Timing for Tohatsu M2.5A

[spike7638]

I'm trying to resurrect (on the cheap, of course) an M2.5A from my father in law. It used to work OK, but then it went for a swim in some salt water (ughh!) and gradually stopped working. I've stripped it down to nothing and built it back up. I found that the condenser was shot, so opted for one of those "electronic ignition" modules you can throw into a lawnmower to replace the points/condenser, hoping it might do the trick. It didn't. Actually, it sort of did: the motor DID run for a few seconds with the module, but roughly. Anyhow, it gives me the confidence that I got the reed valves in properly, and the new rings on the cylinder, etc.

Anyhow, now I'm back to the points/condenser. I've gotten a replacement condenser (OK, it's not really the right part, because they're no longer available, but it's a comparable capacitance, and I'm hoping it'll do the job), but now I need to know how to set the timing.

Surely there's SOMEone out there old enough to have set the timing on an engine with points/condenser . And MAYBE that someone has a tohatsu 2-stroke shop manual and can let me know what the right setting might be (and how you adjust it on this motor).

Profound thanks in advance.

--John

 

[TOHATSU GURU]

Re: Timing for Tohatsu M2.5A

The timing is fixed and the point setting is....Set by measuring the arm with a spring balance and should be somewhere between 400 and 425 grams of pressure. And then you use a multi tester to check the insulation resistance.

Or, you can find a project with less difficulty

 

[spike7638]

Re: Timing for Tohatsu M2.5A

Thanks for your answer, but maybe it's just too zen-like for me.

When you say "The timing is fixed", do you mean "the location of the points sets the timing to a particular time"? There's actually a slotted screwhole in the points, I believe, allowing them to move back and forth a bit. If I move them farther from the cam, they'll open later and close earlier (and remain open for less long), won't they?

Perhaps your second statement "the point setting is....Set by measuring the arm with a spring balance and should be somewhere between 400 and 425 grams of pressure" somehow explains this, but I don't get it. The points seems to have a spring built in; I don't see any obvious way to adjust the spring pressure. I can certainly cobble up something to MEASURE the spring pressure, since I happen to have a quite accurate (like "tenths of a gram") scale on the workbench. Do I measure it when the points are at their most open? most closed?

Or are you implicitly saying "you screwed yourself when you unfastened the points from the plate, and it's pretty much hopeless for anyone without years of experience to get this working again"? If so, I can live with that, too (albeit with some disappointment).

--John

 

[spike7638]

Re: Timing for Tohatsu M2.5A

Just in case anyone cares, it turns out that the problem might NOT have been the ignition module...it was my stupidity in assembly: I didn't tighten the flywheel nut enough, and sometime in the first test-run, the woodruff key sheared off. That messed up the timing, of course. So...time to get a new woodruff key and start again.

Any hints on how to assemble the flywheel on the shaft? I've never really understood tapered fits. Should there be any lubricant between the flywheel and shaft on the taper? Or do we just trust that the fit will be so tight that no moisture will ever get in there and start it rusting, etc.?

Thanks in advance.

John

 

[pvanv]

Re: Timing for Tohatsu M2.5A

The flywheel must go on a completely DRY taper. No oil, grease, nor antiseize compound at all. The shaft, flywheel bore, and woodruff key need to be degreased thoroughly. Brake cleaner or acetone both work well. The fit is so close that it won't rust on. The taper causes it to squeeze like a press fit. In fact, on some older OB's it was a requirement to lap the taper with valve compound, like you would for a 4-stroke valve. You can use a tiny amount of antiseize on the threads of the nut.

 

[spike7638]

Re: Timing for Tohatsu M2.5A

The flywheel must go on a completely DRY taper. No oil, grease, nor antiseize compound at all. The shaft, flywheel bore, and woodruff key need to be degreased thoroughly. Brake cleaner or acetone both work well. The fit is so close that it won't rust on. The taper causes it to squeeze like a press fit. In fact, on some older OB's it was a requirement to lap the taper with valve compound, like you would for a 4-stroke valve. You can use a tiny amount of antiseize on the threads of the nut.

Wow!...thanks. I learn something new every day. Fortunately, in this case the lesson wasn't TOO expensive.

Best,

John