On our 29.5 we have an 18 horse yanmar 2 cyl. It is rated at 3400 rpm. At full throttle ours only makes about 1800. The previous owner replaced the prop with a three blade unit. The boat is in the water so it can't be measured. Does anyone have any insight into this. The engine runs fine with good oil pressure and engine temp.It will still do about five and a half to six knots depending on conditions.
engine RPM
- Thread starter John Howitt
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Have your tach & prop checked out.
John: It is doubtful that you are getting that sort of speed at 1800 rpm with that motor. I would suggest that you get a mechanic that has a device that can check out the actual RPM's and see what they find. You should also know which prop you have. These engines are suppose to operate at 2500-2900 rpms for max efficiency.
John: It is doubtful that you are getting that sort of speed at 1800 rpm with that motor. I would suggest that you get a mechanic that has a device that can check out the actual RPM's and see what they find. You should also know which prop you have. These engines are suppose to operate at 2500-2900 rpms for max efficiency.
RPM
thanks for the reply Steve. the boat has a cambell sail prop.and the boat speed is confirmed with my GPS.plus or minus a knot or so for current. I must admit that I don't know the accuracy of the tack but the idle speed is right.I don't usually run above 1500 but wanted to see what it would do. I even removed the engine covers to see if breathing was the problem. It wasn't. I will be checking the prop for size at the next haulout. I can definately get the tack checked though. Thanks
thanks for the reply Steve. the boat has a cambell sail prop.and the boat speed is confirmed with my GPS.plus or minus a knot or so for current. I must admit that I don't know the accuracy of the tack but the idle speed is right.I don't usually run above 1500 but wanted to see what it would do. I even removed the engine covers to see if breathing was the problem. It wasn't. I will be checking the prop for size at the next haulout. I can definately get the tack checked though. Thanks
Silly Question.....
John, does it give you the same rpm speed in reverse? When you are in neutral, i.e. forward or reverse not engaged at all, what does she rev to when you put the throttle to the maximum? I have a 29.5 with a 15 R10 three blade prop and she is fine. Revs to 3400 with clean bottom and prop, runs all the way to 4000 out of gear. Interested to hear what you find. Neil
John, does it give you the same rpm speed in reverse? When you are in neutral, i.e. forward or reverse not engaged at all, what does she rev to when you put the throttle to the maximum? I have a 29.5 with a 15 R10 three blade prop and she is fine. Revs to 3400 with clean bottom and prop, runs all the way to 4000 out of gear. Interested to hear what you find. Neil
I agree, you are getting top speed
out of that engine. Your tach is not recording actual RPMs. Clean the contact points at the sender. It is located at the top of the bell housing.
out of that engine. Your tach is not recording actual RPMs. Clean the contact points at the sender. It is located at the top of the bell housing.
Perhaps the mixing elbow
Mixing elbow is the Achilles' Heel on Yanmar 18. No way to know for sure without taking it apart to see if it's coked up, but... No way to know how many hours, but how many years? If 3-5, you may need a new elbow. Ask a fellow Yanmar owner on your dock for an opinion, since we've all been through this.
Mixing elbow is the Achilles' Heel on Yanmar 18. No way to know for sure without taking it apart to see if it's coked up, but... No way to know how many hours, but how many years? If 3-5, you may need a new elbow. Ask a fellow Yanmar owner on your dock for an opinion, since we've all been through this.
Not the fringin' mixing elbow
Once again, if a Yanmar burps somebody says its the mixing elbow! I ran a 29.5 for ten years and never once had a ME problem (ha-watch it happen to me now!) But I still contend that the previous posters may be correct. Either the prop is to to big, to much pitch, or the tach is erroneous.
Once again, if a Yanmar burps somebody says its the mixing elbow! I ran a 29.5 for ten years and never once had a ME problem (ha-watch it happen to me now!) But I still contend that the previous posters may be correct. Either the prop is to to big, to much pitch, or the tach is erroneous.
thanks
for all the input. I will be going to the boat tomorrow and will check out a few things, and then I will post again.
for all the input. I will be going to the boat tomorrow and will check out a few things, and then I will post again.
Rpm
I went down to the boat this weekend and ran the engine. After it reached operating temperature, I put it in neautral and reved the engine, it sounds good and doesn't miss a beat, but will achieve only 2100 rpm. I guess my next step is find a boat in the marina with the same engine so I can do a sound comparison. I really have nothing to compare to. On the bright side it was a beautiful day and any reason to be on the boat is a good one.
I went down to the boat this weekend and ran the engine. After it reached operating temperature, I put it in neautral and reved the engine, it sounds good and doesn't miss a beat, but will achieve only 2100 rpm. I guess my next step is find a boat in the marina with the same engine so I can do a sound comparison. I really have nothing to compare to. On the bright side it was a beautiful day and any reason to be on the boat is a good one.
