Yam F100 problems.......loud knocking noise.

[Okeanos]

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.

[Rich L]

Has the cam belt been changed at the correct interval?

[matt h]

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,

[Nos4r2]

Originally Posted by Rich L

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.

[Okeanos]

Originally Posted by Nos4r2

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.

[Okeanos]

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.

[Downhilldai]

What about grinding the crank? May be a cheaper option than a replacement powerhead, depending on the condition of the rest of the motor.

[Simon B]

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.

[Okeanos]

Originally Posted by Downhilldai

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.

[Okeanos]

Originally Posted by Simon B

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/