Monster Beetle Refurb Help Required

[moblies]

Hi all,

I inherited a Monster Beetle in need of some TLC, I have removed the original MSC and associated wiring, and installed a donated but functional ESC ( A dodgy cloned Futaba ESC courtesy off ebay I guess) seems to work ok with no setup needed for the Acoms kit.

Q1) The beetle was already fitted with an old 27mhz AM Acoms receiver so I just purchased a new Acoms Transeiver and a matching set of xtls which works apart from the beetle twitching forwards and hurtling off even when I'm standing over it. If I extend the Aerial fully it seems better but not sure it should do that so close - any thoughts? I have a re- re Lunchbox with Acoms but 40mhz and can happily leave the aerial down and still use it a fair distance.

Q2) When accelerating there seems to be a sort of grating noise which I can only describe as the wheels are turning but the Gearbox Cogs are slipping or missing teeth under full throttle ? I guess the age of it its fairly possible - again any thoughts or suggestions would be gratefuly received. If it is gearbox related what parts would I need for the overhaul and are they available anywhere?

Many Thanks

[terry.sc]

1) Usual cause is a broken aerial wire or a damaged receiver. You could replace the aerial wire with a new piece of wire the same length as the aerial to see if that is the problem. If not check if the solder around the crystal socket has cracked and resolder if it has. if not then you will need a new receiver.

2) The problem is either worn driveshafts or worn diff bevel gears. The hex drives in the driveshafts are known to wear at an alarming rate. The other problem is over time the load on the diff pushes the bevel gear apart, which eventually bends the alloy gearbox sides outward slightly. This extra play in the diff is enough to cause the gears to start to click past each other, which increases the wear, which makes it worse, etc,etc.

Both problems can be easily fixed as the replacement parts are the same as in the rerelease Frog. The new pin driveshafts in the rerelease Frog are a massive improvement over the hex drive ones that are in the Monster Beetle, and the diff parts are identical.

[mongoose1983]

Yes, you should replace them bevel gears.

They're not expensive and, best of all, you're going to feel the beetle runs just like the first time.

Enjoy your beetle. It really is a nice Tamiya.

EB

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[moblies]

Thanks guys, i'll give it a go.

[mymonsterbeetleisbroken]

Here's a breakdown of the bits we'd recommend you fit to get your bugs gears working again:

(from the monster beetle manual)

BM1 Shaft - This runs right through the differential and could be worn

BM6 (x3) - These are the small bevel gears which are made of soft metal and wear out if the diff isn't greased properly. They do wear out eventually under normal use anyway.

SA6 and SA7 - These are the left and right differential bevel gears, which are again quite soft and wear at the same rate as the small bevel gears.

Part B 2 (x2) - These are round plastic bearing carriers for the differential. The outer flange can wear down, allowing for more slop in the differential. Team CRP made hard plastic replacements to compensate, though the stock ones only wear down after a very long time.

Gearbox plate right and left - As terry.sc said, they are aluminum and therefore eventually become deformed, allowing for excess play in the differential assembly. They can be bent back, and even over done so they push a worn differential back together (this is the quickest way to get a little more life from the gearbox but is only a temporary fix!)

The hex drive shafts could be worn, though your problem sounds like a worn differential, which produces rather loud cracking noises under load. Slipping hex drives give a clicky noise as the truck drives around.

All the parts can be sourced from the re release frog and brat, though original monster beetle bits won't cost much more

[moblies]

Thanks for that, I was just about to ask about the actual parts required but thats me ready to order. It seems to drive fine when going slow but give it a fist full and it looks like the wheels skip abit. Could you recommend a place to get these and any other MB bits from? I have a few other bits that are either broke or tatty.

Thanks Again

[B.M.T.]

Replacing the bevel gears might not fix your problem.

Back when, people, magazines, etc all thought Tamiya's metallurgy was getting worse, because every time someone replace the gears in their Blackfoot/Monsterbeetle/Mudblaster the new gears didn't last as long as the old ones. I realised the reason, about 15 years too late....

The gearbox was not orginally designed for a diff. The Brat and the Lancia had a solid spool, and only later, did the Frog appear with a diff. Diffs then, were not contained inside the ring gear (in a hemisphere). The support bearings and gear case took the thrust load of the diff center trying to separate under load *any sort of gear will try to repel it's self away from the gear turning it, before it turns it's self, and bevels do it worse*.

So, what happens, every time you load the gearbox - accelerate, brake, land from a jump, go up hill etc, - the little gears in the diff center push apart, loading up on the side of the gear casing.... Which is soft aluminium, not originally designed for side load. Slowly, the side plates stretch outways, slacking off the mesh in the diff center. Every time it slips a tooth, it deforms the side plates worse and worse.

The quick fix is to get new ones, from a Nu-Frog, or to press the plates flat again. Easily done, as they are really soft. The permanent fix would be to make a pair of circular girdles, that attach with the 3 lower through bolts on the gearbox, that reinforce the thickness of the material around the diff bearings.

I actually made my Blackfoot's sideplates fractionally concave, to add more pressure to the diff center, and has worked a treat, so far.

[mymonsterbeetleisbroken]

Replacing the bevel gears might not fix your problem.

Back when, people, magazines, etc all thought Tamiya's metallurgy was getting worse, because every time someone replace the gears in their Blackfoot/Monsterbeetle/Mudblaster the new gears didn't last as long as the old ones. I realised the reason, about 15 years too late....

The gearbox was not orginally designed for a diff. The Brat and the Lancia had a solid spool, and only later, did the Frog appear with a diff. Diffs then, were not contained inside the ring gear (in a hemisphere). The support bearings and gear case took the thrust load of the diff center trying to separate under load *any sort of gear will try to repel it's self away from the gear turning it, before it turns it's self, and bevels do it worse*.

So, what happens, every time you load the gearbox - accelerate, brake, land from a jump, go up hill etc, - the little gears in the diff center push apart, loading up on the side of the gear casing.... Which is soft aluminium, not originally designed for side load. Slowly, the side plates stretch outways, slacking off the mesh in the diff center. Every time it slips a tooth, it deforms the side plates worse and worse.

The quick fix is to get new ones, from a Nu-Frog, or to press the plates flat again. Easily done, as they are really soft. The permanent fix would be to make a pair of circular girdles, that attach with the 3 lower through bolts on the gearbox, that reinforce the thickness of the material around the diff bearings.

I actually made my Blackfoot's sideplates fractionally concave, to add more pressure to the diff center, and has worked a treat, so far.

I think terry.sc and I already said that

Making the side plates slightly concave does work, just dont over do it or the spur gear will rub on the diff bearing carrier. When I installed my thorp dirt burner recently I had to take the slight concave bend back out, as the thorp counter gear is fatter than the stock one, and fouled on the bearing carrier!