Dont they still have to be lapped?

I worked on this very issue for the lower gears as those are what fail on my 1000+ hp boat, I have very little problems with bravo uppers. After testing various coatings/processes and heat treating of stock gears I found that cryo treating /iso- rem finishing seemed to make the lower gears last twice as long before cratering. The upper xr gears on the race boats they were tested on still spit teeth off in record time how ever. Me and RM BUILDER were looking into having lower gears made out of a different material, a single test set was going to be upwards of 5000- 10,000$ and a small production run was going to be 10 times that with no guarentee that they would even last a few hours, the upper gears are even worse to re-produce, the other Smitty was working on it, never heard what final outcome was but I do know that everyone wants someone else to foot the bill on getting something built, sell it to them at cost and guarantee it will last forever plus never damage their drive if it does fail, I stepped back from the project after spending a good amount of cash and time on it and just settled on cry/iso rem treatment with high end oil and that increases the life of a full out upgraded bravo by about double, Smitty

Thanks for sharing Smitty!

That's the problem, most boaters know nothing about manufacturing, nor do they have the multi million dollar equipment to produce a precision gear set. I have all of that, I own it, I can use it whenever I want, not on someone else's time. What I am saying is, I can machine the gear set from any material conceivable, however I don't have the expertise to digitize a set, and generate a working 3D model, with smooth surfaces adequate enough to generate tool pathes from. All I have is touch probe CMM's, that's not going to cut it as far as generating a perfect, accurate model. Need scanning laser, and someone smart enough to use it (very hard to find).

Kieth, I can achieve a RMS 8 finish with my Mori 5 axis machine tools. That is slick as glass. Some fine polishing can be done after the fact though.

By the way articfriends, that post wasn't directed at you. Just adding to it more or less.

Waid

Oh no problem, we couldn't ene find a set of new gears that were consistent enough to digitize, they seem to have alot of inconsistencies. I would like to know the truth on the stock merc gears though, some guys claim they are made in China, sanother claim (that I believe) is the same forging dies have been used so long that they start to lose their consistency.
Rm builder talked to a gear vendor company at PRI or SEMA that had built sets of gear for a drive rebuilding company,they failed during testing and they never picked up the last few sets although nothing I would invest in as it was a guaranteed failure.
The problem every person in the know told me again and again was even though there are all kinds of kick ass alloys out there it would be hard to get the root strength in a "cut" gear vs a forged then machined gear, not saying it can't be done though, Couldn't a gear be digitized then "touched up" electronically to average out aspirations and abnormallitys?

It seems a lot of us have went down the same path on the gear sets in the last few years, that is how and why we developed the Bravo Shop gear lube.
For the size of the gears in a bravo drive there are not a lot of options to improve the strength of them, so the next thing was the gear lube and with the technology of today and additives available we were able to build a very successful Gear lube that has proven it self in all kinds of outdrives to be the best oil on the market.
Along with the special Cryo treatment and heat treat that we had help with from Dr Barron we have been able to improve the life of all types of drive gears.
While this is only scratching the surface of this very talked about issue it seems to be what most believe to be the root cause of the failures so we will leave it at that.

Just an idea but why don't you approach Mercury as a vendor to make the gears for them, someone is making them, if you were to make the gears for them in bulk you could experiment with different materials on your own. Maybe someone has already tried that.

As I said earlier, I have access to a hand held laser scanner, if anyone is interested. The surfacing of the digitized data is a lot of work though. I don't really agree with the need for near net forgings though. When you look at high end connecting rods, many are made from billet, even cranks are made from billet.

There are cad programs for gears. Plug in a few dimensions and the program will build a cad model for you. Nobody wants to do it for free though. Then, how do you machine the clutch side after heat treating?

IMCO made brand new gears for the SCX. Why couldn't it be done the same way they did it?

Among a combination of things like a weak design because they are designed to shift internally . The thing that makes bravos fail is actually the cases flexing and causing the gears to push apart under extreme torque causing the gears to chip. This is why all the aftermarket stuff is a lot heavier.You can not fix this problem with gears. Also a reason why the big drives have tranys.

Would't it make sense that if it was as easy as just making stronger gears Imco, Bravo Shop, Max Machine worx, etc would have done it already? Trust me I hope someone makes them some day.

