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1989 50hp 3 Cylinder Timing

B

BAS

Member
Hello,

Thank you for reading my first post.
I have a 1989 50hp 3 Cylinder with a rebuilt powerhead with new crank and new fuel system from tank to pump. (original crankshaft driveshaft yoke corroded, compression is 125/126/124 so I opted to replace the crank being the cylinders were in good shape) The motor starts, runs and trolls up to appox 1500 rpm well but bogs down at half throttle, hence the new fuel system and rebuilt carbs.
After confirming that spark was present in all cylinders at the time of bog down, I brought it in to start the process of troubleshooting the ignition. (though there are no signs of backfire, spitting, bucking or typical tell tales of ignition issues)
First was to confirm spark at idle and all three cyl had good white hot spark. next I went to check the carb and ignition sync and this is where I was confused!
I brought the #1 (Top) piston to TDC and then to 0.459 BTDC on the dial indicator. I went to the pointer on the front of the motor and and it was pointing to appox 30 degrees BTDC:confused: Shouldn't the pointer be at or very near 0 degrees TDC?? This was well outside the range to adjust the pointer.

Did some research and confirmed the crankshaft model numbers. All is good Crankshaft is Part #8839a2 but after looking it is for a 1989 60hp 3 Cylinder, which uses the same part number crank and flywheel, but could the flywheel have different magnetic placement and marks? I really dont want to tear this motor down again as it is tight and clean and wants to run but right is right... If indeed the flywheel is the issue can I a change out the flywheel to the 60 hp (if different) and be ok with the rest of the ignition system.

Maybe I'm way off and missed something when bringing the TDC around, thought I did it several times to confirm the whacky reading.

Thanks for any help you can give.
 
Do the carbs open at exactly the same time? Have you adjusted engine sync or throttle pickup? You want the first line on the throttle cam to be center of the roller when the carbs just begin to open?
 
To check for true TDC you need a piston stop tool. Disconnect the battery and turn the motor clockwise to around 15 degrees after TDC. Then install the piston stop tool and screw it in until it touches the #1 piston. make a mark on the flywheel where the pointer is and then rotate the flywheel clockwise until the piston touches the stop tool and make another mark. TDC on the flywheel is half way between the two marks.
 
Sorry thought this was a evinrude motor you can use the dial indicator to find true TDC in a similar fashion just mark on the flywheel both before and after at .459 TDC and TDC should be half way between the two marks. Allways turn the flywheel clockwise with the gearbox installed!
 
HTML:
kimcrwbr1 said:
Sorry thought this was a evinrude motor you can use the dial indicator to find true TDC in a similar fashion just mark on the flywheel both before and after at .459 TDC and TDC should be half way between the two marks. Allways turn the flywheel clockwise with the gearbox installed!
Click to expand...

Well this is actually a relief! I missed the splitting the two measurements in the manual, which doesn't describe that action! Just eyeballing that measurement would bring the flywheel into timable range.

Ill post up results later this week.

Thanks!
 
That is just how to confirm TDC is correct on any type of motor. Confirm TDC is correct on the flywheel then adjust the throttle pickup according to the manual (engine sync). It just sounds like your carbs are not in sync with the timing advance.
 
I was just fearful when the piston was at TDC and the Flywheel marks were so far off. Had I known about the two measurements and split the total I wouldn't have been so confused
 
What does your book say for primary pickup at idle and max timing? Engine timing is fixed with the flywheel key, primary pickup is when the throttle butterflys begin to open with spark advance and max timing is with the engine is at WOT.
 
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