Prop/gear question

[flmike02]

This is very general, but when the engine in off and it is put into gear, forward or reverse, is there supost to be some play in the prop or is it supost to be tight? I can move the prop back a forth about an 1/8 of a turn before it hits a gear. The engine in question is a 1999 50 hrp Johnson.

Thanks

 

[Paul Moir]

Re: Prop/gear question

That's normal for it to be able to turn a bit. It's just the play between the clutch dog's ears and the gear's ears. Some outboards will turn a lot more than 1/8th, but always less than 1/2!

Here's a dog and gear set:

Those things (ears) that stick out of the dog go into the groves in the gear. The gear is always spinning on the propeller shaft and the dog is splined to the propeller shaft so it cannot turn but can move fore and aft on it. When you shift into forward, the clutch dog is slid along the propshaft until those ears go into those grooves. Once ingaged, the turning of the gear is tranmitted to the turning of the clutch dog, which cannot help but turn the propeller shaft.

As you can see by the size of the groove verses the size of the clutch dog ears, there's a lot of play. That set allows a bit over 1/4 of a turn with the engine stopped.

When shifting the engine into forward or reverse with the engine stopped, occasionally the ears on the dog will not go into the grooves in the gear and instead hit the gear's ears directly. When that happens it's important not to force the gear shift lever but rather to turn the propeller shaft a bit so the dog's ears line up with the grooves.

Well, there you have the whole explanation!

 

[flmike02]

Re: Prop/gear question

Thanks. You definitely explained a lot. The manuals don't exactly explain these things very well. I really appreciate it.

 

[Paul Moir]

Re: Prop/gear question

I'm glad to help!

One thing that becomes obvious once you see how it works is that it's so important to shift briskly with an outboard. Unlike a manual transmission car which uses a friction clutch, this is has those metal ears which are either engaged or not.
If you look closely at the clutch dog ears, you can see where their tips have been worn away due to lazy shifting. As a matter of fact, this set has excessive wear and was causing the outboard to pop out of gear.