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

Okeanos · 30 July 2008, 20:24

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 · 30 July 2008, 22:03

Has the cam belt been changed at the correct interval?

matt h · 30 July 2008, 22:17

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 · 30 July 2008, 23:09

Quote:

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 · 31 July 2008, 09:58

Quote:

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 · 02 August 2008, 16:44

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 · 03 August 2008, 10:38

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 · 03 August 2008, 11:36

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 · 03 August 2008, 16:57

Quote:

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 · 03 August 2008, 16:59

Quote:

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/

Ian Sharlot · 03 August 2008, 17:16

Not 100% sure but I think the 90hp and 100hp are the same engine but the 90hp is not sold in the uk.

Alex-341 · 04 August 2008, 22:13

The 80, 90 and 100 are the same. The 90 is not sold in the UK.

As far as I'm aware

Simon B · 06 August 2008, 15:33

Quote:

Originally Posted by Okeanos

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...

markg · 07 August 2008, 07:23

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

Okeanos · 11 August 2008, 17:33

Quote:

Originally Posted by markg

hope you have some luck soon

Have you seen my latest post on YD? I may be unemployed soon!

markg · 13 August 2008, 14:30

Quote:

Originally Posted by Okeanos

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.

Okeanos · 15 August 2008, 02:57

Quote:

Originally Posted by markg

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!