articfriends

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Whitey,I am estatic when I look at these lower gears.They look like they should last 4-8 times longer than what I have been accustomed to. I been saying oem prepped gears last me 20-40 hours but when I look back the stock set I ran while waiting on my current set to return from this newest treatment (after the hardened ones lasted 17 hours) were getting galled and starting to deteriate already and they didn't have ten hours on them. I was basing my hours on the set of gears I ran until the verge of complete failure-(see the pic). These latest gears have as much wfo time as all the other sets I ran this summer COMBINED and they barely have any marks on them,on top of drive being torqued from the 5 blade SO HARD IT SHEARED OFF THE PROP SHAFT!!!. My next step is to re-assemble my lower in next few days,then try running as much time as possible before the water turns to ice with 80/90 synthetic instead of 75/140 to see if the thicker oil is helping them live or if they can be ran with the thinner stuff and still live. I have a few local customers that trust me to do there drive work (I have all the neccesary tools and have been rebuilding rear ends and transmissions for 20 plus years) who I am going to try to sell on treating their gears (although most these guys are not running the kind of power I am).
As far as uppers,I have been a dealer for Max Machine worx since the xr gears first came out and they did have some problems with the first stuff they sold. I initially ran my bone stock 2000 bravo for about a season with my blown 502,i sheared the floor out of a stock gear when I added headers and went to a 28 pitch prop. At that point I bought all the upgrade parts Max worx was selling at the time-shafts,modified xr gears,a few different bearings that were supposed to be better. I sent my upper to them and had there steel tower installed,got it back and put the other parts they sold me in it and my lower. At that point I bought most the merc tools too. After a year they came out with a better short shaft that goes in the cone clutch,a better middle coupler,a billet seal retainer and a humungous aluminum cap that was supposed to act as a heat sink. When I installed these parts I flipped the top gear to the bottom and bottom to the top to even out the time each gear had on it (right hand rotation). First time out I sheared the floor out of the lower gear in the upper just like the stock ones do,I was beating the pizz out of it when it happened.Turns out they were machining the xr gears for their heavier duty caged bearing and in-advertently had weakened them. I installed their newest xr upper and lower gears (which weren't machined out) and there current heavy duty bearings (i think that was in 02). Later that season I tore drive down to inspect it before going on a long vacation and pinion gear had scallops in it about .005 deep so I replaced just it (the original was one of the early soft xr pinion gears ). Those same gears have been in my drive since then (5 seasons). The only part I have broke (other than the lower gears eating them selves up and the original max worx prop shaft breaking the other day that had 300 plus hours on it) was one of their vert shafts that I sheared off driving like a retard 4 years in 2003 (I was hole shot-ing my boat over and over again from almost a dead stop showing off). I still believe they have the very best upgrade parts that can go in a bravo housing,now that I have found a way to get the lower gears to live a more reasonable time, I expect my boating to be more enjoyable. I don't plan on trying to turn any 5 blade props though with 950 plus ft lbs of tq though because I feel it will just break something else ,Smitty

Whitey

Smitty,
With what you have done I would think someone running a stock set up would never wear out the drive. I too am hoping to hit the water a few more times before the ice. I have B1 lower case coming from Chris at Sterndrive spec. Hopefully it will be here in the next week or so. Dwight

PatriYacht

Interesting work Smitty. Are you using a solid driveshaft hookup with that Stellings box? I'm convinced that the Imco torsional driveshaft plugged into a standard Merc coupler is better for drive life. Other than that, it looks like you have this drive thing figured out. Do you think that 2 of your drivetrains would live in a Black Thunder?

articfriends

iTrader: (1)

