Engine repair information

Hard starting - diagnosing a troubled engine

1) Fuel delivery

The first thing to check is the in tank fuel filter. Often these are plugged up so badly, the fuel can't flow. Just carefully pull off the rubber line coming from the tank bottom (carefully, the nipple is plastic and can be broken easily) and fuel should flow freely. If your filter is clean and flowing well, the fuel transfer pump should be checked to ensure it's working. Best way is to crack the fitting where it leaves the pump and make sure it's spitting fuel strongly on the side going to the injection pump when turning the engine over. Next is to crack both fittings at the injectors a couple of turns and loosen the lines. When turning the engine over, they should both spit fuel. If all this works, it's not fuel starvation.

2) Compression

If fuel delivery is adequate, all the engine needs to start is compression and air. I often remove the air filter and ensure that when cranking the engine, there is strong suction into the intake manifold. Just put your hand over it when the engine is cranking and it should suction strongly. If it doesn't - either your valves are burnt, valves need adjusting or the rings are worn.

3) Timing

The least likely thing to affect starting is timing, but it is possible. There are two things that affect timing. Someone changing the injection pump out and not properly ensuring timing is correct (unlikely) or worn injectors that are releasing fuel too early. Neither of these are likely unless the engine has a lot of hours on it or hasn't been cared for.

If you have good fuel delivery, good compression and adequate air - a diesel will start.

Rebuilding and overhauling engines

The earlier Italian diesels are almost all air cooled. Lombardi, Ruggerini and Slanzi diesels are the most commonly found; although VM and other diesels have also been used. Rebuilding Italian diesels is similar to working on a motorcycle engine. The cylinders and pistons can be easily removed without disassembling the entire engine making an upper end overhaul relatively simple.

Ring Sets

Most early Italian diesels used four ring Pistons. Later Italian diesels use only three rings and this is what is commonly encountered when purchasing new parts. It is not a problem using an older four ring piston with only three rings. You simply disregard the uppermost ring land and install the rings on the lower three lands. This allows an easy overhaul without worrying about a ridge in the cylinder wall and surprisingly it offers no disadvantage in engine power. A common practice is to simply renew the Pistons in which case three ring pistons are often provided. Slanzi engine replacements are still using four ring pistons and parts are provided in this manner. Lombardini engines are the engines where three ring pistons are now commonly encountered. Three ring pistons have the advantages of less drag and thus better fuel efficiency. Power will not be affected.

When considering whether you should be replacing your pistons, always measure the top ring land clearance. This is easily done with a new ring and the feeler gauge. If there is more than 5 thousands clearance with the new ring consider replacing the piston or using ring spacers. The most important part of good compression in the engine is that first land. Excessive side clearance on a ring will allow ring distortion and compression bleed by. Underestimating excessive side clearance on the first ring is a common mistake when rebuilding engines. Great care is often given to moving the rings of the gaps do not line up with each other, but the amount of compression escaping by the piston this way is negligible. Excessive ring clearance in the first piston land is a far more common problem and contributes to excessive blow by.


Normally by the time the rings need replacing, valve guides have worn enough to be a problem. Worn guides are often more of a problem than the rings. Using a micrometer or veneer caliper, determine if the valve stems have worn. If so, replace them – valves are inexpensive. Regardless, replace the guides.

Also check your valve seats. Valve seats can be pounded into the head and create problems with the valve clearances. If you find a valve seat that’s been pounded into the head, consider having the head overhauled. A machine shop can cut a new valve seat, press it into the head and renew clearances. You can often assess a bad seat without disassembly, by recognizing very little adjustment at the valve stem. This is caused by excessive valve stem height as a result of the seat pounded further into the head. When adjusting valves, adjust to the manufacturers specification. Excessive clearance to prevent valves burning is not a good idea, use the manufacturer’s recommendations.


Removing the guides leaves most backyard mechanics uneasy. They are a pressed fit with about .004 thou interference to remain tight. The best way to remove them is to tap the guide with an applicable tap, thread a bolt into it and use the bolt for drifting or pressing it out. When inserting the new guides, freezing the guides overnight and heating the head to 150 degrees in the oven makes the job easier (except for handling the head). Make sure you press the guide into the head to the right depth (check your manual) to prevent sealing problems. 

