Honda BF50 gear ratio's

[Skinnywater]

JD, I'll do my best to keep this brief. Since I have to make an important decision, explain both a situation and problem. And get multiple options; receive a Forktail crash course in outboard ratio, power and torque in specific applications. This won't be easy.<br /><br />Several months ago I posted on this list that I bought my boat with a very specific plan. My whole intention was to use this particular boat as a fishing/hunting/utility boat. The main use would be in the "Skinny" stretches of the Sacramento River. This particular 16'' NorthRiver welded aluminum boat with a Honda factory equipped BF50 jetpump is used for this purpose. It has been absolutely perfect and continues to exceed all expectations on the river.<br /><br />pictures: (Hope this works)<br /><br /> http://www.fishingworks.com/Users/Photo_album/viewPhoto.cfm?photo_id=43320 <br /> http://www.fishingworks.com/Users/Photo_album/viewPhoto.cfm?photo_id=43321 <br /> http://www.fishingworks.com/Users/Photo_album/viewPhoto.cfm?photo_id=43322 <br /><br />The secondary uses are equally as important to me and here is where the BF50 problem occurs. All with in hours from here is Lake Tahoe, Shasta Lake, Clear Lake, The Sacramento/ San Juaquin Delta, all big water. An easy (one would think) conversion involving a simple manual jackplate and a complete lower leg, with prop for my Honda is the ticket for those waters.<br />This swap normally takes 1-2 hrs to do and increases the boats versatility immensely. It's important to note that all my fellow fishing buddies and several others in this neck of the woods have this very capability with their boat/motors.<br /><br />Several times throughout the purchase process I made this desire known to my salesman. He agreed that it would be very desirable thing to do. Fine, I'd save the money to purchase the needed hardware and make it my winter project. Soon after my purchase I joined the iboats board and eventually brought up this conversion topic. Hondon (thanks) was the first to send up a red flag!! He stated that a jetready BF50 Honda uses a 1.1:1 ratio primary gear under the powerhead. He stated this is unique with ONLY the BF50 Honda specifically. Three different primary gears w/part # are listed in my Honda Marine manual. One of the part #'s is the 1.1:1 ratio for the jet. One would be for a prop application. The other for an unknown application for a differing final ratio yet. So, the BF50 has a listed 2.09:1 (prop) ratio, yet it achieves this with both the primary gears AND the pinion/bevel gear in the foot. As was discussed, this primary gear problem created a flood on my parade! The pump to prop conversion now needs collaboration and options. Hondon offered the possibility of careful prop selection. Fine, what would that mean? <br /><br />My first visit to my dealer. I wanted an exact quote for a complete lower leg with linkages, hardware, waterpump assy., CNC jackplate and a "special" high quality prop. All for this "sweet" conversion. Oh! And by the way, someone told me there might be a problem converting this motor, like I want. The part man is all over this! I told him $2, 000 wasn't going to scare me. Before he gave me a quote the service manager got involved, saying something like there might be a problem. He assured me he would do some research and get back with me. I assured him I had the money to buy the parts. <br />I've called a couple of times, got a total runaround."I'll get back to you" but never will kind of thing. OK, call another Honda dealer, money in hand I say, to buy expensive parts. He says,"Well, did you know the BF50 jetready, blah blah, primary gears, blah blah, …..why don't you sell your brand new (30hrs. at the time) Honda, take a massive loss, buy this Yamaha F60 at full pop, with a jet and a lower leg, from me and you'll be ………way to many thousands in deep."<br />I ask,"That’s it? My only option? Really? Come on man!! Don't tell me it CANNOT BE DONE!!!!!!!!!!!! ANYTHING CAN BE DONE!!!!!" His final reply, "Maybe, it just that I don't think it been done before. It will be a gamble."<br /><br />So, here it is. I've scoured the www. I've written for prop help. Hondon told me "maybe" careful prop selection. My dealer has proven worthless on fewer requests. The other dealer says its never been done. I'm asking for help on RATIO's and practical advice. Here are my questions.<br />1. A standard BF50 with prop has an advertised 2.09:1 ratio. What is the ratio of the pinion and bevel gear? <br />2. What is the ratio of the same motors primary gears?<br />3. There are 3 different primary gears listed as spare parts. <br />what are their ratio's?<br />4. If I have 1.1:1 primary gear ratio for the jetready. What would my final ratio be with a standard lower leg installed to those primary gears?<br />5. What would my prop selection be?<br />6. Would it work?<br /><br />Forktail, if you can talk ratios to me so I can say it back to a Honda rep. Anyone one else with the specific knowledge I'm needing, by all means weigh in. <br /><br />I need all the odds before I'll gamble. <br /><br />Thanks very much.

