The Steamboating Forum

I have now obtained copies of all of the drawings and have spoken to Hugh Mothersole which has cleared up several of my questions. However the question of the differences in the laps on the HP and LP piston valves remains unresolved. We are going to modify the existing piston valves by turning the heads off and shrinking new heads on which will be machined to closer tolerances on the bores but more importantly we can reduce the head dimension to match our thinking on equal valve events in mid gear. If that works and when the engine is optimised the new piston valves can be machined to these final dimensions.

The different laps are probably to arrange an earlier cut off on the H.P cylinder, as there are no eccentrics and assuming all the links are of the same size then this would make sense? Marine engines of more than one cylinder were always considered as separate engines. With Stephenson gear it was normal to have different laps top & bottom but this is probably not necessary with this gear.
Regards
Jack

Thank you Jack. Yes the links are the same on both cylinders. I can now start machining the valves knowing what I am trying to achieve without doubting the info on the drawings.
I will let you know how I get on.
Martyn

The large laps are giving me an early cutoff at about 50% when I would expect to run at 75% cutoff, however we tried the engine with the original slack piston valves and it runs. I will play around with reducing the lap to alter the cutoff to try and obtain the best events and then machine the new valves.
Thanks again for the comments, help and support. I will report back when the new valves are in.
Martyn

We are now beginning to finalise the valve timing and there are minor differences between the clockwise and anti clockwise operation. As we want to optimise the forward running can someone please tell me which way the propeller turns? If I am sitting in the back of the boat and look at the prop shaft, is it turning clockwise or anti clockwise when running ahead?
Sorry to be showing my ignorance again.
Thank you, Martyn

Clockwise when steaming ahead when viewed from the rear is the most common. And easier to find propellors.

Lopez Mike wrote: ↑

Fri Nov 09, 2018 6:34 pm

Clockwise when steaming ahead when viewed from the rear is the most common. And easier to find propellors.

Or if you are comfortable with screw threads, right-handed is the same for these as propellers.

Of course some of us may find it easier to remember as the way to turn a corkscrew. (Though personally I like screwtops anyway).

If you have a propeller and are unsure of it's direction of rotation, the side of the blade further away from you is the direction. For eexample, if it is a right-handed propeller the right side of the blade will be further away from you than the left.

Thanks guys, I just want to make sure we set this engine up in the best possible way. There is not much difference between one direction and the other but with locomotives we always optimise the forward direction.
Martyn

I don't get it Wes. I went and looked at my prop and both blades are the same distance from me when I'm looking at the rear or the front. The trailing edges follow the same track. The leading edges follow the same track.

Of course I often don't get it.