1 Maiden america

I agree with that. But my guess is that Imco came out with gears that were similar to the XR gears just LARGER to gain the strength. (same with B Max upper) This is just my guess and someone can correct me if I am wrong. XR gears can only be so big and the strength, IMO, comes in size. Offroad Rock Crawlers fight with size and strength also. They want the strongest axles with the most ground clearance. Its a give and take.

I also was told when I owned my tool business, that a impact socket is actually softer then a chrome socket, to absorb the shock and not crack. The factory explained that theres way more to the design then just making the sockets "harder". To hard and they will just Shatter in pieces.

Great thread though and lots of good ideas

I've been running BMax since 2006 and have had good luck with them. The boat is a 36' Apache, flat bottom boat that weighs about 10,500 dry, without any fuel. I lost 2 mph top speed when I installed them but gained 1 mph mid-range speed with the BMax and didn't have any cavitation issues like I had with my old IMCO Extreme SC drives. I believe the main reason I lost any speed was the change from a 1.50 ratio drive to the BMax 1.30.

The first year I had them I was running 720hp. The year after that I bumped up to 830 hp and ran that for several years until last winter and now I'm pushing 875 hp. I've logged well over 350 hrs on theses drives since I've owned them. I've done full rebuilds on the lowers last winter with all new gears. They were in decent shape but I wanted to replace them anyway. I typically replace the bearings in the lowers every-other-season (minimal investment in this power range).

When I installed the drives my investment was pretty minimal, in my opinion. I paid the cost of the drives, which back then were being offered with a 2 yr warranty. I had to install new props ($1,200, much cheaper than a surface piercing prop or Herrings) and my tiebar had to be modified ($150) to fit the new wing plates. By the time I sold my IMCO Extreme SC's, which took about 2 wks., I was $5K out of pocked on the BMax's. So for me, I felt I bought 2 new drives for $5K with a 2 yr warranty and didn't have any more blown up IMCO Extreme SC's. For me it was a no-brainer at that time. If I had to do it again today (2013), I would have done it all over again but I may have chosen to use the new BMax 1.50 gear ratio that's available and I doubt I would have lost any speed. I'm still not sure I would have gone with a surface style drive these days because I have 2 small children and the thought of them swimming behind the boat with a set of Herrings gives me chills. Or, the thought of hitting a piece of driftwood and ruining a set of Herrings also give's me chills. But that's just my opinion. If I was looking for all-out performance and top speed, I would probably go the surface drive route. But then again, if I wanted all out performance I'd probably sell the Apache and get something that's faster with newer technology. :daz:

If you have any questions feel free to send me a PM.

Frank

Wasn't somebody working with Doug Fortin on gears a while ago?? I was at his shop years ago getting a porsche tranny set up for a class 1 car and remember him talking about doing something for a couple of off shore teams. That was a while ago and I do not remember specifics, but I destinctly remember it being brought up. That man knows how to make gears work.

Of course, but it needs to fit, and function correctly in a bravo drive. So you still need a stock set of gears to work from. I have solidworks 2012, we are a manufacturer for the oil and gas industry as well as the aerospace industry. I'm currently bravo less, so let me talk to a buddy and see if he has a bravo I can dissect. Then I will have a better understanding of the whole situation.

Never as simple as it seems, I see. What about the XR case is it "stiffer" or do the larger gears just coupe with the flex better?

Waid

Yes. because the XR gears are a straight forged gear it can witstand the small differences in backlash. If you go onto the bravoshop web site you can see the difference.

Was at the Bravo Shop this weekend. He pulled apart a Bmax upper from his black thunder.850hp triples. Roughly 200hrs on the uppers. There was hardly even a wear pattern on the gears. The lowers he pulled apart that had been hard shimmed were the same way. There is definitely something he is doing that is working.

That's the problem with the newer XR gears. No metal on the magnet because the faces hold up great. A tooth just decides to let go nowadays. My last one busted a tooth. Rotate the gear 180* and it looked perfect. It didn't get chewed up because it locked up and broke the stub shaft in the coupler.

Been there and done that in 2005 with Imco Extreme SC's. How they dealt with it sorta burned me on the IMCO brand. Glad I got rid of Bravo's.

What brand top cap is that? is the drive shower integrated into the cap?

