How tight is too tight when trying to spin motor by hand

[ChronoFish]

Hi,
The regular newbie here trying to rehab a 1990ish 3.0 Mercruiser motor.
I've gotten the motor to crank and smoke and shake, and it sounds like it wants to start. It seems like the starter motor is cranking too slowly and I want to blame this on the starter motor, because that seems like an easy fix. But after reading advice in these forums, it sounds like maybe I need to not jump the gun and look into some other possible issues.

For "starters" how tight should the motor be? Sounds like I should be able to easily rotate the motor. I can't. If I put some effort into it, I can get the motor to back up. But I can't get a good enough grip to spin the motor in the same direction the starter motor spins it. For instance the belts will slip if I try to spin it from the alternator.

If this is "too tight" what steps should I take to free it up?
Thanks!
CF

 

[Scott Danforth]

first, do not try to turn your motor over by the crank bolt. you will snap the bolt off in the crank

second, if the plugs are in, you wont spin it by hand

pull the drive to make sure you are not fighting drive issue

is your starter a direct drive or PMGR?

what RPM are you getting when cranking?

 

[ChronoFish]

first, do not try to turn your motor over by the crank bolt. you will snap the bolt off in the crank

second, if the plugs are in, you wont spin it by hand

pull the drive to make sure you are not fighting drive issue

is your starter a direct drive or PMGR?

what RPM are you getting when cranking?

Well... In previous post with pics you suggested it was a direct drive (and I'm confident you are correct)

Initially I tried with plugs in, but this afternoon I took the plugs out, but no real change that I could discern.

This is about as good as it gets in terms of cranking speed. Sometimes the starter just stalls (clicks).

0 new items by Christopher Fowler

photos.app.goo.gl

 

[Scott Danforth]

This is about as good as it gets in terms of cranking speed. Sometimes the starter just stalls (clicks).

0 new items by Christopher Fowler

photos.app.goo.gl

start with cleaning all battery cable connections (both positive and ground). just clicking is bad connection 99.5% of the time

 

[ChronoFish]

start with cleaning all battery cable connections (both positive and ground). just clicking is bad connection 99.5% of the time

Thanks - I can't get over how good this advice is. I cranked the battery connections down earlier today and was surprised by the change. I had no idea how profound the difference would be.

Thanks
CF

 

[GA_Boater]

Thanks - I can't get over how good this advice is. I cranked the battery connections down earlier today and was surprised by the change. I had no idea how profound the difference would be.

Thanks
CF

Don't just crank 'em down - Clean the posts and battery terminals or the fix may be temporary.

 

[Scott Danforth]

you need to clean them. grab some 150 grit sand paper and make them shiny clean. as in clean enough your mother or mother-in-law would eat off them.

then you tighten them down

then you seal them with marine electrical varnish.

https://www.grainger.com/product/1D275?gclid=CjwKCAjww5r8BRB6EiwArcckC3UdMpmAGROV2kEqPztPv5eO2CMC4oEhEjmCjx8W02_2PMJxvfPfVxoCkWMQAvD_BwE&cm_mmc=PPC:+Google+PLA&ef_id=CjwKCAjww5r8BRB6EiwArcckC3UdMpmAGROV2kEqPztPv5eO2CMC4oEhEjmCjx8W02_2PMJxvfPfVxoCkWMQAvD_BwE:G:s&s_kwcid=AL!2966!3!281698275750!!!g!470563673014!&gucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231

 

[Rick Stephens]

Might also do a compression check next time you have plugs out. Love to know what the base condition of the motor is before making a comment on what's next.

 

[Scott06]

You should be able to turn a 3.0 easily by hand with the plugs out

pull the drive try to turn again this will separate any issues with drive or gimbal bearing that is keeping engine from turning easily

if with drive And plugs removed you still can’t turn it easily and smoothly Pull the engine and tear it down

 

[ChronoFish]

you need to clean them. grab some 150 grit sand paper and make them shiny clean. as in clean enough your mother or mother-in-law would eat off them.

then you tighten them down

then you seal them with marine electrical varnish.

https://www.grainger.com/product/1D...ucid=N:N:pS:paid:GGL:CSM-2295:4P7A1P:20501231

The battery is practically brand new. It has a born-on date of 1/2020 and was purchased this past July and has only been used a half dozen times (if that) on the water with a different boat. There is zero corrosion on it.

With regards to sealing it up, is there any point in doing that while I'm experimenting and fixing the motor up? This boat won't see water till next spring.

 

[ChronoFish]

Might also do a compression check next time you have plugs out. Love to know what the base condition of the motor is before making a comment on what's next.

I was kicking myself for not doing a compression test while I was pulling the spark plugs.... Hopefully I can get that done tomorrow (weather/time permitting).

Thanks!