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Old 25-01-2016, 18:24   #16
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Re: yanmar 2gm20 rebuild piston ring gaps

a burring hone is used to put cross hatching in the cylinder walls. this is to help the rings seat. Chic was right on the end gap for the rings. when inserting them in the cylinders to measure you'll need to set them just below the top of the cylinder, below where the carbon built up, that is the combustion chamber betwixt the head and piston and then again at the bottom of the stroke, the point that the piston goes at the bottom of the cylinder. I believe it has about a 3 inch stroke. you'll usually find the gap wider there. if it is more than 4 to 5 thousandths you'll need to re bore or put new sleeves in. i'm not sure if the 2 gm has sleeves. most of the older Yanmars I've worked on did. The number on the piston is to show what orientation the piston is to be set in. the manual will tell you what side it goes on. if you remember what side it came from put it back the same. Like wise with the connecting rods, a number at the big end. if you don't remember, get a manual, as you could be running into some serious trouble.

when assembled, to break in the new parts run the engine for 30 or 40 minutes, at idle, till it is fully wormed up and then let it cool and retork the head bolts. Then crank it up and worm it up again then get under way. give yourself a few hours to do this. run it at low rpms (1000) for at least 15 min.s and then bring it up to around 1500 for a few minutes then back down to 1000. do this a couple times then go to WOT for 3 to 5 minutes. then your good to go.
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Old 25-01-2016, 18:25   #17
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Re: yanmar 2gm20 rebuild piston ring gaps

How do u get a US address? I know no one in the US, or u use a freight forwarding company? Good thing w using the local supplier is the info they supply free of charge, and I can take things back. And yes the precombustion chamber holes have all connected, the cone shape is missing on one cylinder, managed to pop them out, after advice from the local parts distributor, so I'm replacing both, if one side has blown off guess the other one may have limited time too!

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Old 25-01-2016, 18:32   #18
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Re: yanmar 2gm20 rebuild piston ring gaps

Perhaps it is just glazing causing the oil drop when I filled both cylinders w oil, one dropped over night. Glad I did pull the head off before putting this second hand motor in my boat, as the small amount of excess diesel smoke might be due to the busted pre combustion chamber ( pointy bit)

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Old 25-01-2016, 18:59   #19
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Re: yanmar 2gm20 rebuild piston ring gaps

Quote:
Originally Posted by miabellabrian View Post
How do u get a US address? I know no one in the US, or u use a freight forwarding company?

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Look at MyUS, a forwarding company in Florida. We have used their free service with good results.

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Old 26-01-2016, 12:32   #20
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Re: yanmar 2gm20 rebuild piston ring gaps

Ring end gap and groove clearance, are measured with a feeler gauge
and are pretty critical.
You can file the rings to fit the end gap, and clean the piston ring grooves with a groove clean tool.
The ring groove , called ring lands should be inspected for cracks.
The Yanmar service manual has the specs. For end gap.


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Old 26-01-2016, 14:25   #21
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Re: yanmar 2gm20 rebuild piston ring gaps

Thanks for that !

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