225 optimax - slipping prop?

[Btuvi]

Six weeks ago I had a cracked hub inside the prop which was replaced by dealer. Prior to this rpm's had topped out consistantly at 5500 with a speed of 48mph. When I got it back rpm top was 5600 with a top speed of 46mph. I didn't think much of it. Meaningless increase in rpms and slightly reduced speed could be extra weight.

Little by little since then the rpms have constantly increased and the speed has dropped. Then the change became more dramatic each time I went out. Today it was 6600 rpm with a top speed of 31. I immediately went back to dock and pulled it out.

I have not run aground nor bumped into anything so there is no reason for the plastic hub to be damaged. Yet all the evidence (to me) points to a slipping prop.

I did put it in gear to see if I could move prop - and I could move it almost a half inch back and forth. That doesn't seem right.

I plan to take it back to shop but would appreciate any thoughts on why this is happening.

Thanks

 

[sschefer]

Re: 225 optimax - slipping prop?

From the sounds of things you either have the wrong prop hub or your shop tried to reuse one from another prop. It might have been new and in a different prop but it's the same thing. I know I'm gonna get blasted by some one on here for telling you that but I have proved it beyond the shadow of a doubt on my own props.

I know the box say's it's reusable and if you're lucky they might be. I think you're finding out they are not. Sounds to me like your shop just did what they thought they should be able to do. They'll make it right I'm sure.

Smart move shutting it down and bringing it in. You probably saved your engine.

 

[Jeff_G]

Re: 225 optimax - slipping prop?

The engine should have a rpm limit of around 6000 rpm with a wot of around 5600-5800, so the 6600 bothers me. Did you notice any other problems with the engine?
As for the prop there are two types of flo-torq hubs the normal pleasure boat type and a hi-performance hub.
If you have a really large load on the engine you can strip out even a new hub. Go to your dealer and ask for the hi-performance hub, cost a few bucks more but will probably cure your problem.

 

[Btuvi]

Re: 225 optimax - slipping prop?

Engine seems to run fine although I do feel that I can detect a barely perceptible (rattle?) when I apply throttle which is not detectable at idle. Neither passenger could hear it and my hearing isn't perfect so I dismissed it but there was a slight difference in the way engine sounded.

Thanks for opinions. I'll post a note after shop takes a look.

 

[Btuvi]

Re: 225 optimax - slipping prop?

Mercury mechanic removed prop only to learn that hub is in good shape. He was stumped. Manager spun prop and suddenly we could all see that it wobbled. Conclusion was that shaft was bent.

My theory is that when I ran over stump which created need for hub to be replaced a couple of months ago the shaft was also bent at that time. New hub made a difference but over time shaft deteriorated eventually causing present problem. The question I have about my "theory" is that, once the shaft was bent I would think the impact would be immediate and not worsen over time.

So - if the shaft is bent what damage might it cause over time that would mean a continuing increase in rpms and decrease in speed. Draw me a verbal picture if you will.

Thanks

 

[sschefer]

Re: 225 optimax - slipping prop?

A verbal visual would be a broken drive shaft about dead center of the clutch pack which is now carrying the load and melting down on you. That's only a guess. I can't see how it could break anywhere else and still remain engaged. That's pretty far fetched but I suppose it might be possible.

The only way to know for sure is to tear into the L/U.

 

[j_martin]

Re: 225 optimax - slipping prop?

A verbal visual would be a broken drive shaft about dead center of the clutch pack which is now carrying the load and melting down on you. That's only a guess. I can't see how it could break anywhere else and still remain engaged. That's pretty far fetched but I suppose it might be possible.

The only way to know for sure is to tear into the L/U.

It has to be torn down anyway. You'll find it.

Another thought is that water has less drag than grease, for a little while.

hope it helps
John

 

[Jeff_G]

Re: 225 optimax - slipping prop?

Hold on. You can't tell a shaft is bent from turning the prop. You have to take the prop off the shaft and turn the shaft over by hand. Prop can and do wobble, particularly out of the water. It still would not stop the prop from working correctly. The prop doesn't know if the shaft is bent unless the hardware would not go on correctly. Spinning the prop for a "bent shaft" is one of those old BS tricks some shops use to replace a perfectly good shaft. Not saying they are dishonest, just make sure yourself.
Take the prop off and visually check the shaft!!!!

The most common place for a shaft to bend is at the rear bearing. There is no "clutch pack" and nothing to melt inside the lower unit except the seals. Don't know where that came from. If the shaft is broken it will not turn so you would have no propulsion.

