Tractor Service Manual - Repair Guide

How to Replace a Blown Head Gasket

For more information or help with replacing a tractor blown head gasket or any other tractor service topic, please visit www.YanmarTractorStore.com

Diagnosing a Blown Head Gasket

Our tractor service department often gets the question “How to know if my Head Gasket is blown in my tractor engine?”  A failed engine head gasket can cause several specific symptoms that are noticeable while operating the tractor, or upon inspection of the engine itself. These symptoms often include persistent engine misfires or skipping, engine overheating, coolant anti-freeze in the engine oil crankcase and-or engine oil entering the radiator, and oil leaking the itself. Below is a summary of the symptoms to look for to determine if you need to replace your head gasket. These symptoms include: 

 

Engine Skipping / Misfire

A head gasket that fails between cylinders will generally cause the engine to skip while running. A gasket failure can cause compression from one cylinder to pass by and leak into another cylinder. This reduced compression will also cause a rough idling engine. When the head gasket leak is located between a cylinder and the coolant port, antifreeze may leak into the cylinder causing misfires on startup. This condition will be especially noticeable the engine has run for a period of time, warmed up, shut off, and subsequently restarted shortly thereafter. Pressuring the cooling system and then starting the engine, may make the misfire more noticeable. It is important to note that while you will probably notice the misfire while running, it may be intermittent. Also, This type of head gasket failure is not usually accompanied by other more obvious signs of failure like discolored exhaust or significant high-knocking sounds.   

 

Engine Overheating

When a head gasket fails between a combustion chamber and the cooling system, often the engine will overheat. You may also notice a loss of antifreeze from the engine cooling system. Here again, the overheating condition may only be intermittent. For example, the tractor may overheat after operating for longer periods or under rigorous operating conditions but may not overheat after successive intervals of running the tractor and then shutting it off in shorter periods. If you notice this pattern of overheating symptoms, monitor the engine temperature while allowing the engine to run uninterrupted for a longer period. If the tractor does begin to overheat, this is a likely sign of a failed head gasket.

 

Engine Oil in the Radiator or Antifreeze in the Engine Oil

Head gaskets can fail at points between the internal engine coolant passages and the lubrication system. This type head gasket failure may cause engine oil to leak into the coolant, coolant to leak into the engine oil, or both. The first step is to inspect the radiator cap to see if the seal is building or out of shape, as this is a telltale sign of this type of failure. Also, check the engine oil dipstick to see if the engine oil if over full. If so, this is a relatively clear indicator that coolant has found its way into the engine lubrication system due to a head gasket failure.

 

External Engine Oil Leaks

An oil leak from a head gasket is not common and sometimes it is mis-diagnosed. For instance we may think oil leaking from the head gasket is leaking from a valve cover. Because valve cover leakage is far more common, this is an easy mistake to make. Other times the oil may drip from the area below the transmission. Gravity causes the oil to flow down and this is the lowest point, and a rear-main seal or oil-pan gasket leak can be mistaken for a leaking head gasket.

If your tractor is showing any of the conditions described here, you may want to condiser doing an engine compression test. See our tractor service guide "How to do an Engine Compression Test

How to Replace a Tractor Head Gasket

If you don’t mind getting your hands dirty, you can save a lot (and learn a lot) by replacing your tractor engine head gasket yourself. It is a bit of a process, but if you are up to the challenge, here is a step-by-step guide on how to do it.

 

Step 1. Disassemble the Engine Cylinder Head

 

Prepare for the job. Prepare a clean, flat working surface on a workbench large enough to accommodate the cylinder head assembly. Besides installing the new Head Gasket, be sure to use new gaskets, O-rings and seals on reassembly of cylinder head. We also highly recommend washing your engine thoroughly to avoid grease, dirt, and other contaminants from falling into your engine. 

