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SuperChamp82

Shimming - do, or do not ...

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It’s clearly unreasonable to expect TamIya to mass produce kits with tolerances that don’t end up with a little slop 

Or, if they didn’t, we’d all end up paying Bugatti Veyron kit prices 😂

But what’s the consensus on reward vs return in shimming to tighten things up ? 

Is it really down to the margins in racing or do runners really benefit ?

Personally, I think the latter - if only for wear vs performance ...

And what do you guys use - noting I’m a bit anchored to the old red n blue !

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I find shimming has benefits on on-road racers used on high-grip surfaces where small adjustments can have noticeable effects on handling and performance, so my F1s, touring cars and on-road M-chassis cars are all carefully shimmed.

On cars likely to see use in dirty conditions, a little play left in suspension and steering components is actually helpful as it reduces the chances of these seizing when dirty, so I typically leave them un-shimmed, only shimming the drivetrain where necessary to ensure solid mesh between the gears. The only shims in my CC-01 for example are inside the rear axle, keeping the diff input gear and ring gear meshed correctly.

 

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Personally, I shim pretty much everything to get a nice, tight, pure mechanical action. I hate it when things are wobbling all over the shop. I’ll do it maybe less so on a Hornet type or that end of town, but I have shimmed some fairly old school cars for various reasons in certain places. (Sometimes this might be due to a mod that is being applied)
 

But mainly, yes, I shim for mechanical tightness. Steering, shocks, arms, etc. As long as all the components move freely, all is good.  Haven’t had any issues with this approach so far, but I don’t get to run that often either.
 

It might also be that I have a veerry slight OCD syndrome going on! :) 

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I shim onroad racers and thats it. I never remember to add shims to any order and then when I remember its the only thing I need and the shipping would cost more than the shims and we all know that it isn't possible to pay more for shipping than the item so I don't buy them. I may have resolved this by having a wishlist at rcmart of those little things which may help me remember. But it hasn't. Man that got out of hand.

Anyway, like @TurnipJF says, a bit of play in an onroad racer like a TA07 could change the handling. I don't bother on my offroad cars as the track is so bumpy anyway.  I was asking a HB driver about my car and the amount of play it has (8th nitro) and he just shrugged and said thats what happens. Hes really fast so if its good enough for him...

In saying all that, my race cars don't actually need any/many. My TA07 Pro had a few but then I swapped out some plastic for alloy and they weren't required. My TRF102 just needed some on the front wheels. The offroad cars don't need them. Then again these kits all cost a lot compared to a TT02. The TA07 pro is the cheapest of all my racecars and that is more than a TT02 and doesn't have a body, tyres etc, so I guess you get what you pay for.

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I would shim everything if I had any shims.

Where do you guys get your shims from?  What are the common sizes you keep stock of?  I'm assuming M3 / 3mm sizes for standard screws and suspension pins and 5mm for wheels?

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4 minutes ago, Mad Ax said:

I would shim everything if I had any shims.

Where do you guys get your shims from?  What are the common sizes you keep stock of?  I'm assuming M3 / 3mm sizes for standard screws and suspension pins and 5mm for wheels?

Tamiya do sets of 3mm bore and 5mm bore shims. The 3mm are perfect for suspension arms.

for std bearing sizes. I buy them from MB Models, they stock A huge range of shims. On the TF I used 8x5x0.3 / 10x5x0.1 / 10x5x0.3 / 10x5x0.5

the latter two were for the drive axles if needed.

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11 minutes ago, Mad Ax said:

I would shim everything if I had any shims.

Where do you guys get your shims from?  What are the common sizes you keep stock of?  I'm assuming M3 / 3mm sizes for standard screws and suspension pins and 5mm for wheels?

Rcmart have 3Racing in 3mm, 4mm and 5mm in 5 thicknesses for not much money, 50pc in each in total. They are on my wishlist now, along with TRF stickers and V parts for my shocks that I should replace. And double cardan shafts and a TRF420 suspension conversion for my TA07...

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I shim where I can.  

Sometimes I see (vintage) arms move to and fro, as much as 1 to 1.5mm. That's just too much slop.  If the servo pulls a link, the wheels should turn, arms shouldn't be pulled in.  So I shim.  Also, this can change the wheelbase a bit.  221mm could shrink to 219.5 or stretch to 222.5mm, depending on how you shim.  When you are turning, left arm could pull in 1.5mm, while the right hasn't yet, visa versa...  Why upgrade steering linkages if arms are left sloppy?  

