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Joined: Jan 2017
Posts: 637
Likes: 3
Senior Contributor
Would anyone have one of these pawl nuts by any chance. Fits 60s, early 70s Victa 2 stroke with the G3 carby and wind up starter. It threads on to the top of the engine shaft above the flywheel and fastens down both the pawl (starter cup) and flywheel. It is a special fit nut, being 1/2" internal BSF thread. I know it must be this size because I recently purchased some BSF 1/2" locknuts for another project and they fit perfectly. UNF lock up after just a few turns of the thread.

I took one off another Victa mower to show what they look like. I have a few of the old Kirby Lausen type, but they are an even smaller thread diameter and probably UNF in any case.

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pawl_nut5.jpg (17.43 KB, 96 downloads)
pawl_nut4.jpg (15.83 KB, 95 downloads)
pawl_nut3.jpg (21.87 KB, 96 downloads)
pawl_nut2.jpg (33.31 KB, 95 downloads)
pawl_nut1.jpg (46.26 KB, 94 downloads)
Last edited by vint_mow; 17/05/22 07:28 PM.
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Joined: Apr 2014
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Apprentice level 3
G’day

I asked a similar question and there weren’t any available, I hope you have better luck.

They were available from a couple of suppliers up until relatively recently when they both dropped them.

I’ve seen them called “starter cup nuts” and “flywheel retaining nuts” depending upon which era the parts list is from.

I was told there are some Tecumseh starters that appear to use a similar nut but I couldn’t confirm it so didn’t order them.

I’m half way through making some because I need three. I had a few challenges getting the thread cut. Bit more involved than it should be.

For information the thread is a little unusual it’s a 1/2” BSF (16 tpi)

Cheers

Ironbark

Last edited by Ironbark; 18/05/22 02:24 AM. Reason: Typo!
Joined: Jan 2016
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Hi Ironbark,
Couldn't you just buy the nuts from a bolt supplier and just turn the edge down, that should only take 5 mins. I haven't tried getting 1/2" BSF recently but I used to have to get all those BSF nuts when I was working on old English motorbikes

Joined: Jan 2017
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Hi Norm, Sadly I don't have a turner and the local engineering place has a minimum $100 on any work they do.

Ironbark, yes you're right, they are 1/2" BSF. I found some that are the right diameter, but have a smaller thread. So I guess I could put them in the drill press, drill them out to a larger diameter and then thread them? As you say, will take a lot of time and effort and I don't currently own any BSF taps.

The alternative might be to use a different cup. I have an old Southern Cross starter cup that is the right diameter to fit neatly on to the shaft. Then I will just need a standard 1/2" BSF nut to fasten it down to the flywheel. Bit sad that these nuts have disappeared. Tecumseh seem to be all UNF so even if you find one the right size the thread is still a problem.

Joined: Jan 2016
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If I get a chance I will call past the bolt place and see if I can get 10 nuts and then I can just turn them up in a few minutes

Joined: Jan 2017
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Thanks Norm, That will be excellent if you can do that. If you need any other measurements let me know.

Joined: Sep 2015
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I'm not sure how you can do that economically Norm , any machine work would be $10. then
postage is another $10.

It would be easier to go to a Auction, market ,scrap yard ,tip shop , tip ,garage sale ,swap meet,online sales and buy a complete Victa for $10.

Steven from this site was selling mower parts and would have the crank nut and posts out parts ,he is admin on the site.

https://www.facebook.com/groups/1638234439783704/about/

The easiest way would be to send him a message as he had shed loads of parts.

The only other place I know of without buying a mower or trying a mower shop would be to ask on a Facebook mower group.

If Norm doesn't charge for lathe work, just cost and postage it's still more expensive than buying a complete mower.

Cheers
Max.

Joined: Apr 2014
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G’day Norm, Max and Vint

Norm, I had that same idea. I have a great relationship with my local bolt shop and they help me out a heap with all the strange things I make and fix. I asked and they had hardly any 1\2” BSF nuts and what they did have weren’t long enough to get a full starter cup nut out of. I have a few in my collection of bits and pieces but they’re all too short. Hence I’m trying to make them from scratch.

I had a couple of goes at turning an internal thread but there wasn’t enough room with that inside diameter given my skill level. I made two HSS tools but once I’d formed them with appropriate clearances both had way too much chatter. I could probably make one out of carbide but I don’t have access to a d bit grinder.

I ordered a tap, which was double the price I usually pay. I’m hoping that when I’ve finished the big custom fabrication job I’m working on here it should be waiting for me.

If you’ve made some before I get mine done please let me know.

Yes Max, it’s a very expensive way to get nuts but I won’t be selling these mowers. They’re for me to use. I went to a friend who has a massive pile of old mowers but he’d had a clean out of older Victas a few years ago and there was nothing that fitted. I don’t know about the other things you mentioned but I asked about and there was no reliable source as far as I could work out so I got irritated and decided to make some.

Joined: Jan 2016
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Hi Max,
Nothing I do is cost effective,
Hi Ironbark,
If the nuts are too short, no problems, I can weld 2 together. It doesn't need a lot turned off it, it only needs enough to locate the cup. I have a bit of an issue at the moment as I don't have a car as it has failed to go and I'm not sure when I will get it back.

