Mercury 402: Can only turn flywheel with spark plugs out

eldplanko · #1 April 24th, 2009, 12:35 AM

I have a 1975 Mercury 402 SN: 42777XX. It's been in storage 2 years. The flywheel will only turn (either by the pull-start or by the startor motor) with the spark plugs out. Any ideas on what is wrong?

saumon · #2 April 24th, 2009, 03:36 AM

Quote:

Originally Posted by eldplanko

Any ideas on what is wrong?

Nothing! It tell you that your engine isn't seized and, most important, have good compression.

Read this:

http://forums.iboats.com/showthread.php?t=158086

eldplanko · #3 April 24th, 2009, 11:24 AM

Thanks for your quick reply and helpful link.

The part I still don't understand, is why can I not rotate the flywheel (by pulling on the pull handle) with the spark plugs in.

Chris1956 · #4 April 24th, 2009, 12:03 PM

Ed, Is it possible that the tips of the spark plugs are hitting the top of the piston?

You should verify that the plugs are the correct ones. A lot of mercs used the 1/2" reach, gapless plugs(like Champ L-76V) in the older motors. If someone put in some 3/4" reach, gap plugs you might have clearance issues.

eldplanko · #5 April 24th, 2009, 10:59 PM

Thanks for the great adive. I'm using NGK BUHW spark plugs. I've used these ever since I got the engine, with no problem.

I have to admit that I'm unfamiliar with the internals of this engine. Are there valves? Could an exhaust valve be stuck closed?

saumon · #6 April 24th, 2009, 11:48 PM

No valves.

This_lil_fishy · #7 April 25th, 2009, 12:21 AM

Eat yer wheaties lad....

Like a snowmobile, good compression means lotsa armstrong starting. The sparkplug thing was a good thought, but if it turns over fine without plugs it should be fine.

Ian

eldplanko · #8 April 25th, 2009, 12:24 AM

I'm convinced it's an airflow issue. I can put my finger on the spark plug holes and feel a vacuum as I turn the flywheel.

Does this means it's an intake problem? I'll look at the carb...

saumon · #9 April 25th, 2009, 01:29 AM

If you can't turn it, it looks to me that it's stuck in gears. Maybe the shifter has slipped out of neutral. Can the prop be rotated freely in either directions?

BTW, vacuum on the down stroke is normal.

eldplanko · #10 April 25th, 2009, 02:27 AM

Thanks for the great ideas, I appreciate all the help.

It's definitley not in gear. I know the lower unit on this, as I previously did a total teardown and rebuild on it.

Would the intake or the exhaust being plugged cause this?

CharlieB · #11 April 25th, 2009, 10:03 AM

Pull starter does NOT work with the plug IN?

But the pull starter does work with the plugs out?

I've seen many poor connections/starters/batterys have this problem but NEVER with a pull starter. Well, there was one just yesterday that I had to use BOTH hands, (I'm getting weak, I think).

If the pull starter works without the plugs, you (and I) maybe need to start working our arms a bit more to get in shape for fishing season.

saumon · #12 April 25th, 2009, 11:25 AM

Did you try the elct. starter with a fully charged battery?

eldplanko · #13 April 25th, 2009, 11:55 AM

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.

BR · #14 April 25th, 2009, 07:47 PM

Your original post stated that motor was stored for two years. Was it fogged before storage? Maybe try spraying some sea foam or 2 cycle oil in plug holes. Cylinder walls may be completely dry or worse...rusted.

Scoots · #15 April 25th, 2009, 08:47 PM

Hi,

I don't mean to "piggyback " on your issue, but, I am having a similar(apparently compression) problem with a 1970 20hp. The motor turns over nice and easy out of water and wants to start but doesn't. If I put it in water it is next to impossible to pull. There was some debris thatg shot out of the exhaust ports under the powerhead and I could kind of see where some mud wasps had been in these same ports. Could this be the problem perhaps for both of us??

eldplanko · #16 April 25th, 2009, 09:43 PM

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.

daveswaves · #17 April 25th, 2009, 10:10 PM

You said you overhauled the lower end. Did this problem start after that? The lower end is not that hard to take off, I would suggest that you drop the lower end and then see if the powerhead is free to turn over. Something is "bound up" and it is not a blocked exhaust or intake, you still have difficulty turning it over with the plugs removed, according to one of your posts. That leads me to believe the lower end may be the issue.

eldplanko · #18 April 26th, 2009, 01:40 AM

Lower unit was 4 years ago. Worked fine for 2 years after that.

Thanks for the good advice though.

daveswaves · #19 April 26th, 2009, 08:05 PM

Quote:

Originally Posted by eldplanko

Lower unit was 4 years ago. Worked fine for 2 years after that.

Thanks for the good advice though.

Yes but then it sat for 2 years. If nothing else you should be changing the water pump impeller anyway, every 2 years is the norm. So, as long as you have the lower end off to change the water pump impeller you can check to see if it is any easier to turn the power head over. If not, you have work to do inside the power head.

eldplanko · #20 April 27th, 2009, 12:25 AM

Thanks for the great advice. I was thinking the same thing, but didn't want to waste the time on the lower untill the upper was working.

BTW, not sure I ever said it was difficult to turn with the plugs removed. It turns quite freely with the plugs removed.

daveswaves · #21 April 27th, 2009, 08:52 AM

Quote:

Originally Posted by eldplanko

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 · #22 May 31st, 2009, 06:13 PM

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 · #23 June 1st, 2009, 08:40 AM

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 · #24 June 1st, 2009, 09:07 AM

Quote:

Originally Posted by eldplanko

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 · #25 June 7th, 2009, 11:05 PM

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.