Replacing a head gasket on your Yanmar tractor might seem like a daunting task but don't panic! It is actually a lot easier than you might think and can certainly be accomplished by a shade tree mechanic in their garage or back yard. If you are not afraid to get your hands greasy you can do this job yourself and save a lot of money. Here is how to do it*.

• Clean off your engine (with a pressure washer if possible) especially the upper portion around the head area. You are going to be doing surgery on your engine and you don't want dirt and junk falling into your patient.
• Take a couple of pictures of your engine throughout the dis-assembly process so if you have any question about where things went, you can have something to look at. This will help eliminate all of those 'extra parts' you have left over at the end of the job.
• Drain the water out of your radiator into a suitable container.
• You will probably want to remove the muffler and water pump. This just makes the head a little easier to maneuver. This step is not completely necessary though. If removing the muffler keep in mind that those bolts may be rusted and might twist off.
• Remove anything attaching the head to the tractor or engine including any oil lines, fuel injector lines, wire to temperature switch, and radiator hoses.
• Remove the valve cover.
• Remove the rocker arms and pushrods. Keep these parts in order so they go back in the same location. A good tip is to poke holes in a cardboard box and push the pushrods into the holes to keep them in order
• Remove the head bolts or head nuts depending on your model.
• Lift off the head. It might be stuck but, as long as you are sure you removed all of the bolts, it is ok to gently and evenly pry up on the head. Do not pry anywhere near the sealing surface of the head gasket!
• Dry off all of the spilled coolant and put paper towels or rags into the holes on the block that go into the oil ports, water ports, and into the crank case (the big openings that the pushrods went into). This will keep pieces of the head gasket from getting where they should not be.
• Remove the old Yanmar head gasket.
• Scrape off any remains of the gasket or any sealer that might have been used on both the block and the head. Use a gasket scraper, razor blade, and carburetor cleaner to get these parts perfectly clean and smooth. Do not scratch the sealing surfaces of the block or head!
• Inspect the head closely for any cracks. Use a straight edge and a feeler gauge to check the head and block to be sure they are flat. These small Yanmar engines really don't warp often though so they are typically pretty flat.
• It is good practice to run a tap down the head bolt hole to be sure they are nice and clean. This will give you a more accurate head bolt torque. A dirty thread can reduce the clamping force of the bolt by as much as 50%
• Blow out all of the head bolt holes with compressed air. This will make sure that there is no dirt, head gasket remnants, or liquid in the holes. You don't want the bolts to bottom out before they get tight (yes... the bolts can 'bottom out' on liquid too!)
• Remove the rags or paper towels from the holes in the block. Be sure you get them all out!

See that wasn't that hard! You are half way there. Now we just need to figure out how all of this stuff goes back together.

• Your new head gasket will install dry. Never use silicone or gasket adhesive. You can use a product called 'copper coat' if you want to. It is like a copper spray paint and goes on in a very fine layer and helps fill tiny imperfections.
• Head gaskets on these tractors are rarely symmetrical. There should be holes on one side that are not on the other. This is how you know which end is up. Just line up the holes in the block with the holes in the gasket. It is not uncommon for the holes that the push rods go through to look different than you old gasket.
• Set the head down on the gasket evenly and carefully.
• Wipe a little motor oil on the threads of the bolts. You don't want oil dripping off of them because it can fill the bolt holes and the bolt can 'bottom out' on the oil (oil does not compress). Do not use antiseize or fancy greases. Antiseize on the threads will increase the clamping force by as much as 70% (If you put antiseize on threads and torque to 100 ft/lbs you are putting as much stress on the threads and bolt as if you were tightening to 170 ft/lbs...for example) which can cause stripped threads, broken bolts, or other problems.
• Many of the 'F' series Yanmars use a 'one time use' bolt that needs to be replaced each time. Other 'YM' series use a stud or bolts that can be re-used.
• Start the head bolts and tighten finger tight. Then follow the service manual's recommended torque procedure.
• Important! Use a decent torque wrench that has been tested or calibrated recently. This is extremely important! Torque wrenches are not like other tools. They require constant calibration and maintenance. A popular automobile magazine took a brand new torque wrench, left set at 60lbs for 60 days in a drawer, and the reading was off by almost 10%! You can get a cheap digital torque wrench tester for about $35 on Amazon.
• Put the pushrods back in the correct locations. Set the rocker arms back on the studs and finger tighten.
• Adjust the valves according to this link https://www.hoyetractor.com/valve-set.htm
• Clean out the valve cover with carburetor cleaner. Remove the old valve cover gasket.
• Put the new valve cover gasket on the valve cover. Use some gasket adhesive to help hold it in place.
• Re-install the valve cover onto the head and torque to the correct torque specified in the service manual.
• Re-install any hoses, wires, oil lines that were removed
• Start the tractor and admire your handy-work! Pat yourself on the back... you deserve it. Just don't tell your friends about your new master mechanic skills unless you want them to start bringing you all of their broken stuff. Word travels fast!

We strongly recommend that you re-torque the head after the engine has been up to temperature and cooled back down. We also recommend that you re-torque again after another hot/cold cycle until the bolts/nuts no longer move when torqued. This will help lower the likelihood of another blown head gasket due to the new gasket compressing as it settles down.

- Hey!... But why didn't the original head gasket need re-torqued at the factory? Why does the replacement gasket need re-torqued?
- The factory head gaskets are typically rigid (metal in many cases). They don't need re-torqued but they are very picky about surface condition. Everything must be perfectly flat and perfectly smooth... like brand new. Your engine is not brand new and has small scratches, small rust pits, slight warping so these metal gaskets typically won't work very well. Replacement head gaskets are typically composite because they are more forgiving on surface condition. They can compensate for some scratches, minor rust pitting, and surfaces that might not be perfectly flat... like the current condition of your 40+ year old engine. They do, however, compress slightly and it is typically recommend that they are retorqued after they have had a chance to 'settle in'.

What causes a blown head gasket? CLICK HERE

If you are unsure about any of these steps please consult a mechanic.

*These steps are just to help you decide if you want to tackle the job yourself. You will still need to consult a service manual for exact procedures and torques.