checking timing on 1970 25 hp

[BF]

Hiya,<br /><br />I put all new parts under the flywheel yesterday... set points to .020, (at least, as best I could tell) and got it all reassembled and running... It doesn't idle as smooth as I think it should (I also did carb kit at same time) and I did optimize the low speed jetting, as well as I could. So I don't think it's a carb thing.<br /><br />Now I'm second guessing whether I got the timing right. From a search of the archives, I saw that at least for some motors, timing can be checked with a timing light (mark on flywheel, mark on stator plate). Anyone know if my motor would be marked like this? Is there a 2nd set of marks for the 2nd cylinder? The service manual doesn't talk about this, but shows how timing can be set using a sort of rod across the crank with an indicator at the end and either a light bulb or a meter thing. (with the flywheel off)<br /><br />It'd be nice to check timing without taking it all apart! I may have to anyway, because I snugged up the stator plate a bit using Joe Reeves method (it was quite loose and wiggly before) but I may have over done it... the stator plate turns, but is on the stiff side. I thought it was border-line, and was hoping that it would loosen up a bit once it was moved through it's range a few times, but so far still stiff. <br /><br />Thanks for your thoughts!<br /><br />Brent

 

[Chinewalker]

Re: checking timing on 1970 25 hp

Hi Brent,<br /> As long as you've got the points gapped at .020" with the fiber cam rider aligned with the crankshaft keyway, the timing is self-setting on those motors. That's also provided that the linkages and cam followers are present and not overly worn. The only adjustment possible in the whole throttle linkage area is the cam under the armature plate that actuates the cam follower on the carb has to hit the follower at the mark scribed on the cam when advancing the throttle.<br /><br />- Scott

 

[BF]

Re: checking timing on 1970 25 hp

Hi Scott,<br /><br />Yes, I know what you mean, but I'm worried if I didn't set the gap right, the timing would be off, or if I messed up on one set of points, that cylinder would be firing early or late, and it would run on the rough side. If I could check timing and see it's good, then I'd have peace of mind. Otherwise, I'll feel obliged to pop the flywheel off (again)... I'm not a big fan of the feeler gauge thing... seems like it would be easy to be off by a fair amount (at least in my hands). <br /><br />The follower stuff, and the linkage to the carb is OK. That seemed pretty straight forward.<br /><br />Thanks...<br /><br />Brent

 

[Chinewalker]

Re: checking timing on 1970 25 hp

Hi Brent,<br /> In an ideal world, you'd have a depth gauge, buzz box, and set the points at exactly 180-degrees apart. It takes a lot of doing and isn't all that necessary for decent operation with most motors. However, if you do do it, it makes for a sweet running motor. Set one side as per the .020 gap on the high part of the points. Then find where the points break using the timing light and depth gauge screwed into the cylinder head. Set the other set of points to break at the exact same distance BTDC (before top dead center), as the first set does... That's a simplified version, but I think you get the idea....<br /> Good luck!<br />- Scott

 

[Paul Moir]

Re: checking timing on 1970 25 hp

BF - I don't know if your 25hp has them, but have a look. The two marks on the side of the armature plate seem to me to be always on the right-forward side of the engine (right of the carburetor, looking at the carburetor). They're two vertical lines about 3/16" apart - you can't miss them.<br />There always seems to be some sort of mark on the flywheel right above them. Sometimes it takes hitting it with the timing light for me to find them though. Then I colour them with a marker to make them more visible.<br />There's a special tool that can be used for setting the points. It's essentially the same as the flywheel with it's pointers, but it's just a bar so you can get at the points and adjust them. Rather than using a timing strobe, you use a continuity tester.<br />You can pull the same test with a regular flywheel if it's got the marks, but you'll have to disconnect the ignition coils from the points, and run a wire up to them so you can test the point's continuity with the flywheel in place. I've tried doing this without disconnecting the coils and looking for the slight change in resistance with a digital meter(>1 ohm change), but the voltage induced on the ignition coil screws up the meter and makes it near impossible to set right.<br /><br />Hope this helps!

 

[BF]

Re: checking timing on 1970 25 hp

well, I had it running again tonight... it does have timing marks for both top and bottom cylinders. The good news is that I did a consistent job of setting the point gaps... the plugs are firing exactly 180 degrees out of phase... the bad news is that it seems I gapped both sets of points a bit on the narrow side. Both timing marks end up about 1/2" off (to the left) of where they should be... guestimating by the circumference, I come up with the timing being off by something like 7 degrees.<br /><br />So how much difference do you think being off by that much will make? It did run a lot better today.. I think from just having been run for a while, probably first time in a few years.<br /><br />This is a new-to-me motor so I don't know how smooth it should really be at idle, but my gut tells me to just pull the flywheel and do a better job of it next time. Maybe I'll wait until after I actually run it on a boat this weekend. Now that I know my flywheel has the markings, maybe I'll make up a timing tool from some flat stock so that I can set them more precisely (?). <br /><br />Anybody know how many degrees the indicator on the timing tool should be offset from the key on the crankshaft? (I can tell it'd be offset from the picture in the manual). Otherwise I'll have to wait until I pull my flywheel and measure it.<br /><br />thanks ag'in.<br /><br />Brent

 

[BF]

Re: checking timing on 1970 25 hp

OK, so I re-did my shoddy workmanship tonight. Being a relative rookie at this points/condenser/coil thing, I see how I made a couple of rookie mistakes. Things that weren't in the OMC manual, probably 'cause they just expect to you know them. <br /><br />1) there is a little adjustment screw for making fine adjustments of the points. The first time I was just moving the points by pushing the edge of the plate with a 2nd screwdriver. It's mucho easier to be precise if you properly use the adjusting screw.<br /><br />2) I paid less attention to the gap, more to the timing based on using a timing light. I had the plugs out, and the timing light on the appropriate plug, adjusted the points to be close, and then plopped the flywheel on and spun it by hand... I could tell where the timing mark was, and then fine tuned the points until the mark landed right where I wanted it.<br /><br />3) even though I thought I was careful, I could see where one coil wire was rubbing the flywheel. Those wires have to be really bent down, and also away from the center of the flywheel. Lucky I took it apart, or it would've worn the wire and been trouble.<br /><br />It runs MUCH smoother now (so yes being off 7-8 degrees off makes a big difference)... and now it idles right down. <br /><br />Looking forward to lake testing it on the weekend.<br /><br />thanks for the help.<br /><br />Brent