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Old 03 July 2013, 11:59   #1
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Yamaha 4hp 2 stroke

HI.
I have a blockage where the water pipe from the pump enters the power head, most of the cooling water goes inside the leg and I only get a dribble from the tell tale. I have been informed that this is most likely due to corrosion dislodging the seal and blocking the end of the pipe. It looks like the power head will have to come off, I don't have a manual for this o/b. So I was hoping someone on here can tell me how to get the head off.
Cheers.
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Old 03 July 2013, 12:00   #2
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Have you had the thermostat out yet ?
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Old 03 July 2013, 12:20   #3
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Have you had the thermostat out yet ?
I did not know it had one, where is it?
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Old 03 July 2013, 12:33   #4
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Engines with 5HP and lower, usually doen't have/use a thermostat. Need to pull complete head from pan to check upper water tube & grommets condition.

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Old 03 July 2013, 12:53   #5
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removal of powerhead is easy, disconect the throttle cable from carb, disconnect / remove coil, then undo the small bolts underneath the 'tray'.
i did mine over winter and completely cleaned all the waterways etc and still it only dribbles out water!
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Old 04 July 2013, 12:29   #6
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When you say you've cleaned all waterways, was cylinder head also removed and cleaned ? If not, there are wider waterways there that can cause poor peeing when having excess of salt layers and or salt crusts on waterways.

If water pump is in inmaculate working condition, probably peeing port still has a small obstruction inside of engine, run a thin wire up-down several times to clear.

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Old 04 July 2013, 12:38   #7
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When you say you've cleaned all waterways, was cylinder head also removed and cleaned ? If not, there are wider waterways there that can cause poor peeing when having excess of salt layers and or salt crusts on waterways.

If water pump is in inmaculate working condition, probably peeing port still has a small obstruction inside of engine, run a thin wire up-down several times to clear.

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Hi,
Many thanks for your interest, I did not say I have cleaned all the waterways. What I said was I need to take the power head off to clean the waterways, but not having a manual I was asking advise on how to do the job.
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Old 04 July 2013, 12:48   #8
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blow air up the tell tail while running
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Old 04 July 2013, 13:28   #9
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Quote:
Originally Posted by Mercury View Post
Hi,
Many thanks for your interest, I did not say I have cleaned all the waterways. What I said was I need to take the power head off to clean the waterways, but not having a manual I was asking advise on how to do the job.
i think he was talking to me - i cleaned the waterways!
without actually looking im not sure if that engine has a cylinder head or not (could be a blind bore) but if it does then i did not remove it. i did hover remove the exhaust plate from its side - that was completely clear, but all the waterways around the base of the powerhead were pretty furred up.
also looking at the shape of the waterways from the tell tale back, you realise that a piece of wire poked up there wont actually get very far, but of course its still worth trying!
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Old 04 July 2013, 16:41   #10
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i think he was talking to me - i cleaned the waterways!
without actually looking im not sure if that engine has a cylinder head or not (could be a blind bore) but if it does then i did not remove it. i did hover remove the exhaust plate from its side - that was completely clear, but all the waterways around the base of the powerhead were pretty furred up.
also looking at the shape of the waterways from the tell tale back, you realise that a piece of wire poked up there wont actually get very far, but of course its still worth trying!
Yes I think you right, I realized after that he was talking to you.
Anyway I have managed to remove the power head, (Thanks to all who gave advice) and can clearly see the waterways and inlet pipe. I shall give them a good going over first chance I get.
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Old 07 July 2013, 12:40   #11
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Not had much success with this 4hp Yamaha, I suspect there is more crud in the water jacket, but not having a manual I don't know how to get to the water galleries around the cylinder. Does any one know if this is a blind bore? I could maybe take the end plate off to see if I can unclog it.
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Old 10 July 2013, 15:47   #12
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Mercury.

If the crankcase's back has several bolts securing the cylinder head, it's completely removable, just remove all bolts, with a rubber mallet hit upper cyl head. Most times stays near solded between them and needs some vigorous hits to become dislodged.

Once cyl head is removed rub mechanically with a small screwdriver, Chineese wooden stick all crankcase and head waterways of salt layers, salt crusts, whatever is finally found obstructing inside water flow. Will ned a new head gasket, torque to specs when assembling back.

Don't need a manual, just take pictures while disassembling parts, once done with work, put them back together.
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Old 10 July 2013, 16:49   #13
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Grip the drive shaft support tube in a vice and start the engine and run it with your finger on the block until it hurts. Remove the 4 bolts on flat plate nearest the spark plug, this is the head cover, your engine has a blind bore. Start it again to get more heat into the block. Remove the plate with the 8 bolts on the opposite side from the spark plug. You will find the thermostat in there but it's the small slot in the sandwich plate that will be choked with a bit of weed. If its a 6 bolt cover its an early model and there will be no thermostat. When you order the gaskets make sure you order an inner and an outer as they are not the same.
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Old 11 July 2013, 13:20   #14
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Grip the drive shaft support tube in a vice and start the engine and run it with your finger on the block until it hurts. Remove the 4 bolts on flat plate nearest the spark plug, this is the head cover, your engine has a blind bore. Start it again to get more heat into the block. Remove the plate with the 8 bolts on the opposite side from the spark plug. You will find the thermostat in there but it's the small slot in the sandwich plate that will be choked with a bit of weed. If its a 6 bolt cover its an early model and there will be no thermostat. When you order the gaskets make sure you order an inner and an outer as they are not the same.
Many thanks for the help. I shall have a go first chance I get, where do I get the gaskets from?
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Old 11 July 2013, 14:46   #15
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Just had a look, It's a 4 AC. Serial No. 6EO S 054298.
There are 4 bolts on the end, & 9 bolts on the side. I dont know what year it is, maybe someone on here will know.
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