Forum Options

« Back to Miscellaneous Topics Topics

Sign In above to begin adding replies.
 

Whoops!!! One for the less experienced.

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Mon 14th Jan 2013, 9:33pm
Whoops!!! One for the less experienced.

Whoops!!! One for the less experienced.
I have recently been repairing a Romulus for fellow member. It has various problems, but not the least of which was a heavy list to port (left), On dismantling it I found the rear axle box was a little(?) worn, and with subsequent axle damage as well. It is now repaired. How would you have gone about it?

 

Replies To This Post

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Sat 2nd Feb 2013, 9:10am

Well as nobody seems to want to jump in, it was bored out to clean the hole and another piece of cast-iron turned to fit and then bored to the correct size. A simple enough lathe job even for a beginner. If the wear had been noticed a little earlier then an oilite bush might have been used. That took care of the axle-box, but what about the axle?

Also what other symptoms besides the lean do you think the loco might have been displaying?
Well as nobody seems to want to jump in, it was bored out to clean the hole and another piece of cast-iron turned to fit and then bored to the correct size. A simple enough lathe job even for a beginner. If the wear had been noticed a little earlier then an oilite bush might have been used. That took care of the axle-box, but what about the axle?

Also what other symptoms besides the lean do you think the loco might have been displaying?
 

Chris B

Joined: 1-01-70

Topics: 2

Replies: 17

Posted: Thu 7th Feb 2013, 2:09am

Given that it is a Rommy you are talking about if the axle height had moved due to wear then the valve events would have been out as the die block would have been running further up the slide. I saw a tired Rommy that used to belong to one of our club members that actually shot the die block out of the top of the slide and made a bit of a mess.
 

gavinfdavies

Joined: 1-01-70

Topics: 0

Replies: 4

Posted: Thu 7th Feb 2013, 7:37am

My first thought would be to bore out the block and fit some heavy duty sealed roller bearings. I would probably make them a press fit onto the axle, and a snug hand fit into the axle box with a grub screw to locate them.
As for the axle, this area is most likely to be subject to fatigue, so generally speaking I would make a new one rather then bushing the old one or something. Could possible weld and regrind it though.

If the axle boxes are that work, I'd imagine all the valvetrain links would be similarly worn and ovaled, so rather sloppy timing events would be expected.

Just my guesses, I've never built a loco before.
 

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Thu 7th Feb 2013, 11:48pm

Chris and Gavin, 'good on you' for having a go, and yes, mostly, you are right about the valve events being haywire, but only on one side. The odd bit was that it must have been getting bad for while but it seemed to appear rather suddenly (for which I have no explanation) and since the repairs the old girl runs as sweet as a nut. There was considerable wear in the slides and pivot on the good side which were also attended to.

Chris I'm not too sure about fatigue in the axle, but yes, a new one would have been a good solution, but that would also mean replicating the quartering, not all that difficult really, but nicer to avoid in case the other axle was out as well. The solution in this case was to turn the axle down and sleeve it, just the opposite of the axle-box. Had the axle wear been any worse then a new one would have been essential but fortunately it cleaned up at slightly more than the wheel spigot dia.

Of necessity the sleeve was quite thin, around 5/64" [2mm] x 1" dia [25mm] when finally finished, what method would you use to fit it securely?
 

gavinfdavies

Joined: 1-01-70

Topics: 0

Replies: 4

Posted: Sun 10th Feb 2013, 6:51pm

My instinct is to get the crank really cold, get the sleeve REALLY hot, and very quickly knock it into place. But given it's small size, I suspect it would lose all the heat in seconds in contact with the cold shaft. Also, interference fits do not scale. I.e. 0.05mm of interference is still that whether it's on a 1" shaft of a 40inch dia combustion casing for a jet engine. But thermal expansion does scale. So heating a 40inch case to 200 degree will make it expand a hell of alot, but on a one inch sleeve, you'd be really hard pressed to notice the difference.

So i'd use a press if possible, combined with some permanent setting loctite. If there's part of the sleeve that is open to the atmosphere, I'll also be tempted to pin it. Open to atmosphere so that the pin isn't rubbing against anything since pins are hardened and wouldn't do bearing faces any good.
 

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Mon 18th Feb 2013, 11:49pm

You've identified the problem pretty well, yes the sleeve being thin would not hold the heat for long. I therefore left the sleeve a lot thicker than required, around 3/16" (5mm) and used the normal interference fit, less another 0.001" (just in case), and froze the axle overnight in the deep freeze and then heated the oversize sleeve and tapped it on, with a specially shaped drift, basically a bit more sleeve with a clearance hole. It all slide together nicely and then all that was left was to turn the sleeve down to fit the re-bored axle-box. Because of the cold and heat no Loctite could be used. I suppose there could be a slight possiblity that the sleeve could split, but hopefully it has remained soft enough just to give as necessary with the temperature variation of the rear axle (close to the fire-box).
 
 
« Back to Miscellaneous Topics Topics

Web design by Slingshot