Rotor puller (OT)

fredintoon

fredintoon

Fred Hill, S'toon.
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bought a 1956 Yamaha 100cc TwinJet that my son is rebuilding for me.
New points and correct timing got it running kinda OK but not altogether reliable.
Symptoms indicated bad crankshaft seals which means a complete engine teardown
to replace them. All apart except we needed a puller to take the rotor off the crankshaft.
Photos show a simple threaded thing that screws into the rotor and pushes it off the
crankshaft. But what thread is it, eh?
M8 is too small, M10 is too big and there ain't no M9.
E-mailed a fellow CVMG member who's had TwinJets for years and he sez:-
Those cunning bastards at Yamaha used an inch-sized thread for that puller.
Sure enough a 3/8"NC bolt threads right in there.
WTF, EH?
 
angus67 said:
Yeah. Funny the 1/2 inch thing with the brake mc too
Click to expand...

Hi angus,
I'd suppose Yamaha used inch-size threads on their extractors in an attempt to keep their
Japanese customers from doing their own repairs?
And OK, you got me. What 1/2" thing on the brake m/c?
Presumably the m/c is on an XS650 because the TwinJet has a massively powerful cable operated 6" sls drum brake on both of it's wheels.
 
MaxPete said:
Very odd - but you might be right about the service issue Fred.
Click to expand...

Hi Pete,
my son speaks metric & Unified as do I plus Whitworth and even so,
Yamaha had both of us fooled until we were told about their thread choice
but once the secret was out all we needed to do was to pick a 3/8-16 UNC bolt out of our fastener stash.
I can well imagine that the average shade tree mechanic in a metric-only country would be totally screwed.
Even if he was told what the thread was, what could he do about it?
 
Some Honda rotors have the same thread dia. and thread as the rear axle, onboard rotor puller at all times. Chain and sprocket teeth have always been imperial sizes. My 650 front brake master cylinder has 5/8 on it from the mold, I think that means 5/8" bore. Tires and wheels were always imperial standards, Firestone standards?

Strange that they even stayed metric after the war, when they were tooled-up with our war time production machines to supply the west with parts and hardware.

Scott
 
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IPT? and there are several variations of THAT! Don't even start on hydraulic and other fitting threads.
Ala the QWERTY keyboard?
 
Never hurd of that Fred !
I had a Yamaha 125cc twin for a while and I had it all apart and I imagine I scrounged around and found a bolt that fit the flywheel and pulled it off and never noticed it ! Uh ! very curious ! .... we had a "Hell box" ( so named because you had to go through hell to find the right bolt in it)
about 2ft wide and 2ft deep and the width of a 2"x6" deep and it was FULL of nuts bolts and doo-hickies.... believe it or not I miss that box now !
HAHAHAHA ! I have no idea what happened to that motor.... the frame I made into my Mom's sidecar.... handlebars went on something and so it goes..... I made another sidecar out of a rear section of a DT1 250cc yamaha frame..... it worked out much better than the other one did
but the Knobby sucked ! HAHAHAHAHA the front forks on my VW trike came from a 1959 Zundapp 200cc.....that worked out ok till I goosed it and it turned sideways and took me through the bob-wire fence !....guess I should'a locked the differential ! HA !
oh well.....
Bob....
 
Spark plug threads are world unto themselves. In spite of a "metric" designation they have their own separate specifications.
 
TwoManyXS1Bs said:
Here's your weekly brain teaser, Fred.
You have almost daily contact with another threadform on your bikes (and cars), that isn't English, Imperial, BS, Whitworth, or Metric.
Ready?
Go...
Click to expand...

Hi 2Many,
another threadform eh?
Not the 60º Vee of Unified & Metric threads or Whitworth's 55º?
How about the rolled threads on lightbulbs?
But no, none of my '84's bulbs or the bulbs in my car are like that.
OK, you got me, I haven't a clue.
 
yah I think spark plug threads too...... their in a world of their own .... I discovered this when making valveless Pulsjets the only nut with the threads that fit a sparkplug are Lugnuts..... believe it or not ! LOL
.....
Bob.....
 
fredintoon said:
...How about the rolled threads on lightbulbs?
Click to expand...

Another good one, Fred. But, no.


Just a silly little trivia challenge.

Born in the 1800's, the era of proprietary thread designs.
Has found ubiquitous, worldwide adoption.
Found on just about every form of transportation, plus others.
Easily overlooked, taken for granted, obviously unobvious.
The greatest holdout after the establishment of thread standards.

xjwmx said:
Tire valve I suppose, ...
Click to expand...

And, xjwmx gets it.

Google: "Schrader valve thread size"...
 
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