Minnie boiler problem

[David Bothwell 1Participant @davidbothwell1]

Minni boiler too long!

[David Bothwell 1Participant @davidbothwell1]

I bought a part made Minnie traction engine from a local dealer and they also supplied the boiler (which looks professionally stamped) I came to try the shafts and other parts including the hornplates. I was unpleasantly surprised to find that the boiler is too long, hence one drive shaft is fouling the backhead. After pondering what could be done I hit upon moving the mounting holes on the hornplates. This means that that parts such as the eccentrics and the main drive need to be made longer to compensate. Just wondered if anyone else has come across such a problem? At first I was going to make a new set of hornplates with the drive shaft holes moved, but realised that this was not as easy. Any helpful comments accepted

[JasonBModerator @jasonb]

Moving the hornplates is probably teh easiesty option, just need new conrod, eccentric rods and pump rod unless the thickening pads have also been placed too far back in which case you may get away with it.

Has the boiler got any form of test certificate? if not I would get it tested first before altering things

 

J

Edited By JasonB on 24/06/2016 20:15:04

[David Bothwell 1Participant @davidbothwell1]

Thanks for that Jason, already lengthened the main con rod, and I have two new eccentrics (part made) hopefully this will solve it, I will post a "confirmation" sometime in the next couple of days or so

[duncan webster 1Participant @duncanwebster1]

Assuming we're talking Stephenson's gear, if you change the length of the eccentric rods without changing the expansion link to suit you will get strange valve events. You could try altering the suspension of the expansion link to move that back, so not shortening the eccentric rods

[David Bothwell 1Participant @davidbothwell1]

Sorry I missed the about about the boiler test. I have made a rig but the handpump is not functioning as it should, but it is very well made and I think I have the steel balls in the wrong place!

[David Bothwell 1Participant @davidbothwell1]

Thanks for the input Duncan. I take your point and I think I will assemble the motion with the original eccentrics. We are only talking of a 1/8th of an inch (at maximum) alteration ( The amount the hornplates, or rather the mounting holes) have been moved backwards to stop a gearshaft touching the rear of the boiler. Would your suggestion altering the suspension just mean increasing the length of the valve rod?

[JasonBModerator @jasonb]

You would need to make the two blocks that support the weighshat longer as that would move the all teh links etc backwards and then extend teh valve rod though its possible there may be a bit of adjustment by screwing teh valve rod out of teh valve slide and also moving teh valve nut on the rod.

J

[duncan webster 1Participant @duncanwebster1]

Without seeing the actual drawings, I'd go with Jason's answer

[David Bothwell 1Participant @davidbothwell1]

Thank to you both, will try that solution today and (hopefully) get bak to you this evening!

[JasonBModerator @jasonb]

Duncan, a picture may be better. Extend the two blocks shown by the blue arrow which will move the whole assembly back to suit the length of the rods. Then extend the valve rod shown by the blue arrow either by screwing it out or if needed make a longer one.

Less work than new eccentrics

[David Bothwell 1Participant @davidbothwell1]

Many thanks to those who responded to my query. I am most grateful, just spent the weekend re-working the two eccentrics which look a lot better. should have the engine running in the next few days.

[duncan webster 1Participant @duncanwebster1]

Jason, that works. Might need slide bars lengthening as well, looks like crosshead already part way off at back centre.

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