Slip eccentric

[nigel jones 5Participant @nigeljones5]

OK – decided just to scale up the 31/2" invicta lbsc slip ecc…theres the dog part fixed to the crank, then theres the eccentric itself, but theres nothing to keep the eccentric close up to the dog i.e. no stop collar to hold it from trying to move on the crank. I apreciate that if everything was machined to perfection the conrod and linkage should hold it in place, but it doesnt look correct – anyone?

[nigel jones 5Participant @nigeljones5]

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Fizzy ,

As a piece of engineering design it's certainly crap but nevertheless that is how slip eccentrics are conventionally arranged – they just flop from forward to back setting depending on direction of travel .

To work anything like successfully there has to be some friction in the valve rod and linkage to bias the loading on the eccentric in the right direction against the stop when running in chosen direction . Easiest is to have the valve spindle gland a bit sticky .

In real locomotives there have been a few attempts to make a controllable slip eccentric work – ie some mechanism to move to fore or back position and lock ..Success rate apparently nil .

Another variant uses one eccentric which can move sideways a few inches on a cam track so that it changes from fore to back setting . This has been used succesfully on a few locomotives and a derived version of it with cams survives to this day on marine diesels ..

Regards ,

MikeW

[nigel jones 5Participant @nigeljones5]

Thanks Mike – but should there be a stop collar either side the eccentric?

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Yes – there must be something provided to stop eccentrics from sliding sideways and causing rest of valve gear to run crooked .

Exactly what arrangement is used doesn't matter much but pinned collars certainly ok .

MikeW

 

 

Edited By MICHAEL WILLIAMS on 18/06/2013 19:07:44

[Sub MandrelParticipant @submandrel]

Hi Fizzy

That's the way it works. My trojan runs at about 3000 rpm with one, so I reckon you'll be OK.

I still think fitting Juliet/Tich type stephenson gear would be worth looking at, but you can alwasy retrofit.

Neil

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