Another B1 chassis

davebradwell
Posts: 385
Joined: Fri Jan 18, 2019 3:48 pm

Re: Another B1 chassis

Postby davebradwell » Tue Aug 04, 2020 7:33 pm

Perhaps turn to the body if you're not in an engineering mood. Surely it has to be worth sorting out the running or you'll avoid using the finished model and it's easier to do this without the valve gear.

The quartering and centres are easily checked by setting the thing on its 4 centres (front, back, top, bottom) in turn - turn the model so the rod on top or bottom cntrs is on the far side and observe line of coupling rod and/or angle of spokes on nearest rod and record if error is clock or anti-clockwise. The nature of any errors iseasily deduced. Easiest way to deal with rod centre error is to bush the rod with 1.5 bore tube. There's plenty of other sources of binding - just turn wheels until they drag and look for brg that isn't free. Every brg should have visible endfloat that you can see and feel.

DaveB

Bellerophon
Posts: 33
Joined: Sat Feb 25, 2012 3:37 pm

Re: Another B1 chassis

Postby Bellerophon » Sat Nov 14, 2020 9:21 pm

Lockdown number two created an incentive to have another go on the B1. Actually apart from a couple of failed rivets, the valve gear was much easier to do than setting up the chassis. Attaching the completed set however was a bit awkward. The valve spindle had to go in first but screwing on the return crank was a problem. There’s probably some knack I’ve missed.

All so well and good, I fixed the return crank to the correct leading position and tried it under power. Unfortunately, despite pinning the screws with 0.31 wire they spun round and of course the valve gear knitted itself in knots. The reason being having drilled the wheels to take ultrascale pins there’s hardly any plastic to hold the retaining wire.

I’m at a bit of a loss as to what to do. (It’s packed away at the moment for it’s own safety!). I could remove the valve gear and rods and try and glue the crank pin from the front. I did try a bodge from behind with loctite 603 and araldite but neither held.

I might wait for lockdown three...
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DougN
Posts: 1070
Joined: Wed Sep 01, 2010 9:57 am

Re: Another B1 chassis

Postby DougN » Sun Nov 15, 2020 7:06 am

Don't give up !

There will be a solution. I think the entire forum will put their thinking hats on and come up with something!
Doug
Still not doing enough modelling

davebradwell
Posts: 385
Joined: Fri Jan 18, 2019 3:48 pm

Re: Another B1 chassis

Postby davebradwell » Sun Nov 15, 2020 7:51 am

I'm out all day until dark so will look at solutions this evening. First thoughts are to eliminate the possiblility that the thing is tearing itself to pieces so check everything is free and there's no tight spots. I'm not convinced this is the case from previous postings.

DaveB

davebradwell
Posts: 385
Joined: Fri Jan 18, 2019 3:48 pm

Re: Another B1 chassis

Postby davebradwell » Sun Nov 15, 2020 5:14 pm

Return crank is most easily screwed on with final drive gear grubscrew released so wheels can turn - or motor with worm removed to achieve this. Wheels are rocked to and fro between front and back centres as crank is wound on. It's a bit tedious but there you are and there's no need to force anything. Much worse if gear can't be released as you have to spin motor shaft.

The valve gear should be free enough that just tightening up the return crank on the Ultrascale crankpin should be adequate without any wires. The problem comes with time as the screw head sinks into the plastic and it comes loose but you seem to be getting it to work for zero time hence my suspicion of stiff valve gear. Most use a wire but I overcome the problem by turning a new crankpin as per the U/scale but tapped 14BA thru so the crank tightens directly onto the metal pin with no plastic to move.

I realise this isn't very helpful but it leads to the thought that you might drill out your failed crankpin hole 1.5 and use a piece of 1.5/1.0 tube as a crankpin so once again there is no plastic and you can tighten up on metal. You'd need a vertical hole in a block to hold it while the Loctite set and there'd be great danger of gluing it to the block. My A1 has similar, but they're tapped - you might do this by starting with 1.5/0.5 tube. Reducing return crank throw is a cheat that helps here.

Alternatively, see if Colin Seymour will sell you some new plastic wheel centres and just start again from there being careful not to drill the U/scale counterbores too deeply - website used to give too great a depth.

You really should very carefully check the whole thing as just a hole in a coupling or conn rod out of square will work the crankpin until it fails. Crossheads should be free enough to fall under gravity if loco upended and conn rods released from crankpin. Valve gear should move freely under gravity, too. At times like this I've taken all rods off and found that an axle isn't running freely in its axlebox - chassis should roll down a reasonable slope even with all motion in place.

Try that for starters. It doesn't sound as if just beefing up the crank fixing will cure it for long.

DaveB

Bellerophon
Posts: 33
Joined: Sat Feb 25, 2012 3:37 pm

Re: Another B1 chassis

Postby Bellerophon » Sun Nov 15, 2020 5:54 pm

Thanks Dave. Your time and help is very much appreciated, I hope it’s useful to others too. There’s a great deal to think about and I’ll have a try at some of your suggestions. The Joints in the valve gear were moving freely and all very “floppy” before I fitted both sets. It may well be the rest is stiff though, plus my propensity to bugger things up without knowing how or why.

davebradwell
Posts: 385
Joined: Fri Jan 18, 2019 3:48 pm

Re: Another B1 chassis

Postby davebradwell » Sun Nov 15, 2020 8:12 pm

With motion parts, it's possible to assemble the joints off the engine so that they are nice and free but when placed on the chassis perhaps the conn rod gets a slight twist or the radius rod is pulled to one side so there is instant friction. This is worse with forked joints or when just trying to make the thing less floppy. When fitting the valve gear, perhaps put the expansion link in its bearings and see if the return crank is able to take up its position or that the valve spindle can lie on top of the cylinder pointing in the right direction and the combination lever is vertical - you get the idea. With conn and coupling rods put a drill in the holes and check it lies square in all planes. Is there end-float on the crankpins with the nuts tightened?

My later kits include a drawing showing the motion in 4 extreme positions so that the swing of forked joints can be checked - I think I posted this somewhere. The 2 at the top of the combination lever usually require particular care.

Big question is did the chassis run smoothly with just the coupling rods and no extra bits? The clue may be here.

DaveB


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