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Old 16 June 2010, 05:52   #1
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Yam 9.9 converted to 15, head cracked.

i know this is an old thread but will post in here since its related

i got yamaha 9.9FMH and i just replaced the reed valve to 15hp.

the day after i went to test the motor in the sea the head cracked and water start comming out. some ppl told me that it doesnt have to do with the reed valve and maybe the head was corroded.

also attached there are some pics of the motor. and got some questions.

pic:

1 : which metal do i have to bend. in order to get more speed? (already replaced the reed valve)

2 : when i removed the head i found some salt etc. with what can i clean it?

3 : the pic when i removed the cover.
4 : close up of the cracked head.

i already ordered the head +gasket, and wanted to check what could have caused the crack so that when i replace it, it doesnt happen again.
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Old 16 June 2010, 12:08   #2
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Quote:
Originally Posted by dejv View Post
i know this is an old thread but will post in here since its related

i got yamaha 9.9FMH and i just replaced the reed valve to 15hp.

the day after i went to test the motor in the sea the head cracked and water start comming out. some ppl told me that it doesnt have to do with the reed valve and maybe the head was corroded.

also attached there are some pics of the motor. and got some questions.

pic:

1 : which metal do i have to bend. in order to get more speed? (already replaced the reed valve)

2 : when i removed the head i found some salt etc. with what can i clean it?

3 : the pic when i removed the cover.
4 : close up of the cracked head.

i already ordered the head +gasket, and wanted to check what could have caused the crack so that when i replace it, it doesnt happen again.
Moved it to it's own thread so more people see it

Welcome to Ribnet

It's speculation,but I reckon you've got one of 2 likely causes here.Either
1) You may have an air leak after disturbing the carbs. A better pic of the lower bores and piston crown would help. Is there any bore scuffing/scoring or discolouration on the piston?From the image, the bottom piston looks dry. Btw, now you've got the head off, it needs a decoke!
2) (sh)It happens, sometimes things fail through age and use.
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Old 17 June 2010, 04:15   #3
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1st of all thanks for the quick reply and for the welcome

im still a bit green on 2 stroke. so basically i must dismatle the carb and check the gasket and if its ok i tighten the screws.

will try and post a pic tomorrow of the pistons
what do you mean by dechoke. i remove the salt etc that there is in the water path and clean the piston crown(the bottom of the piston)?

it was bought back in 2000 and wasnt used more than 30 times. (although i used to start it every year in the garage)
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Old 17 June 2010, 11:45   #4
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Originally Posted by dejv View Post
1st of all thanks for the quick reply and for the welcome

im still a bit green on 2 stroke. so basically i must dismatle the carb and check the gasket and if its ok i tighten the screws.
Yes, but use a new gasket.
Quote:
Originally Posted by dejv View Post

will try and post a pic tomorrow of the pistons
what do you mean by dechoke. i remove the salt etc that there is in the water path and clean the piston crown(the bottom of the piston)?
Yes.

it was bought back in 2000 and wasnt used more than 30 times. (although i used to start it every year in the garage) [/QUOTE]

It appears it's only the water jacket that's cracked. Is there significant corrosion in the head waterways? I'm wondering if it's a symptom of being standing for a long time.
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Old 17 June 2010, 12:46   #5
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did you fire it up for a short run in the garage without any water ?
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Old 17 June 2010, 16:12   #6
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did you fire it up for a short run in the garage without any water ?
Shirley Knott?
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Old 18 June 2010, 02:15   #7
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did you fire it up for a short run in the garage without any water ?
no never started the motor without water.

will go and check the motor tonight. and take some photos
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Old 18 June 2010, 02:34   #8
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Ok thats good to know, you'd be surprised at how many that do, ignorant of the damage it does.

My yard used to have a troublesome resident next door who thankfully has now moved away, and he used to start his every couple of months, it would have been easy for me to lean over the fence and offer him some friendly advice but .. after the trouble he gave me, I some how didnt feel the need
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Old 18 June 2010, 04:02   #9
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lol

also with what do i have to clean the water path and the bottom of the pistons ?

(sorry for asking too many questions )
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Old 18 June 2010, 16:40   #10
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more pics.

1st pic: the throttle - what do i have to remove.
2nd pic: Top piston
5th : bottom piston

are these pics enough ?
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