If the shaft is indeed bent check around, some shops have a shaft straightener that is designed to straighten the shaft on the engine without disassembly. Some machine shope can also straighten shafts. So you do have some options.

 

[Btuvi]

Re: 225 optimax - slipping prop?

Thanks all for replies.

Jeff G - You sound very certain - adament even - in your comment. Let me be a bit clearer.

It appeared, not that the prop revolved unevenly, but that the shaft itself appeared to rotate unevenly. Watching it turn I certainly had the impression that it was not turning smoothly. You are saying, if I have it correct, that they all do. If I accept that then the question is:

If hub is ok - which it certainly appears to be - then why the dramatic increase in rpms and decrease in speed?

And, out of curiosity - if I took prop off of shaft and turned it by hand what would be indication that shaft was bent? Though I haven't done it I find it difficult to imagine being able to turn it by hand in a way that would allow me to detect a difference.

And Sshefer - we haven't met so you are unaware of my ignorance. A verbal visual does not include words like "clutch pack". You might as well be saying "clerk perk". I can grasp that the prop fits on to a shaft since I can see that it fits over something that protrudes. I picture a shaft as something longer than an inch so have a mental picture of something extending into the foot beyond my vision. Beyond that I have an idea that there is probably something that that grabs that shaft and makes it turn. Could be a mouse, maybe. Something relatively small, anyway. Guess I'll look in the manual. I was just hoping for words that would describe what I will see in the manual to pull it all together for me. Thanks for the effort though.

Don't give up on me yet, fellas.

 

[sschefer]

Re: 225 optimax - slipping prop?

No problem. Yes, I did not understand what you were asking. I was trying to think of a way that might cause a slip in the lower unit that would cause a gradual increase in RPM. I know that on the L/U's that I have torn apart there is a part known as a ratchet sliding clutch. The shaft slides through it. I thought you may have one also but according to Jeff G you don't. I did look at the parts manual for a 2004 225 and the L/U does show a clutch. I guess that Jeff has inside info about your engine that I don't so sorry if I made it confusing for you.

To get a better idea of what's going on inside your L/U you can go to www.mercurymarine.com , sign up and then use their parts finder to look at a parts breakdown of your lower unit. www.crowleymarine.com also has one that is easier to access then mercury's but it only goes up to 2006.

 

[Jeff_G]

Re: 225 optimax - slipping prop?

To the OP;
A bent prop shaft will not cause the engine RPM's to go up while the speed slows down.
Turning a prop, kicking it over with a foot as you described the service manager doing, will not tell you the condition of the prop shaft. To see or measure any wobble in a prop shaft you will need to take off the prop. Unless it is real visible you measure it with a dial indicator.
As I posted an old trick of some less than honest shops was to spin a prop on the lower unit, point to the prop obviously wobbling and say the shaft is bent. I was only telling you to be careful with this scenario.
The drive shaft is splined into the crankshaft. It turns at the same rpm as the engine. On the end of the driveshaft is a pinion gear. Meshed with the pinion gear is a forward and a reverse gear. When the driveshaft turns both gears turn.
The clutch is a round part with "ears" on either end. It is splined to the prop shaft and moves forward or back to change the gears. The prop shaft free spins on bearings and bushings through the forward and reverse gear. When you shift the clutch moves and engages "ears" on the gear mating the spinning gear to the propshaft, thereby turning the propshaft and prop. The propshaft extends all the way to the front of the housing.
If the propshaft is bent it will still turn just as a good one will as long as the clutch and gears engage properly.
If the gears are stripped it could cause higher rpm and less MPH, conversely if the hub wasn't holding the same symptoms.


Steve, clutch pack is an automotive term, not a marine term. It is called a clutch or clutch dog. Secondly there is nothing to melt inside the clutch or the gearcase for that matter. Third if the prop shaft was to break inside the gearcase it would not cause the symptoms described, nor would the lower unit continue to shift. Finally I have never seen or heard of a prop shaft breaking in the splined area. I just don't understand where you come up with some of this stuff.

 

[sschefer]

Re: 225 optimax - slipping prop?

To the OP;
Steve, clutch pack is an automotive term, not a marine term. It is called a clutch or clutch dog. Secondly there is nothing to melt inside the clutch or the gearcase for that matter. Third if the prop shaft was to break inside the gearcase it would not cause the symptoms described, nor would the lower unit continue to shift. Finally I have never seen or heard of a prop shaft breaking in the splined area. I just don't understand where you come up with some of this stuff.

