SlotForum banner

1 - 20 of 23 Posts

·
Registered
Joined
·
2,509 Posts
Discussion Starter · #1 ·
Bought an SCX BMW 320i this afternoon.

Gear mesh is diabolical - hardly turns in the right direction yet reasonable if turned by hand "backwards". What's the recommended practise to sort this out? I've already tried reversing the pinion which produced only a tiny improvement.

Coop
 

·
Registered
Joined
·
1,550 Posts
Easiest way would be to heat contrate up until it starts to so soft
do this while the car is under power with the body off
you will know when you have applied enough heat as gear noise will reduce
keep car running until contrate has cooled down
If you get this wrong you will require a new chassis !!! to much heat will obviously distort it

or replace gear with either another SCX one or slot-it type

Pain when you get a new car and it doesn't work straight out of box
Depending on where you bought it ask to be replaced ?

John
 

·
Tore
Joined
·
1,692 Posts
I'll second Alexis advice, but if the the gear is very rough you can use auto polish/rubbing compound instead of toothpaste to speed up the process. It's also worth inspecting the crown for any bad teeth first, especially if it catches in a certain spot, and if so then use a nail file to clean up between the teeth's.
 

·
Registered
Joined
·
2,509 Posts
Discussion Starter · #6 ·
I suppose heat could be applied safely by alternating a hot iron on the brass pinion with periods of running it up.

It's not a single bad tooth, the whole thing feels like someone has done some drastic and abrasive lapping in, but the wrong way around. Clearly this hasn't happened (it's brand new and sealed box) but that's what it feels like!

Coop
 

·
Tore
Joined
·
1,692 Posts
If you feel different resistance when you turn the wheels it can be a bent crown, but if the resistance is relatively even but just rough, then lapping the gears with paste will sort it out quickly.
 

·
Registered
Joined
·
1,365 Posts
I had this problem on an SCX Nascar. On closer inspection the crown wheel was very warped. Nothing to be done really so I swopped the back axle with another I had. Quality control not great then but as it was one of the £10 Nascars I didn't feel I could complain much!
 

·
Registered
Joined
·
3,646 Posts
the only problem with rubbing compound is that it embeds itself in plastic crowns. your safer with toothpaste but it will take an awfully long time to bed in the gears if there that rough. john
 

·
Registered
Joined
·
2,509 Posts
Discussion Starter · #11 ·
Toothpaste mixed with baking soda seems to be doing the trick, but now all my 9V batteries have gone flat! Should be able to finish the job at Oaklands Park on Wednesday.

Coop
 

·
Registered
Joined
·
3,646 Posts
use a pencil blow torch and angle it upwards onto the crown nothing gets warped and 10-15 secs later its done. you,ll know when its done cause the noise chages to quiet, remove heat and keep it running till its cool. you only need to apply the heat to the back top edge and teeth of the crown. john.
 

·
Registered
Joined
·
213 Posts
Owen, check the armature shaft is horizontal and at the correct height in relation to the axle centre line. Plenty of lighters at Oaklands wed night.this is an alignment problem.OR there is aforeign object in the motor catching the pole piece as the motor rotates in one direction.
 

·
Nobby Berkshire
Joined
·
2,015 Posts
SCX are like Cartrix - two Spanish producers who can never get their gearmesh sorted out after decades of attempts. Some cars seem fine, while others are screwed up.

Toothpaste is never going to make any difference unless it's and incredibly abrasive brand (unlikely!) or if it runs for hours. It's never made any difference from my experience.

If you apply heat a cigarette lighter is the best application as a narrow flame will drag around the axlegear when it spins, but this is very hot and miss and if you melt the chassis on motor mount then you can't get a new one without buying a new car. The gears have to be free of all grease befor you try this or melting will be uneven.

The only way you can get happiness with no risk is to get the wheels off, fix a better brand of axlegear, a pinion that meshes, and there you go.

Alternatively, simply take it back to the place you bought it and get a replacement or refund. You have consumer rights not to be sold junk that does not work.
 

·
One petunia in a field of onions
Joined
·
6,455 Posts
Surely the cigarette lighter is a risky method. Too easy to get it wrong.

I've used Jiff Cream Cleanser quite successfully (You'll usually find it under the sink in the kitchen guys). It's a mild abrasive, but more power than toothpaste. Or "White Lily" an old fashioned coarser paste version of the pot cleaner. Or if those options don't suit your non-domestic sensibilities, what about the coarse Tamiya cutting paste.
 

·
Registered
Joined
·
2,509 Posts
Discussion Starter · #16 ·
Thanks to all who replied here.

Using a cigarette lighter I've managed to get some improvement on the mesh but it's never going to be great - it appears that the crown is warped in the vertical plane. Because it's intended for a box stock class I'm just going to rip some nylon gears in the 9:27 ratio off a scrap Scalextric car and be done with I think.

Coop
 

·
Registered
Joined
·
873 Posts
the only solution is the mini heat gun ,
iroda do a good one available on ebay. Heat it till it sounds right, ie hardly any noise.

if you use grinding pastes etc they will eventually destroy your gear unless you get all ther paste off once youre happy with the mesh.
The lighter is a disaster the heat is too intense and uncontrollable and could enflame your gear/warp your chassis...
toothpaste ... takes ages

ive tried all these methods mini heat gun is the only one that works 100% of the time..
oh .. and run the motor slowly when youre doing it like 3 to 5 volts.

cheers
Peter
 

·
WRP World Champ 2015/2016
Joined
·
4,279 Posts
Some great ideas there, thanks all.

For heating the crown and pinion, would it be safer to use an old knackered chasis? I use an old scaley chasis for tyre truing and running in new motors - very handy.
 

·
Registered
Joined
·
3,646 Posts
yes it would if your,e new to it. once you,ve done one you wont believe how easy it is, then you can do any more in situ.
 

·
Registered
Joined
·
2,509 Posts
Discussion Starter · #20 ·
Surely lapping the gears in in a chassis in which you don't intend to run those gears is a bad move? You'd potentially get them great in the scrap chassis but all bets are off when transferred to the intended chassis with it's different geometry. Furthermore as you kept using the scrapper it would more and more warped which would make matters even worse.

For the record the SCX crown was warped and heating improved it but to the point where a lot of the teeth started to resemble tiny irregular stubs rather than triangular teeth. Seems to mesh a lot better on Scalextric gear and pinion looted from a scrap car.

Coop
 
1 - 20 of 23 Posts
Top