MR4-BC Gearing

[Stew Noble]

i use a 19x2 with my BC and was wondering what a rough starting point for gearing was

cheers

stew

[mike.stening]

with a 19x2 you should be more than fine with an 18, 19 or 20 pinion.
;D

[Doomanic]

That sounds really undergeared!
In my MR4MT I used an 18 pinion with an 11 Double.

[mike.stening]

er.. maybe a 23?
i use an 18 on a 10x1, not really used stock :-
what would you suggest doom?

[BC Rog]

Oh my god!!

In the words of the norths motor hero "Ger Tup"

I run my 10x2 BRM on a 22
12x2 trin armed BRM on 25
12x2 Ti armed BRM on 24 and my 13x1 Trin BRM on 27!!!!!!!!!

A nineteen would probably need a smaller spur gear!!! lol

Seriously though, somehting like a 25 to 27 would be a good place to start 7.13 to 6.6. Maybr 23 to 25 if it's a Reedy Spec as they need to rev more. Gear it like that and drive smoothly, never using full left stick unless there is room to rev the motor out!

Doom will tell you the silly gearings Glyn has me running and now I'm smoother I can get away with it ... try it...!

Rog

[Yokomo Team]

19 x 2 !! is there such a motor? dont think that would be fast enough for the com lathe! only kiddin, Neil runs a 10 or a 9 double on 18, 78 , so i would say 24 or 25 pinion would be fine


Mick

[Yokomo Team]

unless it's a BRM , then 45 pinion should do it (Grin) ;D

Hi Glyn

[mike.stening]

ok mick the maybe you could give me soem idea of gearing my yoke, i am using the 84toothe spur with slipper from the Mx4, on a 10x3 Peak Aurora and 10x1 Reedy Krypton. i have been using an 18 but was worried about dumping on an 3000's so i didnt go higher, should i be looking at 19, 20 or something? gearing is a sore point for me, would this explain why things get a little toasty? ???

[BC Rog]

Mike,

things will get hotter if your undergeared than overgeared!

Try a 19 on the Peak, can't advise with the Reedy but sure you have found out how far it needs to be from the Peak.

I run a 22 / 81 on a BRM 10x2 (Trinity armd).

How do you get an 84 on ...... can hardly fit an 81 in mine!!

Rog

[jimmy]

my special 2003 came with an 84t ... its white..

[mike.stening]

i didnt have to do anything to the chassis to fit the MX4 84t+slipper
if its tight on yours you may have to do a bit of dremeling.
hmm, maybe i've been undergeared all season then cos things have got a bit too hot at times. just wish i'd had that advicce earlier :-[ kept being told i was over geared if it was hot.
i have seen some of the japanese drivers running bigger spurs than that,

[BC Rog]

J H Ch!*t,

an 84t spur! I have to run an 81 (or smaller) to be able to get my gearing right! I run my 12x2 on about a 25, 13x1 on a 28!!!!!!!! Thats against an 81. Thinking of going 78 (maybe smaller but I have a 78 already from the B3 days) to try and give myself a bit more room to play with. Also moving the motor back would be no great shame either!!!

[mike.stening]

in some areas i really am a dunce! :- ::)

[BC Rog]

Mike,

should remind you that I run BRM motors and every time I speak to Glyn about them trackside or take him one to fetle I pretty much get the same response ... "Gear-Tup" ;) Seriosuly though, since I actually started doing what Glyn suggested motor / gearing wise my cars have always been quick AND punchy. Need some good cells though to cope and also some delicate thumbs ...... Doom can help with the cells but my super thumb set has been on back oreder for more than a year now (must be coming in with the TTech bits ...... lol)

Rog

[Tim Fry]

hi all

I use a 20 tooth pinion on a 15x2 and it seems to be ok though must admit it does get a tad on the hot side when on tight tracks :-[

[darryl]

on my bc (not the special) there is a 84t spur,but not sure what to gear it at pinion wise ???,im using an orion pro bb 11 triple,and orion 3000's any idea fella's ???,also can any one tell me the internal gear box ratio please,is it different than the special ???
many thanks
darryl

[BC Rog]

same as special at 2.2:1

I run an 11x2 BRM on 22/78. my guess is that something like a 21/84 will suit the orion. At least it will give you a starting point to work from.

PM me if you wan t any more info.

