Yanmar Fuel Injection Pump Timing

The injection pump on almost all "YM" series Yanmar tractors is timed by a series of shims between the engine and injection pump body. These shims are not nearly as magical as they might seem and are simply there to determine how late in the rotation of the cam the pump will reach the required pressure to pop open the injectors. Over-simplification...  but that is the general idea. 

Your injection pump timing will generally never need adjusted unless you replace your injection pump with a new or used pump or you just like the challenge of trying new things. If you remove your injection pump and will be re-installing it- just be careful to re-use the same shims that you removed and the timing will be correct.

If you replace the injection pump with a new/different pump then most of the time those same shims will get you very close to correct-ish timing but if you want to dial it in correctly- follow these steps. 

• Bleed the fuel system and be sure you have fuel to the injection pump. 
• Disconnect the battery so you do not accidentally arm wrestle the starter while you are turning the engine over by hand... you will lose. 
• Pull the decompression lever and leave it pulled to make turning the engine easier and be sure it does not accidentally start.
• Put the transmission & PTO in neutral & set the parking brake so you are not trying to move the tractor or turn your brush mower by hand. 
• Remove the steel injection line on the #1 port (closest to the flywheel) of the injection pump. 
  
• Move throttle lever to warp speed (full throttle) position.
• You can use a socket (usually 27mm or 1-1/16") and ratchet on the engine crank pulley to turn over the engine by hand. Do not use the starter. 
• Turn over the engine a few turns (clockwise running direction when looking at front of tractor) and watch fuel get pushed out of the injection pump. 
  
• Screw a small section of clear tubing into the injection pump's #1 outlet port. You can find hose that will work at any local hardware store's plumbing section or you can contact us for a small piece of what we use. You can even just wrap a drinking straw with electrical tape in order to make it the right size to poke into the injection pump and not leak. This is not rocket surgery here and there is virtually zero pressure. 
• Turn the engine over until you can see fuel move up into that tubing and then the fuel will stop moving. Make a mark on the tubing at that exact level where the fuel is in the tube right now. A razor blade makes a nice sharp scratch line or the edge of a piece of tape works well. The level should not be leaking down or you need to re-seal your clear tube. 
• This mark you made is technically called the "almost top of the #1 cylinder's compression stroke" which is when the injection pump was done with its shot of fuel for that stroke. You are going to turn the engine over almost two more times to get through the power stoke, exhaust stroke, and intake stroke and get back to right before the compression starts. You want to get back to this moment right when the fuel starts to rise (no you cant just turn the engine backwards) and catch it right before it happens again.  
  
• Slowly continue to rotate the engine (the normal running direction.... clockwise) until you start getting close to the timing mark and pointer aligning. This means #1 cylinder is coming close to the compression stroke and things are about to get exciting.   
• Keep slowly rotating the engine and soon you will see the fuel juuuuust start to move up the tube. Stop right there! Yea... that was it. That was the exciting part.  
  
• Regain your composure... we've still got work to do. Check the timing mark A and see if it is aligned with the pointer B. 

• If the mark is before the pointer- add shims. If the mark is past the pointer remove shims. 0.004" of shim changes approximately 1 degree. 
• Once they line up... you are timed.
• "Pretty close" is probably "good enough". You are mowing the pasture- not competing in a NHRA event. 
• Fun fac:t: The marks align at 21 degrees before TDC on most Yanmar YM tractors... just in case you really want to impress your friends at parties. ;)