b-max gearing

[branstonpickle]

hi i need some help managed to kill two 10.5 motors today i think the gearing was way off was running 81 spur 23 pinion was running at off road wars so medium size carpet track using a hobby wing 120a speedo basic settings no boost or timing any advice would be helpful thanks....

[RoyalCBR]

Hi Jamie,

In my Bmax I have run a couple of different gearing options, both using the 83T spur with a 6.5t motor - both times the motor gets very hot, but I am not sure if this is because I don't get enough air through to cool it or what.

So I have run 83T with a 21 pinion - mad acceleration, still got hot - way too hot, the other time I think it was with a 19t pinion (I will check later on the car) this was much better balanced, but still got hot. I run a 120a HobbyWing as well set as standard I think. I am still working out the bugs but I will keep you posted of my progress.

Oh and by the way it was indoors on carpet, track size medium I would say.

[Naushad]

Run 84 spur with 25 pinion....see how you get on. This worked for me indoors with a 10.5T Orca.

My current Bmax runs on a 8.5T Losi Xcelorin with 22 pinion and 84 spur....warm but not that bad! Interestingly, the Xcelorin has a heat sink built in as part of the can.

Try and get a heat sink on your motor and cut airflow slots on your shell.. I think this does help a little.

Oh...I've got lots of Bmax spares. So if you have a list of things you want let me know and I can set a price.

[branstonpickle]

cheers for the help i think the main problem from looking at it is the 81 tooth spur putting to much load on the car im gunna get a 87 tooth one and go from there...

[CODMAN]

Pickle, 81T/23T gives you a FDR of 8.27. Personally, I don't find that outrageously low for a 10.5T motor... but then again, that depends on track style, driving style, and a whole bunch of other things. Whatever your gearing or track, or driving style, you need to gear your Bmax according to temperature in line with the motor manufcaturer specs (each motor is different in this regards). In general, they usually recommend no higher than 150-160ºF at the4 end of the run.

What you need to do is setup you car with the gearing you want, then drive it on the course for 2 minutes, pull over and immediately check the temps. if it's still cool, drive another 2 minutes, pull over and check... Still cool? another 2 minutes and check... If you can make it through 6 minutes without going over your heat threshold, you are OK (or undergeared if you are way under the threshold). Then, you can start making gearing adjustments 1 gear at a time checking temps at the end of your race practice heats.

This is the only safe way I know of to set gearing properly for your motor. Also, as others suggested, a good heatsink/ fan combo can reduce your motor temp up to 10ºF...

Hope this helps!

[Si Coe]

I've been running my 10.5's at either 25 or 26, 81 or 84. I fitted the Bmax II motor mount to allow a better fit with those spurs, and 26/87 would mesh just about with that.
I've been using a SP V3.0 and an Orion 10.5t running fully boosted on a GM120 if that helps - runs warm but not silly hot.

[MILKY]

Unfortunately there seem to be a lot of motor overheats reported for the b max. Most seem to be to do with the diffs shimmed so tight they bind,coupled with a lack of airflow. Unfortunately the b max hates a loose shimmed diff so xtra shims in smaller increments to fine tune gives a good balance. Then work on airflow and gearing. Most cut out below the motor so might be worth a shout