Mercruiser 470/485 starter does not always turn over.

[tlizakow34]

Cutting to the chase, I have replaced the entire electrical portion trying to isolate the issue but now I suppose I am still at square 1. My 485 seemed hard to crank, eventually not cranking at all. Things I have done in order:

1. Cleaned Grounds and all electrical contacts
2. New and bigger battery cables.
3. New battery 1050 CCA AGM
4. New starter with new solenoid
5. Outdrive maintenance to check engine allignment and binding. Realligned engine. (was off by mm's). New gear lube and waterpump impeller.
6. Soaked engine cyls in MarvelMystery Oil and in the crankcase.

All of these had micro improvements to the engine starting but it still has a 50/50 shot at not turning. Solenoid clicks but it seams the starter is not powerful enough? Brand new starter so unlikely especially since the old one did the same thing. I fear something internal (hydrolocking, bearings) but dont want to open it up just yet. Can turn by hand with a tire iron on the front bolt but hear a hissing sound from under the valve cover. Will turn over after I get the engine past compression stroke.

 

[Bondo]

Ayuh,...... Welcome Aboard,...... Is the drive Up, or down,..??

I'd just pull the drive, to know whether yer dealin' with a motor problem, or drive problem, as they're splined together,....

 

[nola mike]

Can pull the plugs, see if water shoots out when you crank. Pretty easy to remove the valve cover as well to see if anything jumps out at you. Does your engine have a slave solenoid? The old ones didn't, I'd have to refresh my memory on what that would affect if you're wiring a new starter.

 

[tlizakow34]

Outdrive was completely removed to see if that was the case. It was not. No water or coolant in the cylinders after removing plugs. Haven't yet removed valve cover . The starter is newer gear reduction with solenoid attached to it as one unit. I removed the old solenoid when I installed this one. I was messing around today and I think im on to something. If i turn the motor by hand a smidge like 0.000001 degrees at a time eventually it will start. Almost as off the starter needs to engage the gears perfectly before it will crank. Unsure of the internals but are there contacts inside the starter that will only crank is the pinion is fully extended? Might be binding and not extending fully. Cant really get a look under there to see.

 

[Scott Danforth]

Stop turning the motor by the crank bolt. That is best way to damage the crank

Pull the plugs, if it turns over and spits water out, you have an exhaust elbow leak at the joint

If you turn the motor over and coolant comes out, you lost your head gasket

If there is no change, go bact to your battery connections. If any of your cables have any corrosion, replace them

 

[Luv2fish36]

"removed the old solenoid when I installed this one"


Some 470's have a 2nd slave solenoid. One mounted on the starter and one mounted on the block.

 

[tlizakow34]

Scott Danforth, that was no help whatsoever. Terminals, battery and cables are new. Absolutely spotless with no corrosion. No coolant to be seen. I checked in the cylinders. I didn't know that you must have 2 solenoids though. Im guessing the voltage across the starter solenoid should be higher? Hence the need for the original block mounted solenoid?

 

[Bondo]

I didn't know that you must have 2 solenoids though. Im guessing the voltage across the starter solenoid should be higher? Hence the need for the original block mounted solenoid?

Ayuh,..... From the back of the boat, to the front, to the back is a long ways to carry voltage in a 14 gauge wire,.....

Hence the slave solenoid,.....

 

[xltier]

whatabout rigging up a separate wiring to the starter only to isolate the system. if it turns good then u would know.

 

[Scott Danforth]

Scott Danforth, that was no help whatsoever. Terminals, battery and cables are new. Absolutely spotless with no corrosion. No coolant to be seen. I checked in the cylinders. I didn't know that you must have 2 solenoids though. Im guessing the voltage across the starter solenoid should be higher? Hence the need for the original block mounted solenoid?

New doesnt mean good

as Bondo pointed out, the pilot solenoid is to get good voltage to the solenoid on the starter because you have 14' of wire to the dash, and another 14' of wire back to the motor.

if you have good connections everywhere, then jumper the S and B terminals together on the starter with a screw driver and your motor should be cranking over about 450 RPM with the plugs out and about 300 RPM with the plugs in. 200 RPM is about the minimum cranking speed it takes to start a motor.

 

[Luv2fish36]

It sounds like your missing the other slave solenoid mounted on the block. When you turn the key to start the motor this activates the slave solenoid which then activates the solenoid on the starter transfering small voltage into big voltage. Wire back in the block solenoid and you should be good to go.