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Old 30 July 2008, 15:24   #1
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Yam F100 problems.......loud knocking noise.

Well, during a run the other day the port side engine started knocking. Sounds quite loud so I come back on one engine. It sounded like a dropped valve or a big end.

Had another listen today, it starts ok, but knocks heavily. Removing one plug cap at a time, 1 or 2 makes no difference to engine running but quietens the noise. Removing cap 3 or 4 and the engine won't start, so it does point to maybe a couple of valves in 1 or 2 bent or broken springs etc.

Does anyone have any ideas/experience?

Does anyone have a working powerhead for sale in case mine is gonna be expensive?

I'll be looking more closely at the weekend.
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Old 30 July 2008, 17:03   #2
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Has the cam belt been changed at the correct interval?
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Old 30 July 2008, 17:17   #3
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this would be a easy one, do a compression test on all cyl to establish what the compressions are or should be, that will tell you what to do next,
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Old 30 July 2008, 18:09   #4
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Has the cam belt been changed at the correct interval?
Won't make any odds. A cam belt going will stop the engine dead. If it's still turning the valves it'll sound fine.



Pull the plugs and look for debris. Turn it over by hand and look down the plug holes with a torch,and do a compression test. It sounds like there won't be any quick fix though.
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Old 31 July 2008, 04:58   #5
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Pull the plugs and look for debris. Turn it over by hand and look down the plug holes with a torch,and do a compression test. It sounds like there won't be any quick fix though.
Will do that, if I don't find anything I'll remove the powerhead and then see what I can find stripping it down.
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Old 02 August 2008, 11:44   #6
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Big ends have gone on cyl 4 and 3. No. 4 has about 1mm movement!!!

Expensive I think, second hand powerhead if I can find one.
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Old 03 August 2008, 05:38   #7
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What about grinding the crank? May be a cheaper option than a replacement powerhead, depending on the condition of the rest of the motor.
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Old 03 August 2008, 06:36   #8
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Did they make to F100 in large numbers? I'd heard it was discontinued and replaced by a commercial version F90, do not know if this power head is the same though.
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Old 03 August 2008, 11:57   #9
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What about grinding the crank? May be a cheaper option than a replacement powerhead, depending on the condition of the rest of the motor.
I've suggested that and everyone poo-poos the idea, not sure whether undersize bearings are easy to get.
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Old 03 August 2008, 11:59   #10
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Did they make to F100 in large numbers? I'd heard it was discontinued and replaced by a commercial version F90, do not know if this power head is the same though.
They still make the F100, they have been for over 7 years. Never seen nor heard of an F90!

http://www.yamaha-motor.co.uk/produc...s/four_stroke/
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Old 03 August 2008, 12:16   #11
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Not 100% sure but I think the 90hp and 100hp are the same engine but the 90hp is not sold in the uk.
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Old 04 August 2008, 17:13   #12
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The 80, 90 and 100 are the same. The 90 is not sold in the UK.

As far as I'm aware
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Old 06 August 2008, 10:33   #13
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They still make the F100, they have been for over 7 years. Never seen nor heard of an F90!

http://www.yamaha-motor.co.uk/produc...s/four_stroke/
I was getting confused (not difficult) looks like the US dont have the 100 (but we do) and we dont have the 90 (but they do)

F90 Specs

115 to 150 Specs

Not sure whether they are all now efi or not, I'll get my coat...
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Old 07 August 2008, 02:23   #14
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cant see any reason why it cant be rebuilt unless parts are unobtainable, it might be worth trying bike engine builders, i know the cooling systems different but the principle is the same,also the bike engine builders seem to have access to a large selection of aftermarket shells and pistons etc. are the conrods and pistons all ok? if it was mine i would try to get someone to grind the crank, supply bearings to suit and assemble it myself
hope you have some luck soon (seen your post on yd) same toerags tried it on me but just kept asking for the owner of the house, we are ex directory as well
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Old 11 August 2008, 12:33   #15
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hope you have some luck soon
Have you seen my latest post on YD? I may be unemployed soon!
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Old 13 August 2008, 09:30   #16
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Have you seen my latest post on YD? I may be unemployed soon!
thats a crappy situation to be in, i hope things improve for you soon.
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Old 14 August 2008, 21:57   #17
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thats a crappy situation to be in, i hope things improve for you soon.
Now umeployed! Or should I say a self-employed dive instructor/skipper who is very quiet!
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