Heat Treating OE Gears a waste? 4

[apex944]

I've got a guy with a big turbo on a small car that used to make 100hp. Now he's pushing 350 and breaking gears all the time (imagine!)

Anyway he wont pay for proper racing straight cut gears and shafts so he wants to try heat treating.

Is there anyway that a heat treatment could be this successful on gears made for 1/3 the HP this engine now makes?
And if so, what type of treatment are we talking about?

Thanks in advance.

- Bill

 

[TVP]

It all depends on the type of gear, the materials used, and the failure mode. The highest strength gears (both bending and pitting) are case carburized, shot peened, and then superfinished. It may be possible to improve the existing parts using this combination, but without knowing geometry, stresses, etc. it is difficult to know the extent of any potential improvement.

 

[swall]

I have heard of drag racers overtempering gears to make them a little tougher. This is anecdotal and supposedly the trade off was making a softer gear that could take more impact loading but not wear as well. But, I wouldn't recommend this option for a street car. I think you need to tell your customer that it costs money to go fast and he needs to shell out for some gears that can handle the load.

 

[MikeHalloran]

Regular OEM gears are probably already case carburized, and with better process control than anyone could manage on a one- off basis. Shot peening and superfinishing might improve them a bit ... or you might do as well by retrieving moderately high mileage used gears from salvage yards and assembling them with new bearings.

But he's apparently expecting miracles.

Racing parts are ordinarily used for N events (where N is a single digit integer) and then discarded, so their lifetime in a street car is not known, and may be shorter than OEM parts.

How does your customer feel about pre-emptive replacement of the OEM gears at regular intervals?

Maybe it's time for him to buy a 350HP car.



Mike Halloran
Pembroke Pines, FL, USA

 

[IceStationZebra]

Tell him to stop doing burnouts and learn how to shift correctly. ;-)

Seriously I concur with Swall. If you make the gears harder you will probably make them more brittle, depending on the material and existing hardness of course. You also risk distortion, and without touching up the gears could end up with problems.

And I would think that a set of gears would be cheaper than a ruined transmission and a tow from who knows where.
ISZ

 

[Javier72]

It is not a good solution to do a heat treatment. So big power increase will break the gear teeth by fatigue in the internal zone of the teeth, while the heat treatment in gears is interesting principally to avoid waste problems and pitting in the surface of the gear. Like ISZ says, if the heat treatment goes to the internal zone of the teeth, they are going to be more brittle, and it is going to be easier to break them. Sorry, but it is going to be necesary to change the gears if it is wanted to have this power increase.

 

[NickE]

"Regular OEM gears are probably already case carburized, and with better process control than anyone could manage on a one- off basis."

EXACTLY!

Anyway holding the surface finish, tolerances, and dimensions by attempting to re-heat treat an already finished product is silly. I just dont think it can be done reliably.

other than going to a completely different material (S7 comes to mind if shock is killing the gears) Maybe a softer clutch, and a restrictor in the slave cylinder will prevent him from sidestepping the clutch.

I have a feeling that the biggest benefit of aftermarket parts would be the changed geometry. Rarely does material or heat treatment actually solve failure problems, it may only mask them.

Nick
I love materials science!

 

[thundair]

As others have said it is impossible to anneal and reheat treat finished gears..
In a post process I was wondering if you could reduce some shear load friction with nitriding and add strength with cryogenics?

..Maybe the real kids could answer that...

Cheers

I don't know anything but the people that do.

 

[NickE]

Cryogenic treatment will not raise the strength of properly heat treated gears. Nitriding has the same problems as trying to re-heat treat.

One thing that might help increase the resistance to failure from shock loading is using Redline Heavywt Shockproof gear lube.

But its not reccommended for daily drivers, and is kinda like pancake batter at temps below 50F.

 

[patprimmer]

Drag racers actually heat treat gears to anneal them, not to harden them. This increases toughness and allows higher shock loads without breaking, but greatly reduces wear resistance. This increases life as drag racing gears normally break well before they have any significant wear.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TVP]

patprimmer,

Can you provide some references related to annealing of drag racing gears? It may just be a matter of terminology but I think it is more likely that drag racing gears would be quenched and tempered (through hardened in a neutral atmosphere, oil quenched, tempered above 200 C) than annealed if good toughness is desired while retaining adequate strength. Typical automotive practice is to case harden (carburize) gears, but some gears are still through hardened. Annealed gears would not have sufficient strength to resist the bending stresses induced at the tooth roots.

 

[patprimmer]

My reference was purely anecdotal.

Drag race gears are advertised and promoted as soft.

I am sure your description of the process is more accurate than sales promotion material.

