Crankshaft from Parts

Making the Burrell crankshaft from parts has allowed me to then have a split. The split is at the crankpin and allows me to then have a single piece connecting rod.

Background Elements

Over 12 months ago I was concerned with the crankshaft to firebox clearance.

miniature traction engine sketch

Traction Engine Crankshaft Clearance

With this comes the fundamental issue of the crankshaft centre to firebox clearance, the centre of the crankshaft was set by scaling it from the original drawing. This is not the most accurate, but it gives me the correct look. This distance as shown on the drawing is 9.5mm and with a piston stroke of 10mm this means I need a crankshaft throw of 5mm and probably a crankpin diameter of 3mm. This gives me 6.5mm from crank centre to outer edge of the crankpin and so just 3mm of clearance in which to fit the conrod bigend.

However, at the time this was all based on the centreline 2D drawing of the traction engine. The curvature of the firebox introduces a lot of extra space. Also, when I made the crankshaft bearing blocks I made them so that they could be lifted.

Burrell Traction Engine

Sandwich Crankshaft Bearings

Bearings in place, phosphor bronze bushes added. However, at this stage they had not been reamed as I need to fix and align them. Then I could ream them in place and both at once.

However, my main issue is the height of the crankshaft and the clearance of the crank with respect to the top of the firebox. This is an area that needs more thought around the design.

Design Direction

With the cylinder centreline being offset 10mm from the boiler centreline, the bearing blocks that could be lifted 1-2mm and the idea to split the crankshaft gave me scope to increase the crank throw to 7mm.

The fundamental idea for the design is shown below.

crankshaft schematic

The flywheel and valve eccentric will be driven from the left hand side of this shaft. The traction engine motion will be driven from the right hand side. Thus the crankpin is shown silver soldered (red) to the right hand web. A brass bolt pulls the crankpin into a tight fit recess in the left hand web. Both webs then being silver soldered to the crankshaft.

Assembly

The crankshaft was made from 5 parts including the bolt. Note that the main shaft was kept as one part nearly to the end of the process.

crankshaft parts
crankshaft assembled reading for silver soldering

The crankshaft assembled and on the hearth ready to be heated with the blow torch.

Two pieces of 4mm diameter rod were used to space the webs of the crankshaft during this process.

Easy flo silver solder paste was used to join the parts together.

silver soldered crankshaft

When silver soldering it is a great feeling when the silver solder flows.

You can just see the silver solder on both sides of the web around the main shaft.

All Parts Machined

Sorry, but I haven’t included much about machining the crankshaft from parts. Note though that I had pre-centre drill the main shaft both ends. This really does ease the process of aligning and support.

final crankshaft assembly

With this balanced on my hand you realise the scale of it. Finally just to prove that this is in parts.

Burrell crankshaft in parts

Leave a comment