Post by klank on Feb 16, 2011 14:05:08 GMT
I am slowly getting to grips with building the wall engine kit "Rachel" but having difficulty with understanding the plans dealing with the slide valve rod/eccentric rod arrangement.
There is the usual valve eccentric/strap fitted to the crank shaft - which, incidentally, is 1.5 mm ABOVE the centre line of the cylinder/valve chest bores (according to the plan). (Note :- This is not a problem with the piston rod/connecting rod which is linked by a fork/stirrup arrangement and weird cross head).
Specifically, the valve rod appears to be connected to the valve eccentric strap/buckle via a SOLID 5mm dia stainless steel eccentric rod, with an adjuster at each end. There is no swivel joint at all in this arrangement.
The off-set of the eccentric is only 1.75mm, but even so, surely the valve rod, where it passes through the steam chest gland, will be put under some stress and wear the gunmetal bore of the valve chest gland as the "solid" linkage tries to move both "up and down" as well as "in and out" as the eccentric buckle rotates around the crankshaft?
Has anybody come across a similar (solid) arrangement either as a model or in full size practice? - I cannot help wondering if this will work in a model?
Most slide valve arrangements I have seen as models have a "wrist pin" type swivel joint - this does not.
There is another eccentric driven rod linking the crankshaft to a feed pump on the other side of the cylinder casting. The off-set here is 6mm. and there IS a wrist pin swivel in the eccentric rod linkage to the pump rod emerging from its bore/gland.
Could the difference in off-sets - one being very small (valve) compared to the other (pump) be a factor? Also, with a "solid" rod (rigid) arrangement, with such a small off-set, the valve timing could possibly be more precise - with no chance of "slop" in a wrist pin?
Peter
There is the usual valve eccentric/strap fitted to the crank shaft - which, incidentally, is 1.5 mm ABOVE the centre line of the cylinder/valve chest bores (according to the plan). (Note :- This is not a problem with the piston rod/connecting rod which is linked by a fork/stirrup arrangement and weird cross head).
Specifically, the valve rod appears to be connected to the valve eccentric strap/buckle via a SOLID 5mm dia stainless steel eccentric rod, with an adjuster at each end. There is no swivel joint at all in this arrangement.
The off-set of the eccentric is only 1.75mm, but even so, surely the valve rod, where it passes through the steam chest gland, will be put under some stress and wear the gunmetal bore of the valve chest gland as the "solid" linkage tries to move both "up and down" as well as "in and out" as the eccentric buckle rotates around the crankshaft?
Has anybody come across a similar (solid) arrangement either as a model or in full size practice? - I cannot help wondering if this will work in a model?
Most slide valve arrangements I have seen as models have a "wrist pin" type swivel joint - this does not.
There is another eccentric driven rod linking the crankshaft to a feed pump on the other side of the cylinder casting. The off-set here is 6mm. and there IS a wrist pin swivel in the eccentric rod linkage to the pump rod emerging from its bore/gland.
Could the difference in off-sets - one being very small (valve) compared to the other (pump) be a factor? Also, with a "solid" rod (rigid) arrangement, with such a small off-set, the valve timing could possibly be more precise - with no chance of "slop" in a wrist pin?
Peter
