need help bringing old 1982 merc 40hp 2 stoke back to life

[gps4]

Im trying to bring an old motor back to life.

before I drop alot of time and $ replacing fuel lines and water pump, themostat and the like, i want to make sure i'm not wasting my time on account of a seized or shot cylinder head.

when I take the spark plugs out, i can easily turn the flywheel by hand with little resistance.

when I hook up a battery and turn the motor over, the starter motor spins the flywheel quickly and i can hear the pistons cycling in the head.

when I put the spark plugs back in and try to turn the flywheel, it is considerably harder to turn by hand. when I try to turn it over using the starter motor, the pinion gear on the starter will not turn the flywheel. what usually causes this?

Thanks,

gps4

 

[airshot]

Supposed to be harder to turn with the plugs in....check the battery, 12.6 volts is a full charge, 12 volts is a very low battery. Is the starter bad ? Have it checked, if you can turn it by hand, the starter should be able to turn it easily. Sounds like a starter or battery issue at this time.

 

[lckstckn2smknbrls]

Corroded battery cables and connectors.

 

[LaqueRatt]

Can't really judge the condition of your battery without a load tester. IMO anybody who messes with engines and batteries should have one laying around. You can score a cheapy at Harbor Freight for around twenty bucks. I paid just a little more for my Schumacher.

Or just put in a diff battery that you know is good. If not bad connections, it's pretty likely the battery just isn't up to the task. Keep in mind that a trolling battery may well crank your boat, but that's not what they're designed for.

 

[SAABologist]

Im trying to bring an old motor back to life.

before I drop alot of time and $ replacing fuel lines and water pump, themostat and the like, i want to make sure i'm not wasting my time on account of a seized or shot cylinder head.

when I take the spark plugs out, i can easily turn the flywheel by hand with little resistance.

when I hook up a battery and turn the motor over, the starter motor spins the flywheel quickly and i can hear the pistons cycling in the head.

when I put the spark plugs back in and try to turn the flywheel, it is considerably harder to turn by hand. when I try to turn it over using the starter motor, the pinion gear on the starter will not turn the flywheel. what usually causes this?

Thanks,

gps4

I have A 40 HP mariner, 2 cylinder. It's normal or it to be very easy to spin with the plugs out. i agree with the comments below that it must be the starter or battery or connections. If yours is 2 cylinder model, it should not be hard to start it by pulling the rope if it's properly tuned. good luck.

 

[thill]

You need it to turn over at a normal speed to properly check compression, which should be your #1 test.

Connect a known good battery or a jump box, if you have one, and see if it will turn over. Harder to turn with plugs in is normal and very desirable, as it indicates that you have some compression at least.

 

[martha lin]

Remember, a qualified mechanic can provide a proper diagnosis and repair recommendations based on their comprehensive evaluation of the engine.

 

[mirrocraft16]

I have two Mercury 40hp motors, one is from 1981, the other from 1971, both have recoil and electric start and both will start on the recoil but it takes a strong grip to hold onto the rope. They pull start easier than my 35hp Johnson but they still have a fair amount of compression to overcome.

 

[airshot]

I have two Mercury 40hp motors, one is from 1981, the other from 1971, both have recoil and electric start and both will start on the recoil but it takes a strong grip to hold onto the rope. They pull start easier than my 35hp Johnson but they still have a fair amount of compression to overcome.

Some years back, in my younger days, I had a 3 cylinder 70 hp Jonnyrude. Great motor, and it had an emergency cord to pull start if needed...well ...one day I thought, what if ?? Could I do it, if I needed to. Especially if the motor was cold where a couple extra pulls might be needed. After that experiment is when I decided to add a kicker motor on my boat, for that just in case day that might come along. Have had a small kicker motor on every boat since then !!

 

[thill]

GPS4,
Did you ever do anything with the motor?