 

[Bear]

Re: Honda BF50 gear ratio's

Hi Skinnywater,<br /><br />A couple of years ago when I first saw the Honda with a jetpump, the picture below, I sent an e-mail to them. The answer I recived was "you can get a water jet for the honda outboard by calling this number 1-510-562-6049 in the USA"<br /><br />Ed Fields<br />ed@tuffboat.com<br /> http://www.tuffboat.com <br /><br />

<br /><br />Maybe he can help you. They seem to do this conversion. What if the have the parts you need?

 

[Skinnywater]

Re: Honda BF50 gear ratio's

Hello Bear,<br />I have that same jetpump you have pictured.<br />Now I need to go back to prop and back again at will.

 

[Forktail]

Re: Honda BF50 gear ratio's

Hi Skinnywater. Sorry, this might be long winded. I'll cover ratios at the end.<br /> <br />The Honda BF50 uses an offset crankshaft design. Others like Suzuki use the same concept. It does not provide a direct "in-line" route for the drive shaft (which would be a direct 1:1 ratio). Rather, the engine's crank shaft is connected to the drive shaft just below the power head through offset gearing. This offset helps improve the forward center of gravity, balance, and reduces transom vibration. It also allows some engine parts to be smaller, thus the lighter weight of the BF50. Smart engineering. I don't have a Honda manual, but as you said according to member "Hondon", apparently this gearing provides a 1.1:1 ratio to the driveshaft.<br /><br />With that said, it is my opinion that it doesn't matter whether the BF50 is equiped with a jet or prop. Each BF50 produced should have this same 1.1:1 set-up. After all, all BF50's are "Jet Ready". Final gearing for a prop is done at the lower unit...when it is installed. And the jet unit would also incorporate the proper turning ratio through its own design. As long as the BF50's drive shaft is sized and interchangable with both the jet unit and the lower prop unit, they should both interchange without a problem (or extra parts).<br /><br />Now, on to gear ratios. A 1.1:1 gear ratio means that the engine turns 1.1 times to every revolution of the drive shaft. That's 360 degrees plus another 36 degrees. Or in other words, the engine has a mechanical advantage of 1.1 to 1 over the drive shaft. This means the drive shaft is turning slower than the engine...but with a positive result....more torque. 1.1 times more torque. And in outboards, torque is what the hp measurement comes from. So you can see how one could take a smaller displacement or lower hp outboard engine, and through gearing, make it produce more hp...at the prop shaft.<br /><br />Gear ratios can be multiplied together to find the final ratio. We already know the BF50 (non-jet) has a 2.09:1 final gear ratio at the prop shaft. And we already know we have a 1.1:1 ratio between the crank and drive shaft (according to "Hondon").<br /><br />So 1.1 X (some additional ratio) = 2.09<br /><br />2.09/1.1 = 1.9. So the additional ratio we need is 1.9:1. This is assuming "Hondon" is correct with the 1.1:1 ratio at the crankshaft.<br /><br />Therefore, the lower unit would need a pinion gear and prop shaft gear (generally forward gear) ratio of 1.9:1. In this case the pinion gear is the "drive gear" and the prop shaft (forward) gear is the "following gear". The "drive gear" is always stated first in a ratio. So we know the pinion gear must turn 1.9 times to every one revolution of the prop shaft gear. Or in other words, we know the pinion must be smaller....about half as small.<br /><br />Any combination of gear sizes can obtain a 1.9:1 ratio. Dividing the number of gear teeth on the prop shaft by the number of teeth on the pinion will get you the ratio. For example a pinion with 10 teeth and a prop shaft gear with 19 teeth will get you a ratio of 1.9:1. Because 19/10 = 1.9. Or a pinion with 20 teeth and a prop shaft with 38 teeth will also get you a 1.9 ratio. Because 38/20 = 1.9. Regardless, in the end ( @ prop shaft) we know the outboard's engine will be turning 2.09 times for every 1 revolution of the prop shaft (prop).<br /><br />All in all, a 1.1:1 ratio change at the crankshaft is probably not a big deal since you only occassionally use a prop/lower unit. It's almost a direct 1:1 ratio. So I'm guessing you could easily just swap out the two and possibly adjust by trying different props.<br /><br />Hope this helps.