Head Gaskets

Since head gaskets are made of copper, they can be re-used in a pinch by gently heating to dull red and quenching in cold water. This expands and softens the copper gasket. New gaskets are inexpensive though and should really be considered unless no longer available.

Push rod tubes

The rubber o-rings or gaskets used for pushrod tubes should be replaced as soon as they start leaking or whenever taken apart. Reusing tube gaskets is never a good idea and frustrating at best. We carry spares in stock and they are inexpensive.

Oil Specification - Use 15/40 W diesel rated oil

Never use standard engine oil in a diesel. Regardless of what you may have been told, there are significant differences with engine oil types, none of them more important than diesel engine oil. Diesels create serious amounts of soot and carbon as a bi-product. The engine oil used for diesels suspend these and render them harmless for a period of time. The additive package used in diesel rated oils is critical to the longevity of diesel engines. It creates a different film characteristic, suspends contaminants, cleans and protects  the engine. A modern 15/40 W diesel rated engine oil is what should be used and it should be run for no longer than 200 hours. The API code on modern oils should read CH-4, CI-4 or CJ-4, but any 15/40 W rated specifically for diesel engines will work fine in an Italian diesel.  Changing your oil and filters every 200 hours or less is key to engine longevity. Personally, I change my oil and filters every 100 hours on the clock.

New Engine Break In

Breaking in a rebuilt or overhauled engine is important. Consider three stages. Set the valves, bleed the fuel system and start it up. Do not run the engine over 1500 RPM for the first stage. Vary the speed between 800 and 1500 RPM for about 10-15 minutes before shutting down and letting the engine completely cool. Once cold, start up for stage two. In stage two you still keep RPM's less than 2000, but you accelerate harder while keeping the speed varied, again for about 15 minutes. Let the engine completely cool. Stage three you drive the tractor somewhat aggressively for about 15 minutes, but still keep maximum RPMS to about 2000 - 2300 RPM. The idea is to vary the speed while loading the engine under acceleration, BUT NEVER LUGGING THE ENGINE. This is best done in normal range, first gear. Manufacturers recommend not running the engine at full throttle (usually 3000 RPM for most Italian diesels) for the first 50 hours, but some quick accelerations to 2800 or so will not hurt the engine and will help seat the rings. 

There are special 30W oils for breaking in engines and can be used with advantage, although most mechanics do not bother (except for racing engines). If available in your area, it is a great way to go for 10 hours, then drain and refill with standard diesel oil. PLEASE: Do not use any oils but diesel rated oils for your diesel engine.

Advice you won't necessarily find in the manual

Cleaning the tractor

Always pressure wash the unit before working on it. The best is steam cleaning, but they are hard to find now. If you have particularly difficult tar like oil that won't come off, scrape as much as you can and try soaking the rest with oven cleaner before scrubbing with a brush and wiping clean. CAUTION: Oven cleaner is a caustic, it burns skin and will remove paint. Do not use it unless unconcerned about the tractors finish. I don't recommend using a pressure washer on oven cleaner either. Oven cleaner is caustic and will burn small animals feet, leave stains on nearby parked cars and is a general safety hazard. It works well, but use with caution.

RTV gasket sealer can be used almost everywhere

We carry complete gasket kits for engine work and recommend using them for rebuilds. If you need to pull the pan or ruin a cover gasket, just use RTV gasket make in a tube. All Italian manufacturers now use it and it makes sense. There are a few places where gaskets are critical and those will be identified in the manual. It doesn't however mean you need to buy a gasket. Take a caliper or mike the thickness of the gasket. If you can purchase the same thickness gasket material, you can make your own.

Making paper gaskets

To make a gasket, cut a piece of material larger than the needed gasket. Place it over the cast piece you need the gasket for. Take a small ball peen hammer and using the ball head, tap around the outside edge until the material breaks away from the casting. Once you have the outside shape, hold in place and tap through on the bolt holes and other internal shapes. You can make excellent gaskets this way and a complete roll of gasket material is cost of two gaskets.  

Push rod tube gaskets

The one exception to the above are the push rod tubes. Those gaskets are unique and seal during head torque. We sell upper end gasket sets with new push rod seals. If yours are leaking, replace them. Nothing else works as well. Avoid trying to seal it with bathroom caulking or tube sealant, that will just make a mess.

