engine timing....

[byordy]

I've just refurbished my '78 175 Evinrude and am getting it ready for it's maiden voyage. I want to check the timing at full throttle to insure that it's not advanced to far. I seem to recall reading somewhere that this could be done by removing the plugs, grounding the spark plug leads, fully advancing the throttle and then cranking the engine with the starter while observing the timing with the strobe.<br />This seems to make sense. Does any one have any comments/experience with this method?<br />Bill........

 

[kev_79]

Re: engine timing....

I have done this with my 115 merc, and it worked fine. I don't know about grounding the plug wires though. You need to pull the plugs, put it in gear. If you have a neutral safety switch, you will have to jump across the solenoid to get it to crank. Make sure you have a good hot battery. Make sure the advance is full pushed, and crank, and check with strobe.<br /><br />This worked perfectly for me, but I would check again on water to be sure. My wrench recommends 1 degree retarded because something about today's fuels. I do it, because I can't tell the differece in performance, and it is more dangerous to be too advanced. <br /><br />BTW, you don't have to be @ WOT to check WOT advance. Just enough throttle to bottom out your timing arm. Good luck, let us know how it goes.

 

[Dhadley]

Re: engine timing....

That's an OK way to do it but like kev says make sure you double check it under a load in the water. On your particular OMC motor if you set it like that it will advance as much as 4 degrees under load. When you check it try to get as close to wot as possible. The mechanical advance will hit the stop at just under 4000 rpm but it will actually gain another 1 degree per 1000 rpm.<br /><br />Good luck!

 

[byordy]

Re: engine timing....

Thanks for the replys.<br />Can you explain how the timing advances under load? Is there some form of rpm sensitive advance device as on a car?<br />Also you mentioned 1 degree retarded. This seems like a good idea. Would it make sensed to retard it further on my old motor? There supposedly was a change in the headgaskets, (making them thicker) to lower the compression, but retarding the timing still seems like the thing to do. <br />Bill.......

 

[grandx]

Re: engine timing....

Timing? You get the most accurate timing with the boat under load on the water. How much more accurate? I'm not sure. My two strokes were timed (Cranking method) by the dealer, and purposely retarded 1 deg, because he knows this is not what it will be on the water. I plan to check the timing on the water one day soon to see how far off it is under load, and then I will advance it to the manufacturers spec, exactly. Make sure your timing pointer is accurate and be careful on the water if you do this. Retarded timing creates more heat and less mechanical energy...less power...less fuel economy... I won't advance mine above specs, but I would like it as advanced as I can get it and stay in spec, if there were need for any more safety the engine folks would put it in writing, follow the procedures carefully.

 

[Rex]

Re: engine timing....

THIS WORKS JUST MAKE SURE THE PLUG ARE<br />ON THE BLOCK OR YOU MIGHT BURN SOMETHING

 

[Dhadley]

Re: engine timing....

The additional advance has to do with what they call "rise time" in the electronic components. No matter how you set the timing initally make sure you check it under a load. <br /><br />Good luck!

 

[byordy]

Re: engine timing....

Well Dhadley, that makes sense. I'm familiar with rise time, (I've made my living in electronics for the last 40 years) and it's logical. As the flywheel spins faster, the trigger voltage becomes greater and the SCR's triggering point is reached sooner. The question would be at what rpm do the trigger coils/scr input conditioning circuitry saturate and the voltage, hence the triggering point (timing), no longer increase significantly. <br />I think I'll time it in the cranking mode a degree or so retarded, and then check it while running full tilt to see how much additional advance occurs. I need to run it a few hours at reduced throttle settings to break it in before any full throttle operation. The idea of standing in the back of the boat hold a timing light over the uncowled motor while running 40 mph plus does NOT appeal to me. <br />grandx, as far as retarding the timing, I concur. Excessive retard is just as bad as excessive advance. Excessive retard will take longer to do damage but it can eventually cause an engine to destroy itself. A few degrees of retard should be benificial, however, to my old motor which was designed to run on late 1970's fuels.<br />I'm still trying to decide what grade of fuel to use, 87 or 89. I've not see a clear consensus of which is best on this board. I'm concerned that the compression ratio on my oldie but goodie is to high for today's 87 octane fuels. <br />The whole issue evolves into two questions; what grade of fuel and what max advance timing spec to use. I'm still not certain.<br />Thanks for all the input and I'm still soliciting comments.<br />Bill.........

 

[clanton]

Re: engine timing....

Service bulletin 2159, Rev. 1 dated Oct. 1986 recommended timimig to spec for 91 grade fuel, or retard timing 4 degrees from spec for 88 grade fuel.

 

[kev_79]

Re: engine timing....

FYI: when you were wondering about the rpm that rise time reaches an equilibrium, my merc service manual says to set timing no lower than 3K rpm. I would guess that that would be around the speed, and I have tested mine at about 3k and about 5k. <br />Also, I looked at my manual last night, and when I am setting at cranking speed, I have to set it at 25 degrees, and when it is running under load, it goes automatically back to 23 degrees, but I don't know how. I'm not sure that any other motor does this but the 2+2. Might ask an omc wrench what rpms you have to run so it doen't blow your hat off when you're checkin the timing

 

[byordy]

Re: engine timing....

Thanks,<br />That information helps a lot. <br />clanton, does the service bulletin say anything about thicker headgaskets allowing a return to original timing with 87 octane fuel? Somewhere I've heard somthing about that but I can't remember where.<br />In any event I'm probably better off retarding the timing 4 degrees and not worrying about it.<br />kev_79 thanks. The idea of leaning over the open flywheel holding a timing light in one hand while running flat out scares me. I'll experiment and see where timing advance stops, and use that rpm in the water.<br />It's gonna be a while before I get it in the water. I started cleaning up the trailer and found more rust that I anticipated. I think I'll use some Ospho on it and I probably need to splint one small section of the frame. It looks like the galvanizing was compromised and the trailer was allowed to just sit there and rust. Oh well, I bought it as a project boat and it's living up to that!<br />Bill.......

 

[clanton]

Re: engine timing....

If you use 91 octane fuel timing does not have to be retarded. Service bulletin 2155 dated Oct 1986 for head gaskets, with this gasket supposed to be able to run 86 octane fuel. Pn for your gasket is 397826. You should verify number with dealer. When these gaskets installed you may loose a few rpm and have to reprop.

 

[byordy]

Re: engine timing....

Thanks clanton, that's the info I was looking for.<br />Bill.......