Timing: How do I read my flywheel, and other timing questions?

[Fishsqueezer]

I?m working on a Mariner 50 hp, 4 cylinder, 2 stroke, electric start, serial # 6542853


1. Here is a photo of my flywheel. Are the numbers left of zero ?degrees BTDC? and the numbers right of zero ?degrees ATDC??



2. The Mercury shop manual says to adjust timing in forward gear with engine running and to use a test tank or launch the boat. Is this for cooling or does the prop need submersion in water for resistance while working in forward gear? If only for cooling, can I complete timing adjustments on land while cooling with a muff (prop removed for safety)?

3. Adjusting the ?maximum spark advance? requires advancing the throttle in forward gear until the marks on the flywheel read 32 degrees BTDC. How much force will the prop be generating at this point? Can this be done while tied up at the dock, or will I need to be free since the engine will be under power in forward gear? OR, are the RPMs low enough when the 32 degree BTDC mark is reached that I won?t need to worry about how much thrust the engine is producing? Again, curious to know if this part of the adjustment can be done with a cooling muff while the boat is on the trailer.


Thanks in advance to all the great people who help me out with understanding this.

 

[ticondo46]

Re: Timing: How do I read my flywheel, and other timing questions?

At idle, definitely do it with the propeller in the water. With only the muffs on, you don't have the same back pressure on the exhaust, and it would give you a wrong reading.

Don't attempt a WOT adjustment of maximum spark advance with the boat in the water however! At the very least, you are going to get covered in splash, and at worst, you will be climbing over the dock!

I'm not particularly familiar with your exact type of motor, but I would say that if nobody disturbed the original factory settings, you should be OK for maximum spark advance once you've got the idle spark advance right.

Alternatively, you can do a max spark advance adjustment with the lower unit in the water, but the prop taken off. Just blip the gas toward WOT, have somebody hold the timing light to the marks and check it out. Don't keep the motor at high RPM's and no load for anything more than a second or so!

Good luck.

 

[Chris1956]

Re: Timing: How do I read my flywheel, and other timing questions?

Fish, The timing marks left of zero is BTDC. Remove all spark plugs except #1 and install these into their plug wires and ground them to the block. Now you can crank the motor to set the timing, and it will not start. You may set idle and max spark advance in this way in your driveway. Carb mixture adjustment needs to be done in the water, engine warm and in forward.

32* max advance is a lot. Since I do not know the year of that motor, it may or may not be right, or still recommended.

 

[Fishsqueezer]

Re: Timing: How do I read my flywheel, and other timing questions?

Thanks! That?s a good bit of info to help me out. I just scanned the 3 pages out of my shop manual which describe timing adjustments and specifications, in case they will aid any of you folks who are gracious enough to help me understand the material.



1. For my engine?s serial number, the ?primary pickup? timing should be set between 2* BTDC and 2*ATDC. Is this what I want to aim for when adjusting the timing at idle speed?

2. Max Spark Advance should be set to 30* BTDC, but should be adjusted at 32* BTDC in order to attain 30* according to the manual. Additionally, the chart specifies 33* BTDC when cranking with starter. I gather that if I do adjust Max Spark Advance in my driveway by cranking with the starter motor and plugs pulled and grounded, I want the flywheel pointer to read 33* BTDC. Do I understand the chart numbers on pg 1 correctly?

3. The timing light has a little dial on the back of it for spark advance. I suppose I should leave this at 0*? Would setting this dial on the timing light at 3* then mean that I would adjust Max Spark Advance so the pointer showed 30* on the flywheel? Sorry for being such a layman, but you folks are the best teachers!

4. I?ve been doing a whole bunch of work to this engine and figured a timing adjustment would be a good measure to ensure that everything is set correctly. I dismantled the throttle lever to lubricate it's friction points, but did not touch any of the stop screws, so theoretically the stop screws should still be on target, and these are what actually set the timing between the trigger assembly and the mechanical parts of the throttle lever, correct?

Thanks again for all your help! I can't thank you enough.

 

[Chris1956]

Re: Timing: How do I read my flywheel, and other timing questions?

With all spark plugs out (remove prop), except for #1, advance the throttle until the carb is just ready to open. Put timing light with zro advance set, crank motor and read timing. It should match primary pickup spec. adjust as specified.

Advance throttle fully and check that carbs are all the way open. Crank motor and read max advance. I would use 30* BTDC as the spec, because I do not know why the timing would change if the motor was running.

There should be set screws for minimum idle (Idle stop), max spark advance and max throttle. The actuator plate should rotate for adjusting primary pickup timing.

 

[Fishsqueezer]

Re: Timing: How do I read my flywheel, and other timing questions?

Thank you Chris.

I'm not sure why it would call for 33* BTDC when cranked by starter motor but call for 32* BTDC with engine running. I don't understand the real guts of an engine well enough to know why that would be specified by the Mercury service manual. I'm also in the dark on why 32* BTDC should be used to attain 30* BTDC. I think it's time for a new thread on that topic, and maybe someone will be able to say why the electronic timing characteristics of this ignition system require setting max advance at 32* BTDC to attain 30* BTDC.

 

[aussieflash]

Re: Timing: How do I read my flywheel, and other timing questions?

Your engine is a 1984 model.Spark advance characteristics is the same as my V6 1988.I didnt try to understand it....I just did as I was told...lol.
All my timing was done at cranking only...much easier.I couldnt imagine trying to adjust max while motor in water???Is that even possible.

 

[Chris1956]

Re: Timing: How do I read my flywheel, and other timing questions?

Aussie, I think his engine is much older than 1984. I think it is late 60s or early 70s.

 

[Fishsqueezer]

Re: Timing: How do I read my flywheel, and other timing questions?

Aussie, I think his engine is much older than 1984. I think it is late 60s or early 70s.

Actually, it was manufactured in either 1984 or 1985. I can't find a manufacture date stamped on the engine anywhere, but none of the retailers I've found sell anything for a 50 hp Mariner made in 1984. According to numerous sites which sell parts, 50 hp was not an option in 1984. The parts I buy from 1985 diagrams are all spot on. A search for manufacture date by serial number turned up info saying that it's an 84, but again, the parts list for 1984 don't cover any 50 hp engines. For this reason primarily, I believe it's an 85, but also because I bought the engine mounted on a 1985 Lund hull.