I just got an older Great Northern 0-8-0 (6-38046) TMCC version. Runs well, but the chuffs start out at 4 per rev and then go to 3 per rev and will jump back and forth, mainly running at 3 chuffs per rev. I am thinking I have a bad or sticky cherry switch and was going to replace it. Yes I did a engine reset. Do others think the cherry switch or something else. Thanks for your feedback.
Replies sorted oldest to newest
The switch likely just needs adjustment. Not easy to get to though.
Pete
Pete is most likely correct, that's about 99% sure to be the switch, and indeed it's buried down at the axle. 
Do you think switch is on an angle or catching on something.
Thanks
The switch is held on to a bracket with a screw. Its common for the screw to loosen just a bit and move the switch away from the cam just far enough that it doesn’t close consistently. Maybe one cam lobe is off a small amount. ,010” or less is all it takes.
Its almost the same amount of work to adjust the switch as replace it. If you adjust or replace you want to test it before putting it all back together. To do that you want to put an ohmmeter on the switch contacts or connector soldered to it and turn the flywheel to rotate the wheels and make sure the ohmmeter goes to zero 4 times per wheel revolution. Actually if you do that before you adjust it you can verify if thats the problem.
Pete
I find about 90% of the time it's either a loose screw or the actuating arm needs a slight bend for adjustment. The rest of the time it's the switch going bad.
Pete, John
Thanks for the input. I have a couple new switches on order and will tear into in in the next week or so and let you know what I find.
Thanks
Access to this requires an OGR Forum Supporting Membership
