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post #61 of 91 Old 05-17-2014 Thread Starter
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Re: Compression test 2GM20F

The CSP 14"Dx9"P max out at 2700rpm. Which prompted me to start lowering the pitch. 6"P was the ideal maxing out at 3400rpm. These was about 5+years back. The Yannar tachco rpm was only +50 against handheld tachco.
I'm not too keen to send the engine for overhaul just yet. I'll see what the engine condition is first. It has to be for a significant if i were to overhaul the engine.

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post #62 of 91 Old 05-17-2014
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Re: Compression test 2GM20F

According to Mr. Google, your motor is rated at 3400 rpm for continuous use. That's just the rpm you should not exceed for lengthy periods. Wide Open Throttle rpm should be 3600 rpm. It really sounds like you've been over propped for a long long time, if these were the rpms you were getting years ago. If you don't correct that, things will get worse and your repairs with be for naught.

However, clogging the exhaust elbow to the point of stoppage and running the oil low for 500 nm had to have done some damage. It's just hard to tell what exactly. I would even wonder if water flushed back into the cylinders with that elbow stoppage. However, other than the low compressions, you have no unusual starting, smoking or noises. That either defies reality or is a testament to just how tough these motors really are.

With the limited experience you describe, I suppose it's possible you don't know they are unusual and it might be wise to get someone aboard to take a look/listen to help you diagnose.

Good luck.
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post #63 of 91 Old 05-17-2014
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Re: Compression test 2GM20F

to me its a testament

you actually arent NOT getting to max rpms...

my 2gm showd the same resiliency even after clogging injectors with sea water when refuelling at sea...

or getting partially submerged after my bilge pumps stopped working ana drained the batteries or countless hours of abuse in choppy seas...

use the prop that gets you to 3400, if I remember correctlt I never went over 3500rpms...maybe once before leaving on the cruise...

6p isnt that bad... and it willkeep your engine happy and not bogged down

like minnewaska says you have been overpropped more than a few times now...(after testing the 9 pitch prop what prop did you leaveon there for the last 5 years?)

just get the prop that gets you 3400 and your are good to go

prolong the rebuild, you dont NEED it

get thick oil...stp in the oil and call it a day

also and this is just me...always use a fuel stabilizer, or even seafoam or similar that just keeps the fuel clean...this is of course if your tank is clean if not its a waste of money...

seafoam does wonders in cleaning up the small fuel passaged but also does wonders in unclogging injectors over time...

a strong mix of seafoam over a couple of tank fulls of new gas will make an improvement beleive it or not...it also acts as a stabilizer for long periods of time

having said that I once left my small 10 galon diesel tank half empty for over a year only using the engine to charge the batteries once every month or so...and the little yanmar had no issues whatsoever...

anyways

just live with the fact that you canīt get the desired top speed you might of once had

thats just normal but hardly a reason to tear down an engine

if it aint REAL broke dont fix it...

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Re: Compression test 2GM20F

I think a major part of the problem may be the prop?

After about 68 years of working on many different types of engines, I finally learned to make sure there was fuel in the tank before ripping the engine out.

My wife has told me that I have a tendency to "over focus" on things, something about the "Forest & the trees"?

Now, I try to do the easiest/cheapest things first, surprising how often that works.

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Re: Compression test 2GM20F

Curiously, for "wet" compression test, how much oil do I drip into the chamber? Couple of drops or 10mL ....?

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Re: Compression test 2GM20F

More like 10ml

Did you buy a compression gauge?


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Re: Compression test 2GM20F

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Originally Posted by Minnewaska View Post
More like 10ml

Did you buy a compression gauge?
Yes, I bought a diesel compression gauge. US General.

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Re: Compression test 2GM20F

think of a cap full of oil...like a oil quart cap worth in each cylinder

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Re: Compression test 2GM20F

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Yes, I bought a diesel compression gauge. US General.
Is that the US General line that is carried by Harbor Frieght? Probably okay, but I would at least be a tad suspect, if it is. Be sure the adapters are correct and seat properly, or the reading could be wrong.


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Re: Compression test 2GM20F

Maybe take the test after the engine is warm? Then, if the readings do not come up, or close to, spec try the oil?

Paul T
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