Hi, bought a Roco ÖBB Steam loco Rh 77 and originally it had 1 axle with 2 rubber tyres, it couldn't go up an incline with 3 passenger carriages so I thought I'll get another axle with 2 rubber tyres but there was one little problem, the original axle had a cog wheel in the middle and the axle I was going to replace didn't, so there was only one thing to do, remove both wheels on both axles and change them over, the other task was to align them correctly (90° difference) it took me 3 times to align them properly, the other thing was a bit of a surprise, they had plastic inserts to hold the bars on the wheel, Märklin has always metal screws to hold the bars, I've ordered a tap set screw set and hopefully use Märklin screws after I've made a thread into the wheel. anyhow besides this I put the loco back onto the track and she got up the incline without any problem carrying 5 carriages., so this was a relieve and my efforts weren't for nothing.
I think the loco only weighs about 300g

John

the tender is always metal with Roco steam locos but they can't produce the weight it needs to pull a descent amount of carriages, I'e asked them years ago why don't you add a rubber tyres to the main wheels (loco itself) and they sad the rim is to thin they can't do it., they'e introduced a shaft many years ago apparently the loco's speed they main wheels didn't keep up with the speed the loco was travelling, I may get this loco and see if I can go to an engineering work and see if the can put a groove into it, I'll get a spare axle for it.,
there are people at the helm but can't be bothered to do anything about it, the locos they would sell and it would affect Märklin if they add rubber tyres to the main driving wheels or axle., their tank locos are alright.
I'll keep you posted and see what I can do.

John

I got my tap drill set and now waiting for the hexagonal screws, I was lucky as the loco was running around the layout it lost one of its plastic screws holding the side bar, I'm quite disappointed Roco using plastic screws which are just stuck into the wheels hole, as I removed the wheel I snapped the end off it, it lasted but not for good, found the the little plastic screw further back from the track but I'm not going to put it back until I get the metal hexagonal screws, than I drill a thread into the wheels., you pay a lot of money for these locos and if you buy them including sound decoder you're up for over Euro 469.00 but some offer them for Euro 360.00 which is still a lot and these days manufacturers get away with it., at least I don't have to take the axle out again as the wheel is plastic but the rim is metal

John