Lang Bridge Double Diagonal Engine

[John WeightParticipant @johnweight34532]

Help Needed

[John WeightParticipant @johnweight34532]

I am building a model of the above engine based on photo's from an article in a recent issue of M.E. by Roger Backhouse. I have a problem in getting the eccentric to stay horizontal, it tends to drop on one side in line with the valve rod.

If I hold the strap horizontally between my finger and thumb the engine runs well but as soon as it is released it will drop and stop he engine. I am thinking it may be caused by the position of the lugs to which the eccentric straps are connected, the question is should the lugs be 90 degrees to each other from a point in the centre of the crankshaft. If anyone can assist in helping solve the problem I will be very grateful, many thanks. John

[JasonBModerator @jasonb]

I'm not quite sure what your problem is from your description.

The eccentric sheaves should be keyed to the crankshaft or fixed with a grub screw so will rotate with the crankshaft.

The eccentric straps will be free to move but as the end of te eccentric rod is pinne dto teh valve rod I don't see how they can drop.

Picture of the engine for those that don't know it

And a similar model by Ramon Wilson

 

Edited By JasonB on 15/02/2016 20:59:41

[JasonBModerator @jasonb]

Looking again at the photo what you may have missed it that one eccentric rod is rigidly fixed to the strap (left) but the other is pivoted (right) If you have them both rigid then you will get problems

[Ramon WilsonParticipant @ramonwilson3]

Hello John,

Jason has pointed me in your direction. I can only think that your problem is one that Jason suggests.

The two straps are different in that one is fixed the other allowed to articulate. They are at 90 degrees to each other.

I built my version from the original Helix Engineering drawings which were very accurate and excellently drawn. I haven't seen anything produced later so can't comment.

This is the only pic I have which shows the articulated rod the other sits firmly inside a groove milled in the strap.

This engine is a nice runner – if I can be of further help just say

Regards – Ramon

[JasonBModerator @jasonb]

Thanks Ramon, I can also confirm that the engine runs very nicely.

J

[John WeightParticipant @johnweight34532]

Good evening to you both, many thanks for your very helpful replies to my question re the Langbridge engine.

I had not picked up on the fact that one side of the eccentric rod was permanently fixed to the strap as you have shown me. I have now remedied the matter and the engine is running very sweetly on a quite small amount of air. It now remains for me to make a number of finishing touches to and paint it up, when it is complete I will put some photos up to show the result. I had spotted your engine Ramon on the net and watched it running beautifully, I offer my congratulations it looks well, I can only hope mine will look as good. again many thanks to you both for you help.

John

[Ramon WilsonParticipant @ramonwilson3]

Hello John – glad to be of help

Just in case you are thinking of making some oilers I used the protective tubing found on artists brushes for the glass. This is held in with super glue(but you need the non fogging kind) and look very realistic. To cut, the tube is pushed onto a mandrel turned to a nice fit (tight near the chuck jaws to act as a driver) and 'cut' using a sharp pointed tool – like a screw cutting tool only sharper.

I've always enjoyed running my engine (on air) so I'm sure you will too

Regards – Ramon

[Author]

Posts