Need help with MDC Roundhouse siderod attachment
Hi, Guys. I'm totally new here and looking for info/help with an (as it turns out) incomplete old MDC Ten Wheeler kit issue. The kit is old and uses the metal screws to attach the siderods to the drivers rather than the newer plastic(?) fastener. In 1978 my dad wrote MDC for a list of parts and was sent the wrong screws. Now I'm building it and binding is severe with the wrong screws of course. Here's the question: I found a cheap MDC 2-8-0 chassis on eBay that I can rob for parts but it uses the plastic fasteners. Are they interchangeable with the screws that I am missing? If so I'll buy the chassis, but if not, how hard is it to find screws like that? I thought about using the 2-8-0 drivers, but that would leave me with a blind driver on the front axle. Not sure that's good. Any advice from someone well-versed in these things is appreciated. My dad got this when I was 7. I always wanted to see it run, but now that it's mine 4 little danged screws are holding me up.
Hello Mark and welcome to Big Blue.  I am not the expert but here are my thoughts.  If the screws are of the right thread which you will know if they tighten without using an air impact, then it may be they are too short and tightening down on the rods. The rods should show some slop and usually there are a few spacers too.  If you can determine what the screw is and the thread a longer screw can be used and you may find finials at Walmart  to use for spacers if you cant make them on your own.  Also check ho seeker for a diagram of your locomotive which might give you the proper size. As long as the threads are good in the drivers the problem should be easy to solve.  I am sure Wayne will chip in when he has time with even better advise. 
Don't be a stranger. We enjoy new blood. 
Welcome to Big Blue, Mark!

According to the instruction sheet for the MDC 4-6-0, the one-piece siderods (brass stampings) need to be cleaned of all burrs, using a file.  They are then attached to the front and rear drivers using "small brass shoulder screws".

The threaded portion of the screws, obviously, goes into the hole in each driver, with the shouldered portion of the screw fitting into the hole in the side rod.    The hole at the mid-point of each siderod fits onto the extended boss on the main (centre) driver.

The shoulder on these screws is designed to prevent the modeller from over-tightening the screws, which should prevent binding of the siderods.

However, at no place in the instructions, for either the Ten Wheeler or the Consolidation, is the size of those screws mentioned.  They're identified only as Part 6L-120, for which I can find no additional information.  In the drawing, these screws appear to be roughly twice the length of the known screw, mentioned below.

However, the screw which is to be used to attach the main rod to the centre driver is identified as a 'pan head self-tapping 0-80x1/8"  screw'.  It's difficult to tell for sure, from the drawing in the assembly instructions, but it appears to also be shouldered, which seems logical in keeping with the others.

There's a pretty good chance, I think, that the 6L-120 screws are also self-tapping, and would likely be 3/16" long, or perhaps a bit longer than that.  Again, I'm just guessing, but I can't see any reason why MDC wouldn't use the same diameter screws for the siderods, too, so if you can find some 0-80x3/16" self-tapping screws to use in the siderods, you might be able to get your locomotive assembled.

I also note in the Ten Wheeler instructions, that there's pin connection of the main rods to the crossheads, calling for the pin to be inserted from the back (inside) face of the crosshead, then through the hole in the main rod.  The instructions then call for the modeller to use a small screwdriver to "upset" the end of the pin which protrudes through the main rod.

It's been over 40 years since I built mine, and they were sold-off many years ago, and while they ran very well, I don't recall that particular step.  Usually, "upsetting" is done to things like basically involves fiddling with the end of a pin or rivet to make it big enough to not easily be withdrawn from the hole(s) through which it's been installed - similar to "peening-over".

I seldom see self-tapping screws in hobby shop displays, but you may be able to find them at a really well-stocked hardware store.  Otherwise, an on-line search should offer some other options.

EDIT:  I doubt very much that the plastic pins would work in lieu of the screws, and I do recall some buyers being less than pleased with the performance of the plastic pins.

Another place you may find small screws would be a jeweler.  A jeweler might even be able to find the size for sure.  MicroMart also offers an assortment and assortments of screws can be found on eay for a reasonable price. 

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