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Old 08-03-2009, 12:25 AM   #1
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Default Gear Ratio and Prop Size

Anyone know what the gear ratio and stock prop size and pitch on a 1997 2400 SCR with a 350 is?
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Old 08-03-2009, 02:35 AM   #2
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Default Re: Gear Ratio and Prop Size

5.7L with an Alpha I = 1.47:1 drive and 15 X 17 prop.

5.7L with a Bravo II = 2.0:1 drive and a 18 1/4 X 19 RH prop.
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Old 08-04-2009, 03:00 AM   #3
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Default Re: Gear Ratio and Prop Size

Thanks, just ordered a new 15x17 3 blade today, going to put it on tomorrow. I had to have the harmonic balancer replaced because the rubber had completely worn away and it was just floating :shock: I hope that plus a new prop brings me closer to WOT.
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Old 07-21-2010, 02:37 AM   #4
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I have the same question Gear Ratio and Prop Size
Anyone know what the gear ratio and stock prop size and pitch on a 1989 2300 sc with a 5.0L is?
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Old 07-21-2010, 08:48 AM   #5
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so far this is the best answer to prop size and pitch I've found. I hope this helps.
www.mercurypartsexpress.com
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Old 07-21-2010, 01:35 PM   #6
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I found the gear ratio stamped on the left hand side of the outdrive right below the oil vent.
On a 1989 Alpha 1 the gear ratio is 1.47
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Old 08-06-2014, 09:16 PM   #7
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I too need drive ratio info for a 2000 2400 SCR with a Bravo III coupled to a Mercruiser 5.7. Any help would be greatly appreciated.
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Old 08-07-2014, 01:21 AM   #8
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Marineman welcome aboard.

This is a really old thread and I cannot say I have seen any of these folks post in a very long time. You would have been better starting a new thread.

I have not seen a B3 on the 2400, as far as I know it came with either an Alpha or B2. The B2 has a 2.0:1 ratio.
With that said the B2 and B3 use the same transom assy so someone could have bolted one on. What prop set is on the drive and what WOT are you achieving?
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Old 08-11-2014, 09:08 PM   #9
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Default B3 on 2400

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Marineman welcome aboard.

This is a really old thread and I cannot say I have seen any of these folks post in a very long time. You would have been better starting a new thread.

I have not seen a B3 on the 2400, as far as I know it came with either an Alpha or B2. The B2 has a 2.0:1 ratio.
With that said the B2 and B3 use the same transom assy so someone could have bolted one on. What prop set is on the drive and what WOT are you achieving?
Yeah, I don't know a whole lot about this boat, but it's a model year 2000 with a 5.7 MPI TB running a B3 with 24 Pitch props. RPM range unkown right now. There's been a change in the upper drive and it may not be the correct ratio.
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Old 08-12-2014, 01:59 AM   #10
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Turn the engine one revolution by hand and note how many revs the props make. If the ratio is 2.0:1 the props will make 1/2 a rev for one engine rev
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Old 08-12-2014, 03:22 PM   #11
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Default B3 on 2400

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Turn the engine one revolution by hand and note how many revs the props make. If the ratio is 2.0:1 the props will make 1/2 a rev for one engine rev
Ok, I guess I wasn't as clear as I might have been. It's NOT that I don't know what the ratio is per say as the upper has a metal tag that says 2.20:1, but since it was changed out and the boat performance suffered greatly afterwards and now just trying to confirm what ratio was on it before when it ran ok. if the original was 2.00:1 then the 2.20 ratio should actually make the engine turn tighter at WOT. It sounds as if the engine might have been running in a reduced power mode as it wouldn't run above 2200 RPM and strong smell of gas, but there aren't any codes in the ECM to confirm it.
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Old 08-12-2014, 07:09 PM   #12
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Ok with the 2.2:1 ratio the engine will turn more rpms for the same prop revs than the 2.0:1 will which will give lower speed but should not result in what you are experiencing. A strong smell of gas sounds like it is running way to rich or you have a fuel leak, if the latter this needs to be fixed now.

