# Smoothing out gear mesh



## 1976Cordoba (Sep 20, 2000)

Is there any way to improve the crown gear mesh on Tyco HP7 chassis. I have a few chassis that are smooth as silk and fast. Most, however, have a binding gear mesh at one spot. Once past that spot, the mesh is good for one revolution until you come back to that spot.

This is annoying as these chassis are fun to race when they are smooth.

Our rules call for stock pieces throughout, so swapping parts is not an option. Is there some kind of method to smoothing gear mesh?

'doba


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## AfxToo (Aug 29, 2003)

The conventional way to smooth out gears is to load them up with toothpaste and run them on a 9V battery for a while, both directions, then thoroughly clean them and oil lightly. I'd use a spare chassis for this, not your best race chassis. 

Another thing I do when I have less time is to deburr the crown gear teeth using a brass wire wheel in a battery powered dremel on low speed. I also deburr the back side of the gear, where it rubs against the chassis just to make sure it's smooth and has no plastic flashing rubbing.


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## noddaz (Aug 6, 1999)

*Well....*

Binding at one spot usually means a bad tooth on one of the gears.
Hard to fix without replacing the gears.
But..... There may be a way if you want to risk it.
I have heard (but have not tried) that if you run the gears slowly over a low candle flame as the gears heat up (and slightly soften) the gears will mesh better...
Of course the object is not to set the back of the car on fire...
Again, I have not tried this. This may just be part of slotcar folk lore...
BTW, why can't you replace the gears? Are HP7 gears unobtainable?
Scott


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## Montoya1 (May 14, 2004)

AfxToo said:


> The conventional way to smooth out gears is to load them up with toothpaste and run them on a 9V battery for a while, both directions, then thoroughly clean them and oil lightly. I'd use a spare chassis for this, not your best race chassis.


I find valve grinding paste works better. I use Chemico by Hammerite as you get both coarse and fine in one tin. Use the coarse first, then the fine.


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## AfxToo (Aug 29, 2003)

The HP7 is quite an ingenious exercise in how to build a decently functional slot car for the absolute least amount of money. Every part seems to be designed to serve more than one purpose or eliminate the need for another part. The crown gear is designed so you don't need spacers or a boss. My first inclination with the gear mesh problem was to put the HP7 rear end in a Patriot and run it on the track for a while. A car with a metal pinion would be even better. That would fix the gear and be fun. But the HP7 rear end binds in a regular slot car so that was a no-go. I then polished the gear teeth and the back of the built-in spacer with a brass brush in a slow speed dremel and that helped smooth things out. The HP7s that I own all have a lot of gear whine, which I think is just the nature of the beast. I usually setup my rear ends with spacers to get the mesh perfect but on the HP7 there's no room for spacers because of the unique gear. 

Sure, valve grinding paste will work faster than toothpaste but more people have ready access to toothpaste. Well, at least in the US they do.


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## dlw (Aug 17, 1999)

That one binding spot in gear mesh is probably caused from the impact of a crash, or a drop, or other intense impact. 

What I did to fix it was to use a small flat-head screwdriver and gently bend the damaged gear back into its original position. Works for me...........and try less intense wrecks next time:tongue: .


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## Montoya1 (May 14, 2004)

are there gears which will work as well/better?


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## AfxToo (Aug 29, 2003)

Sounds like he's locked into HP7 stock gears.

If given the choice of gears, and with a little extra money in my pocket, I always prefer Slottech crown gears. Smoooooth.


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