17ft fibreglass boat - wrong prop or underpowered?

[FordGT]

Looking at how dodgy the above is making me crack up...

[Roughasguts]

Mate don't give up on the Oil injection just yet. Pull the Oil tank off and clean it out! The Outlet can gel over and block it!

Do the same to the Oil lines! The Oil pump and screen filter probably also blocked up!
All that can happen if you add another oil brand if youre unlucky!

Cheers.

[Roughasguts]

Mate just to add one more point the Oil discharge from the engine is pretty low.

Example

With oil line removed run engine for 5 minutes at 1500 rpm

Run oil in to a syringe with ml graduations.

Flow at 1500 rpm for 5 minutes you should have
2.2 - 3.7 ml as you can see SFA.

Also run 50:1 in your fuel tank while testing.

Cheers

[Andy56]

I would also go back to basics with engine mounting. To me it sounds like your dragging the motor ie it sits too low in the water. Check that when your at max speed, the cavitation plate is out of the water. If its dragging and the prop is over sized, you could be lugging the engine. Is the steering heavy? If it is, the motor is trimmed too far in. It should be relatively light. Get the tachometer fixed, it will be an important tool to suss out the motor.
Don't assume that the previous owner knew what he was doing. I have met a lot of people who say they have had boats all their lives yet know very little about proper setups. Like I said , assume nothing.

[Fed]

What's deal with the oil RAGs I thought all tcw3 oil would be mixable.

[Roughasguts]

What's deal with the oil RAGs I thought all tcw3 oil would be mixable.

Apparently not all Fed!... Just like radiator coolants one coolant doesn't mix well with the other Type and may start to gel causing blockages.

Cheers

[FordGT]

Mate just to add one more point the Oil discharge from the engine is pretty low.

Example

With oil line removed run engine for 5 minutes at 1500 rpm

Run oil in to a syringe with ml graduations.

Flow at 1500 rpm for 5 minutes you should have
2.2 - 3.7 ml as you can see SFA.

Also run 50:1 in your fuel tank while testing.

Cheers

Geez that's interesting; I never realised how little oil it is actually going through the engine for the amount of fuel. Is it worth trusting an oil injection system so old though?

[FordGT]

I would also go back to basics with engine mounting. To me it sounds like your dragging the motor ie it sits too low in the water. Check that when your at max speed, the cavitation plate is out of the water. If its dragging and the prop is over sized, you could be lugging the engine. Is the steering heavy? If it is, the motor is trimmed too far in. It should be relatively light. Get the tachometer fixed, it will be an important tool to suss out the motor.
Don't assume that the previous owner knew what he was doing. I have met a lot of people who say they have had boats all their lives yet know very little about proper setups. Like I said , assume nothing.

Hi Andy yes, I measured up the engine when I first got the boat, and it seems to be mounted at the right height; I'll get back you on the cav plate after the next trip.

[Roughasguts]

If your oil tank, lines, pump, and screen are all clean and pump is flowing! I would trust it after all you gonna trust your water pump, fuel pump, trim tilt pump, starter motor,
You getting my drift. Still carry 1 litre as a precaution to throw in the fuel if it ever does play up.

Cheers.

[Fed]

I have no idea how a Suzuki oil injection is set up but if you didn't block the oil intake to the pump it may be drawing in a lot of air into the fuel and playing up at high RPMs.
One for the Suzuki brains trust...?

[Triple]

But then theres Two strokes got ports in the bore so compression doesn't start at the bottom of the stroke.
Mazda Rotarys... hardly any compression more of a sweep than a stroke.
Jet engines compression built up over many stages in a rotary vane arrangement hard to measure that volume.

Do you use corrected atmospheric pressure figures when testing an engine at different altitudes?

Compression "ratio" is a measurement of a difference in volume.
Volume of the piston chamber at bottom dead center divided by volume of piston chamber at top dead center. This works for all piston engines, two strokes can have corrected and uncorrected ratio numbers based on position of exhaust port. Rotaries are worked out the same way as piston engines but the only way to change the compression ratio on a rotary is to change the "tub" size on the rotor face.

A compression test shows only how much pressure is being applied which is a measurement of sealing ability within each cylinder. As an engine gets a bit of wear n tear the compression will drop but the compression ratio will always stay the same. (except when you change something that would affect the cc's).

I am unsure of Jet engines but aren't they worked out by using the compression fans effectiveness with air in compared to air out formula?

Back on topic, Op stated it hadn't been started in a year.. Haven't seen anywhere posted that you have cleaned the tank out and are using fresh fuel?

[Roughasguts]

Hey triple I can use corrected pressure heights and temperature height if you like.
But most boats go in the Ocean that being Sea level so the international standard pressure at sea level has already been determined at 14.7 psi.

Of course there is room for variation.

Here are some ISA standards for you.

1 mb variation = 30 feet

2 deg C variation in temp = 1000 feet.

All those figures you use are great for designing a motor but not much use to us now unless we look those specs up and find a motor has 8.5:1 compression ratio! Then we do a compression test and convert the numbers! And I come up with 8.24:1 then with all those variables we should be pretty happy with the result.

Cheers

[tassjo]

thanks triple: some 1 with some brains..a compresion ratio does not change unless you alter something internal,eg head gasket thickness,re shaping combustion chamber ,fitting a domed piston or decking block.I dug out my old text books so i can send the publishers name to roughasguts,all i need is his email, but maybe he is not a real merchanic after all.

[Roughasguts]

Let's make it easy for you guys! Let's say the bore is square 100mm by 100 mm.

So that there bore holds 1000 ml 1 litre.
Now let's put a pretend head on it with a combustion chamber that holds 100ml.

To work out the ratio of the combustion chamber compared to the bore is simple
1000 divided by 100 will give us 10!

There for 10:1 that's if you can compress water but you can't.

But you can compress air and measure the result.
So you get you're 10:1 from above and apply that to standard air pressure at sea level
Being 14.7 psi multiply that by the 10 and you get a compression pressure of 147 psi
Easy huh there exactly the same.
147psi diveded by 14.7 gives you back that 10:1 compression ratio.

Magic huh.

Happy to teach you guys something.

Cheers

[tassjo]

whats the email so i can send you those names
when a motor is built,and lets say it was built with a comp ratio of 10:1 .Out of the box or maybe after a few thousand ks be it in a vehicle the compression presure is 180 psi.10 years later it comes in with a problem and we do a compression test and we have 1 cylinder down ,say it be 80psi,then we do a wet test.no difference,so we do a cylinder leakage test & find the exhaust valve is leaking ok.back to basics you cannot work out the comp ratio from a compression test reading,if you like i can get you in contact with 1 of my tech teachers which i still keep in contact with if you like