 

Mark all components. During disassembly, be sure to mark all valve train components so they can be installed in their original locations. Take some photos of your engine throughout the disassembly process so you have references about where things go when reassembling parts. It is critical that all parts are returned to the correct position during the reassembly process. Drain coolant from engine into a suitable container and then remove the coolant pump itself.

 

Remove the fuel lines. Remove the Fuel Lines Carefully remove the high-pressure fuel lines and fuel injectors from the cylinder head. Start by removing the high-pressure fuel injection lines as an assembly. Always remove or install the high-pressure fuel injection lines as an assembly whenever possible. Note: Disassembling the high-pressure fuel injection lines from the retainers or bending any of the fuel lines will make it difficult to reinstall the fuel lines. To prevent "rounding" the fuel line nuts use a "line" or "flare nut" wrench. Close fuel valves in the fuel supply line and clean the area to keep any contaminants from entering the fuel system. Place a drain pan under the fuel injection pump to catch any spillage. Loosen the fuel line nuts at the fuel injection pump and fuel line nuts at the injectors. Use a wrench to hold the fuel return line nut and use a second wrench to loosen the fuel line nut itself. Repeat with the remaining fuel injectors and remove the high-pressure fuel lines as an assembly. Take extra care not to bend any of the fuel lines. Protect the fuel system from contamination by plugging or covering all open connections.

 

Remove the intake manifold and valve cover. Start by removing the intake manifold bolts and valve cover bolts. Then, remove the valve cover/intake manifold and discard the gasket. Remove the exhaust manifold bolts and nuts, then remove the exhaust manifold and the exhaust manifold gasket. Next, remove the glow plugs by disconnecting the glow plug harness from the glow plugs, and remove the glow plugs themselves from the cylinder head.

 

Step 2. Remove the Rocker Arm Assembly

 

Remove the rocker arm components. Loosen the rocker arm bolts and nuts that retain the rocker arm shaft supports. Next, remove the rocker arm shaft assembly from the cylinder head.

 

Remove the push rods and identify for reinstallation.  Note: Identify the push rods so they can be reinstalled in their original locations. Next, Remove the rocker arm shaft alignment set screw from support. Note: The set screw is in the center support. Remove two circlips. Note: The rocker arm shaft fits tightly in the rocker arm supports. Next, clamp the support in a padded vise. Twist and pull out on the rocker arm shaft to remove. Reverse this process when installing the rocker arm shaft into the supports.

 

Slide the rocker arm shaft out of the rocker arm supports springs and rocker arms. Note: Mark the rocker arms so they can be reinstalled with the original matching valve and pushrod. Remove the valve adjusting screw and lock nut from the rocker arms. Again, be sure to mark parts so they can be reinstalled on the same rocker arm.

 

Step 3. Remove the engine cylinder head

 

Remove the cylinder head bolts. First loosen the cylinder head bolts and remove the bolts. Next, lift the cylinder head away from the cylinder block.

 

Scrape old head gaskets surface area clean and discard the old head gasket. Place the cylinder head on the work bench to prevent damage to the combustion surface. Place the combustion side down.

 

Step 4. Remove the Intake & Exhaust Valves

 

Remove the valves. Place the cylinder head on the work bench with the combustion side down and remove the valve stem cap and keep with the valve it was installed on. Using a valve spring compressor tool, compress one of the valve springs and remove the valve keepers. Slowly release the tension on the valve spring.

 

Remove the spring retainer and valve spring. Repeat this procedure with all remaining valves.

Note: While we recommend replacing the valves while doing this job, you can reuse the valves if they are in good condition. If the valves are to be reused, identify them so they can be reinstalled in their original location.

 

Step 5. Clean and Inspect the Cylinder Head Components

 

Note: Always read and follow safety related precautions found on containers of hazardous substances like parts cleaners, primers, sealants, and sealant removers.