Rog

[darryl]

cheers rog much appreciated
thanks
darryl

[Andy Taylor]

on my bc (not the special) there is a 84t spur,but not sure what to gear it at pinion wise ???,im using an orion pro bb 11 triple,and orion 3000's any idea fella's ???,also can any one tell me the internal gear box ratio please,is it different than the special ???
many thanks
darryl


Now comes the rub :) We run our BC on Kit spur with a 29 Pinion and it was coming out of corners like a rocket ship This is with a 12 single BRM. So it would seem anything between 21 and 29 would work. motor barely got warm at the F3's but then again he was driving it properly instead of jamming the throttle. But as he Tqed the last round and less than 2 secs off FTD the car is not slow. I find gearing a black art and really struggle to get my head round why one thing works and not another.

My "guess" is that Gareth was geared (nearer the 21) lower and was effectively spinning the diff more which resulted in broken diff screws so staying up near a 29 might, I say might, be easier on the car.

[darryl]

andy thanks for that ,but i thought the bigger the pinion the higher the gear ratio?? i used to race 4wd a while back and was told to gear around the 11 mark,but using a 21t pinion would give me 8.8,i would have thought that would be well over geared ???,but at the moment i am geared at 9.7 and that was using a 2400 battery and boy did that come off hot,though bearing in mind that was just a thrash around the field ;D and boy was it fast 8),so on saturday it will get it's maiden run (can't wait) but will be running in doors,so from what your saying if i gear it up by maybe 2/3 teeth it should run more efficiently and come off a lot cooler ???, as you say gearing is a bit of a black art :P
thanks
darryl
ps: what is the standard spur gear is it not an 84t

[BC Rog]

I ran my BC Sp with a 12x2 BRM Ti armed motor at the F3's on 6.8:1

The cells were fine, the motor fine and I only hand to change brushes once in the meeting.

Works for me.

Rog

[darryl]

rog i know what your saying mate,but with a brm motor you do run weird gear ratio's anyway,so you can gear it right up,so i suppose with me running 9.7:1,that will probably be about right ,anyway i'll find out in about 2 and a half hours,also rog the bc spur gear that i have is the one with a flat face one side and a raised face on the other if you know what i mean ???,can i run a standard yoke spur or is there also an after market spur gear that i can use
cheers
darryl

[BC Rog]

Not sure which version of the car you've got mate. By the sounds of it you are using the std BC / MX4 spur (probalby 84 .. the touring car ran a 78T one...). If that is the case then you are stuck with those two (to the best of my knowledge).

If the car is a BC Special then I'm not sure what the spure you have is but you can use the Robinson Racing slim white spurs with no problems.

Rog

[mike.stening]

the gearing on the BC does seem to be a little weird, when i was runnign my MX4 i ran it with and 84t spur and 15 and 16 tooth pinions with no over heating probs. when i changed to the TC special chassis (before the BC special was even a twinkle in masami's eye :P ) the motor was coming of hot and i was still having people tell me i was over geared!!! turns out i am way undergeared and having been through loads of brushes this season, at least 2 or 3 sets a meeting, andat one point being shouted at to top the car cos they could smell the motor it seems that way. though i have not run the car for a couple of months now so not been able to test it. but the car does seem to behave better with a higher gearing even though the MX4 and the BC have the same internal ratio, the only difference was the MX4 had a longer front belt.

[darryl]

rog the car i drive is the bc,not the special,anyway tried it last night on a 19/84 and way too hot,so i thought i would take it down a tooth,but can't give you the outcome of that as on my second lap we had a small glitch near the loop and ended up smashing a wishbone,and i couldn't get a spare for love nor money :'(,still there's always next week 8),but on it's initial run what can i say,well impressed,plenty fast enough and bags of grip,lovely car to drive ;D
p.s: are the wishbones the same as the mx4???

[BC Rog]

Yes, wishbones are MX4 ones front and rear.

[mike.stening]

alot of the MX4 can be used on the BC with certain adjustments, the BC i basically a hybrid of the MX4 and the MR4 TC, and they both used similar gearbox housings etc.