Seized items

It have always marveled at people squirting penetrating oil on a seized bolt and then immediately trying to break it free with a wrench. Penetrating oil is your friend, but don't expect it to work without doing your part. You can't just soak things and expect it to work. Tapping the seized item after soaking it is what loosens it. Tapping it lightly from all directions for a long time will do the trick. How long is a long time? Much, much longer than you think. Rust is about the same as welding something together. You soak it, then the vibration of tapping the item(s) allows the penetrating oil to seep slowly into the rust and eventually between the two items that are seized. That is not going to happen quickly. It comes down to either tapping for 5 minutes or spending a 1/2 hour drilling and threading easy outs. When penetrating oil has done it's job, bolts should wind off with little effort. If you want to save money, my favorite is a 70/30 mixture of ATF and Acetone - but here are some great recipes that won't break the bank:

1) Diesel fuel (or kerosene).

2) Diesel fuel with 10 to 30% acetone or ATF.

3) Vegetable oil with 10 to 30% acetone.

Acetone and oil will not mix easily or stay suspended for long, you just simply shake well before use. Also, acetone will evaporate, so it's best to keep small quantities, preferably in a metal oil type can.  

Never Seize compound

While many people say it's your dog, it's not - Never Seize is man's best friend! I use it on everything except torque requirements. Remember how frustrating it was with all the seized fasteners and think of the next guy. Do not under estimate the value of "Never Seize" compound, it was invented by a genius. You don't need to cover the entire threaded area, a stripe up one side will do it.

Loc-Tite or Thread Locker

Another must have in every shop. Use medium strength and lock any bolt needing to hold a major casting in place, ie: engine to bell housing, transmission to articulation casting, axle towers to differential cases, 3 pt hydraulic mounting bolts. To properly lock bolts, clean inner and bolt threads with a non residual solvent first. Having a small, round bristle brush helps with internal threads.

Do not over torque

Threaded fasteners are designed to be tightened within minimum and maximum torque values. These values are often 1/2 of what we think they should be. Over tightening is as bad if not worse than under tightening. There are many charts available showing the common torque values for normal sized metric threaded fasteners. The type or listing on the bolt head will indicate what type of fastener it is. Over simplifying it, metric 8.8 is similar to a SAE grade 5 fastener while 10.9 is similar to our grade 8. You would use a different torque for both. Try using a torque wrench and a chart for different bolts to get the feel of what you should be applying. NOTE: If using "never seize" compound, you need to reduce the torque about 10% to compensate for the slip of the compound.

Metric torque specification chart

Replace all bolts in their same place as removed

During engine disassembly (or any of the tractor), return the bolts to where they came from. As an example, if you remove the engine - take the six bolts that were removed and thread them back into the housing after the engine is pulled off. When you reassemble everything, all the bolts will be ready and you won't have to sort through a bucket of fasteners hoping you have the right ones.

Mark critical components as or before they are removed

Always mark the heads, pistons, piston rod / caps as to position and install in the same place. Engine components wear differently and need to be returned to their matched or original place.

Removing the heads / injectors

Remove the nuts and tap the head with a rubber mallet. You do not need to remove the injectors, but if you don't remove them - be aware the tips protrude out the bottom and can be damaged. If you decide to remove the injectors, remove the hold downs and pry on both sides evenly to break free. Always retrieve, then replace the copper gasket for the injector.

Head bolt studs

Often the cylinder studs come loose from the block. Clean and secure the studs in the block with thread locker blue when reinstalling.

Making a valve spring compressor

The valve springs on Italian diesels are fairly easy to remove. Make a valve spring compressor by welding an old washer to a piece of 1/2 inch flat bar and simply press down on the spring cup. The keepers can be easily removed.

Assessing valves - IMPORTANT 

Your valves and seats may look good, but mike the valve stems. Once worn, even new guides won't stop the engine from smoking. Worn valve stems / guides are a major source for burning oil. Valves and guides are inexpensive, so if worn, simply replace them.

Head alignment - CRITICAL

Italian air cooled diesels have separate cylinder jugs and separate heads. NEVER replace and torque the heads down until you have mounted the intake and exhaust manifold. This will align the heads so that you don't break the manifold flanges. ALWAYS tighten the manifolds to the heads before torquing the heads down. 

