Kevin: Is there any way to correlate the prop torque load on the engine at wide open throttle when tied to the dock vs underway? Rephrased in other words, can one tell if the prop is overloading the engine by just running it at wide open throttle when tied or secured to a dock? I ran a test in my case and found that when tied to the dock I can acheive a maximum rpm of 2600, whereas underway the maximum rpm is 2900. The engine is rated for 3600 max, 3400 continuos. Any comments on this? Ernie
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Exhaust
Hi, You may have exhaust elbow problems, if service was never done, or not done recently, that is a good place to start. Check to see if all injectors are firing by momentarily releasing compression one at a time while engine is idling, if you release and the engine runs the same, that is your problem. If both of those are fine, go to driveline and prop. Ps, I got this info from Mack Boring. Good luck!
Hi, You may have exhaust elbow problems, if service was never done, or not done recently, that is a good place to start. Check to see if all injectors are firing by momentarily releasing compression one at a time while engine is idling, if you release and the engine runs the same, that is your problem. If both of those are fine, go to driveline and prop. Ps, I got this info from Mack Boring. Good luck!
also valve adjustment
Ernie: John is correct here. You should just pull off the elbow to check the condition. Be sure to have a new gasket available before to try this. If you have never replaced it, you may just want to get a new one and do it. The other maintenace item is valve adjustments. This is suppose to be done every 500-600 hrs. We had a similar problem on our 2GM20F. We ended up having the govenor adjusted by a mechanic when he adjusted the valves and everything is fine now.
Ernie: John is correct here. You should just pull off the elbow to check the condition. Be sure to have a new gasket available before to try this. If you have never replaced it, you may just want to get a new one and do it. The other maintenace item is valve adjustments. This is suppose to be done every 500-600 hrs. We had a similar problem on our 2GM20F. We ended up having the govenor adjusted by a mechanic when he adjusted the valves and everything is fine now.
loads
Hello Ernie, Thanks for the note. You will find that when you are tied to the dock you will see the Rpm’s reduce by “X” amount. We often inform our customers that this % of Rpm loss is apx. 20-25% when compared to the vessel moving through the water. The reason for the difference is that when the vessel is moving the propeller is being presented water verses the propeller pulling water from the other end of the marina. When tied to the dock we are trying to move a greater mass of water with the prop. Since the water is not compressible the propeller is trying to move the whole basin of water in a sense thus creating the larger loads. For the current pitch, I would reduce it by 2 inches. This should increase the current 2,900 Rpm’s to apx. 3,500. This is of coarse only if the tack is reading an accurate 2,900. If you question at all the tack I would check it first. Please feel free to let me know if you have any other questions. Sincerely, Kevin
Hello Ernie, Thanks for the note. You will find that when you are tied to the dock you will see the Rpm’s reduce by “X” amount. We often inform our customers that this % of Rpm loss is apx. 20-25% when compared to the vessel moving through the water. The reason for the difference is that when the vessel is moving the propeller is being presented water verses the propeller pulling water from the other end of the marina. When tied to the dock we are trying to move a greater mass of water with the prop. Since the water is not compressible the propeller is trying to move the whole basin of water in a sense thus creating the larger loads. For the current pitch, I would reduce it by 2 inches. This should increase the current 2,900 Rpm’s to apx. 3,500. This is of coarse only if the tack is reading an accurate 2,900. If you question at all the tack I would check it first. Please feel free to let me know if you have any other questions. Sincerely, Kevin
More confusing data
Thanks to all for the inputs and suggestions. Kevin, if I use the "x" factor you refer to, 20 to 25 %, it would indicate that I should be able acheive max rpm underway of 3250 for the 20% factor and 3450 for the 25%, yet underway I can only acheive 2900, a 10% factor. The tachometer reads 3500 rpms in neutral at max throttle, so I suspect it is fairly accurate. I have just finished overhauling the engine
ne new connecting rod, three new pistons, rings, sleves,connecting rod bearings,fuel injectors and had the head overhauled, valves etc. Prior to the overhaul the engine was hard starting (low compression) and the prop was a three blade 15 inch diameter with 13 inch pitch. The max rpm I could acheive then was also 2900 rpms with that prop, but prior to that the pitch was 11 inches. In reviewing my log I find that at one time the engine would acheive 3600rpm underway with the 11 inch pitch. ( I changed it to 13 to increase the speed at lower rpms settings). I now have a new prop, Campbel Sailor, 3 blade 15 inch dia 9 inch pitch which is equivalent to a standard 3 blade 15 inch dia 11 inch prop. With the recently overhauled engine, I expected to acheive the max rpm underway since the new prop is equivalent to an 11 inch pitch. I replaced the elbow with a new one three years ago, so I doubt that it is a problem, but will check it out. Prior to the overhaul I would get black smoke at full throttle, now I do not have the black smoke, but rpms still limited to 2900. I am exploring the possibility of exhaust back pressure as a potential cause of lack of power. So that is the rest of the story, if anyone has any suggestions, sure would appreciate it. Ernie
Thanks to all for the inputs and suggestions. Kevin, if I use the "x" factor you refer to, 20 to 25 %, it would indicate that I should be able acheive max rpm underway of 3250 for the 20% factor and 3450 for the 25%, yet underway I can only acheive 2900, a 10% factor. The tachometer reads 3500 rpms in neutral at max throttle, so I suspect it is fairly accurate. I have just finished overhauling the engine
