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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.
I had to look it up. Your motor's max rpm is 3600 (continuous max is 3400). Cockpit tachometers are notoriously incorrect by 100-200rpm, but when you're below the target by more than that, you are very possibly over propped. It is also possible that your tach is off in the other direction and you're even more over propped than that. Best is to text your wide open throttle rpm under way with a calibrated test tach attached to the motor.

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.
You can mail your sample away for an oil analysis. While I think they are good idea, they are more valuable when you do them over time and can see trend lines changing.

Are you seeing any smoke from the exhaust? If your rings are as shot as you suspect, I would expect notable smoking. If so, what color?
 

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yeah I cant get an answer on the smoke thing...I have asked many times now...if you have a sheen on the water when really giving the engine some power that means you air blowing oil past the rings...if you are NOT, and ARENT smoking and your only 200-300 shy of max rpms

dont do anything to the engine...like minnewaska says tachs are notoriously innacurate and is not something to base all performance on best bet is get a good digital one...and do test run bypassing the panel one...

for example, is it an easy starter, is idle steady and smooth, smoke, yes no? vibrations, oil? etc all are indicators of good performance or not

also most old engines wont achieve max new rpms well cause they arent new..you cant expect and old engine like that to be in equal or better shape than new....

answer this first

smoke if yes what color?
if black is it just sooty or is there a sheen in the water?

is your fuel pump, diaphragm and all related pump hardware in tip top shape?

cheers
 

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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.
Do the wet test with the engine cold, flip the decompression lever (or leave the injector out) on the other cylinder, and use a fairly heavy oil (40 or 50 weight) to keep the cylinder in question from firing. You only need a squirt, just enough to wet the rings. And only crank it two or three cycles. Crank it too long and you'll build up heat and volatilize the oil, increasing the potential for firing.
 

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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.
Sounds like you have the prop issue dialed in. If the engine can't pull more pitch it appears it is too small or "tired"? Any way to compare with similar size boat/engine combinations? Maybe boat manufacturer specs? Not that it matters, as it will only put out as much as it is, but about how many hours on the engine?

Paul T
 

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it is slightly underpowered by todays standard

my reference point was an old stout wooden h28 displacing 10k pounds...full keel...
 

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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....
I just re-read this.

If you are getting 3300 rpm then there is nothing wrong with the engine. You may have too much reduction in the transmission. A 2GM20 with that big prop, with that much pitch, should push an 8000# boat at or near hull speed, IF you don't have too much reduction in the transmission (Yanmar put several different trannies on those engines). In other words, the engine may be at or near max rpm, but the prop may just be spinning too slow. Look on the tag on the transmission and see if you can find the reduction ratio. It should be 2.21, 2.62 or 3.22. If it's 3.22, at 3300rpm the prop would be spinning at 1025rpm. For a prop with 12" pitch that would be about 10kts (rpm x pitch x 60 then convert inches to knots). Since most props have about 45% slip, you can't reasonably expect more than about 5.5kts. On the other hand, if your reduction ratio is 2.62 then you should be able to get pretty close to hull speed (i.e., 7 knots or so).
 
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I just re-read this.

If you are getting 3300 rpm then there is nothing wrong with the engine. You may have too much reduction in the transmission. A 2GM20 with that big prop, with that much pitch, should push an 8000# boat at or near hull speed, IF you don't have too much reduction in the transmission (Yanmar put several different trannies on those engines). In other words, the engine may be at or near max rpm, but the prop may just be spinning too slow. Look on the tag on the transmission and see if you can find the reduction ratio. It should be 2.21, 2.62 or 3.22. If it's 3.22, at 3300rpm the prop would be spinning at 1025rpm. For a prop with 12" pitch that would be about 10kts (rpm x pitch x 60 then convert inches to knots). Since most props have about 45% slip, you can't reasonably expect more than about 5.5kts. On the other hand, if your reduction ratio is 2.62 then you should be able to get pretty close to hull speed (i.e., 7 knots or so).
I can't remember what the OP did on props, but short of changing the gear box ratio, perhaps fitting a prop with enough pitch to bog the engine down to a bit under 3,000 RPM or so, & then reduce pitch to achieve max RPM might work?

Paul T
 

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Discussion Starter · #30 · (Edited)
Slight white smoke on starting. No smoke after warm up. Of course reducing pitch will bring max rpm up. Which i did when repitching the CSP as well as KiwiProp. But even that did not give the performance expected as reported by many other boats when comparing displacement and engine power. Thats why i suspect my engine has wore some and probably tire. Need refreshing :)
However i do get black sooty exhaust when i gun the engine on reverse in anticipation of hitting the dock... (KiwiProp).
Oh another observation, I notice some/a little oil sheen on water after i ran the engine but didn't check if its from my boat or others. Will take a closer look this weekend.
 