 

[Skinnywater]

Re: Honda BF50 gear ratio's

Thanks Forktail.<br />What Hondon and two Honda service departments have told me is that a BF50 with a prop has one set of primary gears and a jetready have a different set of primary gears. The 1.1:1 ratio came from an instruction sheet from Specialty products, the manufacture of the jetpump.Specialty products also told me the BF50 was the only Honda that had a primary gear set that was unique to only jetpump application.<br />This particular BF50 jet has its own model# coding. To identify my outboard as a factory equiped jet. The differences are:<br />1.No HP designation on cowl, only JET.<br />2.A jetpump instead of lower leg for propulsion.<br />3. Primary gearset that is different then a prop BF50. 1.1:1 according to Specialty products.<br /><br />I completely understand that any other outboard manufacture will have a direct drive to the final drive gears or the pump.<br />My BF50 will have close to direct drive if I leave the same primary gear set in place.<br />However, I'm still missing the ratio of the primary gears that are installed in a prop driven BF50. This might not be as important as knowing the actual ratio of of the pinion and forward bevel gear. Then I'd be able to calculate a 1.1:1 ratio on the actual pinion/bevel ratio and come to a prop choice. <br /><br />Forktail, again for a better understanding in my quest. And assuming my info is correct. You understand a BF50 prop driven has an advertised ratio of 2.09:1. Maybe I'm reading to much into this but I'm really concerned that a red flag keeps poping up everytime I start talking about spending a lot of money at the parts department. I agree with you totally that a 1.1:1 ratio from the engine is a very useable ratio for prop applications. So the unusual ratio, as far as a 1.1:1 ratio is concerned, is in the pinion/bevel gear.<br />What would be the practical purpose of using a different primary gear ratio from prop to pump? Why would it be unique to the BF50? Were they gearing it so extreme for prop performance that it would be to extreme for the pump?<br />It's also interesting to note that it is a fact that any other Honda outboard OTHER then a BF50, uses the SAME primary gears weather being used for prop or pump applications. <br /><br />Sure wish a Honda guy could count the teeth of the pinion gear and count the teeth of the forward bevel gear on a BF40/50. <br /><br />Forktail, I'll let you in on this. I'll spend a month or so on this. Make a plea to a the regional Honda rep for answers. <br />Then I'll put the Honda up for sale to offset some cost. I may be bragging up a new F60 Yami that can go from prop to jet in 1.5 hrs.<br />Shoot, whats another year of overtime?<br /><br />Thanks again.

 

[Schmoky]

Re: Honda BF50 gear ratio's

Skinnywater, How did you make out in swapping out the jet leg for a prop? Is it a viable option or just to much of a pain in the a$$? I have a BF50 that I just replaced with same after hitting a reef in the lake and destroyed the complete motor, almost tore the leg off. I have a new motor but am trying to decide if the jet leg is the way to go. Having the option of both jet and prop would be great. I saw that you were trying for the same options and wondered how you made out. Schmoky

 

[Rotti]

Re: Honda BF50 gear ratio's

Hello Schmoky,<br /><br />read your thread about hitting that damned underwater reef.... Understood that you have replaced the motor with a new one... I need all internal parts of the lower unit (prop-type), even some washers, nuts & bolts would help since I dont have to buyem from Honda then (they calculate their prices for spareparts by simply weighing them up in gold...)- if you still have some parts left could you send me an email to: Wolfg.R@t-online.de<br /><br />greetings,<br />Rotty

 

[Skinnywater]

