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Timing a 1955 johnson 25 hp sea horse

walchorn

New member
my motor keeps "bucking.&#

my motor keeps "bucking." i don't know exactly what the problem is but i think the timing might be off. i don't know how to time it. can anyone out there offer some help or think of something else that might be wrong? thanks. btw it only kicks when in gear.

paul
 
"Paul..... It would be impossi

"Paul..... It would be impossible for that engine to be out of time if it runs at all. The timing is set by the flywheel key being aligned with the crankshaft.

However, to answer your question (to a point). To set the timing, have the flywheel off, then align the flywheel key with the fiber rubbing portion of the points, then set the points so that a .020 gauge will slide thru but a .022 will not. Install the flywheel, having the key in the crankshaft align with the slot in the flywheel, then tighten the flywheel nut to the proper torque specifications. That's it.

Now, your problem is that the engine is jumping out of and back into gear. See the following which is taken from my database.

(Jumping Out Of Gear - Manual Type)
(J. Reeves)

This pertains to lower units on all OMC manual shift outboard engines, or any OMC engine with lower units defined as a Shift Assist or a Hydro Electric Shift unit which incorporates a "Shifter Clutch Dog".

Within the lower unit, splined to the prop shaft is what is most often referred to as a clutch dog, hereafter simply called dog. The dog has at least two lobes protruding from it on both ends, facing both forward and reverse gear. The forward and reverse gears also have lobes built into them near their center area. When the engine is running, in neutral, the gears are spinning constantly via the driveshaft being connected directly to the powerhead crankshaft, but the propeller does not turn due to the fact that the dog is centered between the two gears, and the dog lobes are not touching either of the gear lobes.

When the unit is put into either gear, shift linkages force the dog (and its lobes of course) to engage the lobes of the gear. The lobes of the spinning gear grab the lobes of the dog, and since the dog is splined to the prop shaft, the propeller turns.

The lobes of the dog and gears are precisely machined, most with right angled edges that could be installed in either direction, and some with angles slightly varied that must be installed in one direction only (one end only must face the propeller). Dogs that can be installed in one direction only, if reversed, even if the dog and both gears were new.... would jump out of gear almost immediately. Keep in mind that the lobes are precisely machined with sharp angles!

Due to improper adjustment or worn shift linkages, but usually due to improper slow shifting, those precisely machined sharp edges of the lobes become slightly rounded. Now, with those lobes rounded, as the rpms increase, the pressure of the gear lobes upon the dog lobes increases to a point whereas they are forced apart (jumping out of gear), and due (usually) to the shift cable keeping tension on the engines shift linkages..... the unit is forced back into gear giving one the sensation that the engine has hit something, and the cycle continues.

Some boaters have the mistaken belief that shifting slowly is taking ixt easy on all of the shifting components..... Wrong! Shifting slowly allows those precisely machined sharp edges of the dog and gears to click, clank, bang, slam against each other many times before they are finally forced into alignment with each other..... and this is what rounds those edges off! The proper way to shift is to snap the unit into gear as quickly as possible.

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store"
 
Joe:

Thanks so much for you


Joe:

Thanks so much for your help! What you've explained describes exactly whats happening. I will take it apart the next chance I get to see if I can fix it.

Paul
 
tore the lower end apart and f

tore the lower end apart and found the problem. exactly what you described. the lobes on the clutch dog are pretty worn down but the lobes on the gears look in pretty good shape. any idea where i could find a new or used but in good shape clutch dog?

thanks again

paul
 
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