[darryl]

well ive tried the bc with a 17/18/19 tooth pinions and the thing still comes off red hot,the batteries feel cool yet the motor you can barely touch,so i took out the 11triple and replaced it with a freshly skimmed and new brushed 11 double and it made no difference still v.hot motor,would it be worth going up to a 20t pinion then the motor doesnt spin as many times so it may keep it cooler???,would that be worth a try or has anyone got anymore suggestions.
thanks
darryl

[Andy Taylor]

,would that be worth a try or has anyone got anymore suggestions.
thanks
darryl


Try one run with a 27 tooth based on the fact we ran a 29 tooth at the F3 and he stuck it second on the grid. Cant be a lot wrong with it can there :)

You could also ask glyn from BRM what timing he had on the motor he is a very helpful chap.

[darryl]

thanks andy
but your going on the gearing for a brm ,im only running a orion bb and i only use the buggy indoors,so would the 27 be a bit to extreme ???
thanks ;D darryl

[Andy Taylor]

thanks andy
but your going on the gearing for a brm ,im only running a orion bb and i only use the buggy indoors,so would the 27 be a bit to extreme ???
thanks ;D darryl


We geared a kRYPTON on that gearing also/

Thats why I suggested asking glyn if you Pm me I can send you his web addy.

[BC Rog]

Andy has a point about the driving and "throttle jamming".

If you are constantly on and off the throttle like a switch it will put a huge stairn on the cells, motors, car and probably the marshals too ;)

Think about it. What is quicker around a real race track, something that is reving it's butt off all the time or something that has torque out of corners? Well let me tell you, I've tried this. I have a kit with a Toyota 4AGE 16V motor in that can turn 8500rpm. The power to weight ratio is the same as my Porsche with a 3l lump up front but Percy is still faster. The kit feels faster, is more fun but ultimatly the big bruiser will kick butt!!

It's the same with elec' motors only worse because they produce max torque at exactly 0 RPM!!! If you let it rev the car will be very lively but not as smooth which is what makes for good lap times.

Try gearing high and only using full stick on the straight. You kit will run cooler, your lap times will drop and your results will be better as your not having to push so much and get drawn into those mistakes that you can't explain!!

Not having a dig mate honestly, it took me a long time to get there and I've still got some way to go yet!!!

Rog

[darryl]

rog
thanks mate i realise your not having a dig ;D,and yes i will try the bigger pinion and see what result i get,as long as i can get the thing to cool down then that will make me happy,both you and andy have made some valid points which i am grateful for 8),i'll keep you posted as to how it goes,
thanks again gents
darryl

[darryl]

i may have just found out why my bc is running so damn hot ::),after stripping the gearbox down i noticed that the spur is slightly warped and that one diff half wasn't seated properly so that the diff gear was running wonky,which made the diff gear and the spur rub together,so i reseated the diff half properly and hey presto it only rubs very very slightly,so could this be my problem solved or not ??? ???,that is the question :-

[Chrislong]

Hi Darryl.t
Me too, by MR4 BC ran extremely hot on Sunday, but i think it could be caused by the style of the track. Not sure. As the Cat3000 ran in the A final only had a 19 turn motor and it came off cool as I am far from a throttle jammer.

I ran my Yoke on 12x2 geared 20/84 - seemed perfect, top end was huge and acceleration was about 1200G's, but same as you Darryl, very hot but my transmission is very very free now, only drag on it is a slightly too tight centre belt.

What can I do?.... Can I start a new topic for hot MR4BC's so its easy for anybody to see the discussion?

Chris

[darryl]

chris
are we the only 2 too have this problem,i think mine is down to the rear gearbox,so may try it again on saturday ,but feel a bit reluctant to use it in case it fries another motor >:(,my speedo and batteries came off cool it was just the poxy motor,still ,just need some shims to stop the end float in the diff and that will stop the diff gear from rubbing on the spur (fingers crossed)

[Chrislong]

I haven't had that problem, yet, will check it though. Nothing seems to cause drag on my transmission.

One guy said a few weeks ago to soak the belts in WD40 and let dry before fitting, to make them softer and bendy - but that just sounds totally ridiculous to me - but could I be wrong?

I got the feeling there is a magical cure - just 1 thing me and you are doing wrong Darryl and it'll make perfect sense once we know..

[BC Rog]

Chris,

I have justed PM'd Daryl with the advice you can find elsewhere on the post in this forum.

The WD40 thing is an old trick from CAT 2K days, ask Chris Doughty!

I wouldn't try it with the Yokomo belts as I think they are on the edge of giving up straight out of the packet! I've not had a problem with stiff belts with the Yokomo...

