Suffolk Lawnmower engined Bolting Rabbit project… drive thread size?

[fizzbangwhallop]

I’ve just taken on a ‘project’ to get the club’s old bolting rabbit trap working… it did power a kiddies bicycle wheel but that appears to have never been properly fixed to the drive shaft and just freewheeled on the makeshift axle. Not the best.
 

The Suffolk is a model 75G 14 75cc Iron cylinder and head… got it apart, carb ultrasonic’d and cleaned, head off, de-carboned, valves re-ground and now just waiting for gaskets, float etc etc to arrive.
 

The set up still runs through the clutch so I’m half-thinking to fix a wheel direct to the drive shaft but I’m damned if I can find details on the thread size to be able to attach a wheel to it. 🤨

Any clues gratefully received, the threads fit a 1/4” 20tpi Whitworth size gauge size but the shaft is 1/2” …. I’ll put my hand straight up and say I’m in the dark as regards Imperial threads 😂. 

I’ve also been looking at 12 & 14” wheelbarrow wheels but the narrow ones all seem to have hard rubber tyres which suggests that the running channel height is critical… again any suggestions gratefully received. 
 

cheers

 

fizz

[old'un]

UNF ½"-20tpi

 

 

 

 

Edited August 27, 2022 by old'un

[fizzbangwhallop]

35 minutes ago, old'un said:

UNF ½"-20tpi

 

Brill! Thanks… I’ll have a look for a tap and, as it ‘appens, I know I’ve got one upstairs to clean up threads on some of my moderators! 😂

Cheers,

fizz

😎 
 

35 minutes ago, old'un said:

 

Edited August 27, 2022 by fizzbangwhallop

[old'un]

I am sure its a UNF thread, but if you have a tap you can use it as a gauge to make sure its the correct pitch, or you could try screwing your mod onto it

[fizzbangwhallop]

1 hour ago, old'un said:

I am sure its a UNF thread, but if you have a tap you can use it as a gauge to make sure its the correct pitch, or you could try screwing your mod onto it

Yep, tried a mod earlier and it does go on although a bit of a loose fit, I’ll dig the tap out tomorrow and offer it up.

 

cheers

 

fizz

👍😎

[old'un]

15 hours ago, fizzbangwhallop said:

Yep, tried a mod earlier and it does go on although a bit of a loose fit, I’ll dig the tap out tomorrow and offer it up.

 

cheers

 

fizz

👍😎

are you sure the shaft measures ½” -0.500”?

[Stephen-H]

It's is a unf thread as stated above if you need spares give leachslawnmowers a call wont let me attach a link for some reason.

I took a similar mower to bits when I was 15/16 brillant them Suffolks think the chain that used to drive the cylinder blades is still somewhere in my dads shed 

[old'un]

58 minutes ago, Stephen-H said:

It's is a unf thread as stated above if you need spares give leachslawnmowers a call wont let me attach a link for some reason.

I took a similar mower to bits when I was 15/16 brillant them Suffolks think the chain that used to drive the cylinder blades is still somewhere in my dads shed 

thanks for confirming that, I only queried it because he said was a bit lose when he screwed his mod on with a ½”- 20tpi thread.

[fizzbangwhallop]

G’day all… thanks for the replies and the nod to Leach’s.

Just re-measured the unthreaded section of the shaft at 0.496”/12.6mm so that could well be a fraction narrower than the cut of threads in the moderator which is a snug fit on the barrel’s threads. 

I’ve been having a play with ways to fit the kiddies 14” cycle wheel to the shaft…

I’ve got various M10 & M12 bolts and the longer connecting nuts here… The M12 c’nut is ‘almost’ the same dia as the shaft so I’m thinking to drill it out, tap it to 1/2”unf but for added security, drill and tap a couple of 4 or 5mm holes through the sides for clamping bolts onto the shaft flats.

That would’ve been straightforward but the M12 bolt is too big to pass through the wheel hub, tried drilling that but the in-wheel bearing surfaces are well-hardened and the drill isn’t touching it. 😩

So now I’ve bolted an HT M10 machine screw in there which locks the wheel and gives me a spigot. 👍

All I need now is an M10 to 1/2”UNF adaptor but all the local engineering supplies are now shut til Tuesday so I can’t buy any nuts/drill bits etc…typical! 🤣

But, the original set up had an aluminium ‘bike axle’ thread to 1/2”UNF adapter so I’m about to stick that in the lathe and take the bike thread end out to M10….and see what happens. 
 

Thanks chaps 👍

Cheers

Fizz

[fizzbangwhallop]

Well….so far so good…. Just waiting for the engine and carb bits to arrive now then I can get it all back together and see if the engine actually runs! 😂

 

cheers

 

Fizz

 

[amateur]

It's always good when a project starts coming together. 👍🏻