2 strk Motor trouble

[spuderico]

Hi guys/gals, just want a little advice or opinions on the situation I faced at the weekend! Ran around all day with my old 60hp 2 stroke and was returning back to the ramp when the motor developed a rather loud knocking from the internals Dropped the revs but this didn't stop the noise just the volume.

It was then that I noticed the fuel was very low (50:1 ratio) and switched it over to the second tank. Upon starting it the noise returned when put into gear. My memory is vague now but I think the noise was absent in neutral I was only a [s]stones[/s] fish throw from the ramp at this stage so I shut the motor off 4min after changing tanks.

When flushing the motor at home the noise had dissappeared both in neutral and in gear!!!!
I thought maybe lack of fuel had something to do with it

Any thoughts?

[blaze]

dosnt sound good but anyway lets look a little further.
you say the noise was still there when you dropped the revs, did the frequency of the noise alter, like from 50 taps aminute at revs to 10 taps an min at idle.
check plugs for any foriegn bits
stick finger over plug hole for a rough check of even compressions
back boat in the water and test for noise under load (leave in foward gear and load up motor to WOT)
Also been caught my self looking for a rattle in my motor and it turned out to be a loose bolt in a stainless bracket, so dont discount things like that, things bolted around the transom area.
keep us informed
cheers
blaze

[spuderico]

Yes Blaze the frequency did drop as the revs dropped. Have checked all external parts. Wasn't going to check the leg as I'm not confident in doing so. I will do the compression test as advised when time permits.
Will keep you posted. I still think that even if not under load that sort of noise shouldn't cease if it were terminal!!! Will have to get in the water on the weekend. Have been trying to come up with a cheap container for emersing the prop leg for flushing. I remember that 44 gal drums used to be the go once. Can you advise on an alternative?

Thanks.

[tonylmitchell]

I had heard a similar knock to the one you are refering to possibly, I had a knocking sound coming from my 40Hp 4Stk Yammy, it turned out to be from the fuel pump running dry. When I connected the other tank it stopped after the fuel reached the pump. Being a mechanical pump it does get louder with revs.
It was surprising how long the motor ran before I realised that the tank was empty.
Maybe that is all your problem is.

Regards
Tony

[spuderico]

Thanks Tony, sounds promising!!

[stork71]

As far as drums for flushing i use a 44gal drum that is appropriatly cut off.. Its a heavy duty plastic type container sourced from one of the industrial sites that contained a detergent... Just get a bung or tap put into the bottom to empty it.

[James_Rand]

Spuderico,

From your description, it doesn't sound good. Particularly if the frequency of 'knocks' was directly affected by RPM's!

Had an old holden red motor that made a knocking noise but only under load and only when the motor was at normal operating temperature.

- BOTTOM END BEARING! GOT TO IT QUICK SO SAVED THE CRANK! HOPE THIS IS NOT YOUR PROBLEM AS IT WOULD BE AN EXPENSIVE FIX!

GOOD LUCK WITH IT. LET US KNOW HOW YOU GO!

JR/

[finga64]

where abouts in Brisy are you spud??

[spuderico]

Too Damn cold and windy to take a trip to the water today. Also tried to find a suitable container to use as a motor flushing receptical. $17.50 for a galvanised one at Reverse Garbage. Still would have to chop it down Would like to find a plastic one!! Hmmm

[spuderico]

Futher to my story I have managed to drop the OB into a tub of H2O and simulate load on the motor. Not a sound so I'm going with Tony on the theory about the mechanical fuel pump!!!!

[phewy]

--- ignore this post- mistake

[Kopey]

The motor tonylmitchell refered to is a 4 stroke that has a fuel pump driven off the camshaft so when you get low on fuel the fuel pump diaphragm doesn't put any direct pressure on the cam follower of the pump which is why you get a rattle (think of a loose tappet).

You spuderico on the other hand have a 2 Stoke which has a vacuum driven fuel pump which totally rules out that possibility unfortunately.

To me it sounds like the motor was still in gear when it stopped which would make the rattle however it doesn't really mesh with your story.

Try (without your motor running) putting the motor into foward gear and rotating the prop and you'll hear a clicking noise Hopefully you'll probably instantly recognise the noise. Apart from that I might need some further info to diagnose your problem.

Glad to be of help. Cheers, Kopey

[spuderico]

Could the noise be from a cylinder not firing (3 Cyl) or under lubricated??

[ahoj]

check for compression first --broken ring or bent conrod -- lose bearing could cost you big damage even a new block My advice is not to run the motor untill you check the compression then you will have a peace of mind and loojk for other problems --like gearbox- leg bearings lose propellor etc etc.. use a short broom stick to listen to noices in the motor or leg by placing it to your ear and the motor part--( make sure you don't get tangled clothes to your moving prop...) If you happen to be a doctor use your stethoscope... lol

hope you will find your problem without too much cost

Cheers Ahoj