My reactor was acting up in that the arm was getting stuck and I would have to give it a little nudge to get moving.  It was a pretty consistent getting stuck as it moved.  After taking the gear box apart, I confirmed what others have stated.  The one gear was split which drives the arm.  Others have reported that they went to NorthWest Short Lines to get a replacement gear.  NWSL was not back up to order the gear so I found an exact replacement on Ebay from a Chinese vendor.  The gear was an exact match for the original and pressed on perfectly.  Following what others stated the gear to be helped me find it on ebay - 0.5Mod 10T, inner diameter: 1.95mm; Tooth length: 5mm; round diameter: 6mm.  Others stated the bore was actually 2 mm but this was close enough.  For less than $5 shipped I got a pack of 10 gears.  I did not need a new belt as mine was still in great shape.  After putting it back together I also noticed some binding on the door that opens and closes to release the plastic pellets.  What I found is if you loosen the screw which attaches the connecting rod to the door, it allows the rod to flex properly and not bind.  The door now opens perfectly smooth and also smoothed out the entire movement since it removed some binding.  Its now back together running better than ever.  If anyone else has a split gear, check ebay for the replacement gear.  Its a perfect fit.20191104_17362120191104_17374320191104_17380020191104_17384720191104_17391020191104_174426


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Repaired reactor
Original Post

Thanks for posting.  I have a reactor that may need the same repair.  The issues you outlined are the same as mine.  

Dan Padova


"In the course of my life I have had to eat my words, and I must confess it was a wholesome diet"..........Winston Churchill


I’m glad that you found a solution. Most nuclear reactors I’ve come across have a “no user serviceable parts “ warning sticker.  
I guess if you know what you’re doing go for it.  I think that that would void the warranty on most nuclear reactors. 

The warranty on the reactors are long gone. It has been years since they were made.  Checking Lionel's online parts, a lot of parts are no longer available. The gear boxes are one of the parts no longer available. Repair is the only option. 

I found the repair required a moderate level of skills. You have to take a lot of screws out to remove the gearbox and disconnect wires. As long as you have good basic skills in taking things apart, users can fix it.  Now, to put the gear on, I used my vice as a press. I had a nice hard plastic tube the right size to fit over the shaft but smaller than the gear to allow me to press the gear on. That has to be done right so you dont bend the shaft. Once done, I had mine back together in less than 1/2 hour.



I'd hang on to the other duplicates of your replacement gear, though.  I'd be suspicious that the Chinese gear is of the same the original Lionel gear.  Nylon is a hygroscopic resin, meaning it absorbs water.  As such, its properties..pre- and post-molding...are subject to the material's water content.  I'm told that it's this characteristic of nylon that exacerbates the notorious split gear problem plaguing this accessory and a BUNCH of similar geared hobby products.   The splitting white nylon main axle gear on a bazillion HO engines....from early brass imports to more recent 'improved' designs...created a big chunk of NWSL's replacement product business.

The use of brass or acetal resin (brand names Delrin, Celcon, et al) for these gears takes the hygroscopic issues out of play.  Nylon is obvious preference for high volume manufacturing.  Brass gears are not molded, they're at a time.  Acetal resin is more expensive than nylon, and may have a higher shrinkage rate through the molding process for which die manufacturing can be more expensive and fussy in compensating for this characteristic. 

The thin cross section of these hobby gears between the root of the gear profile and the shaft bore is a natural weak point.  Under the stress of a press fit on a knurled shaft, the load stresses on the gear during operation, coupled with the aforementioned change in properties of the material based on original and ambient water conditions (e.g., humidity, heat) that thin area of the part is the proverbial 'Achilles Heel'.  

I suppose if the gear is easily accessible on a particular assembly, it might be worth the trouble.  However, my recollection of getting to that bugger on Lionel's Nuke Reactor was hardly a walk-in-the-park.   

I know.....more info/perspective than you'd ever want.  Still, it's nice to know that, as NWSL gets back up on its feet, there is another sourcing option of a duplicate gear.

FWIW, always...


Learn something new every day.  That would make sense about the nylon gears.  Once NWSL gets back on their feet, I may just order a spare delrin gear from them so I don't have to keep opening the gearbox up.  With a 2 mm bore and only a 6 mm face size, its a very small gear.  That does not leave a lot of material to handle the stress of being press fit on the axle, coupled with what you stated above.

I would just like to concur with what my fellow "nuclear tech" @KD has stated. I ordered the NWSL gear upon his recommend as well as a belt replacement from another dealer.

The repair was a beast, and I consider myself above average in mechanical skills. In a reactor teardown of this magnitude, go with the best parts you can obtain. You don't want to have to go back in there!😵



Thanks for posting. My 86-year-old walking Lionel Service Station--my dad--has been working and tinkering on this piece for the last several months. We picked up ours about 10 years ago a TCA York Meet. Your advice about the connecting rod to the pellet door might have just helped us complete this repair lengthy project.

We were able to find replacement gears on eBay but just buying bags of assorted gears for RC models.


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