Forward and Reverse not equal?

Hi , I may have brought this up before but can't find it ..: I own a Bach 10 wheeler. she is smooth as silk running forward..But in reverse she kind of has a teensy hesitation..some might not even notice or care..But it bugs me..What causes this ? If it were driver quartering or the eccentric rod position causing binding I'd think it would be encounterd in both directions..In fact I loosened both eccentrics and ran it with them loose and nothing changed. I also tried changing CV values (NCE) which are discribed as being able to make up for inaccuracies in the drive train and motor inefficiency and the (is it ?) bemf ..These are CVs 10, 209 and 210 and a couple others..I followed the recommendations in the CD for its Sountraxx decoder..I even moved the values greatly up and down just to see the radical differences..Yet nothing seems to get the hesitation out, in reverse..I'm guessing you will blaim the motor/gearing as a tad askew. Still, I'll bet there are the same locos out there not doing this. I know there are geniuses out there who know the solution...This seems to be the one problem of on-line purchasing; not being able to test run them..BTW, it's about a year old and has been lightly oiled everywhere but the motor shaft...Thanks for your attention...Mark

 

First thing I'd look at is quartering. One direction hitch inn the giddayup, usually quartering.
Loose or worn crankpins.
Axle bearings.
Seen it as lot over the decades. If you are real careful, you might be able to see it in crankpin position, line up one side, hold the drivers tight, roll it over and see if they all line up 90 off.
I even have a very early Varney Docksider, with a frame that was mis-milled, lead driver is "turned" just a tad, had to glass bead the rod that needed to be longer until it "grew", works fine, but had a hitch in one direction only.
Dave

 

Dave, thanks for quick response...Again, though, if it's quartering why wouldn't it be in both directions ? I'm usually thinking it's the worm and gear which is 'happier' in one direction maybe to do with worm ,if you will, 'pulling' axel gear from motor vs 'pushing' gear from motor: I.E. Some kind of slack/no slack phenominum..motor shaft inward or outward...But i'll try to get a good look at the quartering again...hard to see on a 5/8-ish inch Diam. HO driver...

 

It can be the worm, it can be thrust washers in the motor. You can eliminate quartering by looking.
It's hard to describe in print, but the rods lead in one direction, pushing the drivers, the other rod is in "trail", may or may not be assisting the driver rotation.
If a driver is off, sometimes you will get the other rod when pushing will "cog" up against a out of quarter crankpin.
Like I said, run the engine slowly until all the crankpins on one side are in a quadrant (straight down, straight up), hold the drivers to keep from moving, look at the other side, see if those pins all line up 90 degrees off the first side. Magnifying loupe will tell you. If you can eliminate this as the source, then look at gears and motor.
Sometimes, in the dark past, I have removed all rods and run the engine to see what it does. If the problem is gone, it's rods, crankpins, axle bearings or quartering.
On the old Mantuas, I'd start adding rod segments to see where the issue starts occurring.
Dave

 

I hope that made sense. Two phone calls and two visits by SWMBO whilst typing.....

 

Basically, I yhink he's trying to say that it's a lot easier to pull an out-of quarter rod than it is to try and push against one. I recently worked on a Mantua Hudson that *someone* (whistles) had re-asseembled badly out of quarter. Ran just fine in forward, but it jammed (no bump or hitch, she jammed) in reverse. Same problem, just magnified.

It could be a gear, but usually if its a gear issue, there's a more noticable thumping. The P2K split axle gears on the BL2s come to mind.

Aren't you gld you're not in a smaller scale?

 

Probably should define SWMBO for the younger crowd.
She Who Must Be Obeyed.

 

Thanks to all for the info on this..I do understand the 90 Deg. seperation of rod action one side to the other ( not 180 as newbees might think). I will try and get one side in 'quadrant' and secure it there while examining the other side...One final guestion: Assuming a wheel is out of quarter what is done next ? On this Bach should I be able to reposition the wheel by merely holding other side and turning bad side right there on the axle ? Or does entire drive train need to be removed first, along with other steps/tools ?

 

One would hope not. One would hope the drivers were more firmly attached to the axle. However, we need to know how the drivers are build and attached. Are they plastic centres or castings?
Are the axle ends smooth or splined?
To do this right, you may need a NWSL pulled, Sensi-press, and quartering jig.
You could have a malformed or mis-punched siderod.
Do you have crankpins cast into the drivers with just a bolt, or does the driver use a shouldered crankpin bolt?
Can be the crankpin is off, hole misdrilled...never know.
Also, which driver is geared?
I have seen some times where the lead crankpin hits the back of the crosshead or guide when the driver shifts to one side.
Look for witness marks on the head of the crankpin bolt, and back of the crosshead and guides.
Is this your engine?
http://hoseeker.net/assemblyexplosionbachmann/bachmannspectrum10wheeler460pg2.jpg
Looks like cast in crankpin on centre driver only, and two piece siderods.
You can remove siderods and see how it works (eliminate gearbox and motor), then add front rods, try that, if no problem, add rear rods and try that. When the issue occurs, whatever driver you energized is probably it, unless, you do front and it does it, remove those rods and connect rear and it does it, then I'd look at the main driver.
Dave

 

I doubt if this is the case but when manufactured the brushes in the motor can be offset for better performance in one direction. Normally this is done for maximum speed in one direction. Don

 

But, that would take thought and planning.
We are talking Kader.
They buy these Mabuchis by the tens of thousands at a time.
This motor faces to the rear (brushes to the front), with a belt drive and jackshaft.
They would have had to figure which direction the motor would rotate in "forward" after doing the rotational changes, then order out special Mabuchis for the occasion....which, since they are industrious people, making money, that won't happen.
Dave