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Old 09-10-2015, 12:57   #1
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Compression on Yanmar 3GM30 diesels

Does anyone know what the numbers for Yanmar 3GM30 cylinder compression checks should be?


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Old 09-10-2015, 13:14   #2
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Re: Compression on Yanmar 3GM30 diesels

I'll take a shot from memory of other Diesels and assuming a DI Diesel is a DI Diesel compression wise, but I remember around 300 PSI,
If nothing else I bumped your question up the list to where it will be seen.

What number are you getting and are they all about the same?
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Old 09-10-2015, 13:29   #3
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Re: Compression on Yanmar 3GM30 diesels

It is a relative thing to measure the pressure in the cylinders. It is best to dismount all 3 injectors and connect a pressure gauge in place pulverizers operate the engine with the starter for each cylinder, if all three are the same, then test for blowbuy in cylinders for each cylinder by hand crank to bring the top dead point and measured during the pressure drop if all three of the same probably have no problems or engine is for complete overhaul.
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Old 10-10-2015, 01:06   #4
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Re: Compression on Yanmar 3GM30 diesels

Thanks A64Pilot for helping.
I recently had a compression test from a mechanic, the three cylinders were close to the same from 320 to 330. The mechanic thought this was low. Mastery Marine, the Yanmar distributor, said it is not so much the numbers but that all cylinders are close to the same. Just wanted more info and other opinions.
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Old 10-10-2015, 04:39   #5
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Re: Compression on Yanmar 3GM30 diesels

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Originally Posted by davecalvert View Post
Thanks A64Pilot for helping.
I recently had a compression test from a mechanic, the three cylinders were close to the same from 320 to 330. The mechanic thought this was low. Mastery Marine, the Yanmar distributor, said it is not so much the numbers but that all cylinders are close to the same. Just wanted more info and other opinions.
That's pretty close to the compression tests on my Belize early this year. From memory, they may have been slightly lower than yours but were definitely well over 300. (I tried to find the report earlier for you but seem to have filed in too securely ) My mechanic said they were fine and said the same thing about "close to the same".
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Old 10-10-2015, 06:44   #6
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Re: Compression on Yanmar 3GM30 diesels

Thanks StuM,
They both start right up and run fine. Both reach 3,500 RPM full throttle in gear.
Don't know why the mechanic said they tested low.
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Old 10-10-2015, 07:08   #7
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Re: Compression on Yanmar 3GM30 diesels

A quick googlydoo got me this....
About 5,040 results (0.38 seconds)

Manual reported to be 340... Sailorchick has extensive knowledge of 3gms'

320-330 would seem to be perfecto...
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Old 10-10-2015, 07:11   #8
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Re: Compression on Yanmar 3GM30 diesels

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A quick googlydoo .

Is that googling while otherwise indisposed?



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Old 10-10-2015, 07:19   #9
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Re: Compression on Yanmar 3GM30 diesels

I tried a Google search for this and got nothing. I used Yanmar 3GM30 compression etc. What did you use for a search?


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Old 10-10-2015, 07:22   #10
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Re: Compression on Yanmar 3GM30 diesels

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Is that googling while otherwise indisposed?

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Old 10-10-2015, 07:27   #11
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Re: Compression on Yanmar 3GM30 diesels

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Originally Posted by davecalvert View Post
I tried a Google search for this and got nothing. I used Yanmar 3GM30 compression etc. What did you use for a search?
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just used your thread title, right click search?
https://www.google.com/search?q=Comp...sm=93&ie=UTF-8

I know the chickee has a manual, also gordo might have a link...
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Old 10-10-2015, 08:46   #12
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Re: Compression on Yanmar 3GM30 diesels

Chapter 3,Table 6 of the pdf that I got from Alan Wheeler's Sticky notes: Pressure for all models of Yanmar: 390-470 p.s.i. (2700-3800 kPa)
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Old 10-10-2015, 08:54   #13
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Re: Compression on Yanmar 3GM30 diesels

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Chapter 3,Table 6 of the pdf that I got from Alan Wheeler's Sticky notes: Pressure for all models of Yanmar: 390-470 p.s.i. (2700-3800 kPa)
Discrepancy alert!

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Old 10-10-2015, 08:57   #14
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Re: Compression on Yanmar 3GM30 diesels

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Chapter 3,Table 6 of the pdf that I got from Alan Wheeler's Sticky notes: Pressure for all models of Yanmar: 390-470 p.s.i. (2700-3800 kPa)

But at what crank speed?


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Old 10-10-2015, 09:08   #15
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Re: Compression on Yanmar 3GM30 diesels

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But at what crank speed?


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