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BINGO there you have it!

this is what we were needing to know!

the sheen means blowby cause the rings arent exerting enough pressure on the liners/cylinders therefore letting oil blow by the rings...unburned...

the excessive soot when gunning it is indicative mostly of carbon buildup and soot in the valves, seats area...they dont seal properly...also more than likely major buildup on the piston tops...so every time you gun it a lot of it gets dislodged

a good way of checking on this is to run seafoom through the system many times...if you see an improvement it means you have masssive carbon buildup

if you also see an improvement using thicker oil and an oil additive like stp zddp...that also means your rings are tired...you can safely say now your initial low compression results are from this

it could also point to the fuel system hencee why I asked about condition of fuel pump, diaphragm etc...

Im assuming you have checked the air filter strainer right?

the white smoke after sitting or when cold could mean you have a slight gasket leak at the head or that youre heat exhanger is leaking a bit onto the valves or that its letting coolant backflow into the engine after sitting a while...

basically this is all indicative of a worn engine...

the good news is rebuilds arent that expensive especially if you do the work yourself and just get the machining done at any reputeable shop

the only expensive parts are the heat exhanger and making sure its not badly corroded inside.

the 2qm and 2gm engine rebuild kits go for around 700 in parts...

good luck
 

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A little white smoke at start up, followed by zero smoke after warm up is a fairly normal condition. I would have expected blown rings to have some blue smoke, especially under load. The black smoke after jamming the throttle is also very normal. You introduce fuel faster than combustion can increase, so you get a good belch of unburned fuel. Ignore that symptom.

The sheen on the water is a bit tougher to diagnose without seeing it. Both oil and diesel will leave a sheen. Even coked up diesel soot in the exhaust that is just being washed out by cooling water could cause it.
 

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he did say though that his exaust riser and elbows and all were clean so thats why you cant just rule out the smoke/soot

having said that my 2gm did it all the time and kept ticking like a clock...so yeah you can ignore it

the thing is with diesels you always have some fumes, soot, smells, etc cause diesel is damn dirty...

if it were a gas engine...soot just means you are either way too rich in the mixture and or you are passing unburned fuel trough the exhaust...

thats why its paramount to check your fuel system...

if everything checks, and EVERYTHING is in tip top shape and you are still having low power "symptoms" or desired performance than either you have to live with it, or you can do a simple rebuild

we are kind of reinventing the wheel here, honestly its simple...
 

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I still would not rule out the prop. It's documented above that she does not make max rpm. An engine has to be awfully sick, which would have some severe starting, smoking, knocking, etc, issues before it would fail to do so, without the prop being a problem.

I find the gear reduction ratio to be very unlikely, unless this was changed over the years.
 

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Discussion Starter · #36 ·
Christian, you mentioned on coolant leaks. I did notice coolant level in reserve tank dropping over time (a long time) its so small, i just ignore it. Its like drop by 1cm over 2-3years. Nothing to be concern I suppose? Or am I waiting for a big hit?
 

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That's not much coolant loss, perhaps even just normal heat expansion/contraction.

If you are eating coolant, a bad head gasket is often to blame. Curiously, that could also account for poor compression tests. However, you would probably see more loss, if all cylinders were leaking and you typically see some milky substance on your oil dipstick.

You can have your cooling system pressure tested, which would be a simple task and good idea. You may also see oil or coolant seeping from the gasket line.

If it does turn out to be a head gasket, you will want to consider how it may have occurred. Over heating can warp the head, excess power settings or using starting fluid can put too much pressure on it.
 

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Christian, you mentioned on coolant leaks. I did notice coolant level in reserve tank dropping over time (a long time) its so small, i just ignore it. Its like drop by 1cm over 2-3years. Nothing to be concern I suppose? Or am I waiting for a big hit?
nope thats perfect...thats not your issue for sure...1 cm in 2-3 years...though is that the same coolant...?meaning you change only every 2-3 years?

I would change coolant every season but thats just me....or at least yearly

:)

well I guess I should ask how often do you use the engine...some things like gasket leaks arent really epxposed untill you have the engine real warmed up over a long period of time

might be fine for in and out but a "warped" head like minnewaska says will only be exposed after long running periods of time

but if your oil never gets milky its safe to rule that out for now
 

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My experience with head gasket leaks is some/lots of white smoke at start up, then gradually clearing up. 1/4'' in 2 to 3 years doesn't seem like much, depending on how much you run the engine. I have read that an oil analysis can detect coolant in the oil. Not sure about how much, but that it can be detected.

I had a VW diesel that used to weep coolant at the head/block joint in extremely cold temperatures, but would stop as soon as the engine warmed up a bit.

Also, a leaky head gasket can force hot gasses into the cooling system, causing the expansion tank contents to raise or be blown out, but I think that would be a fairly severe leak.

Paul T
 

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well you can always send the oil to blackstone...

thats what my biker friends did...mostly to see what the fuel mix was doing to the oil and how long certain oils lasted in certain conditions

but for what they charge might as well put it towards a fresh rebuild

all engines need a rebuild after a certain period of time...its not a matter of if but when...

things like seals and orings, valve seals, etc all have a useable lifespan after that they fail...or crack or whatever

so just think of it that way

of course you can prolong the inevitable but someday it will need to be done unless you just plan to run this engine into the ground...take it off sell for parts and repower

thats not unheard of btw! jajaja
 
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