Mercruiser 5.7 won’t make power

[Scott Danforth]

To OP- might be worth verifying balancer hasn't slipped verify indicated TDC is actually tdc ...

simple test done with a piston stop tool

if you dont have a piston stop tool, make one: take an old spark plug and knock the electrode out of it, then weld a nut on it and use a bolt with a rounded end. plenty of how-too's on the web.

using the piston stop tool turn the engine by hand (from the belts or from the flywheel, never from the crank bolt) one way until the piston just kisses the tool. mark the damper with a pen. turn the engine back the other way by hand until it kisses the tool. the damper 0 mark should be directly in between.

 

[tank1949]

not familiar with your ignition system but it may have a knock sensor that needs to be disconnected before setting base timing. also, did you check for debris clogging gas pick up tube filters? my tanks had them and were clogged.

 

[Scott06]

not familiar with your ignition system but it may have a knock sensor that needs to be disconnected before setting base timing. also, did you check for debris clogging gas pick up tube filters? my tanks had them and were clogged.

Both the TB and Delco he references using don't have to have a knock sensor disconnected , just need to be put in base mode to set initial timing

 

[itsathepete]

I have a 1.47 ratio drive how does that calculate?

I used the gear ratio of the original 3.0 drive
Recalculating at 1.47 ratio at 2600rpm gives
19p at 17mph 47% slip
19p at 10% slip 29mph
15p at 17mph 32% slip
15p at 10% slip 23mph
If these numbers are accurate the 15p prop is still too much prop for the amount of horsepower delivered and size of the boat. But that's not saying the engine is making the horsepower it should which it doesn't seem to be
Which prop did you use with the 3.0 and at what rpm were you running 23mph?

 

[nola mike]

17 mph at 2600rpm with a 19p prop and a 1.94 gear ratio (from the 3.0) is 30% slip
17 mph at 2600rpm with a 15p prop and a 1.94 gear ratio is 11% slip.
I'm assuming the 30% slip is due to not planing out and not due to a bad prop.

His wot on the 3l was 23mph. He didn't mention rpms; your slip numbers aren't accurate

 

[itsathepete]

His wot on the 3l was 23mph. He didn't mention rpms; your slip numbers aren't accurate

Yeah I know he didn't mention rpms at WOT on the 3L engine so I asked what it was. The numbers you are quoting are based on the 2600rpms he says he was getting on the new 5.7L engine but I mistakenly assumed the gear ratio of the outdrive was the same as the 3L. Then I posted new slip and mph numbers based on the 1.47 ratio drive which is what he now has. If my slip numbers aren't accurate now, there must be a problem with the mercury racing prop slip calculator

 

[Oldpos]

I used the gear ratio of the original 3.0 drive
Recalculating at 1.47 ratio at 2600rpm gives
19p at 17mph 47% slip
19p at 10% slip 29mph
15p at 17mph 32% slip
15p at 10% slip 23mph
If these numbers are accurate the 15p prop is still too much prop for the amount of horsepower delivered and size of the boat. But that's not saying the engine is making the horsepower it should which it doesn't seem to be
Which prop did you use with the 3.0 and at what rpm were you running 23mph?

On the 3.0 I used the 1.98 drive 16” 13p prop at 4600 rpm

 

[Oldpos]

When I put in the timing plug on the distributor shouldn’t the engine rpm change? I start and warm up the engine, idles 800 warm, plug in the timing jumper and ensure that the 12v wire is hooked up to battery power all while engine running, but the idle does move

 

[Oldpos]

So I’m on the lake now and put in in base timing and set to 8 degrees. Go out to run it and 12 mph at 2200 rpm is all I can get. I put the timing plug back in and rotate the dizzy while going down the lake, almost 1.5 inches to the right until max rpm of 2600 achieved any more it ran like crap. Took plug out and at 2600 rpm I am getting 17 mph. I can see a prop change gaining maybe 1000 rpm at most but that still leaves me at least 1000 rpm low. And after I adjusted it on the lake it idled the same as before I adjusted it 800 rpm

 

[Oldpos]

Last thing the flappers are banging like hell almost sounds like a engine knock but it is the flappers, if they are knocking that means they are letting the exhaust go by correct?

 

[jimmbo]

Have you put a vacuum gauge on the engine?

 

[Oldpos]

Have you put a vacuum gauge on the engine?

I have one with me I will, where is the best place hook up the vacuum line, I have it but have never used one

 

[jimmbo]

I try to find a source near the carb, or on the base of the carb, preferably one that can read both Plenums. On my Boat's Holleys(factory 500cfm 2bbl, and the 4175 650cfm SB I stuck on), I used the choke pulloff vacuum hose, once the engine was warm, and the choke was fully open, it wasn't really doing much

If you have never used a Vacuum Gauge on an Engine, there is a bit of a Learning Curve, not only are the Numbers Important, but so are any Changes to the Numbers

 

[Scott Danforth]

marine carb will have a port in the plenum. there is none on the engine

something is wrong with the dizzy or TDC on the balancer is not TDC on the engine

almost 1.5 inches to the right until max rpm of 2600 achieved any more it ran like crap.

or you are starving for fuel - see post #16


additionally, with a flat tappet cam, you need to run that motor at 2000 RPM's for 20 minutes to break in the cam/lifters. did you do that on the stand?

 

[jimmbo]

additionally, with a flat tappet cam, you need to run that motor at 2000 RPM's for 20 minutes to break in the cam/lifters. did you do that on the stand?

That is one that a lot of People who rebuild their engines miss, and todays Oils aren't Flat Tappet Cam friendly

 

[Oldpos]

marine carb will have a port in the plenum. there is none on the engine

something is wrong with the dizzy or TDC on the balancer is not TDC on the engine

I used a compression gauge to put me on tdc, and watched the valve to set nbr 1

or you are starving for fuel - see post #16

I just got back and it held a steady 4 psi even when I manually opened the secondaries, and spray pattern was even

additionally, with a flat tappet cam, you need to run that motor at 2000 RPM's for 20 minutes to break in the cam/lifters. did you do that on the stand?

It has two hours on the test stand with varied idle and about 5 hours in the water now

 

[Oldpos]

I try to find a source near the carb, or on the base of the carb, preferably one that can read both Plenums. On my Boat's Holleys(factory 500cfm 2bbl, and the 4175 650cfm SB I stuck on), I used the choke pulloff vacuum hose, once the engine was warm, and the choke was fully open, it wasn't really doing much

If you have never used a Vacuum Gauge on an Engine, there is a bit of a Learning Curve, not only are the Numbers Important, but so are any Changes to the Numbers

Thanks I will try it

 

[Oldpos]

marine carb will have a port in the plenum. there is none on the engine

something is wrong with the dizzy or TDC on the balancer is not TDC on the engine

If it’s electronic ignition. What could be wrong with the dizzy? I’m leaning that way but don’t know enough about them, I thought the electronics self timed, it does have a large mechanical head under the rotor button but I’m not sure what it’s for

or you are starving for fuel - see post #16


additionally, with a flat tappet cam, you need to run that motor at 2000 RPM's for 20 minutes to break in the cam/lifters. did you do that on the stand?

 

[nola mike]

The electronics under the cap is the ignition sensor. Did you ever verify that your timing is advancing?

 

[jimmbo]

That has been asked many times, and still no answer