28 replies to this topic

[chasbeeman]

I'm sure it is metric but not sure about the specs.

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[MSwiss]

They are 2MM, and use a 1.5MM Allen key, to tighten, if they are hex head.

[slotcarone]

They are metric like Mike said but more commonly used are 2-56 button head screws that take the same .050 allen as the gears and tires. These will never strip out and go right in. 

[MSwiss]

Mike,
I think you are basing your statement "more commonly used", by your own experience, not hard data.

[S.O. Watt]

 I agree with Mr. Katz on the use of 2-56 SAE fasteners. The thread size and pitch are very close between the the two stated fasteners. The slightly larger OD and ever so slight difference in pitch allows one to use the 2-56 in any of the mini can motors, with two distinct advantages going to the 2-56.

 

 It has been my experience that if the metric threaded fastener is used, one can exceed the safe torque of the threads in the can causing them to strip out. I have yet to experience this failure when using the black, grade 8 2-56 button head fasteners. The 2nd advantage is the slight difference in threads causes a self locking action. And as Mike K pointed out, they use the same Allen wrench  size as 4-40 tyre set screws.  

 

 

 

My experience has netted me a virtually bullet proof mounting system with 2 or 3 advantages over a metric fastener in this use.

[Tex]

the 2-56's work fine but, technically, the cans are tapped for 2mm.

[chasbeeman]

Thanks for the feedback!

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[slotcarone]

the 2-56's work fine but, technically, the cans are tapped for 2mm.

That is correct. But like Tom said the metric threads are very fine pitch and will strip. I personally have never stripped a 2-56 screw in the can. I have worn out the hex in the head and then of course it is time to toss it.

[MSwiss]

Mike,
When do you find out you wore out the hex?

When you tighten the screw down, and then can't get it back out?

Regardless, you just stated the reason not to use 2/56 button head screws.

The hex is smaller, and the cavity is not as deep as a GOOD 2MM screw, like my CR018.

Zero chance of stripping the threads, or socket, on them.

As a matter of fact, I remember when a prominent retro racer (Haruki?) posted how a button head screw cost him.

[Ecurie Martini]

The metric designation for these screws is M2 (should you be looking at catalog listings) and, as stated above, call for a 1.5 mm hex driver.  I routinely use them with a split ring lock washer and have never experienced a failure - unexpected loosening or removal problem. 

EM

[slotcarone]

This has been discussed in length in the past. Haven't seen it much lately but I personally watched many a race be thrown away by the motor falling out in a wreck. Some were soldered in and a few were screwed. In the 11 years we have been using these screws I have never had an issue. If the wrench feels a little loose in the screw I toss it. There seem to be a few different brands out there. Some are better than others. In the end we each decide which method we like and go with it. No different than every other part on the car. We make the car as fast and reliable as we can so we can finish the race.  Hopefully on the podium!

[John Streisguth]

I've had the 2-56 screws strip the thread out of the can from repeated use (back in the puppy dog days).  I use the 2mm screws with either a tiny bit of purple loctite or vibra-tite, then I don't have to torque the screw down so hard.  Never had one back out, never solder the motor in, and have never had a motor come loose.

[slotcarone]

The PD cans were not as good as the FK motors screw thread wise. Never happens on a PD! Plus we don't reuse them as much!

[Tex]

That is correct. But like Tom said the metric threads are very fine pitch and will strip. I personally have never stripped a 2-56 screw in the can. I have worn out the hex in the head and then of course it is time to toss it.

 

and in 11 years of racing retro, I've never stripped a 2mm.

[1A Racing]

Cross threading is better than Loctite anytime!!

[mreibman]

It's definitely an M2, but I can't recall the thread size. there are several different ones with M2.

 

Or you could just solder the motor in place..... :-)

[Foamy]

You guys made drama out of the craziest stuff.

Hex wrench for a 2mm cap screw is .059-ish. Hex wrench for a 2-56 cap screw is .078. What really is more strip resistant?

BTW, I use 2mm in my mini 4wd cars and hate them things. JIS screw heads are crap, not anybody makes a screwdriver that won't strip them.

[MSwiss]

Foamy, the ones Katz says he uses, according to him, uses an .050" tire wrench.

[Jay Guard]

I've always used the 2-56 button head screws with the .050" allen recess, never had a problem in over a hundred races.  That said, if you want to be able to take the motor out without removing the rear axle you will have to use a .050" ball-end driver.  Unfortunately a .050" ball end driver will, IMO, not get the screws tight enough without stripping the ball driver and/or the button head screw.

[MSwiss]

That's why you use the right screw.

 

A 2MM with a deep hex recess, like my CR018.

[MSwiss]

Unlike some other 2MM screws, the hex is crisply defined at the end.

The Allen key goes in that deep.(to my thumbnail)

 

On the CR018, to quote Florida's top racer, whose raceway just got them in; "The motor screws are excellent."

[brnursebmt]

Wow.  This is good.  A guy ask a simple question and I bet before it's over we end up with some FU's and a locked thread!!

[tonyp]

The motors don’t last long enough to ever strip one out. Lol.

I go the Swiss way. I once had a button head strip out and had to cut the motor out of the car.


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[Shiggy]

The motors don’t last long enough to ever strip one out. Lol.
I go the Swiss way. I once had a button head strip out and had to cut the motor out of the car.
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If you strip out a button/Allen head, drill it out to pop the head off. No damage to chassis or motor

[tonyp]

That would require a drill lol.


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