Why does my woodruff key keep breaking?

I'm fairly new to bike restoration so could do with a bit of help.
The bike I'm working on is a 1936 Sokol, which was a Polish knockoff
that is basically a 995cc Vtwin a la Indian combined with Harley front
suspension.
The problem is that the woodruff key on the kickstart keeps breaking.
The engine starts fairly easily with no appreciable kick back. The
advance/retard mechanism of the distributor has been screwed down in
the maximum retard position and will stay like that until I can
fabricate the cable for the manual mechanism.
I'm reluctant to keep on making new keys until I understand why they
keep breaking.

 

SNIP

Could this be the clue? If you have made previous ones are you sure the
dimensions are right? (Do you really mean woodruff rather than cotter pin?)
Also - woodruff keys are usuallt "belt and braces", the primary "locking"
being achived by the mating of tapered surfaces. If the surfaces don't mate
properly then all the stress goes on the key, which may then shear.

 

He's right. Lap your taper bits in with fine grinding paste and then make
sure that your key doesn't interfere with the fit.

Ron Robinson

 

In respnse to the various comments

1. The shaft is not tapered, its parallel.
2. Dimensions are confusing. The groove on the shaft is 5.5mm while the
groove on the gear is nearer 6mm. I have no idea if the difference was
designed in or its just sloppy manufacture.

Regarding material used and manufacturing technique. I used a bit of
angle iron which was the closest to 5.5mm and thus needed the least
grinding down. Also I'm told softish iron is the correct material. it
should break before the shaft.
While grinding into shape I dunked the hot item into cold water so that
I could handle it, did that make it stronger or weaker?

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, sokol

If you got it hot enough, it's quite possible that it will have become
hardened, but very brittle as a result of the rapid cooling. I think
your problem is the material you're using. Use a piece of decent mild
steel, and file it to size.

--
Wicked Uncle Nigel - Podium Placed Ducati Race Engineer As featured in
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Suzuki TS250 "The Africa Single" Yamaha Vmax Honda ST1100 wiv trailer

 

Wouldn't it just be easier to buy one, given the fact you know (or can
work out) the dimensions? At least you'd know it was made of the right
material then, & I can't imagine it would cost more than a couple of
quid at most.


--
Krusty
www.MuddyStuff.co.uk
Off-Road Classifieds

'02 MV Senna '03 Tiger 955i '96 Tiger '79 Fantic Hiro 250

 

For a 1936 Polish bike? Googling for 1936 sokol kickstart woodruff
returned 6 hits. None seem relevant.

--
Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005
WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon)
KotPT -- "for stupidity above and beyond the call of duty".

 

No YTC. Woodruff keys come in standard sizes like bolts.

--
Krusty
www.MuddyStuff.co.uk
Off-Road Classifieds

'02 MV Senna '03 Tiger 955i '96 Tiger '79 Fantic Hiro 250

 

In 1936?

Although there's a solution. RS sell woodruff cutters, so using
an appropriate 6 mm cutter to open out his keyway to match the 6 mm slot
would allow a modern standardised key to be used.

Metric Woodruff Key Kit, incl. 22x9x6 mm key £16.45
Whoops, no 6 mm cutter listed... DIYtools.co.uk has a 22.5x6 mm cutter
for £79.55 -- is that supposed to match a 22 mm key?

--
Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005
WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon)
KotPT -- "for stupidity above and beyond the call of duty".

 

ordinary angle iron is not going to harden significantly, it'll only be mild
steel anyway.

The difference in groove sizes may be related, though. If you're
hand-making it, you can do a special one which is wider at the top than at
the bottom.

 

You can make a stepped key to properly match the keyways, or have the
narrower one machined out.

True. But you then have a slop built in that's going to lead to
breakage. Have you tried Loctite?

It would have hardened it to an extent, and it being a small component
probably embrittled it.

 

To harden steel, you have to a) have the right grade of steel and b) get it
red hot, then quench it. I doubt either applies in this case.

 

Evidently Sokol Motorcycles thought it did.

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, Austin Shackles

Well, it could be any old shite, and on a cross-section that small, I'm
not so sure that hardening wouldn't be an issue.

--
Wicked Uncle Nigel - Podium Placed Ducati Race Engineer As featured in
Performance Bikes

WS* GHPOTHUF#24 APOSTLE#14 DLC#1 COFF#20 BOTAFOT#150 HYPO#0(KoTL) IbW#41
SBS#39 OMF#6 Enfield 500 Curry House Racer "The Basmati Rice Burner",
Honda GL1000K2 (On its hols) Kawasaki ZN1300 Voyager "Oh, Oh, It's so big"
Suzuki TS250 "The Africa Single" Yamaha Vmax Honda ST1100 wiv trailer

 

Thanks to all of you and your input.
In view of the uncertainty of whether I'm using the right material and
also whether my manufacturing is accurate enough, I've decided to try
and buy the damn things.
Now I've just got to find a source.

 

This lot should be able to help : http://www.peterstubs.com/woodruff.html

Steve

 

*Wonderful*