Found something suprising in my 850 merc? timing question

[matt88]

I have been tinkering with this motor for a month or two now and finally could afford to buy a timing light with a built in tach for it today. I have rebuilt the carbs on this motor replaced the water pump and have gotten it running pretty decent compared to the non running condition I bought it in. Or so I thought anyways. When I put the timing light on the motor I was surprised to find that it is running 180 degrees out of time?? The reason that comes to me as a surprise is because I have had this boat out several times with minimal problems. The power seems ok except for some prop issues that I have been trying to address. I may be wrong but I was under the assumption that the motor would not run when out of time like this unless there were maybe some other ignition components wired backwards as well. So that is my main question here? If I take this thing apart and correct the timing will I have a motor that wont run due to wiring issues? I know it needs to be fixed right and believe me I will fix it right but if the engine is actually in time but not the way the factory intended I will leave it until late fall.

motor is a 1973 85hp 4 cylinder two stroke mercury

 

[CharlieB]

Re: Found something suprising in my 850 merc? timing question

What cyl did you have the light connected to?

#1 should be the top cyl, where on the motor are you seeing the timing mark?

 

[Moody Blue]

Re: Found something suprising in my 850 merc? timing question

When I put the timing light on the motor I was surprised to find that it is running 180 degrees out of time??

What makes you think its 180 out of time?

 

[matt88]

Re: Found something suprising in my 850 merc? timing question

The top cylinder showed 180 degrees out of time. The #2 cylinder was on the money. Im thinking I must have a sheared or lost flywheel key but its surprising the motor still runs good regardless. I read somewhere that this motor has two ignition pulses per revolution.Could that be why I am getting away with it?

I identified the timing mark as the three small dimples on the side of the flywheel and the white dot painted on the top. Is this correct?

 

[matt88]

Re: Found something suprising in my 850 merc? timing question

What makes you think its 180 out of time?

When I checked the timing with a timing light the timing marks were 180 degrees off. Also, when I take the plug out of the top cylinder and rotate the flywheel to the TDC mark the piston is at the bottom of the cylinder. When I rotate it 180 degrees it is at TDC. Did you miss the part when I said, "When I put the timing light on the motor" ??? LOL!

 

[chum1]

Re: Found something suprising in my 850 merc? timing question

could be as simple as the flywheel installed 180 out,

on tdc on #1 piston the timing pointer should be real close to the sticker tdc marking

 

[matt88]

Re: Found something suprising in my 850 merc? timing question

I can tell that the flywheel has been off before because the bolts look a little rounded off. Is it possible with this motor that the flywheel could be 180 off with the key pin in? I just want the engine to run right. If it is right now I will leave it but if there is possibly more power to be had then that will defintely be what Im after.

 

[chum1]

Re: Found something suprising in my 850 merc? timing question

On mine there are 8 bolts that hold just the flywheel on.

Just pull those 8 bolts remove flywheel, inspect the wires and then put it on correctly.

That way you can check your timing with the starter and make sure that isnt screwed up too.

The center piece with the big nut is a separate part and just stays on. there are no keys on the center piece it is splined in a way that it will only fit one way

 

[emckelvy]

Re: Found something suprising in my 850 merc? timing question

I can tell that the flywheel has been off before because the bolts look a little rounded off.

It Most Definitely is not only possible, but the only explanation, since there is no flywheel key to shear. The flywheel and crankshaft are splined, with a flat spot machined into both. So the flywheel center can only go onto the crankshaft but one way.

Best thing to do is put #1 piston at TDC, unbolt the flywheel from the center hub, rotate until the marks on the flywheel are properly aligned, then reassemble. Use a drop of Loctite Red on each flywheel bolt and torque to 24 ft-lbs.

Recommend you do the Link & Synch procedure to make sure you're dialed-in:

http://forums.iboats.com/showthread.php?t=168855

HTH.........ed

 

[matt88]

Re: Found something suprising in my 850 merc? timing question

I didnt realize this engine was made that way. All the other outboards I have had were the shear pin type so I assumed this one was made the same way. I really appreciate it guys.

