High strength 4mm steel?

[iansoadyParticipant @iansoady]

Too true Dave, the lightweight Nortons were never very popular and as you say Norton were in their last throes. Although these bikes were produced before the Commando, which was a great bike – I’ve had two but as age encroaches my ability to cope with the weight decreases! I have made every effort to ensure that everything is in good condition. Of course these days I’m not dependent on it to get to work (or anywhere else!) so am not quite as desperate as I might otherwise be.

I’m sure I’ll get there. Eventually….

[Graham MeekParticipant @grahammeek88282]

Welding might distort the hole. I would be inclined to plug the hole with something soft like Mild Steel with a centre drilled hole on one side, (it may need drilling out).

On certain tools we used to produce. Hard wearing parts were built up using a Eutectic metal spray. The material came in different grades and would certainly out perform the parent metal. It might be worth looking into this process as some arc welding could cause small fractures in the parent metal, especially if it is a hardened component and you might be back where you started.

Regards

Gray,

[bernard towersParticipant @bernardtowers37738]

Oxy with satellite?

[Adrian R2Participant @adrianr2]

You could always make up a test rig? 4mm hole in a block to clamp in vice and hold test pins, similar hole in end of a longish bar to apply leverage and and see what you can bend/break? Arm-o-meter should be enough to assess strength for a first pass.

[iansoadyParticipant @iansoady]

Thanks again, hopefully getting there. I’m off to Nametab Engineering who’ve helped me out before. They’re essentially a machine shop but specialise in old motorcycle parts. They will advise re metal spraying – which I hadn’t thought of – vs welding.

I assume Bernard means stellite? (spellcheckers…)

Adrian’s suggestion is good if potentially expensive!

[iansoady]

On iansoady Said:

Many thanks Gray, excellent points. The original (I assume) pin broke rather than bending but both the drill shank and silver steel replacements bent. Both, at 4mm, were a light press fit. I agree re replacing all three so have now removed the pivot pins and pawls. There is a fair amount of visible wear on the pivot pins and the holes in the pawls are (intentionally I assume?) about .010″ larger than the pins and the retaining holes for the pins. This gives a lot of “float” on the pivots.

As you may be able to see all pawls are significantly worn on the face that engages the ratchet, but one (not the one that keeps failing) far more than the others indicating it has taken most of the load.

Advice from the owners’ club experts is to have the worn faces built up with weld which I will need to have done as my welding skills are minimal but I’m sure I can find someone to do it locally. Then I’ll be able to file/grind back to original profile. The pawl material is obviously quite soft.

The operation of the device is that the pins only serve to pull the pawls into engagement with the ratchet attached to the end of the crankshaft and once in contact these should be held in position by the torque from the starter motor until the engine starts when the ratchet spins faster than the starter, pushing the pawls back out so they clear the outer part of the ratchet.

 

Hi Ian,  If you want to consider Grey’s suggestion of Eutectic spraying with a hard facing material I may be able to help, but you need to consider whether any other part of the pawl is hardened ?  with Eutectic it will affect these areas.  The process is very successful and has many applications.  I use it regularly but with a different material but do have some hard facing powder.

Message me with your contact details if interested –I am near Lancaster

John

[iansoadyParticipant @iansoady]

Just reporting back on this – John did a brilliant job in rescuing my damaged pawls. Really saved my bacon there.

 

These are they before John’s attention:

and here after, with all sharp edges restored.

 

I’ve also followed the advice to use hardened and ground dowels for the pins which is working well – so far…… Many thanks to all here.

 

 

 

[southernchapParticipant @southernchap]

There seems to be some not quite correct usage of terms on this thread about strength and toughness (and hardness too):

Here’s a handy little picture I found ages ago that illuminates the difference:

If you look up terms like Youngs Modulus and yield strength (better yet, get Copilot to explain them to you; I did this a few months ago and after a few goes at getting the right questions to get it to expand it’s answers and give me the information at the level I needed, it explained the topic to me rather well), you’ll get a good idea of what you need.

[iansoadyParticipant @iansoady]

For some reason I can’t see the picture.

I do have a general idea of the three variables. In fact when I did my HNC nearly 60 years ago I got a distinction in metallurgy! But have never had cause to use the information which is no doubt in some inaccessible corner of my brain.

These pins have both a bending and shear force on them. They are cantilevered out from the pins shown above and engage with a stack of 3 wavy washers (each about .025″ thick) which are spot welded together. The pins run in arcuate slots in this washer which serve to push the pawls into engagement although there should be no force on them subsequently. So contact between the pins and the slots is a rapid lateral force exerted over a small area. Interestingly the originals had a single washer – the 3 ply one was a later mod.

Taking all this into consideration the pins need to be resistant to wear (hence hardened), resistant to bending (hence need to have high tensile strength) but also need to not be brittle. A tall order.

I have to say that the design is not very well thought out and gives the impression of being rushed into production. One of its major flaws is lack of any means of coping with backfires – most modern systems have slipping clutches of even shear pins.

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