A incorrect gear ratio will not cause this as far as I know. If you cannot fix this yourself I strongly recommend to have a mechanic look at as this can be dangerous.
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Old 08-13-2014, 08:51 PM   #13
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I appreciate your input, however I am a 45+ year veteran marine mechanic. The problem is I can't duplicate the situation as I'm dry land and you are correct to a point, most likely the gear ratio wouldn't cause this kind of performance loss, but you need to appreciate that the morons that worked on it before it was brought to me are much, much less experienced and probably shouldn't even have been touching it in the first place. Since I wasn't present when all of this took place I'm just trying to dot the eye's and cross the T's. If the ECM went into protection mode it would commonly limit the RPM and richen the mixture and that's what I'm thinking, unfortunately I am only able to guess as there are no codes in the ECM to support that!

It's unfortunate for the owner of this boat that the same morons that worked on it were probably responsible for the lack of lube in the drive that caused it's demise. They winterized it last fall and "summarized" it this spring and said it was water ready. Less than 15 mins on the water and I guess the gears in the upper didn't much exist any more.
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Old 08-14-2014, 12:58 AM   #14
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Understood, since you started by inquiring about what the gear ratio should be I went down that path.

With your experience are you Merc certified or have expired nice with them? Just trying to understand your background and not discredit you as this field is has a wide knowledge base, I am no expert by any means just a fellow boater with engineering background. Is there a way to clear the ECM from protection mode to see if the fault goes away for a short period?

I would have thought the alarm would have been singing with low lube unless they disconnected it. Also from my knowledge the lube, OP, and water temp warning is tied into the ECM and will put it into protection mode if triggered.
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Old 08-14-2014, 11:08 AM   #15
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I was thinking about this a little more, since you are not getting any codes I am wondering if it is a fuel starvation issue. I have seen some folks have issues with the cool fuel system getting clogged as merc had painted some internal parts and it is know to flake off. Therefore check the fuel pressure.
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Old 08-14-2014, 04:17 PM   #16
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I appreciate everything you've offered and yes I've been Mercury/Mercruiser Certified for most of my time as a Mercury Dealer, however Mercury and myself fell out of favor and it's become very costly to be even a service dealer for them and they're way too demanding with their dealers so I chose NOT to continue being beaten up with their flavor of Corporate BS. I know with technology such as EFI there can be too many things that can occur that would never be an issue with a carb system and have used CDS as well as Scan Tools such as the Rinda Tech Scan Tool that I rely on now, however in too many cases you also have to be able to rely on good old fashion trouble shooting skills and some common sense. So to answer your question about the possibility of the fuel system being plugged, it wouldn't follow that the customer smelled fuel. Watching the fuel pattern of the TB injectors while the engine is running on dry land on a flush attachment doesn't show that the ECM is running the engine rich and the exhaust doesn't reveal that either. I had a boat in here a few years ago with a MEFI 3 that as soon as you'd started it the TB injectors were producing such a fat mixture it was obvious it was running way too rich, no codes in the ECM and no obvious reason for it to occur other than the possibility that the ECM was stuck in protection mode for some unknown reason. You could replace the spark plugs and after just a few minutes of running take them out and they'ed be black from fouling. The owner didn't opt for the costly repair that it would have taken to fix as Mercury doesn't supply the MEFI 3's anymore. You have to order the kit which is actually a MEFI 4 and a stand alone ignition driver as well as a freakin' octopus harness to connect it all for a mere $2500. No idea what he did with it.

It's funny you should mention the alarm issue and the lube level. When the customer brought the boat to me the drive had been drained, not sure why and it was tagged "No Lube" and also discovered the lube monitor connectors were unplugged, naturally I don't know when that occurred or why. The owner of the boat is appears to be very uninvolved with the care of the boat and expects that the Marina is taking care of everything, which he's being charged for, Butttttt..................I doubt that he's getting his money's worth. Looks like I've done all I can. He's gonna need to take it back to the water and run it again to see what's what. Looks as thou I might be taking a trip to the lake!!!
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Old 08-15-2014, 12:56 AM   #17
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Wow it's funny how folks let things go and then will go crazy when they either cannot use the boat the one weekend the family shows up or get hit with a very large bill that is due to their neglect.

Do you happened to have a used ECM that fits this boat incase it is still not hitting higher rpms that you swap out and try?

Yea the cool fuel issue would not result in a rich mixture but I have head this causing the lack of power and rpms. Is it possible the owner could have flooded the engine by trying to overcome this lack of power? I only stay on the fuel pump issue because to my knowledge no code gets flagged for this problem, so yes I am trying to use TS logic due to lack of data.

Enjoy the ride and hopefully you can learn the problem, if you do please post the findings here as I am curious and always want to learn.
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