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Discussion Starter · #1 ·
I tested the compression of each cylinders of my 2GM20F. Cylinder #1 270psig and Cylinder #2 250psig. :confused: 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. :mad: I'll schedule anither day for this test again.
Comments anyone?
 

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I tested the compression of each cylinders of my 2GM20F. Cylinder #1 270psig and Cylinder #2 250psig. :confused: 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. :mad: I'll schedule anither day for this test again.
Comments anyone?
Have not had this experience, but have read that it might fire if you squirt extra oil in the cylinder. Maybe warm the engine up a bit before taking the readings?

If it starts OK when cold, the compression may be OK? But if it is below spec it may be an indication that the rings are worn or the valves are leaking.

I have read that an oil analysis may show where a problem may be? It would be interesting to know what you find.

Paul T
 

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That the two cylinders have roughly the same compression is more important than the compression ratio per se (if you find more than a 10-15% difference, then I would worry). Getting 270 psi means that you still have about 18:1; not bad for an old engine. Try the "wet" test and see if they are still pretty close to each other. If so, you're probably OK.
 
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Discussion Starter · #4 · (Edited)
Puddin', "wet test" by that I suppose you meant squirting abit of engine oil into the chamber. I'll do that.

Paul, I've no problem cold starting. Cold here in SG is ...like 25degC. I guess that's pretty warm for some sailors. Day temperature is 30 degC in shades and 35degC under sun. Anyway next time will 1)warm up engine before test 2)Squirt some oil then test again.

Appreciated your comment/reply. :)

Lesson learnt:
Remove only the Injector of cylinder to be tested. Rest of Injector/s to be left tighten inplace. I made a mistake of remove both Injectors first then run test on one. In 2-3 cycle of engine chamber gaskets, insulators and all blew right out of the other cylinder and include a fair amount of carbon dust :(:eek:
 

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Puddin', "wet test" by that I suppose you meant squirting abit of engine oil into the chamber. I'll do that.
...
That is exactly what a "wet" compression test is. If there the engine has really low compression, and there is a huge difference between the "wet" and "dry" compression, then the rings are suspect. But given the relatively high "dry" compression that you're getting, I wouldn't worry too much about it.

Why did you do a compression test in the first place? Is the engine running badly? If it seems to be running OK, I would just put everything back together and leave it alone. If it ain't broke, don't fix it.
 

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Discussion Starter · #6 ·
I'm not getting the power I expect of the engine. Most of the time, I've to run at 3000rpm to make 5kts in slack tide. I've tried changing props several time (pitch & diameter) and in the end summise that I probably have some wore rings. I do return couple of years back, I made a 500nm passage (engine most of the way) and at the end of trip found the oil level to be alomost zero. I could only drain out 0.5-1 litre. I could have abused the engine on that trip. That's my suspect.
 

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I'm not getting the power I expect of the engine. Most of the time, I've to run at 3000rpm to make 5kts in slack tide. I've tried changing props several time (pitch & diameter) and in the end summise that I probably have some wore rings. I do return couple of years back, I made a 500nm passage (engine most of the way) and at the end of trip found the oil level to be alomost zero. I could only drain out 0.5-1 litre. I could have abused the engine on that trip. That's my suspect.
I think you're mistaken by blaming the engine.

All the engine does is spin the prop. If it's doing that but you're not getting good performance, it's not the engine's fault. Full throttle is usually 3400-3600. If you can get there, then you don't have power problems with the engine. Period.

Clean your prop and hull and cut down weight.
 

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500 naut.miles would be 100 hours at 5 kts. A 2GM20 only holds 2 liters of oil in the crankcase. So, you burned about a liter, maybe a bit more, in 100 hours. That's probably more than a new engine will burn, but not a huge amount. I would keep a closer eye on the oil, check it every 24 hours or so of run time. And try running as heavy an oil as the manual recommends. In Singapore I would think you could run at least 40-weight, maybe 50-weight (but check the manual). In any case, avoid multi-grade oil, as it tends to "thin" more easily over time. And make sure you are using diesel engine rated motor oil, NOT oil for gas engines.

Also, I agree with asdf38. If you can get the revs up, but the boat isn't getting close to hull speed, it's not the engine that's the problem. A 32' Hunter shouldn't displace enough to over-burden a 2GM20, IF everything else is OK (if she's seriously over her designed displacement, that's another story). What size/pitch prop do you have? Are the bottom and prop clean? Is there something else on the bottom that is making it "un-fair"? Are the clearances between the prop and the hull, and the prop and the rudder adequate? Were you towing a dink? Was there a serious headwind?
 

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Discussion Starter · #10 ·
Prop I used are: stock 2RH 15"Dx10"P, CSP 3RH 14"Dx9"P, & 7"P, & 6"P, KiwiP 3RH 16"Dx20deg, & 18deg.
I've tried SAE40 and SAE15W40. I don't find any difference. I've tried adding STP Oil Treatment (Silicone base). It helps raise max rpm by 100-200rpm.
 

