Merc 800 Timing

[gakpuss]

Hi to all. I have a 1969 80 HP Merc with Thunderbolt ignition purchased last fall on Ebay. It is my first motor. I purchased a service manual from Grubb's and am having a hell or a time getting the thing tuned up. I did the basic timing of aligning the mark on the flywheel with the arrow on the distributor and am now taking the next step of adjusting the spark advance and that is where the trouble begins. By the way I did remove the flywheel to repair the coil wires. I could not pull the flywheel so I unbolted it from its mounting flange. I probed number 1 cylinder to find TDC and reinstalled the flywheel. No matter which way I move the vertical lever I can't get the timing marks to align. Is TDC the high point of the stroke? Does advancing the spark mean to move it BTDC or ATDC? Any thoughts on getting this thing timed? If a little knowledge is dangerous then I am deadly. FYI this site bailed me out when I put the lower unit back on and was stuck in gear. Thanks.

 

[jwilkey84]

Re: Merc 800 Timing

why couldn't you get the flywheel off? I just took one off yesterday, it took about three hours of grief, but I got it off. Is it stuck on? First of all, can you get the 15/16 nut off of the top? If so, use a puller to get the flywheel off. I had problems here too, I was afaraid of breaking something. Just keep cranking on the puller till you cant pull any more and then hit the middle bolt on the puller with a hammer and keep cranking with a wrench. I may take an unbelievable amount of power, but that flywheel will come off. Are you sure the timing marks are lined up? If the motor was running prior to you owning it, the rest of the settings should be good still, all you should have to do is line up the lines. At least that worked for me, but I am by all means an rookie.

 

[Chris1956]

Re: Merc 800 Timing

Gack, You should be able to line up the flywheel flange. It sounds like you are on track. Set the top cylinder to top dead center, and make sure the three punch marks align with the cast arrow on the distributor. Now measure the distance from the spark plug hole to the top of the piston. Add .464 inches to that measurement, and turn the flywheel backwards 1/4 turn and then forward to you reach the .464 point. Your timing mark on the cowling or timing pointer should read .464 on the flywheel decal.

 

[gakpuss]

Re: Merc 800 Timing

Thanks for the response. I did all those fancy tricks with the flywheel and a few more and all I did was shear off the bolts holding the puller down and mangle the puller.
I did the timing thing by the book as far as aligning the mark on the flywheel and the arrow on the distrubutor pulley. When I crank the engine and put a timing light on the the best I can do when I manipulate the vertical arm is get the timing within about 4-6 degrees of the mark. At that point the stop on the distributor is no where near the stop adjustment screw. Am I hung up on something that isn't that improtant?

 

[Sig_Mech]

Re: Merc 800 Timing

Gak, when you unbolted the flywheel from the center hub did you make absolutely sure to bolt it back in the exact same position? The center hub is what turns the timing belt for the distributor and the hub is what keys to the main shaft to insure proper timing. If you put the flywheel back on the hub and you are off by one bolt hole (from those 8 center bolts), your timing will be off and it will be impossible to set it.

 

[gakpuss]

Re: Merc 800 Timing

Sig, Thanks for your response. I must admit that when I first pulled it off I realized what I had not marked the hub or the flywheel. I read the paint and rust marks and am pretty sure it went back on in the correct orientation. I double checked it by bringing number 1 up to TDC and then made sure the flywheel aligned with the TDC mark on the cowl. As I understand things, everytime the flywheel makes a revolution the number 1 fires once without an exhaust stroke. What am I missing? Before I started messing with the timing I had it running. It would not idle below 1000. My dad thought it was running rough but not missing or backfiring.