More news on the B-MAX4

First of all, an apology. I have mislaid the camera case which has the USB cable in it so there are no pictures. I’m more gutted by the fact that the case also contains all our memory cards from the last few years…

Teesside regional

Moving swiftly back to the topic of the Yokomo B-MAX4, I finally destroyed the rear bevel gears at the Teesside regional meeting at the end of last year. I really should have bought some new ones but foolishly thought I could make the damaged ones last. In the end it compromised my last few qualifiers and my final, although not as much as the marshal who, ready to leap into action like a tiger, decided to lean over the top of a jump and obstruct my view throughout.

As an aside, buying the replacements turned into an epic. In brief, don’t expect CML Shopatron to supply the parts they say are available.

All in all though I enjoyed the Teesside meeting, despite the track being a bit narrow in places, mainly because it didn’t have any of the “big air” obstacles that seem to have become fashionable, and it added up to one of the better “racing” tracks I’ve experienced for buggies in recent years.

Setup tips

I also learned a little about setting the B-MAX4 up. Fundamentally, the car does not have enough roll stiffness for UK conditions so becomes edgy at the limit unless you fit the rear anti-roll bar (standard in the champions pack, I’ve tried a few and keep coming back to 1.1mm), and stiffen the front end (I prefer to use Associated blue springs, combined with Associated silvers on the rear, although you can get a similar balance by running the kit front springs mounted in the outside wishbone hole – although this limits droop and makes the car worse on the bumps). Other cars on the market can acheive extra roll stiffness by running an angled link to raise the roll centre, but on the B-MAX4 you can’t as there are only two camber link positions, neither of which gives a very angled link.

Using this basic setup at today’s Jarrow regional gave a well balanced car, although the tyres were excessively worn as I couldn’t be bothered to buy any new ones! As a result I was down in the D final rather than the C that I usually manage.

To get a better fit with the AE springs, get hold of the Tamiya spring bottoms from the 501X (#51282, use part X4), these let the springs sit a little lower for more ride height adjustment.

Gear mesh yet again

Once again I had problems with the gear mesh at Jarrow. This time I had gone too tight, resulting in a plume of smoke and a burnt out motor!

So, having now gone too loose and too tight, I think I am in a good position to advise how to get it just right (rather like Goldilocks!)

1. Get some extra, fine shims. 0.1mm or less. Yokomo do some but these may be hard to find in the UK, I used the ones from TOP Racing, supplied by Much-More UK. You need 12mm ID for the diff, and 8mm ID for the input gear. You can also use some 5mm ID ones on the opposite side of the input gear to take out the slack if you like.

2. Shim the input gear so it has the broadest mesh possible with the diff gear without rubbing it on the edge. The kit setting should be a good starting point, or maybe 0.1mm less.

3. Unfortunately, the mouldings of the top and bottom gearbox halves are not identical (at least not in my kit). So, put the input shaft and diff gear in the gearbox half with the tighter tolerance. If you set the mesh in the half with the slacker tolerance, the gearbox will tighten up considerably when assembled and cause you problems (such as the aforementioned motor cooking!).

4. Shim the diff so that the mesh is as tight as it will go while still rotating smoothly. There should be no backlash, small high points in the mesh should bed in after one run. Make sure all the side-so-side movement of the diff in the gearbox half is taken out with more fine shims, but make sure the diff still rotates smoothly.

5. Assemble carefully and check that the transmission rolls over smoothly. If any axle or gear seems to bind, disassemble and re-shim. Don’t expect the transmission on this car to spin, the tolerances are too tight for that, probably in the interests of durability. Unfortunately these tight tolerances put more load on the motor, it does get rather warm under the shell.

And one last tip

The only other issue I have had with the B-MAX4, and it is hardly a major one, is bending the front shock mounting screws, probably when the exposed threads catch the track surface during rolls and crashes. After a big impact these are close to shearing off.

A very simple solution which seems to have worked is to put a 2mm spacer on the screw before fitting the lock nut, this means that the round edge of the nut hits the ground first instead of the sharp edge of the screw. Despite landing on the roof and rolling a few times today, the shock mounting screws remain resolutely unbent.

That’s all for now. Hope these tips help you out, let me know if they do.

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