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Optimax 115 Prop Hub

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nofearengineer

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"I recently purchased a boat w

"I recently purchased a boat with a 2005 115 Optimax on it, low hours. The motor has a 20" Laser II SS prop on it. I discovered the prop has some fore/aft endplay (about 1mm), and has an almost immeasurable, but clearly there, rock to it. I read that the Laser II is a Flo-Torq III hub design. What kind of hub does/did the Optimax 115 come from the factory with? I think the previous owner might have replaced the prop and reused the factory hub. The prop shaft has no detectable play in it whatsoever, so it appears the loose prop hasn't done any damage...appears, anyway."
 
"It didn't - just about ev

"It didn't - just about every motor over 25 horses produced in the past few years comes WITHOUT a prop.

There is no one prop that could possibly cover the range of rigs that any given motor could be mounted on, so the prop is an option that the dealer would normally help you determine, based on what the motor was going on and how it would be used...."
 
"Ah...I see you're right.

"Ah...I see you're right. And there's really no way I would be able to get ahold of the original bill of sale to find out what the boat came with. I kind of get the idea the Laser is not the original prop though. From what I can see, it does appear to be some sort of Flo-Torq hub. I'll just have to pull it off, and maybe replace it. Thanks."
 
"I put a socket to it...wouldn

"I put a socket to it...wouldn't budge. Now it wasn't a torque wrench, mind you, but I know what 55 ft-lbs. feels like, and it is at least that tight. I have heard a couple other Opti 115 owners with the same problem, told by their local Merc service it was normal (I don't believe that). I've been trying to contact them to see how they ended up. We'll see what happens."
 
"So just to be clear, are you

"So just to be clear, are you saying that the prop is moving "on" the hub...

or the entire unit, prop and hub are tight but have some play on the prop shaft??

It is quite normal to be able to push the whole prop/hub unit back a bit into the gear case (that means the thrust hub is doing it's job), but if the prop is kinda slopping around on the hub itself then possibly the hub is shot/deformed etc from a prop strike against a hard object...

You don't need to torque the prop onto the shaft - normally just a 1/4 turn past finger tight is sufficient..."
 
"There is no play in the prop

"There is no play in the prop shaft at all. The prop nut and retaining clip don't move either. The prop can be moved fore and aft about 1-2mm. The prop also "wobbles". Not like out of balance wobble where the prop is still parallel to the shaft. But where the axis of the prop can be tilted ever so slightly out of parallel with the shaft. Surely, that can't be normal for a hub to be that loose?"
 
"Okay...here is what I found.

"Okay...here is what I found. I took the prop off and it is definitely a Flo-Torq III hub. But the bronze thrust washer sits in the delrin hub loosely. That is where the "wobble" is coming from. The hub doesn't appear to be corroded or heat-damaged in any way. Likewise, the corners on the thrust washer are sharp too. I'm puzzled by the loose fit. I would figure it should be almost press-fit. Maybe it's supposed to expand when heated by exhaust?

Regardless, the entire hub assembly seems to be a bit too short axially for me to tighten the nut down on it completely. I run out of threads on the propshaft."
 
"No that isn't normal - it

"No that isn't normal - it's time for a new hub.

That's the beauty of the "replacable hub" systems like Flo-Torq, Piranna, Solas etc - if they wear out or you hit something and toast the hub it's a quick fix (with a 30 buck part) and you are back in business in a few minutes instead of "wait your turn" at a prop shop.

I would replace the hub and go from there..."
 
"Thanks, Graham. I'm head

"Thanks, Graham. I'm headed down to the local Merc dealer to pick up some fluids. I think I will pick up some grease and a new hub as well. Owning a boat is FUN!
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"
 
"You do know that with regards

"You do know that with regards to parts, maintenance, gear etc - BOAT is an acronym that stands for "Bet On Another $Thousand" right?
"
 
"You bet it is!

I found a

"You bet it is!

I found a way to avoid the prop shop wait on repairing old type hubs: I fix them myself! Done several Mark 25 types and a few Merc 500s as well. All you need is some threaded rod, a bunch of spacers and washers, and lots of patience!

Jeff"
 
"Well, I think I finally figur

"Well, I think I finally figured out what the problem is. I would wager that prop is not supposed to be used with a Flo-Torq III. It needs the shorter sleeve of the Flo-Torq II. The sleeve it has now is actually a little too long, so the hub is loose fore/aft on the shaft.

I bought a brand new thrust washer (expensive little piece of bronze!), and it is also slightly loose in the shaft side of the prop. However, the prop isn't wallowed out or anything. Still, if I get the axial compression on it, it should stop the side to side movement."
 
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