Steering gear
 

Steering gear required.

Worm wheel and worm gear Current gear 2 1/2" across the teeth but could accommodate up to 3 1/2" across..

Any help or ideas gratefully received.

It would help if you tell the make and model of your engine.

The engine is an 8" scale Burrell single cylinder Gold Medal tractor which is physically quite a small engine - even smaller than some 6" engines. It was rebuilt from a 6" Burrell originally built in the 1960's and the steering gear is the original and size wise is unlike anything for a modern engine of that scale.
Any suggestions would be welcome.

With respect, your answer still isn't very helpful. For somebody to help you, you need to give an idea of dimension, pitch centre, one or two start, tooth count, or ratio.

It might be possible to match these specifications up with something somebody has tucked away (I have several small worm wheels), or with commercially available components from companies such as HPC in Chesterfield, or Daval Stock Gears.

Cheers
Carl.