ne new connecting rod, three new pistons, rings, sleves,connecting rod bearings,fuel injectors and had the head overhauled, valves etc. Prior to the overhaul the engine was hard starting (low compression) and the prop was a three blade 15 inch diameter with 13 inch pitch. The max rpm I could acheive then was also 2900 rpms with that prop, but prior to that the pitch was 11 inches. In reviewing my log I find that at one time the engine would acheive 3600rpm underway with the 11 inch pitch. ( I changed it to 13 to increase the speed at lower rpms settings). I now have a new prop, Campbel Sailor, 3 blade 15 inch dia 9 inch pitch which is equivalent to a standard 3 blade 15 inch dia 11 inch prop. With the recently overhauled engine, I expected to acheive the max rpm underway since the new prop is equivalent to an 11 inch pitch. I replaced the elbow with a new one three years ago, so I doubt that it is a problem, but will check it out. Prior to the overhaul I would get black smoke at full throttle, now I do not have the black smoke, but rpms still limited to 2900. I am exploring the possibility of exhaust back pressure as a potential cause of lack of power. So that is the rest of the story, if anyone has any suggestions, sure would appreciate it. ErnieTry throttle linkage
Might sound silly but check to see if your throttle cable/linkage isn't binding. Had similar problem on my previous boat, an H34, and found that the way the cable was adjusted I couldn't get to max RPM. Good luck.
Might sound silly but check to see if your throttle cable/linkage isn't binding. Had similar problem on my previous boat, an H34, and found that the way the cable was adjusted I couldn't get to max RPM. Good luck.
New engine, new prop! Clean Bottom?
Ernie: What sort of shape is the bottom in? If your engine revs to 3500rpm in netural, it appears that you are probably ok. I would definetly check out the elbow. If you were loading up before your rebuild this may be the problem. Be sure to check the exhaust hose down stream from the elbow. I (think) remember that someone had a problem with an exhaust hose getting plugged. If all of this fails, you may just try putting a 2 blade stock prop back on and see what she does.
Ernie: What sort of shape is the bottom in? If your engine revs to 3500rpm in netural, it appears that you are probably ok. I would definetly check out the elbow. If you were loading up before your rebuild this may be the problem. Be sure to check the exhaust hose down stream from the elbow. I (think) remember that someone had a problem with an exhaust hose getting plugged. If all of this fails, you may just try putting a 2 blade stock prop back on and see what she does.
Very Frustrating..
Thanks for all the suggestions. I still am at the same point. The bottom was just painted. I removed the mixing elbow and found it somewhat coked, but not bad. However, after cleaning it out I noticed extensive pitting, so it will be replaced when I can get one from Yanmar..the distributors are out of them so have to wait until the slow boat from Japan gets in. Meantime I have measured the exhaust back pressure with and without the waterlift muffler installed. The pressure is within the 700 mm of Aq as specified by Yanmar for the case without the waterlift muffler, and over the limit with the waterlift muffler installed, but in either case the max rpm is still 2900 in forward and 3400 in reverse, underway. Sounds pretty loud without the waterlift muffler, just a short straight pipe. At any rate, can't see where the exhaust back pressure is the limiting factor. Not much left to try, except changing the prop, but I am not convinced that changing the prop is the answer. Still open for suggestions! Ernie
Thanks for all the suggestions. I still am at the same point. The bottom was just painted. I removed the mixing elbow and found it somewhat coked, but not bad. However, after cleaning it out I noticed extensive pitting, so it will be replaced when I can get one from Yanmar..the distributors are out of them so have to wait until the slow boat from Japan gets in. Meantime I have measured the exhaust back pressure with and without the waterlift muffler installed. The pressure is within the 700 mm of Aq as specified by Yanmar for the case without the waterlift muffler, and over the limit with the waterlift muffler installed, but in either case the max rpm is still 2900 in forward and 3400 in reverse, underway. Sounds pretty loud without the waterlift muffler, just a short straight pipe. At any rate, can't see where the exhaust back pressure is the limiting factor. Not much left to try, except changing the prop, but I am not convinced that changing the prop is the answer. Still open for suggestions! Ernie
don't think you have many options!
Ernie: I don't think you have too many options other than changing the prop. With everything checking out as 'normal' your prop is the only unknown in your equasion. I would suggest that you can someone other than Campbell about the prop. There is a group in San Leandro CA, Kilian Prop. Speak with Tim or Bob and see if they can help you. Give them your trans reduction ratio, the engine model, and the boat model and weight. They can probably tell you what the problem is. I do not have their phone number but you can call information or look it up in the archives.
Ernie: I don't think you have too many options other than changing the prop. With everything checking out as 'normal' your prop is the only unknown in your equasion. I would suggest that you can someone other than Campbell about the prop. There is a group in San Leandro CA, Kilian Prop. Speak with Tim or Bob and see if they can help you. Give them your trans reduction ratio, the engine model, and the boat model and weight. They can probably tell you what the problem is. I do not have their phone number but you can call information or look it up in the archives.
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