Re: Honda BF50 gear ratio's

Hello Schmoky,<br />I didn't have large enough jewels to take the gamble that prop choices would make it work.<br />However, I've got 'em large enough to possibly void my warranty and do some modifying.<br />And this might help those who are wondering.<br />At some previous post I explained I was concerned about a rattle comming from the primary gear/ driveshaft area of my outboard. After taking the jet off I had a dry driveshaft at the primary gears. A healthy dose of grease helped but didn't completely solve this problem. The rattle was an out of balance (stock aluminum)impeller from the factory.<br />Shortly after, I accidently found this problem by sucking in a fair amount of gravel into the jetpump. I had to buy a new liner, it was pretty reasonable at $45.00. So I sprang for a Stainless Steel impeller at the same time, cost $280. <br />All right! This high performance, four blade impeller (the other was three)I blueprinted to the liner myself. I shimed it to within .008" (the other spec. was .032").<br />The liner has an 1/8th in. lip on the intake side. I machined it to taper directly to the impeller. I also ground the square edges of the intake grates on the leading and trailing edges to a taper. I ground all the casting marks inside of the pump housing to a smooth finish. I cut the seperation between two of the four upper bolt holes that mount my engine to the boat so I could minutely slide my outboard up or down as needed. <br />I raised it to the point of cavitation then lowered it to no cavitation at all points. This figure was an additional 1/4 in. higher then before. All this was told to the manufacture of my boat, NorthRiver. They were pretty impressed with my gains and suggested a slight tilt of the motor to bring the left leading edge of the pump shoe higher by 1/8 in. This resulted in less backspray with no cavitation.<br /><br />The results are.<br />Before my boat would do @5750 rpm, 29mph empty with fuel and driver and 26mph full of fuel, full fishing gear, ice chest and passenger. This is typical of this boat as compared to two others. One being a Honda 50 the other being a Yami 50. Same performance.<br /><br />My boat now does @5750 Rpm, 33mph loaded with full fuel, Salmon gear for two, passenger and 70 pounds of Salmon in the big ice chest. My hole shot is twice as fast and I can slide and spin my boat without cavitating. Fourteen gallons still lasts all weekend.<br /><br />I've been out on the big water recently and I'm fine with the boat now. I was thinking about trading up but I'm getting to many compliments on it to give it up now.<br />However, I've been giveing thought to keying the camshaft to experiment with a 3deg. retard....taper the throttle butterflys......NOS through the balance ports........bell cut the pump nozzle......recess the exaust pipe......

 

[Schmoky]

Re: Honda BF50 gear ratio's

Rotti,<br /><br />I had the motor replace with insurace and they kept the old motor. The only thing I have is the old prop and will try to repair it and use it as a spare. Sorry. Schmoky

 

[Rotti]

Re: Honda BF50 gear ratio's

Hey Schmoki,<br /><br />what do these folks do with a blown outboard?! Is there a place where one can buy these things? Any idea? Another thing: Ive read somewhere that Honda didnt start making their own lower-units until 1999- does somebody know if this is correct? The text said that the pre-99 lower units where made by Mercury?! If so it would really broaden my search-area, thats why Im asking....<br /><br />greetings,<br />Rotty

 

[hondon]

Re: Honda BF50 gear ratio's

That primary gearset is there to keep you from peaking the rev limiter constantly on your jet unit.The final driveshaft ratio would be hard to prop as it would require some pretty low numbers,I suspect,and no speedster by any stretch. Primary gears require powerhead removal to be changed.1/2 day job.

 

[David R]

Re: Honda BF50 gear ratio's

Schmoky & Rotti<br /><br />This time last year my boat sank in a storm and received some hull damage.<br /><br />The insurance people and myself did a dance for about three months. Got the money for the boat and got the boat, how does that work?. They payed the replacement value as assessed, to me, because that was less than the cost to repair. They effectively bought the boat from me at market value. Now the insurance company wants to recover some of their cost, they sell the boat for salvage. They set a salvage value and the local people somehow knew it was available and started bidding on it. The insurance company gave me the option to buy back at the salvage price. This was their cheapest route as they just deducted costs from the final payout, no extra parties or fees involved. I opted to buy the boat as I was getting repair quotes from $500 to $3600. I payed the $500 and everything is fine, but I was prepared to walk away, as the bidders were still interested.<br /><br />The point of this story is that when the insurance company replaced the motor, they sold or want to sell it. Schmoky I'm surprised the insurance company didn't offer a cheque, less a deductable, and less the value of the salvage. Then say, do what you will.<br /><br />David R