Toughness and strength, but not wear resistance are required.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[swall]

Pat & TVP--this is what I was alluding to in my post. I heard of this many years ago, probably in Hot Rod or Carcraft magazine. Re-tempering a carburized gear at a higher temperature seems the logical way to make "soft" gears with more impact resistance. I though this might have been attributed to Bill Jenkins, but I check his book over the weekend and didn't find anything.

 

[MechanicalChef]

By re-tempering a carburized gear that wasn't packed in carbon (graphite, charcoal, etc) and without a protective foil (such as used in knife heat-treating), you'd evacuate the carbon in the surface metal. (decarburization) Hence, changing the alloy and reducing the surface hardness of the gear. While doing this might reduce the potential for crack propagation at the surface, I doubt "softening" the gear would have any major impact on preventing catastrophic failure from shock-loading. Plus I'm hesitant to suspect someone doing a secondary heat-treatment would be able to improve the gear properties much over an OEM treatment. (though I have no experience in this area)

"Is there anyway that a heat treatment could be this successful on gears made for 1/3 the HP this engine now makes"

I'd say probably not. But if he wants to try, I'm sure there is a shop somewhere who will be willing to take his money.

 

[swall]

MechanicalChef--re-tempering would involve heating the gears between 800F and 1000F. No decarb going on at that temperature. No argument from me that the OEM gears are optimized for load and fatigue life, but my posts, TVP's and Pat's posts speculate on a trade off--tougher gears even though the end product wouldn't have the durability.

 

[pontiacjack]

I've been carefully following this thread, since we hot-rodders are always encountering some new challenge that involves gears. While I agree that OEM gears are processed to optimum characteristics, I do have hands-on successful experience with one example of re-heat-treating factory gears, out of necessity. In building up the 9" Ford differential for my mini-pulling tractor, adequate strength of some items was straightforward- billet 4340 case, 9310 alloy 'Pro' ring & pinion, 300M axles, etc. But pulling is unique among motorsports, in requiring full 'open' differential action, to enable steering via rear brakes- we can't run a 'spool' as most racers do. So there is no aftermarket supply of strong side & pinion (spider) gears. All Ford side/pinion gears measure at least 58 Rockwell-C (presumably for 100,000+ mile durability) and routinely shatter in my application. I've had reasonably good results by having sets of side/pinion gears re-reat-treated down to around 48-49 Rockwell-C.

 

[IceStationZebra]

pontiacjack - Did you use factory or after market gears? One would assume that late model factory pieces have just enough strength/endurance for the application and use some odd/cheap alloy that facilitates consistent case carburization and low distortion. After market gears probably use more common alloys to facilitate the smaller batch processes which are probably more up to your needs.

And while tractor pulling is definitely stressful you generally aren't shifting under load and you only "drive" a couple of miles a year. And I know you can drive if you can handle that beast ;-) (Thanks by the way - I have a buddy in the sport I will pass this info on to. Modified stock mostly) I haven't shattered any spider gears but I did have problems taking out the thrust bearings (copper discs) with off-road forklifts driven aggressive on ice - couldn't handle the one wheel spinning for any length of time.

ISZ

 

[pontiacjack]

Icestation- aftermarket side/pinion gears weren't available, so I was stuck with compromising the longevity of OEM gears.
Extended "differentiating" action usually mandates re-thinking the lubrication of the thrust washers- extra face grooves, "scoops" on the case to dump more lube onto them, etc. I briefly tried Torrington needle-thrust bearings there (which don't need much lube), but they couldn't handle as much thrust as bronze washers. I didn't actually break any needles, but routine inspection showed the steel 'races' had been marked by the needles, so I went back to bronze.

 

[JEC31]

Good thread.

From a wider point-of-view: at this point in it's development, the little car with the big turbo is essentially using the gears as the fuse in it's overloaded little system. If the gears are upgraded to handle the high shock-loads the driver's right foot is generating, the next thing to break will be the next light-duty drivetrain components along the power path - perhaps the halfshafts. Then the little CV joints, then the little wheel bearings, etc, until thousands of dollars and hundreds of labor-hours later the full-race drivetrain is complete. Then it's onto tackling the suspension, braking, and unibody problems from the high speeds and heavy g-forces. This is the "slippery slope" of modifying a light-duty car for high power.

I happen to know of (via internet forums) several street-driven supercharged V8 owners that use stock-sized high-treadwear tires as the fuse, rather than expensive drivetrain components. They accept the performance trade-off because they aren't building racecars.

- Josh, CMM Jedi

 

[romke]

i doubt whether any type of treatment would be succesful, given the large increase in power (and torque that has to be transmitted. see the graph page 8 of this document:

http://www.gl-group.com/pdf/DEWEK_2004.pdf

it lists the type of damage that can be expected depending on the loas/speed combo in the application. your client seems to be operating above the blue line in the graph...