(However, precise steering isn't always good. Some slop could give a bit of a "cushion" in the steering -- it could transform "twitchy" driving into more "forgiving" driving... If our 1:1 cars have no play in its steering, we'd all have a nervous breakdown. This is why 1:1 cars don't use joysticks.  Also why robots have jerky movements. Their joints are not actuated by stretchy tendons and ligaments.  But I digress as always...)  

 

Hotshot series have bevel gears on either ends of the proper shaft.  These bevel gears were molded in the 80's. They are not perfectly round. They are ever so slightly oval-shaped.  Accordingly, these gears would make cyclical whirling noises if you turn them.  But it wouldn't make that noise when the gears are tiny bit apart.  

The slop is about 0.4mm.  I think I added a 0.3mm thick shim (5x7mm diameter). That guaranteed proper spacing. It runs so much smoother.  They are tight but the outer rings of the bevel gears are not touching.  There is still like 0.1mm play in the mesh.  

Below is the link to what Jonathon mentioned.  I've used Kyosho version. Had I known about the 3Racing version, I probably would have gotten that instead, because it gives you a lot more shims for less.  

https://www.rcmart.com/3racing-stainless-steel-5mm-shim-spacer-0-1-0-15-0-2-0-25-0-3mm-thickness-10pcs-each-3rac-sw05-v2-00028337

xKPmLj9.jpg

4Sd3W7A.jpg

 

The other place I had to shim was DN01 Zahhak's ball differential assembly.  If I remember correctly, this diff moved left to right within the gear box about 1.4mm.  I stopped building and waited 2 weeks until washers arrived.  Three 0.5mm washers were just about binding, but two washers left some play.  I could live with 0.4mm play.   Drive cups are much deeper than other cars, so this may not matter. But it bothered me enough to do it.  

wBkPxaW.jpg

 

My Covid build was this Dancing Rider.  The steering forks moved too easily.  It had the customary 0.2mm gap to allow free movement.  If it was an arm, that'd be perfect.  But if this neck moves too freely, the steering could wobble like a drunk guy falling and catching himself.  That won't do.  

I wanted some resistance.  So I added a tiny M2 washer.  It now turns with teeny-weeny bit of effort.  Along with a stiffer neck spring (not the shock springs), it moves more like a door, instead of like a flag in a storm, if that makes any sense.  Super-precise steering after that.  

3KhoPqP.jpg

3Hqh4Gx.jpg

 

Most arms only have 0.5mm or so of slop. I can live with that.  Any more than that, I try to shim. 

Below is DN01 Zahhak again. I wouldn't care about this much gap in DT03.  But I figured that a performance buggy should be more precise.  If I move these arms without the dampers, they still flap about without any resistance at all.  

QznTeUv.jpg

For backyard bashing, these shims won't make much difference. I don't know why I do it. 

 

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It's the cost that always gets me. I'm tempted to order some 5mm 0.2 ones wholesale. Get a couple hundred at once and never have to think about it ever again. Otherwise you seem to pay about £5 for a pack of ten! 

I shim off road cars, especially the blitzers as they are noticeably wobbly from stock. 

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@SuperChamp82 wait till you've fitted the upper camber links to your ta02! Then you'll see some wobble 😲

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I've heard two opinions on the matter, both opposite but both from enthusiast whose opinion I respect. The first one was, when dealing with racing, fine adjustments must be made to various settings. If there's slop all over the place, those fine adjustments aren't really effective. Grab an RC10  or Optima front wheel and it moves around very little. Grab a Top Force wheel and the "Tamiya slop" is there. Now all that has a lot to do with the manufactures and their intent. The RC10 and Optima were "race cars" in their day. The original RC10, in particular, needed careful fitment of parts to actually prevent binding in some cases. Tamiyas (except TRFs, etc.) are hobby enthusiast level cars and are meant to go together easily so they have some slop. As racy as the Top Force is, its based on an entry level (at the time) 4wd buggy, the Manta Ray. I'm guessing that why Tamiya went through putting bushing at all the pivot points in the Astute series to try to remove some of that slop. The Astute was designed as a racer first and the Madcap was the "watered down" version of that. The upshot is that makes the Madcap a very good performing "entry level" buggy.

The other theory is that Tamiya cars are designed with the knowledge that that slop is present from the get-go. In the big scheme of things, it doesn't matter. Once underway, everything just kinda "settles in". In this scenario, shimming things actually makes the buggy too edgy and actually harder to drive.   

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