Rog

[JV]

From reading the above, it seems like if I want to run stock motors in a BC, I should be looking at no more than 78t, and maybe 75t spur, right ?

The BC instructions suggest 28/78 for a basic 540 motor.

Anyone tried know if Robinson Racing "Stealth" spurs fit ? Or can anyone suggest a manufacturer for spur gears ?

I emailed RR, but the reply I got was basically "Dunno, never tried it".

John.

[Doomanic]

The Robinson Stealth machined spurs do fit, but not the ones with the silencer gasket.
Look here (http://www.robinsonracing.com/catalog/catalog.html) for part numbers.

[Chrislong]

Silencer Gasket? I need a silencer on my Yoke, sounds like somebody murdering a cat!

Is the White one (as supplied with Special) the Robinson? and the black the Kimbrough?

Chris

[JV]

Yeah, I looked at that page before I contacted RR, but the reference to a "silencer gasket" confuses me. The "Stealth" gears look like one-piece gears.

Are we talking about some weird kind of "Deltic" buggy here ?!!??


> Is the White one (as supplied with Special) the Robinson?
If so it would make their reply a bit silly.

[Doomanic]

John, do have a standard BC or an SP?

If you have a stardard BC then you will have to buy the 78 tooth spur from a TC Custom.
If you have a BC-SP then the Robinson Stealth gears fit. The part number is RRP1878 where the last two digits are the number of teeth.

[JV]

> John, do have a standard BC or an SP?
SP. Well, I intend to get one as soon as I've figured out what bits I need.

> If you have a BC-SP then the Robinson Stealth gears fit.
Great. Thankyou.

[BC Rog]

JV,

I use the RR spurs and they do work very well, the most clearance of any I have seen in fact. If you aren't running the SP yet the most important things to change ont eh standard car are (in this order)

topdeck (standard SP seems very good as does the Fastraks carbon one, although this gives a stiffer so less grippy car)

one-way on the layshaft (go for the hard one)

Shocks (plastic ones aren't great), go for the associated (B4 fronts plus B4 rear bodies with 1.32" shafts). Might as well go threaded as doing it now will only cost you a couple of pounds more!!!!

Long wheelbase kit

That was assuming that it's ballraced already.

The best purchase you'll make however is Losi STANDARD (ie. not hard) diff balls and thrusts along with new Yokomo plates. The standard balls are way too hard for the plates and the Losi ones are cheap anyway!!

There you go mate. Hope you enjoy the car as I firmly believe that it is head, shoulders, and even belly button above any other car on the market today (assuming no shops have a Pred P8 NIB .. lol)

Rog

[darryl]

well after a lot of soul serching and headaches,and burnt fingers from a very hot motors,mine has gone to a certain auction site :-

[Chrislong]

Hey Roger,
Interesting what you do to your diffs, but what about screwing them? :o

I don't know if I have a tuff screw in mine or not, so is there anywhere I can buy the ones which don't snap when used in anger? Or better still Titanium?

I heard B4 balls are fitted in some cars, are these much different to Losi?

What part number are the new rings?

Im running diffs totally standard til ive got all the bits to rebuild, ive only got the steel outdrives so far... so your recommendations Roger would be appreciated.

Chris

[Doomanic]

I know where you can get the stronger diff screws.............

The diff balls in a B4 are carbide, so not recommended unless you want to be swapping diff plates every other run!

[Chrislong]

Oh, ok. Are the Losi ones not carbide?

So you acquired some diff screws Dom? I remember you telling me how they were same part number as standard ones but it was 'luck of the draw' whether you got strong or weak ones.

Chris

[Doomanic]

Losi do both steel and carbide balls.

Yes, I managed to get some shouldered diff screws.

[BC Rog]

I run the plastic outdrives all round. Rears last about 4 to 5 meetings but are cheap enough, fronts don't wear even without the savers (which I don't have). Will be interesting to try the savers on the rear diffs to see if it makes the plastic ones last...

Otherwise, shoulder screw, Losi non-carbide balls and a lot of care with the building will mean diff shaped happiness....

I don't think I've ever broken a shoulder diff screw!!

Rog

[Gaz_Stanton]

I have! :o ::)

More than one i think! ::) ;D

[JV]

[Suffering from insomnia]

BC Rog writes:
>I use the RR spurs and they do work very well,
> the most clearance of any I have seen in fact.

