Reversing stand/gear stand (valve related)

[ausdan]

Hello,
The joys of owning somebody else's project..
I am currently replacing some worn motion parts on my Don Young design 5" Hunslet (not built by me). I have made some adjustable eccentric rods to help with getting the timing even, after allot of trial and error, I have got a fairly even cut off on both sides of the valve and forward and reverse, though reverse has more throw than forward.

The final eccentric rods have ended up at different lengths and I have found that my reversing stand is not symmetric from forward to reverse, there is an extra 3.4mm throw for reverse.

Is this why the uneven eccentric rods, I have read in other publications that the all eccentric rods for Stephenson valve gear should be the same length. The Don Youngs drawings I have also show the stand to have equal spacing / notching both sides of mid gear.

What would of been the benefit of this, or is it just a error that may of be made. I think I should remake the radius on the stand and readjust the eccentrics lengths before I make the new ones.

Any thoughts ?

cheers Danny

[Shawki Shlemon]

Hi Danny
You are right ,all ecc rods should be the same ( I make them on a jig ) .The reverser - the neutral should be in the centre ,if there is is an error you should have more movement fwd not in rev as that is when you want to make sure you have full valve opening as most of driving is fwd .The bottom line is when the crank is back or fwd with gear in full fwd , the appropriate port is just opening .The same in reverse .When the crank is up or down the ports are almost full open(give a little for the lead . If you can not make them equal try to do the best for fwd at the cost of rev. Good luck .

[cotswold]

As Shawki says above, the eccentric rods should be equal and the basic length is determined by the radius of the expansion link. To that basic length a small correction is added to correct for errors due to angularity of the rods (See Ashton's book or other learned writings). Also, the mid gear reverser notch should be in the middle. Rather than adjustable eccentric rods a temporary adjustable reach rod may be the best way of achieving that.

Eccentric angles are critical. The real counsel of perfection is to double check the 'as built' component dimensions, use those to calculate the eccentric angles and then set them with the driving axle between centres on the lathe.

[ausdan]

Ok, thanks for the direction.....Club day today, will get back in the shed by the end of the week