X2

Same exact thing on an 8 hour old drive going 30 MPH. Just above plane in zero visibility on radar heading to long beach.

Never got a chance to beat on anything - tooth went - and the whole train stops... snapped shaft ...same deal.

Have about 100 hours of the rebuild mostly from easy lake running.

UD

That is the top cap from an IMCO Extreme SC. They integrate the shower into the top cap.

When I blew this drive the plate which bolts to the top cap (it looks like a disk) also blew off. My buddy who was running next to me saw a shiny, sparkly thing fly through the air moments before the drive blew apart. :poopoo:

Someone needs to catch that with a go pro.

Can an IMCO SC lower be used with a BMAX upper?

Yes, but you'll need a BMax vertical shaft. Basically a BMax vertical shaft is a little shorter and has larger splines. There was a member here on OSO that had a setup just like that on his Fountain with 800's.

on this forum, driven correct would be wide open as often as possible, right???:cool-smiley-011:

With all the XR's and IMCO extremes i went through i should have went the Arneson...but at that point i was commited to a Bravo config.
If i could turn back time it would have saved me thousands.
But my Max's and Modified IMCO lowers are surviving.

Panther, I made XR/IMCO salads just like those... LOL

BTW, I need to see that video again to get me in the mood for the season. Link please :)

if you dont mind me asking, who did your imco sc lowers?

Thanks for the info.

I skipped a few replies so I hope I'm not repeating ground already covered.

Let's talk about straight-cut gears. They are easier to visualize. The principles are the same as on helical gears and bevel gears (or helical bevel gears..) but let's stick to something we can see better in our mind.
Gears transmit power through a contact line to another gear. That "line" is theoretically 0.001" wide and is as long as the width of the gear. Depending on the pitch diameter of the gear, you can have several teeth in contact at the same time, multiplying the number of "lines" you have. The smaller the pitch diameter, the lesser number of teeth that can be in contact at the same time.

If the gears are machined absolutely perfectly (which is impossible in the real world), then the contact lines mesh perfectly as the gear turns. This also assumes there is ZERO change in the shaft centerlines as well (which does change slightly with increased loading). This contact line scrapes across the gear tooth faces and wears away the gears as they are used. The more load, the more wear. Add to that a small amount of case distortion under load which translates into slightly greater shaft centerline distances, and you lose the "help" of the other gear teeth, focusing a greater portion of the load onto the ONE primary contact line. This accelerates the gear wear as well.

So why don't all gears die a horrible death in 3 minutes?
Lubrication.

The lubrication is designed to "live" between the gear faces and buffer the contact line. The oil film increases the "effective width" of the contact line from 0.001" to probably .005" which is helpful, but as long as the thickness of the oil film is "greater than zero" it completely ELIMINATES gear wear.

Operating within a set of parameters that does not cause the film strength of the oil film to break down and allow gears to actually TOUCH results in those gears lasting virtually forever.

So optimally, here is a gear's job.
1) Provide as high of a combined sum of contact line area as possible to allow the oil to work.
2) Provide enough tooth strength to prevent permanent tooth deformation under load.
3) Provide enough flexibility to allow the teeth to temporarily deform under load to buffer tooth impact and load cycling.

A gear made of something insane like tungsten carbide will indeed be strong enough, but when it's lube strength is exceeded, two carbide gears working against each other will chew each other up just like two cast iron gears will. Those ultra strong (unflexible) gears will also transmit harmonics and vibration into the shafts and bearings, shortening bearing life dramatically.

The BEST way to get gear life is to give the oil more tooth area to work with.
How do you do that?

1) Increase the width of the gears.
2) Increase the diameter of the gears.
3) Increase the number of teeth on a given diameter (higher diametral pitch).
4) Increase the number of gears sharing the same load.

Number 3 is a double edged sword. Smaller gear teeth means that you have to control the shaft centerlines better. The amount of case flex and bearing distortion that is acceptable with a lower diametral pitch (larger gear teeth) is no longer acceptable with higher diametral pitch (smaller gear teeth). Therefore, shaft sizes must be larger, bearings must be upgraded, and case material must be thickened or changed to something less flexible. Obviously the aluminum castings we use in outdrives have a limiting factor on how well a smaller gear tooth will work - bottom line is that we're pretty much at the correct tooth size already..