Thankyou. I missed your post before - off the bottom of the browser window.

Any idea who might actually have RR Stealth spurs in stock ?

> If you aren't running the SP yet
I've just aquired an SP. But I think it'll be a few weeks before it gets built.

> one-way on the layshaft (go for the hard one)

You mean "ZS-671H" ? I saw that on the parts list, but I didn't (and don't) understand the significance of the "Hard Pulley" bit.

What's that about ? Does it require a different front pulley too ?

> Shocks (plastic ones aren't great), go for the associated (B4 fronts
> plus B4 rear bodies with 1.32" shafts). Might as well go threaded as
> doing it now will only cost you a couple of pounds more!!!!

The SP seems to come with threaded metal shock bodies with nuts to adjust the preload.
Are they any good ?

One problem seems to be the yokomo mystery shock springs.
Does anyome make shock springs that fit the yoko shocks which are specified by spring rate and not by colour [!??#!!] ?

> The best purchase you'll make however is Losi STANDARD
> (ie. not hard) diff balls and thrusts along with new Yokomo plates.

John.

[mike.stening]

the yoke springs are actually 2 different rates but the same colour purely for aesthetics.
The associated spring kits fit and that is what mr crag was using (but on B4 shocks as he knows them from his other car) they come in a full set for front and rear
The Sp comes with a layshaft oneway, but ihave also been running it with a front oneway as well, now some have found they have been snapping belts with the front one way but i havent suffered but that may bee down to using the MX4 slipper.
You can also mount the servo on tape on the chassis which lowers the Cg a bit more.

[BC Rog]

I have posted a spring guide covering ALL off-road springs.

AE fit, as do Losi, Schumnacher ...lalalala

Yokomo springs are not mystry items and in fact are some of the most consistent (spring to spring) of any I measured!!!!!

Hard pulley just means it's been heat treated to makje it harder and thus lasts longer.

I cut down servo posts to lower the servo. Tape mounting is as bad as running that servo saver anything other than locked up ..... the car will do the driving not you!!!!!!!
I don't even run a servo saver on my 1/8th car!!!!!!!!

The Yokomo shocks are far better build quality than the AE ones but they got their sums wrong!!!!! There is too much oil in the rear shocks and that leads to much pack, worse still the level of pack changes drastically durring the stroke !!!!!!!!!!!!!

That is why everybody changes them. That said the Yokomo shocks are superb and it's only the roughest of tracks that they suffer on!

As for where to shop that is your choice but I can think of only one "all under one roof" shop in the UK ... watch out for the owner though, devilish wit and a demon at the one liners .... need any more clues .... look below !!!!

[kriss]

I know sum one who runs an 84 spur and 19 pinion for a stock motor so usualy if you run a 19t motor u take on tooth of the pinion so try an 84 and an 17 or 18.

[BC Rog]

My god .....

for a stock I suggest running the same gearing as a 13 or 14 T mod. In my case that would be 28 / 78 not 17/84 ......

You wont be getting the best from the motor, might get your money's worth out of the fire blanket though ... ;)

Rog

[sosidge]

28 pinion won't pull too well on a 10s lap indoor track though...

[BC Rog]

But it's a buggy, it needs space to roam .. you wouldn't keep a pet cheeta in a 3' square pets at home special cage would you.

If you must have an indoor pet can I recomend a touring car, like a worm farm ... just less fun!

;)

[Chrislong]

:o oh bugger, where can i get a bigger cage from? Would super market trolley size do?

[Jonny_H]

But it's a buggy, it needs space to roam .. you wouldn't keep a pet cheeta in a 3' square pets at home special cage would you.

If you must have an indoor pet can I recomend a touring car, like a worm farm ... just less fun!


Rog, you've clearly never experienced a Predator on dry foam tyres, dancing in constant power oversteer for 30+ laps :D

Chris, I used to run a 14 double on about 20-21 mmpr so work that out for the tyres you're on and add a bit to allow for the softer motor. I'm a smooth driver usually but I used to throttle-jam fairly indoors...

JV: a Deltic buggy?!? Now there's an idea... are you thinking of an engine at each end though, or a 'Baby Deltic'? It would sound sweet either way! (Or how about Maybach power... mmm, turbocharged V12...)

[JV]

> Deltic buggy?!? Now there's an idea... are you thinking of an engine at each end

How about each corner ?