Sorry Jeff, I was using Merc parts and service manuals to quote terminolgy. Just so I don't get it wrong again, can you please post the references that you are using? I think the poster of this message and other readers would appreciate knowing how you come by your vast knowledge and expertise.

Melt down was used to provide a graphic verbal representation of a clutch prematurely failing. I mistakenly thought common sense would be used to see it that way.

 

[Jeff_G]

Re: 225 optimax - slipping prop?

Steve I'm sorry you have such a need to ask for my qualifications, and references. I could throw the same question back at ya.

Lets clear the air.
I have been in the marine business for over 35 years, started in 1974.
I have owned my own business since 1978.
I raced powerboats both Johnson/Evinrude and Mercury's for about 28 years.
I was the National Champion in APBA Formula V three times. And was US1.
I also set records and many titles in NORA racing.
I was the National Technical Director for DMI Pistons.
I have been certified by Mercury/Force, Tohatsu. Johnson Evinrude. Including being a certified master technician.
I have also written on the subject of powerboats, and racing for newspapers and magazines and produced the first nationally televised series for limited powerboats, the ESPN All American Challenge Series.
My information comes from 35 years experience, OEM service manuals and OEM parts and dealer books.

So what of your qualifications?

 

[Btuvi]

Re: 225 optimax - slipping prop?

So Jeff are you saying that it is likely that the gears are stripped?

By the by, I'm satisfied with your credentials. You and I seem to be at the opposite ends of the spectrum. I once removed the hood from an engine. Well, I didn't do it. Someone else did. But I was there to see it.

I appreciate the advice regarding someone spinning the prop and concluding, because of the wobble, that the shaft was bent. In this particular case the manager is much more manager than mechanic and the mechanic, though good with tools once the problem is identified, is not a diagnostician. The "real deal" mechanic was out for a couple of days and will be the one to diagnose my problem. I'll update you.

Thanks for your reply.

 

[Jeff_G]

Re: 225 optimax - slipping prop?

Not saying the gears are stripped.
The RPM going over the rpm limit of the engine is unusual and should be restricted by the ECU.
In most cases when the rpm's go up but the speed drops the problem is the hub in the prop. Other than that gears stripping would give the same symptoms.
The plastic hubs work well and should work for up to about 300hp. In some cases a engine operating under a big load, large prop etc. will also cause a hub to slip. In rare cases I have found a change to the stainless hub will cure the hub stripping/slipping problem.
Without personally examining an engine it is impossible for any of us to give a definitive answer, we can only give advise and opinions and how to check something.
Good luck with your engine.

 

[Btuvi]

Re: 225 optimax - slipping prop?

When the mechanic and manager (and I) first examined the hub there was no visual damage. The mechanic then got a new hub and compared them and they were exactly alike. He then put the new hub on and suggested that I try it and see if the problem was cured. That's when the prop was spun and - you know the rest of the story.

My question is: If it looks as if the shop, because of backlog, can't address my problem quickly would it be worthwhile for me to try new hub in the interim? If there is any chance a new hub would cure problem I'd rather give it a try. However, given the fact that two reasonably knowledgeable people could compare two hubs side by side and see absolutely no difference I am skeptical that problem would be solved by exchanging them.

What say you? Better to bite the bullet and stay in repair line or worth a shot to try different hub?

Thanks

 

[sschefer]

Re: 225 optimax - slipping prop?

Personally, I would go get a cheap aluminum prop of the same diameter and pitch and try it. If the problem persists then you can pretty eliminate the prop as the problem and have yourself a decent spare which is never a bad idea anyway. It wouldn't be like you were throwing your money away.

 

[Btuvi]

Re: 225 optimax - slipping prop?

The prop itself is ss and in perfect or near perfect condition and I really can't see a connection between the increased rpm and decreased speed and prop. Rubber hub in prop perhaps but not the prop itself.

 

[sschefer]

Re: 225 optimax - slipping prop?

The prop itself is ss and in perfect or near perfect condition and I really can't see a connection between the increased rpm and decreased speed and prop. Rubber hub in prop perhaps but not the prop itself.

Then wait for the shop.

 

[Jeff_G]

Re: 225 optimax - slipping prop?

Steve I'm still waiting for your qualifications. You asked for mine, I asked for yours.