SlotForum banner
1 - 9 of 9 Posts

·
Premium Member
Joined
·
2,998 Posts
Discussion Starter · #1 ·
Hi guys
is it true that it's better to use 9 or 10 tooth pinions for inlines because the 8 tooth ones tend to chew the teeth off the crowngear ? If it's true may I ask why?
Thank you for your attention
Regards
Edo
 

·
Registered
Joined
·
2,457 Posts
Yes, partly.

If possible always use the greatest number of teeth to produce your required ratio. For example, 9:27 is better than 8:24, to produce the same ratio of 1:3.

Not quite sure why, but it's bound to be because the teeth must be further spaced apart (less to go around the same circumference) so there is a greater possiblilty of slippage under heavy acceleration, braking or when excess sideways force occurs. One way of solving the sideways bit, is to place washers in the gap between the wheel and the bearing that the teeth of the crown gear are pointing to.

Anyway, long story short. Your were right, but it's not a massive problem as it probably only reduces the life of the crown by 20% or so. So if you need an 8 tooth, then use it. But if you can get away with a 9 or even 10, then use them instead, but change the crown gear accordingly.

Hope this helps.

Lotus

PS. Waiting for Fergy or Graham to come up with the real scientific explanation for this...
 

·
Premium Member
Joined
·
1,630 Posts
Heres another suggestion to 'chew up and spit out'.
8z pinions are slightly smaller in diameter to 9z and 10z (eg FLY) - therefore ensure that the rear axle is shimmed correctly so that the pinion engages the crown fully to prevent slipping and damging the crown.
As always there are exceptions to the rule and Slot.it released their range of 8,9.10 & 11 tooth pinions with the same diameter.
Sean
 

·
Registered
Joined
·
800 Posts
The larger diameter pinion gears allow the teeth the meet the crown gear at less of an angle putting less stress on the teeth for both gears. You have to picture it in your head at a huge size for it to make sense
Real trucks use larger pinions when possible for this reason.
 

·
Brian Ferguson
Joined
·
3,652 Posts
All of the above are pretty much true. (How's that, Lotus?
)

One word on the Slot.It pinions. Since the diameter is the same, but the number of teeth are different, the profiles of the teeth vary from one size to the next. This is convenient, but it does mean that additional wear on the crown will occur since there can only be one ideal tooth shape. My guess is the 9 is the ideal and the rest have "fudged" tooth shapes. However, I doubt that the extra wear will manifest itself to any great extent, and the convenience makes them a terrific choice.

I even have some 6 and 7 tooth pinions. Yes, they wear the crown somewhat quicker but, for racing, they can be a big performance gain.

The larger pinion yields a longer period of contact for each tooth with the crown. Also, a second tooth will be in contact with the crown well before the first tooth begins to revolve out of full contact. This spreads the load out over a larger portion of the crown gear surface, and does so at a better angle of contact. Thus less wear.
 

·
Registered
Joined
·
325 Posts
Speaking from past experiences, I had a 8 tooth slot-it pinion that gave way in a event I was once in. It's life lasted for about 2hrs of almost solid running and cost my team victory. (It was an endurance race). On my Audi R8C, the pinion became loose and also wore out the crown gear somewhat.
Annoying as I didn't know that they tended to do this until after the event, when someone kindly told me. doh!

James
 

·
Registered
Joined
·
4,634 Posts
anyone got advice on a make of pinion (about 8 tooth) which will stay nicely on a scale-auto motor without undue wear or slippage?

cheers
 

·
Registered
Joined
·
2,457 Posts
Slot.It one is probably best.

Anyway, what's the fuss, so long as it lasts one race at optimum set up, that's fine. Replace it before the next race, and go! See professional motorsport for details.


Lotus
 

·
Nobby Berkshire
Joined
·
2,015 Posts
As long as you are using the right manufacturers pinion on the right gear you should be OK. It's always dodgy trial and error to mix manufacturers on the same running gear.

I've just found out that SlotIt 10t SW pins dont mesh well with plastic bearing Fly gear but work perfectly with metal bearings. It's just down to a minute fraction of sideways movement and I've got a chewed gear.

Mind you, Sean's cool with rest of SlotIt info re. IL.
 
1 - 9 of 9 Posts
Top