 

Thoroughly clean all components using a non-metallic brush and an appropriate solvent. Each part must be free of carbon, metal filings and other debris. Visually inspect the parts. Replace any parts that are discolored, heavily pitted or otherwise damaged. Discard any parts that do not meet specified limits. You can obtain these limits from your tractor dealer or find in the tractor service manual. Replace all parts required as a result of inspection or any part whose measured value. Any parts that does not satisfy the standard or limit must be replaced. Don’t skip this!

 

Mark all valve train components. Mark all components so they can be installed in their original locations.

 

Inspect the push rods to determine if the bend of the push rods is within the

specified limit. Place the push rods on a flat inspection block or layout bed. 2. Roll the push rods until a gap can be observed between a portion of the push rod and the surface of the block or layout bed. Use a feeler gauge to measure the gap.

 

Inspect the rocker arm assembly and Rocker arm shaft hole diameter. Use a telescoping gauge and micrometer to measure the inside diameter of all the rocker arm support brackets and the rocker arms. Inspect the rockers arms for excessive wear or damage. Record the measurements and compare to service limits.

 

Inspect the valve guides. Visually inspect the valve guides for distortions, scoring or other damage. Note: Measure valve guides while they are installed in cylinder head. Use a telescoping gauge and micrometer to measure the inside diameter of the valve guide. . Replace valve guides if not within specifications.

 

Inspect the cylinder head. Put the cylinder head flat and inverted combustion side up on the bench. Use a straightedge and feeler gauge to measure cylinder head distortion. Measure diagonally and along each side. Record the measurements. If distortion exceeds the service limit, resurface or replace the cylinder head. Remove only enough material to make the cylinder head flat, but do not remove more than 0.008 in. 0.20 mm.

 

Inspect the intake and exhaust valves and valve stem diameter. Visually inspect the intake and exhaust valves. Replace any valves that are obviously discolored, heavily pitted or otherwise damaged. Use a micrometer to measure the valve stem by measuring the valve stem near the

combustion end and near the opposite end and check against service limits. Then, place the valve stem on a flat inspection block or layout bed. Roll the valve until a gap can be observed between a portion of the valve stem and the surface of the block or bed. Use a feeler gauge to measure the gap. Record the measurements and check against service limits.

 

Check valve recession.  Note: The valve guides must be installed to perform this check. Insert the valves into their original locations and press them down until they are fully seated. Use a depth micrometer to measure the difference between the cylinder head gasket surface and the combustion surface of each exhaust and intake valve. Record the measurements and against service limits.

 

Check the valve face and valve seat. Check the clearance between the valve and valve guide before grinding or lapping the valve seats. If the clearance exceeds the service limit, replace the valve and/or valve guide to bring the clearance within the limit. Roughness or burrs will cause poor seating of a valve. Visually inspect the seating surfaces of each valve and valve seat to determine if lapping or grinding is needed. Visually inspect all valve faces and valve seats for pitting, distortion, cracking, or evidence of overheating. Usually the valves and valve seats can be lapped or ground to return them to serviceable condition. Severely worn or damaged components will require replacement. Coat the valve seat with a thin coat of bluing compound. Install valve and rotate to distribute bluing onto the valve face. The contact pattern should be approximately centered on the valve face and even in width.  Also visually inspect the valve seat for even contact. Light cutting can be performed by the use of a hand-operated cutter. Valve seat diameter can be adjusted by top-grinding with a 150° stone to make the seat diameter smaller, and bottom-grinding using a 40° stone to make the seat diameter larger. Once the seat location has been corrected, grind and lap the seat angle to specification. See Cylinder Head on page 6-4 for the service limit. Grind the valve face and/or valve seat only enough to return them to serviceable condition. Grinding is needed if the valve and the valve seat do not contact correctly. Check the valve recession after grinding. If the valve or seat require grinding, lap the valve after grinding. Lap the valve face to the valve seat using a mixture of valve lapping compound and engine oil. Be sure to thoroughly wash all parts to remove all grinding powder or compound.

