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Compression test 2GM20F

10060 Views 90 Replies 7 Participants Last post by Minnewaska, Jul 16, 2014

trantor12020

Discussion Starter · May 11, 2014

I tested the compression of each cylinders of my 2GM20F. Cylinder #1 270psig and Cylinder #2 250psig.

These numbers seems way too low as expected is 370-450psig. I should have squit some oil into each cylinders before trying again to see if the pressure will come up. If it does I suppose it means my piston rings are wore. But I forgotten about this step.

I'll schedule anither day for this test again.
Comments anyone?

61 - 80 of 91 Posts

trantor12020

Discussion Starter · #61 · May 17, 2014

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.

Minnewaska

· #62 · May 17, 2014

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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Reactions: 1

christian.hess

· #63 · May 17, 2014

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 can´t 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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dabnis

· #64 · May 17, 2014

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.

Paul T

Reactions: 1

trantor12020

Discussion Starter · #65 · May 19, 2014

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

Minnewaska

· #66 · May 19, 2014

More like 10ml

Did you buy a compression gauge?

trantor12020

Discussion Starter · #67 · May 19, 2014

Minnewaska said:
More like 10ml

Did you buy a compression gauge?

Yes, I bought a diesel compression gauge. US General.

christian.hess

· #68 · May 19, 2014

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

Minnewaska

· #69 · May 19, 2014

trantor12020 said:
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.

dabnis

· #70 · May 19, 2014

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

casey1999

· #71 · May 20, 2014

Just a question on the low oil:
As long as the low oil pressure light did not come on, could the engine have been damaged by low sump oil?

Does the crank run or slosh in the oil bath created by the oil pan? If so, I could see where low oil level would be a problem.

trantor12020

Discussion Starter · #72 · May 21, 2014

dabnis said:
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

Yes, that's the plan.

dabnis

· #73 · May 21, 2014 (Edited)

casey1999 said:
Just a question on the low oil:
As long as the low oil pressure light did not come on, could the engine have been damaged by low sump oil?

Does the crank run or slosh in the oil bath created by the oil pan? If so, I could see where low oil level would be a problem.

I think most "modern" engines rely on oil under pressure, rather than the "splash" systems in older engines. However, that being said, it is probably always better to keep the oil level at the manufacturers spec.

If the low pressure light/alarm didn't come on, probably pressure was adequate? However, if it was down to about a quart or so, the oil may have heated enough to lose some of its viscosity, allowing the pressure to be somewhat reduced, but still in the "allowable" range. A full crankcase is a happy crankcase, but not overfull, which can cause foaming.

Paul T

dabnis

· #74 · May 21, 2014

trantor12020 said:
Yes, that's the plan.

It would be interesting to know what you find.

Paul T

Reactions: 1

christian.hess

· #75 · May 21, 2014

beleive it or not Im brain farting on what the oil system is on the 2gm and my internet foo isnt working

I thought it was splash flow for the crank but I just cant remember or find what it is

having said that regarding oil level...always check after running...and let the oil settle(at least 5 minutes) and avoid overflowing

also make sure your case vent is venting...as it will avoid you squirting oil out the dipstick causes all sorts of messes

jajaja

casey1999

· #76 · May 21, 2014

christian.hess said:
beleive it or not Im brain farting on what the oil system is on the 2gm and my internet foo isnt working

I thought it was splash flow for the crank but I just cant remember or find what it is

having said that regarding oil level...always check after running...and let the oil settle(at least 5 minutes) and avoid overflowing

also make sure your case vent is venting...as it will avoid you squirting oil out the dipstick causes all sorts of messes

jajaja

My 3GM is an oil pressure system ( should be same as 2GM). The 3gm has an oil pressure switch- it is tied into an alarm light and buzzer. For the op check the low pressure alarm as well as high temp alarm (light and buzzer) both work.

I do keep my oil level up to the top end of the fill lines on the dip stick.

christian.hess

· #77 · May 22, 2014

that idiot light though is a very rudimentary buzzer, how much pressure is what you would need to know...a good oil pressure gauge is worth it in my opinion

casey1999

· #78 · May 22, 2014

christian.hess said:
that idiot light though is a very rudimentary buzzer, how much pressure is what you would need to know...a good oil pressure gauge is worth it in my opinion

Your are right. I even bought a oil pressure sender and gauge. However there is a question on the yanmars as to if is is best to install a tee fitting so you have both pressure gauge and press switch (with buzzer and light). Once the Tee fitting is installed, the vibaration of the engine (and with the weight of the gauges/switches hanging off the end of the Tee fitting), there is greater likelyhood of the Tee fitting breaking or leaking. In the end, I have not installed the gauge because it seems it makes it much more likely to have an oil leak at the connections.

Reactions: 1

trantor12020

Discussion Starter · #79 · May 22, 2014

dabnis said:
It would be interesting to know what you find.

Paul T

I will report my test results here. I won't be able to do the retest till later June. I would want to post some pic of my Compression Gauge setup but there seems to be an uploading problem. I'll check again.

trantor12020

Discussion Starter · #80 · May 22, 2014

casey1999 said:
Your are right. I even bought a oil pressure sender and gauge. However there is a question on the yanmars as to if is is best to install a tee fitting so you have both pressure gauge and press switch (with buzzer and light). Once the Tee fitting is installed, the vibaration of the engine (and with the weight of the gauges/switches hanging off the end of the Tee fitting), there is greater likelyhood of the Tee fitting breaking or leaking. In the end, I have not installed the gauge because it seems it makes it much more likely to have an oil leak at the connections.

Yes sometime we introduce a new component and along came new problem. Mr. Murphy is always lurking somewhere

uke

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