John
Theoretical hull speed on your boat is 6.7kts. If you are only able to make 5.5 to 6.0 kts then you really do have a problem. You say that the boat is in the water so you can't measure the prop, why? I would go have a look at it ASAP. You may have a line bound around it or it could be covered in growth. Any of these will factor into RPM's and boat speed. It is also possible as others have said that you are carrying too much prop. Even if your tach is reading wrong you still have a boat speed issue.
Theoretical hull speed on your boat is 6.7kts. If you are only able to make 5.5 to 6.0 kts then you really do have a problem. You say that the boat is in the water so you can't measure the prop, why? I would go have a look at it ASAP. You may have a line bound around it or it could be covered in growth. Any of these will factor into RPM's and boat speed. It is also possible as others have said that you are carrying too much prop. Even if your tach is reading wrong you still have a boat speed issue.
Slow down Alan...
John has to determine whether or not he can actually get the engine to rev to the max while out of gear (4000rpm) as well as the 3400 max in gear. My 29.5 will do around 6.7kn when the bottom and prop are clean at 3300 rpm, only Yanmar do recommend that you do not run it that way for longer than 5 mins, but 26-2900 is cruising speed, which for me gets me around 5.9-6.2 depending on wind conditions. John, are you certain you have full movement of the speed cable and linkage? Interested to follow this through with you. Neil
John has to determine whether or not he can actually get the engine to rev to the max while out of gear (4000rpm) as well as the 3400 max in gear. My 29.5 will do around 6.7kn when the bottom and prop are clean at 3300 rpm, only Yanmar do recommend that you do not run it that way for longer than 5 mins, but 26-2900 is cruising speed, which for me gets me around 5.9-6.2 depending on wind conditions. John, are you certain you have full movement of the speed cable and linkage? Interested to follow this through with you. Neil
rpm
the boat was out in the spring and had the bottom done, so it is reasonably clean. this is our third summer with the boat but I never realized that there was this issue. I don't normally push it that hard, but now I want to know what is going on. I'm not sure if I have full movement in the cable but It probably won't hurt to take it off and lube it anyway. The throttle control doesn't feel sticky. This summer saw, new fuel filters, new fuel pump gasket,I don't buy my fuel at a marine fuel dock and I'm always careful to use the correct amount of fuel conditioner. The cable makes perfect sense. I'll post again with the results. thanks J PS the water is toooo!!! Coooold!!!!
the boat was out in the spring and had the bottom done, so it is reasonably clean. this is our third summer with the boat but I never realized that there was this issue. I don't normally push it that hard, but now I want to know what is going on. I'm not sure if I have full movement in the cable but It probably won't hurt to take it off and lube it anyway. The throttle control doesn't feel sticky. This summer saw, new fuel filters, new fuel pump gasket,I don't buy my fuel at a marine fuel dock and I'm always careful to use the correct amount of fuel conditioner. The cable makes perfect sense. I'll post again with the results. thanks J PS the water is toooo!!! Coooold!!!!
I doubt the tach
John: I very seriously doubt that the 2GM20F will move that boat at those speeds at 1800 rpm's. The mechanics can tell you what the actual RPM's of the engine are reading. Your other option would be to borrow a tach off of one of these engines and see if there is a difference.
John: I very seriously doubt that the 2GM20F will move that boat at those speeds at 1800 rpm's. The mechanics can tell you what the actual RPM's of the engine are reading. Your other option would be to borrow a tach off of one of these engines and see if there is a difference.
John...
find the tach sender unit. Pull the connector to the wiring harness apart, clean the connection tabs (male & female) with stove alcohol, crimp the female's curled "arms" down to make a tight connection, put it back together and see what it reads!
find the tach sender unit. Pull the connector to the wiring harness apart, clean the connection tabs (male & female) with stove alcohol, crimp the female's curled "arms" down to make a tight connection, put it back together and see what it reads!
engine service manual
I'm trying to locate a link to the yanmar service manual.The yanmar site just seems to promote dealers. Can anyone direct me to a good one
I'm trying to locate a link to the yanmar service manual.The yanmar site just seems to promote dealers. Can anyone direct me to a good one
Tachometer check
There is an old DIY method to check your engine RPM and Tachometer. Place strip of white tape near outer edge of the face of the crankshaft pulley. Shine a shore powered (60 cycle AC) fluorescent lamp on the pulley with engine running. At 1,800 RPM you should see four steady, stable tape marks hovering at 90 degrees from each other.
There is an old DIY method to check your engine RPM and Tachometer. Place strip of white tape near outer edge of the face of the crankshaft pulley. Shine a shore powered (60 cycle AC) fluorescent lamp on the pulley with engine running. At 1,800 RPM you should see four steady, stable tape marks hovering at 90 degrees from each other.
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