Winding Engine Peculiarity

The winding engine at Blists Hill Museum has a counterweight arrangement which applies an upward force to the eccentric. This seems to be a feature special to that type of engine. I've also seen one at the Black Country Museum which uses a tension spring for the same purpose. I've heard a number of different theories as to what the purpose is. Can anyone give a definitive answer?

Edited By John Barber 5 on 18/07/2023 10:20:01

Edited By John Barber 5 on 18/07/2023 10:41:47

Edited By John Barber 5 on 18/07/2023 10:43:47

I thought they were something to do with the slip eccentric when reversing the engine

Maybe it just balances the weight of the metal of the eccentric strap and the eccentric rod. It looks to be quite a weighty mass and it is always acting downwards if there is no balancing weight. this would cause wear at the top but not the bottom of the strap. The direction of the horizontal forces for the eccentric rod are going to be balanced by the backwards and forwards motion of the valve gear.

Martin C

But you don't see the weights on other horizontal "mill" type engines which run constantly so would expect more wear rather than a winding engine that is only running when the cage is going up or down.

I may counter some of the weight of the shaft and strap so that it is easier to lift the gab but as that is at the opposite end of the rod I can't see it doing much to help

My guess would be is that it stops gravity from pushing the cam forward. Consider that the cam is effectively a crank with a short throw. If force is applied in an appropriate direction, the cam can be pushed round. Normally the cam is dragged around by a pin, however, there is nothing but friction to stop the cam moving 180 degrees infront of the driving pin.When the cam goes over its top-dead-centre the weight of the eccentric could potentially flip the cam 180 degrees foward.

Sorry Pete, don't follow your train of thought. Surely we are looking at a standard eccentric arrangement keyed to the crankshaft, not a cam. Unless I am not seeing the detail in the photo correctly. Still don't have a suggestion for the counterweights purpose though.

May it be related to the constant fwd / rev of a winding engine as opposed to normal steady operation in one direction or the other?

Some interesting thoughts there. It hadn't occurred to me that the engine had a slip eccentric, but obviously it must if it is to operate in both directions with just one eccentric. I was previously thinking it might have something to do with the need to stop the engine at a precise position to align the cage with the floor, but if it was just a question of balancing the crankshaft it could probably be done in a simpler way. I like the idea that this is more a slip eccentric feature than a winding engine feature. Could it possibly be just to reduce friction so the "slip" happens reliably?

Edited By John Barber 5 on 18/07/2023 13:52:04

Perhaps I should not have called it a cam. I'm talking about the eccentric disk which, if I've understood the mechanism correctly, is not keyed to the crank shaft. It is free to rotate 180 degrees with respect to the crank. May be easier to undertand by considerering that the eccentric can change either plus or minus 90 degrees with respect to TDC of the main crank. This provides the necessary valve timing changes needed to reverse the engine.

Engine direction is determing by the direction it is pushed to start with. Provided the engine is not stopped with the piston at TDC the driver can re-start it in either direction by moving the valve gear handle which is then picked-up by the gab.

Being pedantic (who me) it rotates somewhat less then 180 degrees between forward and back.

I think Pete has figured it correctly in as much as it makes sense that you don't want the weight of the eccentric strap to push the eccentric disk ahead of where it needs to be on the shaft.

Martin C

Yes would probably be about 120deg of rotation if ecc leads the crank by 30deg as the slip is usually the shorter angle between the two positions.

But it is free to rotate.

Edited By JasonB on 18/07/2023 16:41:29

Interesting detail! I'd always assumed winding-engines had Stephenson's or similar reversing-gear. I think some do, but since it would probably run at a set cut-off in both directions a simpler gear would be appropriate.

Some stationary steam-engines were manufactured with a slip-eccentric screwed to a keyed clamp-plate. This was to set during installation, the permanent running direction for its intended use.

The Mann Steam-wagon gear is a slip-eccentric operated by a mechanism on the crank-shaft itself.

Note that although the Blists Hill engine's slip-eccentric is rotated round the shaft to work, other ways are available. Examining the drawing (by LBSC?) quoted by Jason, shows that though that eccentric too turns, moving it in a straight line will achieve the same result; and some engines I think including the Mann, were built in that form. The eccentric has a straight slot sliding across flats on the shaft.

Marine reciprocating-engines were usually fitted with Stephenson's Link Motion, or with Bremme or similar radial gear. These had to run in one direction against a fairly constant load for the voyage, for days, even weeks, on end; did not need notching-up, and if the controlled by screw-reverser that was sometimes fitted with a simple locking-clamp to prevent it drifting out of setting.

The Mann gear provided variable cutoff, not just forward and reverse. Clever in principle, but a mechanical nightmare.

I've just discovered this description of gab valve gear on Wikipedia. It mentions the Blists Hill engine but doesn't refer to the counterweight.