Baja 5b pinion gear heatsink

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Looking for some extra cooling for your HPI Baja 5B? Well look no further than this machined aluminum Pinion Gear Heat Sink from HPI Racing that helps cool the pinion gear and clutch giving the spur gear longer life. The HPI pinion gear heat sink is a...

I can't quite get a grasp on how it mounts? Are they just mounting it right on the end of the gear?? Is there enough room between that & the gear cover?? In the pic it's sitting on the bell side of the gear, I know this doesn't mean anything but it's cornfusing me. It looks almost as wide as the gear so I don't think it'd fit in the gear cover, I can't see a boss that goes into the gear?
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yea, it looks like there is a slot just like on the stockers on the face, and it bolts to the face just like the pinion does to the bell.
i can see it helping to remove some heat form the pinion, which in turn will keep the plastic spur cooler, and should help stop any melting issues.
i just wonder what the over all effectiveness of it is. how much heat does it actually pull out of the pinions?
The more I look at it, it must be small enough to fit inside the pinion gear. I don't see how else it could mount. I'm definately not doubting it works, I can see it would help, how much I don't know.
I wasnt aware there was a need for a pinion gear heat sink. Has anyone had problems with the pinion gear overheating?
The heat sink mounts inside the pinion and just adds a bit more mass of alum and helps draw the heat away generated by the clutch. The pinion itself does not generate heat. It's the transfered heat from the clutch. To me this is a great functional option. I'll be getting it for sure...
I am of the mind set that it couldn't hurt. It's cheap and I don't see any down side to it so I'll be getting one. Since it seems to come with new gears I'll definately have one.

I Find It Hard To Believe That Hpi Takes The Time To Worry About Problems That Have Yet To Surface, Yet Overlook The Obvious. How Is A Heatsink Supposed To Work Under A Gear Cover That Prevents Air Flow? Either Way, Has Anyone Encountered The Problem Of Overheated Pinions And Melted Spur Gears? Instead Of Taking The Time To Machine Heatsinks, Why Doesn't Hpi Use Their Resources To Develope Diferrent Sized Spur Gears Rather Than Just Offering Pinion Gears That Obviously Will Not Properly Mesh With The Spur Gear Due To The Inability Of The Engine To Be Repositioned. I Just Don't Get The Thinking Behind This Company. Also, Keep In Mind That While Under Normal Circumstances, It Is True That Most Of The Heat Will Be Transferred From The Clutch Bell. However, Improper Gear Meshing Will Add Considerable Heat Right At The Point Of The Gear Mesh. Maybe Hpi Knows This And Is Trying To Cushion The Fact That This Pinion Only System Is Lame. If Not, Why Do They Design Their Other Cars With The Ability To Reposition The Engine To Achieve The Proper Gear Mesh? Of Course, This Is Only My Opinion.
The best I can tell you about their 'other cars' having adjustable mesh, they are not gassers. I like the fact that the motor is solid mounted,non adjustable, this part of their thinking I do not disagree with. The rest of it, who knows?
The engine being solidly mounted is due to the fact that the engine is a stressed part of the chassis. It actually accounts for the rigidity of the rear chassis, which is fine. That is why many people have experienced broken lugs on the flywheel covers. My point is that there are two logical ways to go, speaking mechanically correct. Either you provide gears in a variety of matched sets that will accomodate the inability of the shaft centers to move, or you provide a means to change the distance between shaft centers, usually accomplished by adjusting the engine position. It doesn't matter if the car is powered by gas, nitro, or electricity. The fundamentals of gearing still remain. I can think of no other vehicle on the market that does not allow the engine or motor to move to accomodate gear mesh. Hell, the first r/c car that I'd ever owned, a Tamiya Sand Scorcher, had a fixed motor set up. However, the kit came with an additional matched gearset in a diferrent ration. This was 27 years ago and to my knowledge, the geometry fundamentals have not changed. In the case of the Baja, a matched gearset is the only practical solution. To design the chassis any diferrent than it is would require considerable changes.
I understand how gears work, my point is, they used the motor as an integral part of the frame & kept the mesh between the gears constant by not making it adjustable. A nitro doesn't weigh 20+ lbs, I don't think slotted motor mounts on something this heavy would've been a good idea. I also don't feel that turning around & offering the pinion only option was very wise. Seems to have defeated the original idea.
Thank you! I know that many of our fellow members reading this may not understand these situations as well as you and I. In no way is my intent to confuse and or criticize anyones mechanical understanding. I have worked in the retail hobby industry for a long time, and my experiences have shown me that the majority of those involved in r/c cars really don't have a thorough understanding of these things. And truthfully, you don't need to in order to have fun in the hobby. I have seen countless examples of r/c cars whos owners have unknowingly jammed gears together even though a means of adjustment was available. The end result was always damage to the car. This setup just can't work properly. I just don't want to see our fellow modellers damaging their vehicles because HPI claims this will work. The only way I can see this working, as many have claimed that it does, is if there is considerable play in the clutch bearing and transmission input shaft bearings, which would allow the two shafts to misalign. If this were the case, it would appear that the gears are meshing. However, we both know that this only proves to mis-align the input gear inside the transmission, mis-align the clutch bell, etc. A whole list of other problems.
By the way, do you know what the actual pitch of the gear teeth is? I'm assuming it is metric. I have a line on some industrial gears and I may be able to find some that will work with the now offered pinions, but I need to know the pitch. Thanks.
Steve Z
I'll be darned if I didn't figure out that pitch a few weeks ago, wrote it down & now can't find it!! Always happens that way, I have gears, matched pinion & spurs designed, I just haven't had the chance to make them yet. Hopefully in the next month or so I'll get a test set or two made.
I wasnt aware there was a need for a pinion gear heat sink. Has anyone had problems with the pinion gear overheating?