 

Step 6. Reassemble the Cylinder Head and Engine Components

 

We cannot reiterate enough the importance of using all new gaskets, O-rings and seals on reassembly of cylinder head. Also, liberally oil all components during the assembly process to prevent premature wear or damage.

 

Reassemble the valve guides. The valve guides are installed into the cylinder head with an extremely tight press-fit. Before installing the valve guides, place the valve guides in a freezer for at least twenty minutes. This will cause the valve guides to contract, making it easier to install the valve guides in place. 2. Immediately after removing the valve guides from the freezer, insert the valve guides in their proper positions. Finish installing the valve guides to the proper height using a valve guide installation tool.

 

Reassemble of intake and exhaust valves. When doing this job, always install new valve stem seals. The exhaust valve stem seals are different than the intake valve item seals and can be identified by the color the seal spring. Ensure they are installed in the correct locations. Oil the lip of the valve stem seal. Using the valve stem seal installation tool, install a new valve stem seal on each of the valve guides. Then, measure the distance from the cylinder head to valve stem seal to ensure proper clearance between the valve guide and seal. Put the cylinder head assembly on its exhaust port side. Next, install all the valves in their proper location in the cylinder head. Place the cylinder head on the workbench with the combustion side down to install the valve springs. Reinstall the valve spring and spring retainer. Next, using the valve spring compressor tool again, compress the valve spring. Insert the valve keeper and slowly release the tension in the valve spring, then reinstall the valve cap and repeat these steps on all remaining valves.

 

Reassemble the cylinder head. First, carefully clean both the combustion surface of the cylinder head and the top surface of the cylinder lock. Next install the new head gasket on the cylinder block itself. Replace the head by positioning the cylinder head on the cylinder head gasket as closely to the correct location as possible. Lightly oil the threads of the cylinder head bolts and replace and tighten the head bolts to the torque specified by your tractor manufacture or dealer. Finally, insert the push rods in their respective positions.

 

Reassembly of rocker arm assembly. Ensure the lubrication holes in the rocker arm shaft are oriented correctly with respect to the rocker arms and lubricate the rocker arm shaft. Slide the rocker arm supports springs and rocker arms onto the shaft. Note: The rocker arm shaft fits tightly in the rocker arm supports. Clamp the support in a padded vise. Twist and push on the rocker arm shaft to reinstall. The set screw is usually located in the center support. Align the hole in the rocker arm shaft and the hole in the rocker arm support and then reinstall the alignment set screw.

 

Place the rocker arm shaft assembly onto the cylinder head. Reinstall the valve adjusting screws and lock nuts. Align the push rods with their respective rocker arms and then reinstall and tighten the rocker arm shaft retaining bolts to the specified torque. Finally, tighten the rocker arm shaft alignment screw. Adjust the valve clearance per your tractor engine required specifications. 

 

Reassemble the intake manifold and valve cover. First, reinstall the glow plugs, tighten to proper torque specifications, and reinstall the electrical harness. Next, lightly grease a new valve cover gasket, place the gasket in the groove of the intake manifold/valve cover, and place the valve cover on the cylinder head. Reinstall the bolts and tighten securely. Next, reinstall the exhaust manifold using a new gasket and tighten the manifold bolts and nuts securely. Reinstall the fuel injectors and high pressure and return fuel injection lines. Finally, reinstall the coolant pump. Finally, reinstall the alternator. When complete, recheck all bolts and torques. Replace all the fluids.

 

Start and test the engine and monitor for any issues. We highly suggest to re-torque the head bolts after approximately 5 hours of run time, as the components may tend to “settle” during this period.  

 

If you have questions or need help, visit www.YanmarTractorStore.com for more information of feel free to email or call us.  Our expert tractor staff is friendly, and our advice is free!

Yanmar Tractor Store

1100 W Happy Valley Rd.,

PHOENIX, ARIZONA 85085

602-734-9944

email:info@yanmartractorstore.com

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