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Old 26-04-2016, 12:49   #1
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Yanmar De-Compression Levers

Long story short- I had some rusted valves so I had a head shop install new yanmar exhaust valves on two cylinders on my Yanmar 3GMD. Put the engine back together (did do valve clearance adjustment). Engine went together ok and turned by hand without any interferences (both in compression and decompression by using levers). However when I rotate the engine using the starter in the decompression mode (using decompression levers), two of the levers seem to vibrate a lot. I do not remember this vibration prior to doing the head work.

So question is should the levers vibrate some when in the decompression mode? I am thinking the levers may not move the valve down as far as it is moved by the rocker arm, and maybe that is where the vibration is coming from. Also, after taking the engine apart, I see the clearance between the pistion and head is very little (0.7mm) so if the valve sticks down too much, the piston would hit it- I hope that is not what is happening on my engine when in decompression. When in compression engine rotates fine with no interferences and it does have compression. I have not tried to start the engine yet.

Insight to the decompression levers and the vibration on the levers I am seeing would be appreciated.
Thanks
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Old 28-04-2016, 12:03   #2
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Re: Yanmar De-Compression Levers

Just an update. Took the valve cover off to check for any loose parts or problems. All looked ok. I did make some measurements and the engine cam shaft moves the exhaust valves down a lot father than the decompression lever would. so I think the vibration is just the additional movement of the valves that occurs when the cam/push rods, and valve rockers do their thing.

Still it seems like a lot of vibration. Using just the starter to rotate the engine (without starting) one of the decompression levers actually went to compress mode. No real problem as the decompression levers are only used for a short time, however just checking to make sure nothing gets damaged.

would be interested in what vibration others see on the de compress lever of any Yanmar.
Thanks
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Old 28-04-2016, 15:49   #3
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Re: Yanmar De-Compression Levers

When I use the decompression levers on my yanmar 3gm30f and then crank the engine some of the levers do tip alittle back and forth, there is some movement but not like a loose wiggley vibration.
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Old 28-04-2016, 16:29   #4
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Re: Yanmar De-Compression Levers

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Originally Posted by Badsanta View Post
When I use the decompression levers on my yanmar 3gm30f and then crank the engine some of the levers do tip alittle back and forth, there is some movement but not like a loose wiggley vibration.
Thanks, I think that is about what I have. After putting the engine back together, I am a little paranoid...
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Old 28-04-2016, 19:51   #5
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Re: Yanmar De-Compression Levers

Yeah I've got mine in about 50 zip loc bags and the block and head at the shop. breaking it down was easy, sweating the rest. Best of luck.
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Old 16-05-2016, 13:30   #6
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Re: Yanmar De-Compression Levers

Over the weekend I started up my yanmar after having done the partial rebuild. Once the fuel system was primed, she started right away and ran well. the decompression levers caused no trouble.
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Old 16-05-2016, 13:58   #7
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Re: Yanmar De-Compression Levers

Super, hope mine does the same.
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Old 16-05-2016, 14:08   #8
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Re: Yanmar De-Compression Levers

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Super, hope mine does the same.
Thanks. Good luck to you. I kept putting off the starting as I was afraid something bad would happen. So far so good. Make sure to double check everything- cooling water, fuel lines, oil levels. I ran mine in the decompression mode for about 1 minute and with the stop lever on stop to get the oil recirculating through the engine (the oil pressure light did turn off so the engine was seeing good oil pressure), before I started the engine.
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Old 16-10-2016, 13:24   #9
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Re: Yanmar De-Compression Levers

I have a ya mar 3 GMD on board. Three injectors, so three cylinders but only two decompression levers. Any idea why there isn't three?
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Old 16-10-2016, 16:35   #10
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Re: Yanmar De-Compression Levers

They already responded to your other posting

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Old 17-10-2016, 11:40   #11
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Re: Yanmar De-Compression Levers

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I have a ya mar 3 GMD on board. Three injectors, so three cylinders but only two decompression levers. Any idea why there isn't three?
If you have a 3GMD, there definitely were three decompression levers when the engine was made. One may have gotten broken off since it was made. The decompression lever operates a shaft that has a machined end that takes the circular rod and turns it into a half circle. The decompression lever rotates this rod and causes it to contact the exhaust valve rocker so that the exhaust valve does not close fully. Take a look above each fuel injector in the valve cover area. This is where the three decompression valves are located. Compared the two that you know you have to the area above the injector where there is no lever. Do you see a circular area where the decompression lever may have been broken off or if you are lucky, maybe they just removed the screw holding the lever. Do you see a screw hole? If you feel up to it (or hire mech), take off the valve cover (two or three retaining nuts at the very top of the valve cover), carefully pull the cover straight up and do not damage or loose the valve cover "O" Ring that seals this area (it is hard to align it when you go to put the cover back on). Now take a look inside the valve cover, this is where the shaft with half circle is located- one for each cylinder).
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