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Match your pinions to your crowns!

How DO they do that??
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wixwacing
Marshal!!!
Posts: 1871
Joined: Thu Jul 10, 2008 9:22 am

Match your pinions to your crowns!

Post by wixwacing »

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Today, I was tinkering with a body I have had for a couple of years. It's is a mint condition MRRC McLaren M23 'James Hunt' model (yes, the same as the impending Scaley release!) I got on eBay a couple of years back. I restored one to it's condition with Small Johnson 111 motor and MRRC axle and steering unit. The model is good but suffers from the old 111 problems of low torque and overheating, it sounds a bit like a weak magnet problem to me, but I have this second body to play with. I decided I would use some old Scalextric motor mount converters and fit an 'S' can to it.



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Whilst finalising the motor mounting, I popped the axle in with the MRRC white crown gear. To all intents and purposes it looks identical to the Scaley and others. Turning the axle, I noticed the mesh was fair but every revolution it was picking up on something. Being a scratch builder, I have come across this several times before when fitting mismatched gears. Running the gears with fine paste doesn't seem to improve things greatly and the noise level barely decreases.

For some time I have suspected it may well be a pitch mismatch between various manufacturers. Ninco pinions can catch on Scalextric crowns. Scalextric pinions seem to catch on MRRC crowns and Cartrix pinions catch on most makes except Cartrix??? Another cause can be that because the various make pinions can have varying diameters, the motor shaft slot in the crown may be positioned slightly further from the pinion teeth than normal. Nearly all nylon crowns have a small amount of discernable run out and when the crown / pinion mesh reaches its widest point, the next tooth on the pinion can clip the side of the crown tooth at its peak on its way to meshing.

So what is the solution? The only reliable solution I have come across is to match the manufacturers pinions to their crowns. I fitted an eight tooth pinion to my Carrera Bentley XP and fitted a Ninco 24 tooth crown wheel (see elsewhere on this site). The conversion was fine for a while even though it was a little noisy, it eventually got louder and that prompted me to fit a matching Slot.it 8z pinion and 24z crown..... Silence is golden!

Likewise I had problems with a Carrera Aston Martin DB3, Slot.it to the rescue again. In the case of the McLaren, the motor came with a very reliable Scalextric 9z pinion and seeing no reason to discard it. I dug a new Scaley 27z crown gear from my spares box and rebuilt the axle. Hey presto, problem solved. From now on I will exclusively match crowns and pinions at the design stage. It saves a lot of faffing about and the end result is silence and a perfect mesh and nothing less is acceptable!!
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When I'm not racing slotcars,
I'm out in the back yard, burning food!!

When I win, it's because of my talent, not my car or my controller!
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