my bravo outdrive gear experiment
 

As some of you have seen in my responses to bravo questions my boat chews up lower bravo gears on a regular basis. My single engine boat with fuel and passengers weighs around 5200 lbs,I'm running a blower motor making 950 plus ft lbs of tq. I'm running a max machine worx upgraded bravo and I also have a spare max drive. About every 40-50 hours the lower gears are chipped up so bad they have to be replaced,my uppers (other than the first set of early xr gears that were soft) are holding up with no problem.The lower gears start failing right away putting metal in my oil,I change it just about every weekend to try and keep from ruining every bearing in the drive.I been researching better lower gears,so far the bravo shop says they are coating their gears but they are not available outright yet. Max worx is experimenting with heat treating them and is supposed to be developing some exotic high strength gears but again,none are available yet.
I decided to take a set and get them treated myself as was brought up by Raylar and others in a different thread. I bought a used set of gears with no chipping or scalloping from Jamie at lakeside restoration. I wanted to have a set of gears that were "polished/patterned in" already in a low perf application. I took them and a tore up set to a local heat treat shop,we have countless shops like that in my area. The guy rock-welled them and it was around 60-61. They appear to only be case hardened 5 or 10 thous deep,the shop foreman I dealt with felt merc engineered it that way to have more core/root strength but was willing to do whatever I wanted. I went with a heat treating process that hardens them 60-80 thousandths deep.It took 3 days for him to turn them around, and it only cost 33$. I trial fitted them on the vert shaft and prop shaft tonight,they now fit very tight which I expected but they will fit enough to get drive back together.It will be a few weeks before I can get my spare drive back together with them. I plan on tearing lower down every 10 hours and inspecting the gears, its possible they might break in half or spit teeth off the first time I go to WFO which would be a new problem I never had,We'll see. I'll keep everyone posted and I'll post some pics too,Smitty

Re: my bravo outdrive gear experiment
 

When you say "tight", your not reshiming?

Re: my bravo outdrive gear experiment
 

Or did he mean a tight fit on the shaft? I know of one other guy here on this board with even bigger power than Smitty, who is trying some sort of treated gears. His results are not in yet either. Maybe soon we will have some answers.

Re: my bravo outdrive gear experiment
 

Smity did you xray the gears to make sure there were no fractures before treating.



zt260 has the new style B-Max lower gears he's over 1000hp and TQ

Smity I think Dean is waiting to get the sold drives [mine]out first before he sells them out right.I think Deans gears are around 90 rockwell But he does some kind of coating to keep them from pitting from the ep of the oil failing..


Keep us posted

Rob

Re: my bravo outdrive gear experiment
 

Smitty,
Glad to hear you are making progess!! I hope you find the answer. Joe, he meant the gear sliding onto the vertical shaft splines..
Hi Vinny.. sent you an email..

And Rob, I get to your posts and that woman makes me lose all consious thought.. And here we are talking about gears... what is wrong with us!!??

Keep us posted Smitty!

Re: my bravo outdrive gear experiment
 

When I said tight I meant the shafts. It is now very difficult to get the shafts into the gears, they will start into the splines tapping lightly with dead blow rubber hammer but stop 1/2 way. I think I will be able to draw vert shaft on with the nut and drive prop shaft in with carrier nut but getting it back apart later may be a different story.
Strip,I should have had gears x-rayed but didn't think about it,I also was so damn excited when heat treat guy called for me to pick up the gears I forgot to ask him what they now rockwell at,I'll keep everyone posted even if its a total failure,Smitty

Re: my bravo outdrive gear experiment
 

Rob,are zt's gears the new from scratch, extra hd gears or the hardened/coated stock ones,Smitty

Re: my bravo outdrive gear experiment
 

Have you ever considered Cryogenic treating the gears?
One of our members, Jpclear, had his gears treated for his TRS. He is running all of 650 HP through this drive with zero problems to date. He could embellish more on his success than I can.
Check out the sites listed below.
http://www.onecryo.com/onecryo/manuf...manmarch98.htm
http://www.onecryo.com/onecryo/motorsport-imssept98.htm

Re: my bravo outdrive gear experiment
 

Smitty,
No, ZT's gears have a few hours on them. If I remember, 2 hours. Dean @ Bravo Shop did some treatment for him to test. Not sure what was done. The last I spoke to ZT, he had no results yet.

Dick,
You are right about Robs posts, its difficult to concentrate!!

Rus,
I dont remember if I told you or not, but that new oil cooler works great.


Vinny

Re: my bravo outdrive gear experiment
 

There are a lot of different heat treat processes depending on what is required for the usage. More important than the final RC and the depth of hardness is the material being used. I would imagine those gears are some kind of tool steel like H2, H13, M2, etc. Does anyone know for sure or did the heat treater you used run a spectrometer burn to determine? If you know, let me know and I will get a couple metallurgist's I know to review and give their opinions. If the metal was only at a higher rockwell a few thou deep, and a lower rockwell deeper, I would suspect they were used gears and had work-hardened on the surface. On most metals the harder you go, the more brittle it becomes. Your pictures look like an issue with brittleness vs hardness (I could be way off base though). Processes used in high heat/high wear applications have also been improved with the use of new coating processes. Different titanium coatings(plating) have been used extensively in cutting tools, die-cast dies, and gears. Some of the best coaters there are are in the Detroit area. If nothing else can be determined, I will have you send your broken gears to me and we will run them on the spectrograph at work and also take RC tests at different depths. One more tidbit, typically heat-treat will remove carbon from the surface on all carbon steels. The higher the carbon, the harder the steel will become. In most critical surface issue products they will harden the steel in a carbon atmosphere(carborize) so the loss will be minimized and the surface will be hard. When testing for hardness, the actual approved process tells you to grind the surface of the steel to a depth of .010 to remove the decarb area where you will get a false reading.