TDC?

[Brew]

I'm experiencing some problems with my '86 Evinrude 140 and want to eliminate timing as one possible cause. My question is, how do I confirm TDC? I tried putting a screwdriver in cylinder #1 and rotated flywheel by hand, but the cylinder seems to stay at its peak for an inch or so of travel on the flywheel. Am I just not being sensitive to a small movement in the piston? Should I take a midpoint within that inch as TDC?<br /><br />As always, any input is appreciated.<br /><br />Thanks,<br /><br />Brew

 

[Stassson]

Re: TDC?

I am far from haveing a clue but I would think that the moment you think it has toped out that should be it. So I mean that as soon as it hits top that should be it. I am a carpenter far from boat mech. but I think it makes sense to me . Good luck I will be checking to see what the other guys say so I know for future ref. Good luck

 

[Reel Appeal]

Re: TDC?

Thats how I would do it Brew.To get a very accurate measurement a dial indicator would come in handy.

 

[Joe Reeves]

Re: TDC?

Brew.... The proper way to find TDC is to have an object in the spark plug hole that would stop the piston before it reaches the top. You can use a wrong type spark plug with an abnormal inner length or make up some kind of tool.<br /><br />Now, with that tool (whatever) inserted so that it cannot move, turn the flywheel in one direction until it is stopped by the piston hitting that tool. Mark the flywheel at the timing pointer. Now, turn the flywheel in the opposite direction until it is stopped again, and mark the flywheel again at the timing pointer.<br /><br />The halfway distance between those two marks you just made on the flywheel would be TDC.

 

[Boatist]

Re: TDC?

Brew<br />This is a stupid way but has always worked for me. I take and old spark plug and break the center out of it. Make sure you get all the loose parts out so will not fall in cylinder. Now I take a balloon and streach over the metal part of the plug, put a rubber band around it to hold it and screw in in cylinder. Now turn the motor and when gets near TDC the balloon will blow up, at the fullest point is TDC. Works gread for 4 strokes as well as only blows up on the compression stroke not on the exhaust stroke.

 

[Brew]

Re: TDC?

Thanks for the responses guys.<br /><br />Boatist: What a unique solution! I never would have guessed that balloons could play a part in outboard repair!<br /><br />Joe: I must be missing some of the logic in the process you describe. I'm hoping you can straighten me out on this. If I stop the piston before it reaches the top of its travel, reverse directions so the piston travels back down and then up again, wouldn't the halfway mark between the two stop points be the very bottom of the stroke, not the top?<br /><br />Appreciate everyone's time and patience.<br /><br />Cheers,<br /><br />Brew

 

[Brew]

Re: TDC?

Never mind. Just as I hit "add reply" the answer became clear. It's the midpoint on the opposite side of the flywheel to the one I was thinking of. Duh!!<br /><br />Thanks again.<br /><br />Brew