I have had two spur gears melt do to heat tranfer. I don't think its something to worry about with a stock set-up but once you star running bigger motors and high RPM clutches this is when it started for me.
If you need a tester let me know I will stick them on my 30.5cc and give them hell.I agree with you guys they may be working with the other profile pinions but is it really the way to go I think not.How long will these things last with unmatched gears??That remains to be seen.But any thing else just doesn't logicaly make sense.
Anyway Im gong to try one until something better comes along outta desperation.I don't understand HPI's thinking sometimes either but what are ya going to do??
Pinion Gears


I was just on ebay, and I saw an auction for some 5B pinion gears from Germany, which I am sure you have all seen. Upon close inspection of the photo of these gears, each appears to have a different profile gear tooth. I had never seen this before. For example, if you were to use a 15 tooth rather than the stock 17 tooth, there would be consideral slop between the teeth of the two gears. However, the 15 tooth gear pictured has teeth that are considerably different from the 17 tooth. The teeth are "fatter" which would compensate for the normally resulting excessive backlash between the two gears when a smaller pinion is used. The larger the number of teeth per individual gear, the smaller the teeth are machined to compensate for the increase or lack of distance between the gears. Now I can see this solving the gear meshing question. This is is how HPI has to be doing it also. I had never thought , or have come to experience, gears of different tooth profiles use to compensate for correct meshing. But as I sat here and tried to understand this , I forgot one of the basic gearing principles of all and that is that when changing the ratios between two gears, their shafts have to be readjusted only if the tooth profiles between the two meshing gears remain the same and the number of teeth on only one of the two gears involved is altered. Although overlooked by myself and possibly others, this is the only concievable way that this could work. I knew I was missing something. I had never taken a close look at the gears offered on ebay. The photos I've seen of those offered by HPI don't lend themselves to the same "straight on view" as those offered on ebay.
My thought now turns to this. Although I can understand how the gears can be properly meshing, how effective are these gears? The whole effectiveness in a gearing change is to change the leverage ratio from the pivoting center of each gear to the distance outward where the two gears actually mesh. Keeping teeth of the same size and going with less of them, a 17 tooth pinion down to a 15 tooth pinion, makes the diameter of the 15 tooth pinion physically smaller than that of the 17 tooth pinion. This changes the leverage between the center of the pinion gear outwards to where it meshes with the spur gear. However, using larger teeth on the 15 tooth pinion in order to compensate for backlash really does not alter its diameter. It cannot, or the two gears would not mesh because both shafts (pinion and spur gear) are in fixed locations. Also, going with an 18 tooth pinion means that because there is no adjustment between the spur and pinion gear shafts,the teeth of the pinion would have to be made smaller, which the photos indicate, and would mesh with the spur gear at the outer most area of its teeth, thus increasing the leverage ratio of the pinion gear to that of the spur gear. Technically, this provides lower gearing whereas a pinion with more teeth should provide higher gearing. All said and done, I still believe that, under the circumstances, the only way to achieve realistic gearing change results is to change the pinion and spur gears as a matched set.
Steve Z
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Steve, we have discussed this with the manufacturer of the German gears several times on HBF, he swears it works & untill I try it, I can't say it doesn't. My personal thoughts are that you can't beat a set of matched gears, that's not to say that HPI's method won't work, just that knowing the mechanics worries me. I will be trying HPI's pinion gear for sure.
I see it working fine. I have never had a stripped Bell/Spur issue with the Tmaxx useing the same idea. now sure the motors are movable. but until your making 4 or 5 tooth jumps you don't need to move the motor block typically. at least when using properly made pinions.
for instance, my Tmaxx has/had a RRP 72 t steel gear, i can run from a 15 to 22 tooth bell with it, though some wont work like a 19t or 22t due to the profile. but the others worked fine, caused no undue wear or failures that wernt WOT and Hung up wheel

i really don't see the being a major problem wiht 2 or 3 teeth differance. but the limits are at that same 2 or 3 teeth differance. any more or less and the profiles, as well as pitch, and lengths and faces change too much to mesh correctly without different spur size and tooth count/profile changes.

i don't see them being a problem as they currently are. BUT theres more than one way to skin a cat!!!
I see what you are saying, but I will give $100 to whomever can, on a T Maxx, SUCCESSFULLY go up 5 teeth on the pinion and NOT adjust the motor position. No way, unless you were running with too much backlash to begin with. Even then, I say, no way.

Steve Z
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