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Old 10-10-2015, 09:26   #16
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Re: Compression on Yanmar 3GM30 diesels

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Originally Posted by HappyMdRSailor View Post
How long can you go without bringing up illegal drugs...

Depends on how many legal ones I've consumed in any given length of time.


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Old 10-10-2015, 14:32   #17
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Re: Compression on Yanmar 3GM30 diesels

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


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450 lbs is good for the 2GM20 (I have) which has the same cylinder size as the 3GM30
You need a diesel compression gauge. One for a car won't go high enough. I borrowed a diesel gauge from my friendly Yanmar service agent. It is fitted in place of the injector. It prints out the compression on a special piece of paper. Yanmar cylinders are numbered from the back, flywheel end. After much googling I found a free Yanmar service manual rather than the simple operation manual.
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Old 10-10-2015, 14:48   #18
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Re: Compression on Yanmar 3GM30 diesels

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Originally Posted by Sailmonkey View Post
Depends on how many legal ones I've consumed in any given length of time.


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HA HA...

Sounds like an excuse for a cocktail no???
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Old 10-10-2015, 18:01   #19
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Re: Compression on Yanmar 3GM30 diesels

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Manual reported to be 340... Sailorchick has extensive knowledge of 3gms'
Is that gallon meter seconds?

(Sorry, couldn't resist)
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Old 11-10-2015, 07:59   #20
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Re: Compression on Yanmar 3GM30 diesels

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Is that gallon meter seconds?

(Sorry, couldn't resist)
HA!

Good one Stu... Looks like there might be some bleed off from a heated engineering debate thread???
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Old 11-10-2015, 17:23   #21
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Compression on Yanmar 3GM30 diesels

Just from owning many other Diesels, if it starts easily, doesn't smoke excessively, or have excessive blow-by, then there is nothing wrong with it. Oil consumption is almost irrelevant. I've seen nearly new engines use a quart of oil every 10 to 20 hours or so and that never change over thousands of hours, in fact there is a lot of evidence that once an engine begins to consume oil, the upper cylinder wear rate is greatly reduced.
There can be a considerable difference between testing compression on a hot and a cold engine as well as cranking speed will influence compression numbers, the more blow-by, the lower the numbers will be if cranking speed is low. A leak down test like what is done on aircraft engines will tell you much more, like where the loss of compression is coming from by simply listening for where the air is escaping. Exhaust, intake or crankcase breather.

But, the acid test in my opinon, is if it starts easily, runs well and doesn't smoke excessively, what's to fix?


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Old 14-10-2015, 17:58   #22
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Re: Compression on Yanmar 3GM30 diesels

Just a follow up and correction: I final found where I filed the report, I mis-remembered.

Firstly, I don't have the 3GM30, I have 3JH3E (I should have looked at the thread title more closely) so it's probably not relevant.

But in case anyone else is looking for a similar answer:
The compression tests on my two 3JH3Es were 400,390,390 and 400,390,400.
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