the perils of evilbay!!! another engine needed

[ericcs]

Is the scoring the same all around the piston? What is it like on the inlet side compared to the exhaust? Measure the bore up closely as this may be the result of someone doing a repair already- do all the pistons look exactly the same- like original - same part numbers ?

all i have done so fare is taken the plugs and exhaust cover off. i,m in 2 minds what to do, sell it assembled/complete or strip it down and part it out. all the plugs looked perfect and the same colour, a browny grey and dry! i also shone a torch down the plug holes, and all the crowns looked fine.

[Fed]

I'll go with your first theory Ericcs, fuel delivery problem, the bottom cylinder would be the last one to have a problem.

[MudRiverDan]

I'll go with your first theory Ericcs, fuel delivery problem, the bottom cylinder would be the last one to have a problem.

I know I am a bit ignorant here but if there was no fuel delivery then how did the engine keep going to the point of seizure?

Or would they just run leaner and leaner until the piston got too hot and seized?

Dan

[ericcs]

I'll go with your first theory Ericcs, fuel delivery problem, the bottom cylinder would be the last one to have a problem.

sounds very feasable, so asuming the carbies are ok. i guess a fuel preasure gauge would be needed to see if the fuel pump is working ok. i would still like to find out if the oil pump can be statically tested to eliminate it.
if it is only a fuel delivery issue, and the oil pump is still working, it would be safe to assume the crank and big end bearings should be still ok?

[Fed]

Sorry Dan I should have said reduced fuel delivery.
With partially blocked fuel vent, fuel pickup or fuel filter a motor will still run fine at lower RPM but when the revs are increased it will start running out of fuel because it can't supply enough flow to keep up.

I don't think it's a proposition to try and test the fuel system, fuel pump & oil pump on a non working motor ericcs.
What sort of fuel tank is in it?

Edit: I think you would have to count on every part inside the engine to be rooted ericcs.

[ericcs]

Sorry Dan I should have said reduced fuel delivery.
With partially blocked fuel vent, fuel pickup or fuel filter a motor will still run fine at lower RPM but when the revs are increased it will start running out of fuel because it can't supply enough flow to keep up.

I don't think it's a proposition to try and test the fuel system, fuel pump & oil pump on a non working motor ericcs.
What sort of fuel tank is in it?

Edit: I think you would have to count on every part inside the engine to be rooted ericcs.

fuel tank is underfloor with 2 vents(5m quintrex) whick aren't blocked as it pisses fuel out of them when i fill it up

[ovakil]

Take it apart then make a decision on what to do.My engine I got rebuilt after owning boat 18 months.Looked at buying 2nd but didn't want to risk it.Couldn't afford new,so I rebuilt it knowing that I would never get close to the money I paid.But I was keeping boat & I knew it would be reliable.

[ericcs]

will probably pull down atleast to try and find the problem, even if it's too damaged to repair

[Fed]

It might not be practical to do ericcs but maybe you could drain the fuel bowls and see how much comes out of each.

A couple of things I've learned over the years.

Test all the alarms.
Run premix in the first tank until oil usage from the injection is confirmed.
Go for a WOT run and make sure it's getting the right RPM, write it down.
Do a WOT run from time to time and if you ever see the slightest hint of a lower RPM then get it looked at straight away. (I give mine a short test every time I use it)

[ericcs]

It might not be practical to do ericcs but maybe you could drain the fuel bowls and see how much comes out of each.

A couple of things I've learned over the years.

Test all the alarms.
Run premix in the first tank until oil usage from the injection is confirmed.
Go for a WOT run and make sure it's getting the right RPM, write it down.
Do a WOT run from time to time and if you ever see the slightest hint of a lower RPM then get it looked at straight away. (I give mine a short test every time I use it)

g'day fed, your right with your pre purchase checks, would've been handy tho if the motor was still on a boat. one thing i did notice was on my first test run, it only revved out to 5200, spinning a 15k prop on an empty 5m quintrex. my old 70hp yam spun it's 17k prop to 5600 no problem. i planned to address the problem, but it didn't last long enough
i guess you need to have an intimate knowledge of the paticular motor to be able to do a safety circuit test, but in hing sight, it's worth the effort to study it before you commit
when it started to play up, they were classic running out out of oil symptoms, any thing other, i would have probably thrown in a bottle of oil as a precaution. oh well, next time
eric

[dnej]

Eric, how old is the fuel you are using?
David

[ericcs]

Eric, how old is the fuel you are using?
David

dave, the fuel was only a a couple of weeks old.
i learn't my lesson many years about stale fuel. this engine's spark plugs looked perfect, a light brown grey, and the piston crowns all look clean, unlike the skirts. eric

[Noelm]

on 2 strokes, an amount of unburn't oil drains to the bottom of the crankcase, which is normally sucked up under vacuum thru a hose and fed up to the top bearing to dribble down again. my theory was that the middle and bottom pistons survived a bit longer because off the extra bit of oil

you do NOT have an oil problem, do not get side tracked by that, you have either a lean burn or a dud "rebuilt" motor.

[Adam84]

My heart sank as I read this. I bought a 4m Pongrass on the weekend just so I could strip the 2yr old 40hp Suzuki outboard off the back of it for my 4.3 Quinnie. Although my new motor only has 20 hrs on it, and may be still under new motor warranty, I too potentially took the gamble of buying 'someone elses problem' off ebay.
Perhaps you could do what I have done and buy another boat with a decent/near new outboard on it? Then swap motors and sell the other boat with your blown motor? I paid around half the price of a new motor for a 4m boat, trailer and the motor, with gps chart plotter/sounder and new bits like bimini, gauges, winch etc all over it. And when I sell the other boat, it will subsidise the costs and make my 'new motor' even cheaper....
Just a thought but if you shop around you may too find a bargain saving a fair bit of money.

[ericcs]

you do NOT have an oil problem, do not get side tracked by that, you have either a lean burn or a dud "rebuilt" motor.

this makes sense as in the 3hrs of run time, it did use about a third of the oil in the tank. also, it's quite possible the safety circuit still works, as on my understanding, it only picks up either overheating or oil flow/oil level. i was able to comfortably put my hand on the powerhead without burning it off.
i'm curious to know, if indeed it was running lean, with the top piston being the worst followed by the middle and the bottom appearing to be not too bad, could it possibly be a fuel delivery issue, as opposed to blockages within the individual carbies?