Valve lash-3GM30F-questions

Jun 17, 2012
203
C&C 35 MKIII Manitowoc, WI
It is past time for me to do a valve lash adjustment. I am a former automotive technician so adjusting valves is turnkey for me. However making sure the respective cylinder is at TDC on compression is not as simple as a gas engine [you can feel compression in the spark plug hole if you can't find a clear timing mark on gas engines]. That said my Yanmar shop manual instructs to align the flywheel mark visible thru the starter mount hole or thru an inspection hole on the backside of the trans. That works for cylinder # 1 but then it instructs to rotate the crank 240 degrees and adjust # 3 and again rotate 240 and adjust #2. My question is that due to the critical importance to assure that each valve is fully closed-how can you judge 240 degrees accurately without an index mark? I know I can tell when both valves are fully closed on the low side of the cam lobe, but since holding a valve open [to little lash clearance] for even a nano second at the wrong time will burn it-I would prefer a more accurate and dependable indicator. So we're back to the rotate procedure. Long message, but if anyone has specific hands-on experience with adjusting the lash on this model-I would really appreciate your information. thanks
jim
SV SamiDog
2002 Humter356
 
Nov 6, 2006
10,107
Hunter 34 Mandeville Louisiana
I have done my 3 GMF several times and find it pretty easy to work.. The 3 GM 30 is the same basic engine but with 250 more cc's displacement. Doesn't have to be super precise on the crank position for valve set.. Note that #1 TDC can be seen from the front if you look for the keyway right behind the retaining nut.. make sure the fuel kill is pulled so no fuel gets to the cylinders.. it can pop and hurt ya if you have a wrench on the nut.. pull the valve cover and rotate (wrench) clockwise (from the front, looking aft) until both valves on #1 are loose; then note the key position and rotate it until it is straight UP .. that'll be about TDC on #1, firing. Now before ya move anything , make a Magic Marker mark pointing straight up, which should be in line with the key.. now make a mark at 120 degrees and 240 degrees. (a cheap protractor is fine to do this one) .. Those two other marks will be TDC for the other two cylinders.. after setting the #1, rotate clockwise until the next set of valves are both loose.. then rotate until one of the other marks is vertical.. then set those.. then repeat for the last.. This will get you to within 4-5 degrees of true TDC.. not close enough for timing adjustment, but fine for valve setting since the cams in these things aren't radical by any means.. be sure the engine fuel stop is pulled so it dos not try to pop while you are messing with it.
A mechanic's mirror and light can be used to verify the first cylinder very precisely through the hole in the aft side of the flywheel housing.
 
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