TypsJunction Posted October 31, 2023 Share Posted October 31, 2023 Hi all, Just purchased a Bachmann 7F from online. Been told it has never been run, and to be fair it is in excellent condition. Ran it for the first time shortly ago however every wheel rotation the model seems to ‘jump’. Seems to be coming from somewhere in the mechanical at the cab end. I’ve no experience in mechanisms or taking models apart to a large extent so any help would be appreciated. Thank you. video of loco running issue as YouTube unlisted link Link to post Share on other sites More sharing options...
TypsJunction Posted October 31, 2023 Author Share Posted October 31, 2023 Another video of the bottom of the chassis showing one axle wobbling about. Link to post Share on other sites More sharing options...
RMweb Premium SR71 Posted October 31, 2023 RMweb Premium Share Posted October 31, 2023 (edited) Can you film the same as above but running a bit slower/longer and keeping the camera more in one place. It looks likely to be an issue with the motion. Edit also looking at the other side too. Having just played at 0.25 speed the motion this side looked ok. Edited October 31, 2023 by SR71 Link to post Share on other sites More sharing options...
TypsJunction Posted October 31, 2023 Author Share Posted October 31, 2023 3 hours ago, SR71 said: Can you film the same as above but running a bit slower/longer and keeping the camera more in one place. It looks likely to be an issue with the motion. Edit also looking at the other side too. Having just played at 0.25 speed the motion this side looked ok. Thank you for your reply. Here’s a video of it running slower, hopefully is okay. I’ve also got a video of me holding wheels in place and axle gear still spinning (not great I know), but proves issue isn’t with the wheels or con rods. Link to post Share on other sites More sharing options...
TypsJunction Posted October 31, 2023 Author Share Posted October 31, 2023 It seems the issue may be coming from this gear with this slightly wider notch but I somehow feel this wouldn’t make such the major ‘bounce’ and is probably a design feature anyway. Link to post Share on other sites More sharing options...
RMweb Premium SR71 Posted October 31, 2023 RMweb Premium Share Posted October 31, 2023 It looked like the valve gear was clashing but that last video shows you have bigger concerns. The gear shouldn't spin on the axle like that. If you've spun the gear on the axle and the jump happens at the same point in the rotation it's almost certainly valve gear / motion related. It doesn't look like the gear is slipping in your other videos so I don't think that is the cause though it may have been caused by your problem. Trouble is even if you do find the cause that slipping gear is going to stop it pulling much. I don't know the history of these models so it might be worth searching to see if it's a known fault? Link to post Share on other sites More sharing options...
TypsJunction Posted October 31, 2023 Author Share Posted October 31, 2023 38 minutes ago, SR71 said: It looked like the valve gear was clashing but that last video shows you have bigger concerns. The gear shouldn't spin on the axle like that. If you've spun the gear on the axle and the jump happens at the same point in the rotation it's almost certainly valve gear / motion related. It doesn't look like the gear is slipping in your other videos so I don't think that is the cause though it may have been caused by your problem. Trouble is even if you do find the cause that slipping gear is going to stop it pulling much. I don't know the history of these models so it might be worth searching to see if it's a known fault? Okay, the slipping is a bit of a concern, however did require a little force from me to occur. The loco still happily takes my take I need it to pull around. I genuinely cannot seem to find the issue with gears which seem to be causing the problem (the axle gear and the adjacent one). Ran both through with a fine flathead in ever notch, but no change. The way this is happening makes me think it was a factory issue (told it’s never been ran, whether that’s true or not though.) Link to post Share on other sites More sharing options...
DCB Posted November 6, 2023 Share Posted November 6, 2023 (edited) The axles usually jump about on Bachmann keeper plate chassis when the keeper plate is missing. A loose or worn keeper plate is l a common cause of lumpy running but poorly machined valve gear components can cause it, as can a split drive gear. As the gear is slipping its about 98% certain that it's split. and about 98% certain it will get worse. I did have a Triang Hall which had a slipping gear 10 years ago which hasn't been fixed and is a lot better now than it use to be or I would have said 100% If the gear is split then whether it's repairable depends on whether another gear or wheelset is available, even then it's not easy to remove the valve gear without damaging it or a wheel without losing the quartering. Sounds like a display model to leave on shed while a Hornby Dublo 8F reliably pulls trains for the next 50 years... Or send it back for a refund? eBay favour the buyer in disputes, a good reason to use eBay not your local Model shop or exhibition / swap meet. Edited November 6, 2023 by DCB Link to post Share on other sites More sharing options...
steve66 Posted November 18, 2023 Share Posted November 18, 2023 I had exactly the same issue on one of my 76xxx locomotive I have, it was a split gear on the drive axle. Ordered replacement from Bachmann ,well I had to purchase full set of drivers as that's how they come problem solved. 1 Link to post Share on other sites More sharing options...
GWR-fan Posted November 18, 2023 Share Posted November 18, 2023 It does appear from the video showing the drive axle deflect sideways that the rod is contacting the endcap on the drive wheel centre causing it to deflect the axle sideways. I have a similar issue with a Bachmann Manor class chassis. Link to post Share on other sites More sharing options...
Quadrille Posted January 30 Share Posted January 30 (edited) I would suggest removing the motor, place upside down in a foam cradle, and turn the drive/gear wheels slowly and check at the point of the problem. Also check the intermediate and Crown (Top) gear. Also test the motor whilst disconnected and check that the motor shaft is not bent. Also check for excess play where the wheels actually sit in the chassis. Edited January 30 by Quadrille 1 Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted January 30 Share Posted January 30 Rather late seeing this thread, but another possibility is that the piston rod is fouling inside the cylinder moulding. Link to post Share on other sites More sharing options...
Quadrille Posted January 30 Share Posted January 30 Looking back at the video of you holding the wheels then I would say it's obvious that the axle-gear has worn loose and spinning freely. If you hold the wheels as you clearly were then the gear shouldn't move. Remove the complete axle and, holding the wheels in place with finger and thumb, try turning the axle-gear with finger and thumb of the other hand. If it's loose then you could try completely degreasing the axle and gear and use a strong adhesive to bond the gear back in place but make sure it correctly aligns with the intermediate gear and the top or crown-gear under the motor worm-gear. Check to make sure that all moves freely before final assembly. Link to post Share on other sites More sharing options...
micklner Posted January 31 Share Posted January 31 I would suggest new wheelset . The Gear is knackered and i doubt glue will hold it for very long. https://Bachmann-spares.co.uk/product/category/833/7f-wheelset---black-31-010/e3101-103-01 Link to post Share on other sites More sharing options...
Quadrille Posted February 1 Share Posted February 1 (edited) Fitted a new set this morning (53809)...all I was getting was loud thud, thud, thud noise that increased with speed. I wouldn't mind but a new model with a bent axle and a warped wheel and with a deep "V" cut in the flange of one wheel! The rest of the model does look new though...must have slipped through Chinese QC...just hope the spies don't come knocking on the door wanting to film me or play the piano!! ;-) Edited February 1 by Quadrille Link to post Share on other sites More sharing options...
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