XR Gear composition
 

Over the last ten years I've noticed the hardness of the upper Bravo XR gears go from a average hardness of RC54 down to a hardness of RC48 on a set I did last week.
1. Has anyone else experienced this?
2. Does anyone actually know what grade steel is used or the composition of the gears?
3. Could these gears be re-heat treated or has anyone ever taken them to a metallurgist to discuss re-hardening the gear teeth faces.
4. I am assuming the die forging tolerances aren't held to as tight a tolerances as were once used. (It obvious when using gear marker dye
on gear set up) This indicates to me that REM polishing and hard coating the gear tooth faces could be a hit or miss proposition.

I'm very much aware of the break in procedure needed to burnish the teeth in, but after break in under a microscope the grain structure still looks worse than I've ever seen them.

Can anyone feed me any info on the steel used in these gears and if you're seeing the same?

WB

my guess is chinese steel.

Had a set cryogenically treated and they went 300 hrs without failure. Prob still together but I sold the boat.

Mike, Its funny that you mention Chinese steel. I called an aftermarket outdrive distributor called SEI in Orlando Florida and the friendly tech rep took a gear set back to his hardness tester and called me back with a measurement of HRC55. The same Mercruiser used to be ten + years ago. He also said it was of a near net forged design and looked identical to the rough finished OEM gears.

Cryo-treating may help the strength of the gears but it won't help the gear face hardness and the grain structure of the faces.
I am a proponent of Cryo-treating but not till after getting the gear face to correct hardness first. I'm not about to try any heat treating until I know the metal first. Then I'll cryo.

Also I am taking a wild stab here but I have a feeling Eaton gear may be making Mercruisers gears. Please correct me if anybody knows the true suppliers. For grins and giggles just look at the front page of the Eaton catalogue
http://www.eaton.com/Eaton/ProductsS...ears/index.htm
It sure looks like a Bravo lower gear to the right of the sample gears in the picture, heck one even looks like an OMC outboard gear. Like I said this is just a wild guess and nobody's talking. Also I'm still looking for the the type of steel used. Jokingly I doubt its any exotic steel or 8620, maybe it could be in the 4140 ,4320 range somewhere and modified for near net forging.

Thanks in advance for any ideas.
WB

Srq, there are many threads on here with the information your looking for. Just use the search function.

http://www.offshoreonly.com/forums/d...materials.html

http://www.offshoreonly.com/forums/g...xperiment.html

I'll be following this thread. FWIW, I've gone through more than my share of XR gears over the past three seasons. On my boat, the lowers get consumed rather quickly. I'll break an upper if I'm lazy on the throttles on re-entry. Upper pinion gears seem to last 80 hrs or so.

I've cryoed/REM treated every set of lowers I've replaced. Seems like it really does not matter as some are deeply pittted at 35 hrs and some will last twice as long. I feel many of the forgings are porous, occasionally, you'll get a decent set that shim up within spec. (acceptable backlash within a 360 degree spin) Tried all the "special" drive oils, nothing seems to matter.

On my boat, 30 Cigarette T/S 575SCI's with many upgrades, running 5 blade Hering 34's, at 35 hrs, I'm seeing way more metal on the magnets than I comfortable with. I then do a flush run on the lift with cheap oil then swap them from side to side and wear the back sides of the teeth. By 70-80 hrs, the gears are toast and get replaced before they explode. -I've got 4 complete drives, two on the boat and two spares ready to bolt on.

Sure would be nice to have options. While attending the Miami show, Seven Marine had a cutaway of their dual shaft lower. The gears looked very similar to Bravo gears but did not have the part numbers stamped into them like Merc gears do. I had asked where they were having their gears made and was told Detriot. They are also a net forged gear but appeared to have a much smoother finish (did not appear to be REM treated) I had asked if they were in fact Bravo gears and was told no. I had then asked if they would interchange with Bravo gears and was also told they are of a very similar design...would not go as far to say they would but did not say they would not..

Seven Marine is owned by the ex Director of Engineering for Mercury. I'm sure he's aware of the Mercury gear issues and has a better mousetrap for the 557. Who's game to order a set of the 557 lower gears and see if they will interchange?

I've wondered for quite awhile why they don't simply make the upper gears bigger. The upper doesn't need to be hydrodynamic so why not build an upper housing wide enough to hold big, beefy gears? Something more in line with what's used in automotive rear axles. It seems to always be the uppers that fail.

Thats basically what an SCX is - 5 inch gears. I 100% agree with you, Merc should do a 5inch bravo.

Thanks for all the inputs, guys.
Powtown missile since you don't know me I appreciate the fact you directed me to the search functions.
In the past I have spent many many hours and read all the articles by Smitty and Dick Tyce to name a few but again everyone was guessing as to the gear composition. Dick Tyce came the closest by having "a" gear shot with one of those guns for chemical analysis but didn't say if it was a near net forged XR gear or a helical cut XZ gear he was analyzing. These would be two way different metals and the XZ gears seems to run around a Rockwell 64C anyway. .Dick, I want to say thank you for sharing that composition info with us, please let us know what gear it was if you can.
I may be wrong but a "Near-Net Forged gear" is going to be a completely different steel comp. than a hobbed billet gear like an XZ helical gear due to its grain structure . Not to mention a near net forged XR gear having to be hot press stamped into a heated die. I'm sure there may be some lubrication metallurgy involved in there also. While reading some white papers on Net Forging and Near Net forging I bet the chemical composition is even different between those two operations.
"I get it" when all the M1 , S7 9320 , 8620, 4340, 4120 etc etc steels get brought up and I agree we could make a better gear with these steels but the XR gears aren't billet hobbed heat treated gears.
So back to the beginning, I still haven't been able to get to the root of the question and that is "what steel is being used for Near-Net Forged Mercruiser Gears"

The Seven Marine group guys I guarantee know where to get these gears and what steel they're using but probably can't release the info due to non-competes and other various trade secret bindings. But yes, they have some well thought out, very nice looking stuff. If anyone would know, it would be these guys knowing how to dance around the patent infringements. lol
I just love their lower unit design.

I hope more people can weigh in. One thing we all agree on is that the XR gears themselves are not as good as they used to be and that being said the above average performance boater is applying more and more power than ever now. Way more than what the original design was made for. It sure would be nice to just get back to the original quality of the gears ten years ago and do the cryo and rem from there. Btw you don't hear about the "quality" of the XZ gears going downhill, only that they may not stand up to the extra horsepower being delved out now a days. They are pretty brittle 65C and thin.

WB