757HA Timing

[TriHullDano]

Hello All,
Looking through the service manual, for 757HA 75HP Chrysler outboard, it lists an obsolete tool to use for timing the engine.
However, the methods seems to be straight forward. Basically, insert the tool, rotate the engine to find TDC, reset the tool then rotate the engine some more until another mark, on the tool, lines up with the block. This distance indicates 32 degrees BTDC.
My question is what is that distance? I can easily find TDC and insert another tool, for example a #2 pencil, etc, and rotate the engine until the "new" tool has moved some said distance.
If that distance is unknown does anyone know the diameter of the flywheel on these motors? I don't know whether to measure for diameter to the outside edge of the teeth or to the valley between the teeth on the edge of the flywheel....?

Thanks,
Dano

 

[Frank Acampora]

Re: 757HA Timing

That tool is only for finding top dead center when the engine has been rebuilt. It shows you 36 degrees BTDC BECAUSE: Due to clearances in the bearings, TDC may be a little difficult to find. Look in the intertech manual. It gives the distance in depth that 36 corresponds to. I always find TDC with a screwdriver and rocking the flywheel. After a couple of times you will get the knack.

IF the block pointer has not been moved, there is no need for the tool. Use a timing light and timwe the engine to 32 degrees BTDC at wide open throttle. If the engine is 1980 or later, time to 30 Degrees. If you strictly use auto pump gas, 32 is still acceptable.

 

[TriHullDano]

Re: 757HA Timing

Frank,
Is it safe to run the motor with just ear muffs and a hose for as long as it might take to set the timing at WOT?
Or is it ok to run the motor at WOT without the propeller on and the motor in a bucket of water?
The engine is 1974.

Thanks,
Dano

 

[Frank Acampora]

Re: 757HA Timing

1974 is a distributor engine you do not need a timing light and you do not even need to start the engine to time it.

Simply remove and ground all the plugs. With the engine at WOT and the ignition on, slowly turn the flywheel by hand. When the top plug sparks, rock the flywheel back and forth to check. 36 degree mark on the flywheel should be the fourth line to the left of the long line on the block pointer. Adjust the distributor link. Further apart on the two plastic blocks advances timing while closer together retards it.

 

[TriHullDano]

Re: 757HA Timing

Frank,
If I understand you correctly and assuming the top plug does NOT spark when the 36 degree mark is on the fourth line, BUT is close, I can then adjust the distributor link to where the 36 degree mark does indeed spark while on the fourth line to the left on the block pointer or as close as I can get it?

Thanks,
Dano

 

[Frank Acampora]

Re: 757HA Timing

Correct!

 

[TriHullDano]

Re: 757HA Timing

Frank,
That worked very nicely!
I also adjusted the throttle linkage as directed in the service manual and after about 2 or 3 four second COLD cranking sessions she hits and comes up quickly on the RPMs at WOT, with the little silver button pulled out on the remote control. From there she starts within less than a second of turning the key.

Thanks,
Dano