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Can you get the engine up to 3400-3600 rpm underway?

I have a 2GM20 on a 27'/6700# boat with a 13x12 2-bladed prop. I have no problem achieving hull speed (~6.3kts) at ~3200rpm. If you can get the engine to rev to 3400rpm, but you are still well shy of hull speed (~7.1kts for a Hunter 326), I would think that you need more prop pitch. In fact, those pitches you list in your post look a bit low to me.
 
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op only you know if you have suffered performance

my 2gm would getb to hull speed easily on my 10k displacing old boat...

it was a 2 bladed prop btw...not even 3...

our typical cruising rpms was 2800, but if we wanted to sip fuel wed go down to 2200 or so...and still do 4-5 knots depending on what the sea was like...

like on motorcyles gearing can make a huge difference to engine performance so if you can Id try extreme opposite type props

like a low pitch 3 blader and a high pitch 2 blader...just to rule out the actual engine

ps its normal for engine to use oil of you are sort of abusing it...

while a quart at that throttle is a bit excessive many engines drink oil all the time NORMALLY

are you smoking a lot? do you get a sheen on the exhaust water?
 

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Not familiar with that engine, 20 HP? Maybe not enough power to swing a bigger prop? If you are running it close to max RPM's for long periods of time that may be why it is using some oil, or it may be a bit on the tired side? Was there any work recently done on the engine? Is the timing spot on? Injectors clean and up to spec? If you can run it that fast, it appears it is getting adequate fuel?

Any info on similar boat/motor combination, forums, owners clubs, etc?

Paul T
 

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Not familiar with that engine, 20 HP? Maybe not enough power to swing a bigger prop? If you are running it close to max RPM's for long periods of time that may be why it is using some oil, or it may be a bit on the tired side? Was there any work recently done on the engine? Is the timing spot on? Injectors clean and up to spec? If you can run it that fast, it appears it is getting adequate fuel?

Any info on similar boat/motor combination, forums, owners clubs, etc?

Paul T
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Found the info on adding oil on a diesel compression test:

Unlike a gasoline engine, adding oil is not recommended due to the high compression in the cylinder. You risk having the compression tester be damaged or personal injury due to the cylinder firing. Remember, a diesel engine can run on oil and the peak compression reached from the combustion process is in the thousands, way beyond the range of the compression tester. In addition, if you do a compression test and the results are bad, you can do the test again. There would be no point in adding oil since you already know there is some problem either with the gauge or engine
.

How to do a compression test on a VW TDI or Audi TDI engine and results | VW TDI forum, Audi, Porsche, and Chevy Cruze diesel forum

Paul T
 

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this is gold info...part of the reason I didnt recomend doing wet tests per se here...they are usually for gas engines wiuth lower compressions and ease of testing...doesnt mean you cant do it though

basically even compression tests wont be really iluminating for the op here...

if the engine starts, doesnt sputter, has good fuel pump and injectors you either live with it(yes it might be a bit underpowered) or you tear it down and rering, deck and cleanup up the valves and tolerances

usually though if it AINT broke no need to go there

I would look into repropping better for the meantime

again is it smoking bad, or just losing oil at high rpms? oil loss at high rpms is a given in most engines...especially low reving ones...:)

anywhoo
 

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this is gold info...part of the reason I didnt recomend doing wet tests per se here...they are usually for gas engines wiuth lower compressions and ease of testing...doesnt mean you cant do it though

basically even compression tests wont be really iluminating for the op here...

if the engine starts, doesnt sputter, has good fuel pump and injectors you either live with it(yes it might be a bit underpowered) or you tear it down and rering, deck and cleanup up the valves and tolerances

usually though if it AINT broke no need to go there

I would look into repropping better for the meantime

again is it smoking bad, or just losing oil at high rpms? oil loss at high rpms is a given in most engines...especially low reving ones...:)

anywhoo
Agree, the OP says it starts OK, & can run up to 3,000 + RPM, so who knows? I too, would try a prop that bogs it down & then go lower on the pitch?

I have done many compression tests, but all on gas engines. I imagine that if the diesel fired it would damage the gauge, & maybe the person, when the whole mess blows out of the head? :D

Paul T
 

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Discussion Starter · #20 ·
I can't swing a larger or higher pitch prop as it would not reach 3200rpm. I forgot to mention I've a 2 blade 15"D x12"P Flex-O-Fold as well. Max it could make is shy of 3300rpm.
So far all checks and feels points to rings wear. Compression test seems to confirm that. Anyhow, I'll try the "Warm" and "Wet" test and post results here. Unfortunately, test analysis of crankcase oil isn't common or known here.
 
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