help with MDC loco kit?

[Anonymous]

Hi!

I'm returning to active modeling after a hiatus far longer than I'd care to admit. I'm trying to build an MDC HOn3 kit of the D&RGW C21 (outside frame). I'm having trouble with the side rods binding and can't figure out what to do about it.

One of the side rods gets real tight when the cranks are in the horizontal position, which suggests that the spacing between the crank pins and the holes in the side rod are not the same. I've swapped the side rods and the problem remains on the left side of the loco, so it would appear to be a problem with one or more of the cranks. Beyond that I'm stumped.

I followed the instructions about keeping the punched side of the side rods in on one side and out on the other, but have also tried other combinations to no avail.

Does anyone have any ideas on how to fix this?

Thanks in advance!

[lonewoof]

Is this a new kit? my first thought would be "driver quartering", which would be a manufacturing problem, I'd think. I can't get it clear in my mind WHY the problem would only be on the left side...could the frame be warped?

[andrechapelon]

QUOTE: Originally posted by Synergy_RR

Hi!

I'm returning to active modeling after a hiatus far longer than I'd care to admit. I'm trying to build an MDC HOn3 kit of the D&RGW C21 (outside frame). I'm having trouble with the side rods binding and can't figure out what to do about it.

One of the side rods gets real tight when the cranks are in the horizontal position, which suggests that the spacing between the crank pins and the holes in the side rod are not the same. I've swapped the side rods and the problem remains on the left side of the loco, so it would appear to be a problem with one or more of the cranks. Beyond that I'm stumped.

I followed the instructions about keeping the punched side of the side rods in on one side and out on the other, but have also tried other combinations to no avail.

Does anyone have any ideas on how to fix this?

Thanks in advance!

Since MDC used one piece siderods, the most likely culprit is that one of the siderod holes is off a bit. That was a fairly common problem with MDC engines. The usual fix is to buy a couple of extra side rods, cut them into sections and install them piecemeal until you find a combination that works. Since that would require an ability to buy additional siderods, that's probably out of the question since all MDC's inventory is currently on pallets at Athearn.

Have you tried this? remove the siderod entirely rotate it so that the rear crankpin hole becomes the front crankpin hole and v.v.? My guess is that it won't solve the problem, but it's worth a try.

The only other thing I can think of (since it's unlikely you can get extra siderods) is to ream out the hole that's causing the bind if you can determine which one it is.

Also, have you tried moving the non-geared drivers to different slots to see if that makes a difference?

AND, if all else fails, you might want to go here: http://www.steamlocomotive.com/model/HO-steam.html#mdc for some hints.

Hope this helps

Andre

[Anonymous]

Assuming the individual axles turn freely without side rods attached, the problem is most likely with poor fitting side rods or out-of-quarter drivers ( cranks on this model). Does the engine roll smoothly when you push it back and forth by hand without the motor installed? Try doing this while leaving one or two driver sets off (and various combinations of "installed" drivers).

MDC should have designed the kit so the holes in the side rods match the axle slot spacing in the frame, but it wouldn't hurt to verify this. Be sure to carefully smooth the sharp edges found on one side of the side rods (this is an artifact of the punching process). Also, the side rod holes should be just large enough to slip over the crank pins (if the holes are too large the drivers can get out of sync).

Make sure the "quartering" of the cranks on all axles match exactly (this is easy to say, but not so easy to do). A perfect 90 degrees is not necessary but consistency of all axles is necessary. The cranks on this model are add-on parts and they may be twisting as the engine is running (i.e. the drivers are dynamically going out of quarter). Can you detect any movement if you grab the drivers by the cranks and gently twist them?

[twhite]

I had this problem with several MDC kits in the past. I cured it by reaming out all of the holes in the siderods, and they worked fine. The brass punchings for the siderods are not exact, especially with the 2-8-0's (the HOn3 is pretty much a narrow-gauge version of their 1880-style standard gauge 2-8-0) and reaming each hole out carefully will usually correct the problem. After that, the locos run quite nicely.
Tom

[nfmisso]

IMPORTANT: do NOT ream out all the holes in the side rods, leave the hole on the geared driver a tight slip fit, carefully ream out the other holes, one at a time.

As mentioned above, get all of the axles rotating freely without the gearbox or rods in place. Next remove two of the driver axles, install one side rod, ream the non-geared axle hole in the side rod to achieve smooth running, then ad the other side rod, repeat. Next take out the non-geared axle, and repeat with each of the other two axles. Finally, assemble all drivers, with both side rods, no gears, should be smooth.

[Anonymous]

Thanks to all who replied!

Everything turns freely until I install the side rods. I hesitated to ream out the holes because the instructions warn you not to do this. I'm pretty sure the side rods are identical, because the problem does not follow the side rod when I swap them.

Quartering might be a problem, but I don't know how I could verify it nor correct it if it is the problem. Quartering in this kit is kind of strange. There are flats milled onto the end of each axle onto which the crank & couterweight casting is pressed. The quartering is achieved by D shaped holes in the crank. There are two different sets of castings with the D shaped holes at 90 degrees to each other - and that makes the quartering.

I reckon I'll try the reaming the side rods - if I can figure out which hole is binding..

Thanks again everyone!