(Resolved, seemingly) Upgrading Two SD70MAC's for Double Heading

Man, this is me!

Just change the tape!

tach tape that is...

Which way would I change it? 

Cheryl,

Have you tried running them as a lashup, even disconnected?

If the two tach tapes have the same number of stripes, the two engines have same size drivers and the two engines have the same gear ratio, I would expect them to run at close to the game speed.

However, if the gear ratios or driver sizes are different, all bets are off.

If you want to slow the faster one down, you'd add stripes to that flywheel, and vice versa.

 When you did the upgrade, did you use the two different tapes for each flywheel size? or did you use the same tape on both?

 This may sound lame, I don't know the formulas that the pros use to match these. I'd get one engine running the correct speed that matches my fleet. It takes me a little extra because I just start with a guess and then add or subtract stripes using my computer and printer.

 I'd then fine tune the other one to match. It takes me a little longer and I waste some tape stripes. I fiddle with them until they're perfect. Sometimes I just color in a white stripe with a sharpie, to make a quick minor adjustment. You only notice that at super slow speed (1MPH). I can then, print out what I need, once I've determined the correct number of stripes.

 Once it's dialed in, it will stay for good.

Sure. You need to try stuff like that to correct the speed. It won't hurt. What I would do though, is get them to match known well working engines. That way you can make them in a consist with anything.

 So try each and determine if each one needs to go slower or faster.

Okey doakey   Will be tomorrow's project, watching my bb team win right now!! 

"One other thought I had was putting the 30mm tape on the 27mm fly wheel.  Any thoughts?"

I believe that will speed that engine up?? (It has to spin faster to read same number of stripes.)

 I like to pace the engine with a known correct one, and get an idea of how far off it is. When it's close in speed, it's easy to add (or subtract) a stripe or two.

 Make sure the reader has the correct spacing off the flywheel or it will skip some stripes and you'll be chasing your tail trying to fix this!

Ooops! Sorry. I like to chat!

Back w/ you tomorrow.

No worries, I can chat and watch the game, it's just that I can't test out the locs while watching the game and typing, lol.  Game is over and my team won!  Yeah!

Charly, Flywheel size doesnot matter as long as correct tach tape used. The number of stripes will be the same regardless.

I put a mark on top of the flywheel and also a wheel.  Rotate flywheel and count how many turns to get one revolution.  Do same for other engine.  Are they the same?

If not that is the issue.  IF they are, make sure tach reader gap is good, especially on the faster engine.   Make sure you used correct size tape on the flywheels.

G

3mm Diameter is 9.42 mm circumference. A few extra strips but the space between strips should be the same.

(1.) Flip the motors faster to slower/ slower to faster. You would determine if the worm gear ratios of the trucks are the same, if they fit and work properly.

(2.) You could change flywheels.  (Frank Timko)

I could be wrong and often.  Mike CT 

Mike,  Not for MTH, it expects a set number of stripes to indicate one revolution.  So a larger flywheel get larger spacing, but the same # of stripes as a smaller flywheel.

Need to find compare ratios first, then find out why one is faster, or slower.  G

Hey Charly

Why not see if you can just swap 2 of the motors , so you get a large flywheel and a small flywheel in each loco, then put the reader tape on the same size flywheel .

Problem solved , chances are the gear into the trucks are the same , just compare them carefully. The collar that is on the bottom of the can motor can be moved if ness. also .

This would seem easier than matching tapes . 

Also if you can swap the motors , with all electronics disconnected , once you move the motors use a DC transformer and temporarily wire the can motors to pick up power from the track , then run the locos and see if they run the same speed , one other cause may be one of the locos is broke in more , because it is older. If that is the case , then if both locos have the same side frames , swap out the truck and motor and see if you can get them to run at the same speed .

Already have established reader spacing on both engines, well within the MTH parameters, thanks! 

Proper tapes were used, measured fly wheel with a micrometer to be sure.  Have not checked rpm on fly wheels, will give that a go.  Thanks!!

Interesting thought, thanks for the reply!!