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Old 16 June 2010, 04:52   #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, 11:08   #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, 03:15   #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, 10:45   #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, 11:46   #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, 15:12   #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, 01:15   #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, 01:34   #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, 03:02   #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, 15:40   #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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Old 18 June 2010, 15:43   #11
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a pic of the bottom

more pics in previous page.
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Old 18 June 2010, 22:28   #12
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Pics are fine and it looks quite healthy- what I thought I might be able to see on the original ones is nothing.

Re cleaning the corrosion out, use anything that'll do it without marking the metal. A sharpened plastic toothbrush handle works well-and will do the carbon on top of the pistons too.

It looks very much like your throttle stop has been removed. Did you buy the engine new? It may already have been turned into a 15hp.
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Old 19 June 2010, 03:04   #13
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yes i bought the engine new. attached is a pic of the reed valve when replaced.
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Old 19 June 2010, 04:13   #14
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yes i bought the engine new. attached is a pic of the reed valve when replaced.
Did you use a new o-ring when you fitted it? It looks like you did.


The throttle stop is puzzling as there's no metal throttle stop in your pic of the engine.
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Old 19 June 2010, 05:28   #15
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Can you post a picture of what the other side of the head looked like from the piston side. There's a lot of corrosion, just interested to see if this contributed to the failure and eventual crack. Definantely clean up the engine tray. Spray engine degreaser on it, leave then wash off. Also clean all the old gasket material off the head, remove any surface corrosion and salt before refitting and use new sparks. There's a sequence to tightening the cylinder head bolts - another member may be able to help that has access to a manual and specific torque setting.
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Old 19 June 2010, 07:30   #16
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Did you use a new o-ring when you fitted it? It looks like you did.


The throttle stop is puzzling as there's no metal throttle stop in your pic of the engine.
o ring if im understanding correctly is the thing that tightenes the pipe ? no o used the same one. but it isnt loose thats why i kept the same one.
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Old 19 June 2010, 07:54   #17
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Can you post a picture of what the other side of the head looked like from the piston side. There's a lot of corrosion, just interested to see if this contributed to the failure and eventual crack. Definantely clean up the engine tray. Spray engine degreaser on it, leave then wash off. Also clean all the old gasket material off the head, remove any surface corrosion and salt before refitting and use new sparks. There's a sequence to tightening the cylinder head bolts - another member may be able to help that has access to a manual and specific torque setting.
thanks for the info, posted some pics. had a closer look to the cracked head. seems like there was some corrosion and the water path got blocked. probably that was the problem that caused the head to crack.

if someone has a soft copy of the manual would be greatly appreciated (9.9FMH)
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Old 19 June 2010, 12:25   #18
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Head bolts should be 12 ft/lbs or 17nm and the tightening sequence is cast into the head next to the bolts.


I think you're fine with the reed block as is-looks like the o-ring/seal on it is captive.


The old head looks a mess!
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Old 20 June 2010, 02:59   #19
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Head bolts should be 12 ft/lbs or 17nm and the tightening sequence is cast into the head next to the bolts.
Well spotted!
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Old 20 June 2010, 03:08   #20
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The old head looks a mess!
so i guess the only problem was that the head.
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