How important is this B12 part on Clod/Bullhead?

[nowinaminute]

Just began rebuilding an old Bullhead I've had laying around for ages and I noticed the B12 part is missing. It seems to have been doing ok without it but I wanted to check how vital it was. Seems to just be a spacer tube to go between the plastic bushings but the gear itself has seats moulded into it, so I can't quite work out the purpose of it? Maybe it's as backup if the plastic bearings start to wear out?

Like I say, it has apparently been running fine like it until now, and I'm converting it to bearings so there should be plenty of strength there. Just don't want anything to implode!



 

[KEV THE REV]

looks like a back-up spacer to give the plastic bearings stability ? , and give the counter gear some support inside the hollow . Does the B12 spacer fit in flush against back of the bearings ?

[nowinaminute]

3 minutes ago, KEV THE REV said:

looks like a back-up spacer to give the plastic bearings stability ? , and give the counter gear some support inside the hollow . Does the B12 spacer fit in flush against back of the bearings ?

I honestly don't know lol

[KEV THE REV]

Looking at it a bit more I think it would be good idea to fit one as the spacer runs on the shaft to support the bearings and counter gear giving a larger support area overall

[Juggular]

It looks like the spacer keeps the two gears from touching each other?  

SA14 shafts look identical.  If you stood them up on a desk, the 2 gears would sit level.  But these two gears should be staggered.  Instead of making two metal shafts with different steps in the middle, Tamiya just added a spacer (cheaper that way).  The outer teeth of both gears wouldn't have a chance to meet side by side. I doubt that the teeth would catch, but at least, the spacer would reduce friction. I'd cut up a ball point pen to length, it only needs to prevent rubbing of two gears (obviously, it shouldn't bind either).

 

There used to be gears with raised lips, they also prevent two gear teeth from catching. (I couldn't find a sample. Just imagine the red ring is raised like 1mm.)  

 

[nowinaminute]

Doesn't say to grease it, though, that's the weird thing. 

EDIT: I see now, it's supposed to move as one with the gear and independently of the greased SA4 part.

 

[nowinaminute]

2 minutes ago, Juggular said:

If you stood them up on a desk, the 2 gears would sit level.  But these two gears should be staggered. 

The moulding of the gearbox case seems to deal with that, though, it's impossible for the 2 gears to be level because the seat for one of the shafts is "higher" than the other one by the amount necessary to prevent rubbing and I can't see any sign of rubbing in previous use. Quite odd. I'd be reluctant to put something in there and it foul the bearing shields, too.

 

[nowinaminute]

Just took a look at someone building one and it doesn't come close to touching the larger bearing:



Seems like it occupies the space between the small bearing and the step on the shaft, but like I say, the design of the gearbox prevents the gears from rubbing and I can see no signs of rubbing or wear and this thing has been sealed with super glue on the screws since the 90s! 

I wonder if it's more vital when you use plastic bushings to compensate for wear?

Not really eager to have a part in there that's just rubbing against the shaft, even with grease, seems to defeat the point of switching to bearings. I wonder if I could fit a few more 8x5x2.5 inside instead

[nowinaminute]

Just took a look inside mine, plenty of space between the gears and you'd have to apply enough force to make the bearing collapse before it would be able to get any closer.


I'll have a think about it...

[nowinaminute]

Hmm. Spoke to a friend who's an old school Tamiya guy (I could only admire them from afar as a child, being "only 39") and he said he has seen those gears melt before when using fast motors or 3s and he thinks the spacer is to blame, reckons it can be a source of friction over time as the grease gets gradually thinner, especially with fast motors. He reckons it's not an uncommon thing to do but I've never heard of it tbh. Now trying to google for damaged clod transmissions to see if I can find any correlation  I need to get a life

[87lc2]

For what its worth, if I'm missing that piece I just go ahead and slap it together, never had an issue.  I've built/rebuilt dozens of Clod gearboxes and never noticed and difference with our without that part.  So to answer your question, go ahead and run it without you should be fine.  

[nowinaminute]

21 hours ago, nowinaminute said:

Now trying to google for damaged clod transmissions to see if I can find any correlation  I need to get a life

Found this one that looks a bit melty

 

[87lc2]

1 hour ago, nowinaminute said:

Found this one that looks a bit melty

 

I've cracked a few Clod gear sets on race trucks running 3-4s.  Spacer made no difference, have broken them both with and without that part.  Definitley not common, I actually find the Clod gears to be quite tough, but it does happen from time to time.  I think its generally from a bad landing under power where the diff doesn't have time to catch up.  Usually an axle shaft will break first, but I have broken gears without breaking shafts as well.  

[nowinaminute]

1 hour ago, 87lc2 said:

I think its generally from a bad landing under power where the diff doesn't have time to catch up. 

I think that's the leading causes of gear damage for any Rc, really. Even modern super tough ones will break if you land on throttle so there's no shame in it happening to the Clod on high power.

I have faith in the gears, the diffs are the same as the hopper/hornet/lunchbox etc and I've always found them to be incredibly durable as long as you avoid stuff like landing on heavy throttle where possible. 

I'm just going to not worry about that part and get on with it. Not planning to run big power any time soon, maybe put 3s through a pair of silver cans as the gearing apparently allows for that, but I haven't got anything spicier planned for the time being. Thanks for the heads up!

[87lc2]

You should be fine for now, run it!