Good thread.  I had the same experience installing ERR in a Lionel train set 4-4-2, which uses a very similar motor (except that the steam loco only has one of them.)  One thing I've found is that the cogging seems to be VERY strong when new.  It gets smoother as the loco accumulates years and miles.  Perhaps the field permanent magnets lose some of their strength?

Lionel started using those walnut-sized Mabuchis circa 1979 in their DC-only sets.  They first bolted one into the truck of a diesel around 1982.  Later in the 1980s, K-Line followed suit.  They are used in low-end train set locos right up to the present day.  At some point early on, the motor case changed from a shiny gold sheen to a dull metallic grey jacket.  Almost all of these motors that I've seen have a white nylon end bell, except the NASCAR series 4-4-2 steam locos.  The motors in the NASCAR locos are the same length and diameter, but the end bell is yellow, and I believe there are two little orange components that look like candy drops (PTC thermistors?) on the brush terminals.

I would love to know if the motor in the NASCAR 4-4-2's is a premium, high-performance variant.  I couldn't find anything definitive on the Lionel parts site.  These were special commemorative items, and usually part of sets.  I think the only link I found was to the generic train set 4-4-2 with no mention of an alternate part number for a different motor.

Another thought:  The R/C car hobby has a lot of adherents.  Installing and upgrading motors, changing gearsets, etc., is a much bigger part of that hobby than it is in 3-rail O gauge.  Surely there must be an R/C car motor that would fit in these "transverse" applications, and offer higher performance than the Lionel 8008 motor and its K-Line equivalent.  Following!

Ted

Thanks for your response, I may have to start looking for motors on rc car sites.

Marty

Getting motor is easy.  Getting the worm gear/spur depending on type Kline used on MP is the difficult part.  Take off the old and install on the new motor may work, but you need to be careful not to damage gear or new motor when installing.  G

I found some motors on Amazon with 12 teeth which are shown as either 12 volt or 18 volt. ( Fielect 550 Electric motor 12 teeth) Any thoughts on which voltage is needed on the mp 15  I have a gear puller but I would like to avoid pulling the gear if possible.  My next move is to compare the size of the motor to the size of the motor on the mp 15

Marty

This is a classic issue, especially with the horizontal truck motors on many K-Line and RMT locomotives.  I never did find a motor that worked well in these and handled back-EMF cruise.

The motor you found appears to be way longer and larger in diameter than the one in the K-Line powered truck, I don't see how this is going to work.

John

I assume that you have probably done a lot more research on this attempted project than I have.  Thus, should I just live with the cogging at low speeds?  I don't want to tear this apart only to still have the problem persist.

Marty

The way that engine is designed, it’s not worth the fight IMO, …..sell it, and find a comparable MTH, Williams, or Lionel model,…..

Pat

I gotta' go with Pat here, time to move on.  Those engines were strictly a budget affair, if you sink a lot of money into it, it's liable to throw a plastic gear and be out of commission!   It's not like the MP-15 has never been made.