipment Manufacturer) dealer, or if you are doing the work for them you can use their manuals.  We work for several OEM dealerships and have developed a relationship with them and they share their information with us.  Not all dealers will do this, but they will gladly sell you the manual for the engine.  I have not found one yet not willing to take my money.  Also AERA’s PRO-SIS SA is a valuable tool to use on any engine you are working on.  If the engine or specifications you are looking for are not in PRO-SIS and you are a member of AERA, call the AERA Tech Hotline and they will do all within their power to get you the information you need.

Once you have the information in hand, the next step I recommend is to get out your digital camera.  If you do not have one, I highly recommend purchasing one or find some way of taking pictures of the engine.  This step is essential if you are not familiar with a particular engine. Taking pictures as you tear down the engine can be very valuable when you put the puzzle back together.  Take several pictures of the assembled unit first.  Then as you tear down, take pictures of brackets, mounts, housings and any other external items that may present a question when reassembling the engine.  As with any engine you work on, the tear down process can tell you more about the problem with the engine than any other step you will perform.  I look at it as the engine is talking to you and your success with this engine will depend on whether or not you listen to the story it is trying to tell you.


Failure Analysis

The failure analysis step is next and is the same as with any engine you will rebuild.  No matter the size or number of cylinders, the basics still apply.  Some common problems we see with these engines vary by where they are being used.  You may have to spend some time getting familiar with the conditions in which this equipment is being used.  As an example, the engines from the salt mine we work on are almost always damaged from overheating.  Once we started seeing this damage on a consistent basis, we contacted the equipment manager at the mine.  After a couple of conversations with him, he reveled the radiator was located under the rear of the vehicle.  As these vehicles are driven all around the salt mine, loose powder salt flies up off the roads and becomes packed in the fins of the radiator.  Those salt packed radiators do not exchange heat very well and were causing engine overheating failures.  Another enemy of these engines, just like any engine, is dirt and dust.  Many pieces of lawn equipment, tractors, stump grinders and generators operate in severe dusty conditions.  Another common problem we see is with generators in the bilge of a boat.  The boat engines may be leaking exhaust and the nearby small generator engine is ingesting all those fumes.  It is always important to know what type of environment the engine is running in to help you and your customer have a successful rebuild.


Ready to Machine?

Up to this point, everything that has occurred should be fairly familiar to you as they are steps we do every day on most engines we work on.  Sure, you may not have been familiar with the engine but all the steps that are done are the same.  You are ready to start inspecting and measuring to determine what you need to do next.  Start by getting your new manual or information you gathered beforehand.  Be warned, in many OEM manuals, they may cover more than one engine.  Always verify the model of the engine you are working on and verify you have located the proper specification for this engine.  We have many manuals that cover several engines in one book, look carefully and don’t assume the specs are all the same.

On many of these small diesel engines, finding a cracked cylinder head is common.  These head castings are not forgiving to overheating.  Once everything is cleaned and inspected and all castings are determined to be repairable, you are ready to machine.  In many of these compact engines, you need to also verify what oversize parts are available.  It is very common for some applications to have piston and rings available only in .25mm (.010”).  A limited number of these engines have a dry sleeve in the cylinder bore.  Many more engines have no sleeve and the block may not clean-up at .25mm (.010”).  Many of those blocks can be sleeved and we’ve had great success installing sleeves. When we install a sleeve, we leave a ledge on the bottom just like we do with any other sleeve installation.  Some engine applications offer other oversize bore choices but you will find that .50mm (.020”) is the largest on most.

When you are ready to machine the crank be careful as some manufacturers supply uncommon bearing undersizes. They may not be the common .25, .50 and .75 mm you’re accustomed to dealing with.  Kubota, on many, but not all of their engines supply crank bearings in .20mm (.008”) and .40mm (.016”).  So, be sure and verify parts availability before performing any machine work.  Many of these engines use a one piece front and rear main bearing, similar to a cam bearing.  These bearings usually press into the block up in the front and press into a bolt-on housing in the rear.  When machining the rear main journal in these applications, the rear journal must be machined all the way to the end.  Do not machine just where the bearing rides as the rear main bearing will not fit over the end of the crank where the rear main seal rides. Even though the main was ground smaller, we’ve never experienced a seal leaking after machining this surface.


Cylinder Head

When rebuilding the cylinder head, do not be afraid to repair cracks using your regular crack repair method.  We have had success repairing cracks on these heads, although there have been a few that are not repairable or not feasible ($) to repair.  Many of these engines were very slow to go to direct injection and used pre-combustion chambers.    When they’re cracked in this location, the cracks will extend well under the pre-combustion chamber.  Many of those cracks are not repairable and a new cylinder head is your best option.  There are a few aftermarket sources for heads for Kubota models, but not for this Yanmar head.  When replacing valve guides in the head, many of the new guides have an unfinished inside diameter that is not to the proper size.  There are some guides that are .040” small on the inside diameter.  After installing the guides, use your seat and guide machine to step ream the guides to the proper inside diameter and finish. Make sure to do all the guide work before you machine the seats.  If integral seats need to be replaced, I recommend machining your counterbore first and then pressure testing the head.  If the head passes the pressure test, install seats and recheck. Then, finish your seat angles as required. Make sure to set valve protrusion or recession to proper specifications (obtain specs from your new book).  Many of these engines have small diameter valve heads but they can be machined if they remain within specifications.  Many times when performing a complete rebuild it is wise to replace the valves.