Joined: Jan 2017
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Senior Contributor
Classic Fasteners sell 1/2" BSF nuts in a range of types. https://www.classicfasteners.com.au/std-hex-nut-1-2-bsf-steel-zinc-pl/

Joined: Feb 2006
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My theory as to why they used British Standard thread is the Victa two stroke came out in the 50s when were still attached to Britain's apron strings, and the motor just kept evolving from the same crankshaft and they just stuck to the established nut and thread even though we were moving away from British imperial thread systems.


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
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MF,
a few years ago I needed a piece made up to fit an alternator to an Enfield motorcycle. When I was asked what the thread was I said I had no idea. Mate said it didn't matter he could cut it but he was curious as to what it was. He couldn't wait to tell me that it was a Villiers thread and Enfield in India continued to use that thread on the alternator nut till that engine was discontinued in 2008

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India have a lot of old school manufacturing.


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Joined: Apr 2014
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I was explaining some of this to my daughter recently, who was very polite but was probably thinking, “another long dad story about the olden days”.

Prior to World War 1 threads, by and large, were not standardised, even up to the advent of the Second World War there were lots of proprietary sizes. Fasteners were often made by individual manufacturers or groups of manufacturers within certain geographic regions. They would make nuts and bolts for their own unique usage in their own plants.

It was only when manufacturers needed to work together to make a complete assembly that this became an issue and standardised sizing became more prevalent. When Rolls Royce sent the plans for the Merlin engine to the US for them to make; the US engine manufacturers tolerances were more than ten times greater than the standards used in the UK, they couldn’t build it. There was a lot of catching up that needed to be done for US manufacturers to be able to achieve the necessary tolerances.

Being part of the broader British Empire, Australia was part of a more standardised grouping than existed within other jurisdictions. The British Standards were widely used and reinforced across the British sphere of influence. This was more economically efficient and had huge strategic value as, warships, for example, could be more easily resupplied and repaired where components would actually fit off the shelf. A steam engine made in Scotland and exported to Victoria could be repaired using Australian made components and someone wouldn’t need to make a specifically indexed thread for a bolt or wait for spares to arrive from Scotland. The engineers all knew what the dimensions meant and what tolerances applied within those dimensions.

While 1\2” BSF may be uncommon now it was much more common previously. Usage of British Standard threads has largely been supplanted by metic threads with the US persisting with the standards they somewhat reluctantly adopted 80 years ago and now refuse to modernise.

1 member likes this: Mowerfreak
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I've come across Whitfield a number of times on old mowers as well. There are not only different threads but different pitches among the threads. It can get very confusing trying to match up nuts with bolts at times. My father left behind a large bucket of bolts from the olden days that I still haven't properly sorted. There is a mix of just about every thread. I sometimes pick up a bolt or a nut but am unable to find a match for it.

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I can recall an instance where two threads worked together but just felt a bit too loose. You could jiggle the nut.
Ford Falcons are known for their mix of imperial and metric nuts and bolts. I'm not sure it went on up until the end in 2016, but I do know it occured in the 1988 -98 generation E series.


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
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The UC Torana was a classic, all the body bolts forward of the firewall were metric and all the bolts from the firewall to the back were UNC, obviously as a runout model the factory wanted to use up their stock of UNC bolts before switching over to metric

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Also consider the bodywork was changed from the firewall forward for the model update from the LX, with new panels, by which time they must have adopted metric as a policy.

Last edited by Mowerfreak; 21/05/22 09:43 PM.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Joined: Apr 2014
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Marine engineering is where British Standard threads really asserted themselves or, more precisely, were mandated by the British Admiralty. British Standard Whitworth, which is mostly known simply as “whitworth” today was the first standardised thread, from the middle of the 19th century. There is a story in the text books which goes some way to explaining British Naval superiority through the efficiency of production techniques achievable through standardisation.

British standard fine was a later development for precision applications in steel. The thread profile allows parts to be placed under higher torque prior to failure. From memory BSF is still at the same pitch as Whitworth but has less depth of cut (and is obviously finer).

Whitworth was developed prior to steel being readily available, inexpensively at consistent quality so it’s coarser pitch and form reflect the tooling, materials and applications of that time.

I have a set of taps and dies for Whitworth that predates me by three generations, they are in a very well made Cedar box. The quality of the parts is amazing and the grandfather who passed them down to me explained that they were extremely expensive. I was told that they came from his father and were used to repair the steam engines that powered their sawmill. I have used them to repair threads on vintage machines, they’re a little more fiddly to set up than more modern dies but work just fine despite being around a century old.

1 member likes this: Mowerfreak
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I had no idea there were all these regional threads as well. I used to say how my Metrinch socket set, designed to work in both metric and various imperial hexes, including British standard, will work on Russian bolts of there's such a thing. There probably is.

I always wondered how BSF related to BSW, if at all.
Americans must lose their minds working on the multitude of cars from the BL fold and more.

And discussions on thread sizes, standards and pitches would take a very special girl indeed to enthrall her!


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
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