Piston assessment - IMPORTANT

If the top ring has excessive clearance between the top ring and the top of it's ring land, replace the piston or add ring spacers to get it back to spec. A new ring in a new piston will have about 1.5 thousands of an inch clearance in the land. You can tolerate up to 5 thousands of an inch, but if you are 6 or more, the engine will be trouble. People are obsessed with the gap clearance, and not to say it's not important - it's just your side clearance is a game changer. Reusing the piston without spacers will lead to nothing but trouble. Ring spacers require turning the pistons on a lathe to accommodate them, so new pistons are often an easier solution for customers without a lathe.

Removing or reinstalling pistons - CRITICAL

Never remove or reinstall the pistons (when on the rod) without protecting the crankshaft. The easiest way to do this is to use 4 inch lengths of plastic tubing slipped over the bolts. This prevents the bolts from banging against the crank.

Always lubricate the rod and main bearings when replacing - IMPORTANT

It's nice to use assembly lube, but standard engine oil is fine.

Use an air gun to remove the front pulley / flywheel crankshaft nuts

We're often asked how to secure the flywheel so the crankshaft nut can be removed. The trick is not a 6 foot extension on your wrench while a friend levers a wrecking bar against the teeth of the flywheel (breaking teeth off or the case). These large nuts are torqued on with significant torque. The best (and safest) way to remove them is using a 3/4 drive air wrench before the heads are removed.

When rebuilding the bottom end of your engine always ensure that the crankshaft end play is within specifications. If not, a new crankcase piece or new thrust washers can renew crankshaft end play to new specification. See the service manual for more details.

Older Lombardini engines used main bearings that were dimpled into the crankcase. New bearings no longer have these dimples and this should not be seen as a problem. When the older dimpled main bearings were spun on a crankshaft damage to the engine crankcase was often severe. If you have a damaged crankcase from spun bearings we can provide oversize crankcase bearings or new crankcase parts where available.

Some diesels require re-torque on certain nuts like flywheel nuts to 200+ foot lbs of torque. That is a lot of torque and the easiest way to accurately achieve it is to use a torque multiplier / torque wrench combination.

Renew all copper fuel line gaskets

While copper gaskets can be heated to a cherry red then quenched in cold water to anneal them for re-use, they are inexpensive and should be replaced.

Tachometer drives

The tachometer drives for the older Ruggerini and Lombardini diesels are fragile and tend to fail. The mechanical tachometers are usually fine and if your drive is working, we can provide you with replacement cables. To test your drive, remove the cable at the engine and watch while the engine is idling. If the center is turning, it's good. If on disassembly it falls apart, it's bad. If good, replace the cable and remove the other end at the tachometer. If turning, the cable is good and your tachometer should work.

If your tachometer drive or the tach itself has failed, we don't suggest replacing it. The cost is just not justified. There are other economical solutions like the "Diesel Tiny Tach" available on line. By installing the "Tiny Tach" transducer on the injection line, the Tiny Tach reads the fuel pulse and determines the RPM. It will give you the information you need at a reasonable cost. Even a better deal is the electric tach conversion by David Mendenhall in California. You can find his information under our "Tractor Parts" section

Bleeding a diesel fuel system

If diesels are run out of fuel or the engine has been rebuilt - the engine will not start again until all air is removed from the fuel system. There are specific bleeding instructions for different engines, but we always use the simplest method that always seems to work.

NOTE: The fuel line starts at the fuel tank, goes to an optional fuel transfer pump (some engines don't have them), then to the fuel injection pump and finally to the injectors. To bleed a diesel injection system, do the following:

1) Find your diesel injection pump.

2) Your diesel injection pump will have either one or more injection lines going to the top of the engine (to the injectors).

3) Follow the fuel line(s) up to the injector(s) and identify the connection nut(s) where the line connects to the injector(s).

4) Take a wrench and crack the nut(s) about a 1/2 turn or so and loosen the line(s) by wiggling. Do all lines at the same time.

5) Turn the accelerator lever to full throttle.

6) Crank the engine over until all lines are spitting fuel. 

7) Tighten the nuts (do not over tighten) and start the engine.