Time to Order Parts

Parts have been very slow to become available in the aftermarket.  Many of these parts are only available from the original manufacturer.  Now some of you are thinking, “That is why I do not work on these engines because I cannot buy the parts and make a profit.”  Well, let me tell you from experience that is simply not true.  These engines are not readily available rebuilt from anyone.  There are not many options for the owners of these pieces of equipment and other than purchase a new engine or replace the piece of equipment, the best choice in many cases is to rebuild the engine.  There are a few sources that have recently become available that offer aftermarket parts but it is limited coverage at best.  Some O.E.M.’s separate their dealers depending on the type of equipment.  For example, a Kubota tractor dealer cannot look up parts for a Kubota engine used in a Bobcat skid steer.   When ordering parts, be aware that some manufacturers do not refer to parts the same as you are used to.  For example, Kubota calls rod bearings “crank pin metal”.  Always check the quantity required as some rod and main bearings are sold individually and not by the set.  The parts personnel at your parts source should be able to help you.  If you are having problems, have them print out the diagrams for you and show them exactly what you need.  These diagrams are also very handy when assembling the engine if you have any questions about where or how an item fits.  Also note that many full gasket sets do not come with the front and rear crank seals.


Ready to Assemble

Now that all machine work is done and you have all your parts, you are ready to assemble.  Assembly is just like any other engine you have assembled.  There are a few things to look out for that I have learned through the years.  When you install the new pin bushings in the rods, many of these bushings have a finished inside diameter.  After installation, all that may be required is a light hone to get the proper size and finish.  When assembling the piston to the rods, you might have a “FW” marking on the piston.  Take a note from my experience that “FW” stands for “flywheel” and not the front of the engine.  The piston pin is a zero fit in the piston on many applications.  The pin is tight to install in the piston.  Use caution as a new piston can be broken when installing the pin.  Heating the piston first helps immensely. Many Kubota engines use a dowel pin with a hole in it to supply oil to the rocker arms.  When you install the head gasket on these engines, there is a separate O-ring that goes around the dowel pin.  If the O-ring is not installed, the engine will have an oil leak from between the head and block.

If you removed the fuel injection pump and injectors rebuild them or send them out if you do not do this in-house. If the customer removed these items, make sure they’re not reinstalled without rebuilding them.  Most of these engines use a pump that is driven by a camshaft. The pump timing is set by changing the shims under the pump. When installing the injection pump, make sure to install the same thickness shims you removed and then verify pump timing to proper specifications.  The manual should give you step by step instructions on verifying pump timing.  All you should need is a degree wheel and some clear tubing for most engines using this type of pump.  What you will be doing is checking at what degree of rotation the pump starts to pump fuel to the injector.  If this is off, it can be corrected by changing the thickness of shims under the pump.


Ready to Run

If you can get the complete engine in your shop, there is no reason not to run it before it leaves.  This also gives you the opportunity to be sure it is primed correctly, the proper filters and oil are used.  It is also a good opportunity to add dollars to the shop ticket.   Many of these are small and light enough where they are easy to run.  You can use a water tower or a barrel for water.  Use a clean supply of diesel and hook up a battery to the harness.  Always verify and duplicate the operating voltage is for the system for that engine.  If there is a start/stop solenoid, use the wiring diagram in your manual to hook up to the harness to start the engine.  Once the engine is running, you can check for air/oil/coolant leaks, overall engine performance and document everything on the work order. When the engine leaves your shop both you and your customer will be pleased with the job and have a printed reference for the next job.

So now you’ve learned that small compact diesel engines can be rebuilt and it can be done profitably.  Do not be afraid of them and never say you cannot build that engine because it will cost the customer too much. Remember, your customer does not have a lot of options. We jokingly call it a “license to steal” because it is profitable and there is no big challenge in rebuilding them.  Be careful to make sure the profit you require is in the job and let the customer decide WHAT is too expensive.  If you are still shy on rebuilding these engines, remember, someone assembled it when it was new, so you can rebuild it and assemble it now.


Dwayne Dugas is the owner of Dugas Engine Service and holds the position of second vice chairman on the AERA Board of Directors. He has also been involved in the ASE Machinist Certification Program for the last 11 years. Dugas Engine Service was started in 1969 by his father, Cloures Dugas. He opened a parts store in 1966 and then started rebuilding heads in 1969. He progressed into a full engine rebuilding shop and in 1979 sold the parts business to concentrate on the machine shop. Dwayne bought the business from his father in 1999 and although his father retired after that, he still comes to work — at age 77, he still does all the crank grinding.

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