Mercury 402: Can only turn flywheel with spark plugs out

[daveswaves]

Re: Mercury 402: Can only turn flywheel with spark plugs out

With the plugs out, it will turn over, VERY difficultly with the pull start (and I'm not light in the arms). It is definitley more difficult than it should be, and no where near fast enough to fire up. With the electric starter (jumped via the boat battery wires to my truck's battery... truck running), it turns maybe once per second. I'm thinking poor electrical connections also (and will try jumping directly to the starter), except for the fact that it is so hard to pull with the pull starter.

Again, thanks all the advice, you guys are great.

This is where you mentioned that it was difficult to turn over with the plugs out as well.

 

[claytonshaw]

Re: Mercury 402: Can only turn flywheel with spark plugs out

I have the exact same problem!!! If i pull even just one plug it will turn over woth both the rip cord and the starter. It dosent matter what plug i pull it will turn freely and start. If i take out all plugs it spins freely and there dosent seem to be any problems with the cylinders. It is driving me up the wall. It wont even turn with my truck pushing the battery... I was going to replace the starter but then i remembered that the rip cord dosent work..Is there a pressure release valve?

 

[CharlieB]

Re: Mercury 402: Can only turn flywheel with spark plugs out

I'd almost be willing to bet that there is nothing wrong with your motor, except the starter is weak and needs cleaning, possibly a new armature.

Did you ever regularly pull-start this motor or did you always rely on the electric starter.

Some of those 40's hard great compression and are a real PITA to pull start.

 

[j_martin]

Re: Mercury 402: Can only turn flywheel with spark plugs out

Not flogged, butI don't think piston binding on the cylinder wall is the problem. I turns fine with the plugs out. I pulled the carb, and the intake sideof the engine was nice and shiny. I'm thinking exhaust side might be plugged.

Make up your mind. You said it pulls over very hard with the plugs out, now you say it turns fine.

With the plugs out, you should be able to turn it over very easily, especially fairly slowly. It should suck and puff through the spark plug holes. If it's binding, something is wrong, like a mouse nest in it, rusted cylinders, etc.

You should be able to peek in the cylinders through the spark plug holes. If that looks good, you may have rusted, siezed bearings.

It could be something under the flywheel, also. Magnets fell off and are binding or something like that.

hope it helps
John.

 

[eldplanko]

Re: Mercury 402: Can only turn flywheel with spark plugs out

Sorry for some confusion, above when I typed "with the plugs out" I meant "with the plugs in." That makes a big difference. I guess I just typed too fast.

I sprayed a bunch of PB blaster in the spark plug holes, let it sit a few weeks, sprayed some more and now it seems fine. I guess something inside was binding up, but got worked free.

Thanks everyone for your suggestions and advice.