Shay Diagnostics
Dear Dooch,
Irrespective of whether this is
- an early open-frame-motor 2 or 3 trucker kit
- a later can-motored 2 or 3 trucker kit
- or a late-model MDC/Horizon China-assembled 2-truck RTR unit
The key with most any MDC shay is "divide and conquer".
- first, remove the decoder. If any loco does not run well on analog, it won't work well on DCC.
- now disconnect the sideshafts between each truck and the "steam engine" on the RH side.
(If it's a 3-trucker, disconnect and remove the 3rd truck/tank for the purpose of diagnostics)
Test run, any improvement?
if NO:
- remove the sideshafts from each truck, the axlebox ends should pop off the sideframes, releasing the sideshafts and bevel gears. CAUTION not to loose any washers, bevel gears, axlebox covers/keeper-plates, or the Uni/sleeve/uni sets.
Test run, any improvement?
(Suspect yes, incorrect assembly of the truck<> sideshaft array is a key point-of-failure)
Going furthur:
- Remove each truck, being careful not to loose the centreline driveshaft. NOTE The stock system uses wipers to get the power from the truck to the loco frame. Such trucks will literally "pull off". However, if the previous owner has attempted to hard-wire the trucks, you may need to un-solder some non-standard feeder wires.
Once removed, hold the truck with one hand, and turn the end drive socket with the other, should turn smoothly in _both_ directions, for as many rotations as it takes to make the wheels complete at-least 1x revolution. _ANY_ binding in either truck, whether "constant resistance" or "clicking"/"popping"/momentary-binding is an issue which _needs_ investigation and resolving.
Also try (carefully) pull/pushing the socket fore-aft thru the truck. If it can move much more than 0.001 - 0.005" fore-aft, there is too much slop in the driveshaft positioning, This can cause the worms which are internal to the truck to bind in one or both directions.
Assuming both trucks are OK,
(unlikely, another common point of failure-to-assemble-properly failure)
- using a temporary connection (aligator clips work well), apply analog power to the motor/central-gearbox assembly. If everything is working _as_designed_, you should be able to smoothly turn the volts _up_ and _down_ and get a nice smooth reproducible start/stop rotation from the gearbox output socket, without any jerking/juddering/"RRrrRRrrRRrr"-or-"click-click-click" sounds.
Assuming this is not the case,
(again, highly likely, insufficient patience and attention-to-detail when assembling the gearbox and linking to the motor is a common issue),
- remove the boiler to access the top of the gearbox
- apply _minimum_ analog volts to the motor
- and from the underside, loosen the 2 screws holding the gearbox in place
Loosening these screws will have 2 effects:
- if the gearbox body halves have not bee adequately cleaned-up, or are malformed, they may have been pulled-apart by the tension of the gearbox mounting screws. This can cause the shaft holes thru the gearbox halves to deform and add friction to the gearbox
- if the alignment of the gearbox and motor is not correct when the gearbox is fully-screwed-home, loosing the screws may add some "slop" which will manifest audibly as a smoothing-out of the motor motion/sound, and a lowering of the "starting voltage"
Having now effectively completely disassembled the shay, take the _time_ and _patience_ to pull each assembly apart in turn, and carefuly store each assembly's worth of components in their own container or zip-lock bag. Start with the central gearbox, clean out any/all lube, and check-for and remove any sign of excess flash, crud, and/or malformed castings (mis-shapen gear teeth, not-deep-enough troughs, etc). Once all components have been checked, reassemble the gearbox, and re-check for smooth operation.
Remount the gearbox, taking care to ensure correct motor<> gearbox alignment. At minimum volts you should be able to tighten up the gearbox screws with _no_ change in minimum motor RPM/audible loading. Using small pieces of paper or 0.005" styrene may be required.
Now head to one of the trucks.
- Check the worms on the driveshaft for burrs.
- Check the driveshaft for bowing/warpage, some have been known to be slightly "banana" in shape, which means the worms do not rotate in perfect position all the time.
- Check the slots in the end of the truck casting, ensuring that they do not "pinch" the driveshafts. (Be careful not to _over_file them such that they are _too_ wide though!).
- Shim the driveshaft with washers to avoid that fore-aft "slop" or end-play in the driveshafts when installed in the truck casting.
- Check all axle gears for cracks (more likely in Horizon-era RTR white-nylon gears).
- re-assemble the axles into the truck castings, and re-install the bottom keeper plate
- manually rotate the driveshaft, any hint of binding or restriction is a call to go back and recheck.
- once both trucks have been tuned and re-assembled, mount _one_ of them to the frame, and insert the related gearbox<> truck driveshaft.
- apply _minimum_ analog volts, and test for smooth stop/start/stop behaviour of the assembled mech
If OK, add the 2nd truck and retest.
That should get you most of the way back to a working _basic_ mech. From here you're into checking the assembly and tuning of the side-mounted steam-engine, uni/sleeve/unis, and truck sideshaft/bevel assemblies.
(Get the above done first, _then_ you can take-on the sideshaft system).
Sounds like a lot of work, and when compared to a HO diesel, it is. However, this ammount of
"attention to detail" mech tweaking is situation formal for _any_ geared loco, and many "normal" steam loco models. MDC shays _appear_ particularly prone to such issues because many modellers approach assembling it as they would a MDC "shake the box" boxcar kit (IE quick, twist-the-parts-off the sprues, press-together-and-go).
Rest assured it only takes patience, and observing correct mechanical assembly to get your shay to run sweetly...
Happy Modelling,
Aim to Improve,
Prof Klyzlr
PS if you're keen, a copy of Jeff Johnston's "MDC Shay Handbook" is an invaluable workbench partner while working on these shays.
PPS if you _really_ don't want to have-a-go yourself, Floyd at http://www.shayfixer.com would possibly be willing to have a go???