 

[Gomer50]

Re: Found something suprising in my 850 merc? timing question

This is what was explained to me I have a 1972 Merc 800 same timing as yours.I had taken my flywheel off awhile back to do some checking and didnt pay attention on how it was before I had taken it off.So I found TDC on number 1 cylinder and used the the 3 punch dots as my TDC mark in reference to my top cowl timing decal.I then rotated the flywheel counter clockwise so that my crakshaft the 3 dots and the center off my distributor shaft were lined up and then rotated my distributor pully so that the arrow on the pully is lined up directly at the 3 dots on the flywheel put the belt back on.And your good to go.This is also the way it is explained in my manual.Also take a look at your flywheel 180 degree's out might be another set of three dots (mine does).From my understanding it really doesnt matter where the flywheel is (as long as you can find TDC and make you own marks)all that the flywheel does is keep your battery charged.Here is an equation to find out exactly how many degree's in case you would want to mark your flywheel starting with TDC.

25.4 mm = 1 inch
208 mm flywheel cir.
208 x 3.142 divided by 360 = 1.81mm per degree.
21 x 1.81 = 38.12mm

1.5 inches or 38.12mm equals 21 degree's BTDC
6 degree's BTDC = 0.42 inches

25.729 inches flywheel Circum.

 

[j_martin]

Re: Found something suprising in my 850 merc? timing question

(deleted)

 

[Gomer50]

Re: Found something suprising in my 850 merc? timing question

Whats that (deleted) ??

 

[matt88]

Re: Found something suprising in my 850 merc? timing question

That makes sense to me. Better to make more timing marks versus ripping the flywheel off etc,etc... Now I have another question. The first timing light I bought quit working after its initial use. I assumed it was bad as a lot of things you buy from autozone. I was checking the new light this morning and although it is working. The last time I cranked the motor before taking it off a spark arced off of the red alligator clip connected to the timing light and lost connection. The light is an actron digital unit with a built in tach. Should I run it off of an external battery to keep from getting damaged?

 

[Chris1956]

Re: Found something suprising in my 850 merc? timing question

Matt, The inner flywheel fits only one way on the crankshaft. As Ed succinctly stated, set the top cylinder to top dead center, remove the 8 5/16" red bolts, and rotate the outer flywheel until the timing mark or timing pointer indicate TDC. Put some locktite on the 8 bolts and reinstall.

Just to be clear, all cylinders in a Two cycle motor will fire every revolution, vs 4 cycle motors which require two revolutions to fire all cylinders.

Your timing light should work OK on that motor. The Tach may not read correctly if it does not have a 2 cycle motor setting. You might try the 8 cylinder 4 cycle setting for correct RPM.

 

[j_martin]

Re: Found something suprising in my 850 merc? timing question

Whats that (deleted) ??

Every once in awhile I find myself breaking a little wind. In this case I discovered it and deleted it.

 

[matt88]

Re: Found something suprising in my 850 merc? timing question

The timing light does have a setting for 2 and 4 cycle motors. The hookup instructions for the light state that an external 12 volt power source must be used on 6 volt systems. I know the merc does have a 12 volt system but with the lack of a voltage regulator I think that may have caused damage to my first light to cause it to stop working. Has anyone else ever had this problem or was my first timing light a dud right out of the box??? I have also read that some people add an extra battery to run stereos,lights,etc..for the same reason. The high voltage coming from the merc charging system can damage sensitive components. Or so I have heard or read?

 

[chum1]

Re: Found something suprising in my 850 merc? timing question

Just go back to autozone and tell them the chinese dilithium crystals gave out and get a standard timing light and a tiny tach

http://www.apelectric.com/ProductDetails.asp?ProductCode=TT2B&gdftrk=gdfV21065_a_7c276

for probably cheaper then what you paid

the minimum wage employees probably don't care one way or the other anyway

 

[matt88]

Re: Found something suprising in my 850 merc? timing question

Tested the light on my truck tonight and it worked fine. It did however act the same way it did on the merc when I unhooked the ground wire first so Im thinking I might have a bad ground wire on the outboard.

 

[Bradmph]

Re: Found something suprising in my 850 merc? timing question

I sure hope your truck was not off 180 degrees also, that would be terrible.