A problem with my Tich running gear that I can’t solve at the minute :-(

[Mike PalingParticipant @mikepaling69128]

HI …

I have a problem that I am unable to sort out at the minute and is driving me bonkers L

I seem to have developed a problem with my running gear on my large boiler Tich.

I have just completed every last bit of manufacturing and on the point of stripping it all down for cleaning up and painting etc.

About 3 years ago, when I had completed all of the running gear and before starting on the boiler, etc., I tested the chassis on a rig with compressed air and everything worked like a Singer Sewing machine with the Reversing lever in all positions. I have never changed the position of anything since that time. I do not remember dropping the whole assembly at any time.

However, when I now run the chassis, I can see that one of the back wheels is binding at one position and “jumps” slightly and I can’t understand why his has started to happen. Is it possible that one of the crank pins on one of the rear wheels has become bent slightly? … or …. has one of the Return Cranks been moved slightly? Or has something else caused this problem???

This is a real mystery for me … does anybody have any suggestions?

Mike

[Mike PalingParticipant @mikepaling69128]

[Nigel Graham 2Participant @nigelgraham2]

It would take some doing to bend a crank-pin without other damage, so that seems unlikely.

Baker Gear on the 'Tich', I seem to recall – I'm not familiar with it but I know it's similar to Walschaerts.

I'm not sure if a displaced return crank would produce those effects but I suppose it's possible, by putting the valve-timing out enough to widen the lead or delay the exhaust enough to create the limping. Nor am I sure how the part can move, if it's on a square as conventional.

I would suggest, not running the engine on air; but instead moving it by hand on a couple of feet of rails, for testing problems like these.

Move the loco with the drain-cocks open, and see what odd happens in mid and full gears. There may be varying resistances as the pistons compress and rarefy the air in the cylinders, but these should be fairly easy to feel, and should be symmetrical.

If you can establish which is the faulty side, disconnect the eccentric rod from the return-crank and try again. If that alters the effects then yes, I would look to see if the return-crank has moved or come loose. I don't know how it's fitted on that loco, but if it uses a split-clamp method that may have slackened slightly.

'

If you can't find anything amiss with the valve-gear then we need think more drastic – that a wheel has moved on the axle. Whether that's possible depends how the wheels are fitted and if they have keys, but that would certainly create binding effects.

To test for that, disconnect both eccentric-rods and connecting-rods so the pistons and valves have no influence on things, then again push the loco slowly back and forth..

[Jan BParticipant @janb]

I have a large boilerd TICH in 31/2” and mine has Walschaerts valve gear. I have never seen a TICH with Baker valve gear, but I don´t think there is any problem with the valve gear.

Have you checked that all axel boxes are at the same height when you test run your chassi? If not, this may be the reason why one of the back wheels is binding at one position.

Jan

[Nick Clarke 3Participant @nickclarke3]

I suggest looking to see if an axlebox is sticking in the horns.

If not look to see where the boxes are vertically in the horns – you have added weight so they will be higher up in the horns than before so does it run if the loco is supported under the boiler to take some of the weight off?

[Mike PalingParticipant @mikepaling69128]

Many thanks for all of your replies … I think that I have found the solution to my problem after watching an excellent YouTube video about setting Walschaerts valve settings.

It seems that the return crank on one side of my loco had rotated out of position slightly. I have now adjusted the crank and all looks to be good

Not sure why that had happened ( the plans did not show any permanent locking system ) so I need to keep an eye on this!

Mike

[Nick Clarke 3Participant @nickclarke3]

Drawing and extract from magazine:-

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