Ian,I am using a solid driveshaft but this box has netted negative results all the way around so its coming off and a heavy duty coupler is going back on.These lower gears failing seems to be a problem with single engine boats with big power. Zt260,gpm,others and me have ran into this with 800 plus hp motors,everything in drive seems to hold up for most part then the lower gears start going away after long wfo passes,I think this treatment process is a good solution. In my case the Max worx parts in the upper have been holding up a very long time. In the bigger twin engine boats that are 8000 lbs plus ,even with less power, lower gear failure doesn't seem to be the case,most of us single engine guys run 1.50 ratio gears (the least durable ones),most the big boats run 1.36's which seem to be more durable). Them guys can't get ANY upgraded bravo drive to last,they blow max worx uppers right apart,shear off vert and prop shafts that are the best material out there,etc,etc. When I run a 30 labbed on my boat and I'm going 60 mph and wack the throttle,my boat rockets to 85 mph in less than 10 seconds.When I tried the 5 blade and I wacked the throttles at 60 or 70 mph,boat strained real hard and built up speed about 1/3 as fast,alot like the way a heavier,bigger boat accelerates. Sure enough after 1 day of testing that prop I broke a prop shaft and my boat has never broke one before.Your boat has had very few drive problems for as big as it is but I bet if you added superchagers like you have talked about or went to 5 blade props or both you would start disentegrating drives. Max worx advertises guys with 1000 plus hp boats using there drives but they are 4000lb to 6000lb single engine boats (and they also go thru lower gear sets). You don't hear them saying alot about 800 hp 12000lb boats though,Smitty

articfriends

iTrader: (1)

I been busy but here are a few pics of some batches of gears I have had prepped and treated for some oso'ers,local guys,mr gadgets and myself.Anyone interested let me know,I will have a few sets of new lower gears on the shelf that are cryoed and treated soon for anyone wanting to upgrade. Heres some xr uppers and pinions,trs gears,lower gears and even a set of 12 bolt gears I had done,they all looked beautiful after the gear processing,Smitty

articfriends

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Rexx

How have these bravo mods held up?

I'm looking to amp up my motors with boost, but, drive mods might be in order to keep parts flying in close formation of one another.

I read some interesting things in this thread. Being a design engineer, I can appreciate the good thoughts. Someone had mentioned a "coating" that is 90 Rc. If it is the coating I'm thinking of, it is called XADC patented by Armolloy of IL. I've dealt with these guys and the coating has very impressive characteristics. They guarantee 95 RC min. It has a low coefficient of friction of 0.09. It is a thin dense chrome with diamond particulate...goes on with about 0.0002-0.0005" thickness. Good for reducing contact stresses on gear teeth. However, it does nothing for bending stiffness of the tooth. As with all coatings, beware of the 95 Rc hardness claim. At the end of the day, the hardness is only as good as the base material hardness. Most steels won't get much past 60 Rc with reasonable fatiguing characteristics. Go to 70 Rc, and you will have glass gears ready to shatter with the slightest impact load.

The reason the Bravo drive only has 0.010" case hardening is.. this is the best penatration depth for fatigue life with reasonable tooth stiffness. Yes, you can thru harden to bump up the static ratings, but the fatigue life will be reduced considerably. Where this cross-over point is for a modified sweet spot...dunno. If I had access to a gear program, I could tell ya what torque can be put into for some reduced fatigue life as a function of case hardness thickness.

Anyhoo....please post updates. I'm interested in some real world results and I'm sure the rest of the boating community would love to learn more about modded Bravo 1 drives as opposed to the unobtainable speedmaster option.

Wobble

Smitty, it is time for an update, how are your mods holding up?

articfriends

iTrader: (1)

My boat is still apart (Motor freshening) but I did gears for guys in australia that ran them all winter with good results,a couple with serious single engine power. In a few weeks I'll be running again too plus I did up gears for about 20 different boats state side,haven't heard anything good or bad back yet,Smitty

powerabout

BBB
Your right, the top box ratio change lowered the torque transmitted to the lower unit on an Alpha.
The critical measurement in the lower unit is the lever that you would measure between the driveshaft centerline and where the tooth contact is.
Changing this measurement will reduce tooth loading and you do this by upping the ratio ( on a Bravo) as the lever gets longer i.e. the pinion gear has a larger diameter and or you up the top box gears to reduce the torque.