Look at a BMAX.
Larger upper gears - huge massive gears. The same torque that kills an XR will live happily on those larger gears. The lowers, however, use pretty standard gears and set the limit for the torque.

Look at a Six.
Huge upper gears.
DOUBLE vertical shafts.
This shares the load between two complete transmission devices and allows a small gearcase bullet while doubling the torque capacity.

Lets talk seriously now.
Magic gears can indeed give you "redline" protection. In other words, when you DO choose to operate the outdrive in excess of what it's lubrication can protect, then magic gears can allow you to run in that zone a bit longer - but you are still operating in a zone where the gears are not protected properly.

Premium lubes, proper lash setup on the gears, good metallurgy on the gears, and upgraded bearings and case stiffening devices (good billet caps, etc) will do the MOST for letting your drives extend the zone in which you are operating where the lube still works.

Operating above the lube's effectiveness, however, is a temporary proposition.
Space age hardcoatings can help, ensuring good metallurgy (cryo treatments, etc) can help.

But the bottom line is that if you are running beyond the film strength of your lube, you're on borrowed time. Period.

MC

Nice post. Thanks for the engineering explanation.

+1

my choice now would be BMAX had them on for 5-6 seasons and only lost a propshaft and that's with 850s on a 98 42 fountain, but if I have to do this again im going to look real hard at arnesons. RIK sounds like a nice guy.

There is a local guy that does the setup on those lowers for me.
It takes a few assy and dissassy to get the exact shimming but its worth the extra hour or so spent on eachgetting them perfect.

Let's dig a little deeper into exactly what we are asking our gears to do in our outdrives. Here's what comes out of an industrial gear calculator used in sizing gears for industrial applications. This spreadsheet will calculate the max hp you should run through a specific gear.

First is the loading environment the gear will see. The choices are uniform, light shock, med, and heavy shock. Let's consider this in industrial terms and settle on "light shock". Okay.

The next choice is duty cycle. The choices are: Intermittent Duty up to 3 hrs a day. Medium Duty 3-8 hrs a day. And constant duty 24hrs/day. Let's go with Intermittent. Okay.

The next choice is helical or spur. Non XR's use helical bevel, XR's use straight bevel, but a helical choice will translate into a higher hp load so let's go with that. Ok.

The next is the tooth form. I say we choose a DP of 4. That's pretty close to the big beefy teeth of an upper gear. Ok.

Pressure angle - not sure what those drive gears use, but let's say 14.5 deg. Ok.

Number of Teeth: 16. Bravos run 16, 17, 19, 21 tooth upper gears. We will go with 16. Ok.

Face width of the gear. Ah, let's say the upper gears have a 1.1" long tooth form. Ok.

RPM: 5000 (the pinion will run at crank speed).

Helix Angle: 45. I would say the helix angle is actually closer to 25 degrees, but we will go with 45 since it gives us a higher result.

Material: The meanest material on the chart is 8620 case hardened, so let's go with that.

Guess what the chart says is the max hp you should attempt to transmit through that gear?
Cmon guess.

Yep, that's right - 97 horsepower.

Wait, that calculator uses a 3:1 load factor. That means that the rating is based on 1/3 of the yield strength of the gear material. Let's change that to 100% of the yield strength......Manually change the safe stress factor from 57000psi to 170000psi. Now what do we have?

Now we have 290 hp.

But how do we run boats with 600hp through gears that are rated to fail at 290 hp?
Hang on - they still aren't rated to FAIL at 290hp. They are rated to have no safety factor at 290hp.

THAT's where a garden variety industrial duty gear lube in a splash environment would start giving problems with this gear. What if we run the gear submerged in lube?

The number jumps to 380 hp. But that's still for garden variety gear lube.

So, it's safe to say that any Bravo that is being fed more than 380 hp is relying on the magic properties of its lube to protect the gears from eating themselves.

If the best lube is 30% better than the baseline (in EP scuff resistance and film strength properties) then you MAY be looking at an effective limit of 510hp.

Even with the best lubes, and magic gears, running above that is causing incremental damage to your gears. Hopefully a little bit at a time, but still is damaging them.

Larger gears is the only good answer.

MC

Great gear/engineering analysis! This is why i love this site!

I have that set up on my OL