Author Topic: Bomber crank refurb  (Read 2781 times)

Offline AshimotoK0

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Bomber crank refurb
« on: March 03, 2021, 02:08:13 PM »
My good buddy Graham Curtis just sent me this pic of my rebuilt '67 Bomber crank ... sludge traps totally full of crud but otherwise just needed stripping and cleaning. Evidently the copper coating is part of Honda's original hardening process.

We did a deal where I gave him my three spare cranks I got from Crawley (well 4 actually as I gave him one to 'experiment' on last year  ;D) .... to make me one good one and used the rest for other peoples refurbs.

If you have a pressed-up Honda crank ..Graham is your man.


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“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline Johnwebley

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Re: Bomber crank refurb
« Reply #1 on: March 03, 2021, 03:38:29 PM »
ASH,are the sohc 4 s cranks pressed up?

I know the Z1 is,from watching Allen Millyard.

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Offline Bryanj

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Re: Bomber crank refurb
« Reply #2 on: March 03, 2021, 04:06:17 PM »
Nope cast and ground with shells

Offline Johnwebley

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Re: Bomber crank refurb
« Reply #3 on: March 03, 2021, 04:10:52 PM »
Nope cast and ground with shells
That's what I thought.

It makes it almost impossible to build a 6

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Offline AshimotoK0

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Re: Bomber crank refurb
« Reply #4 on: March 03, 2021, 04:44:33 PM »
my understanding

CB400F ...  CB500/550 /4's , CB750 SOHC's have plain bearing one-piece cranks

Z1 /Z900 cranks pressed -up roller bearing

Z650 Plain bearing one-piece crank

GS550 .. GS750  .. GS1000  crank pressed-up roller bearing   .. so you could make a Suzuki GS825 6 /cyl  from 1.5 GS550 cranks :)
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

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Re: Bomber crank refurb
« Reply #5 on: March 03, 2021, 04:51:04 PM »
"It makes it almost impossible to build a 6"

I believe his replica of the Honda racing 6 is plain bearing construction,  made from combining more than one engine,  but I've not seen what he did to construct the crank.

Usually,  the route would be to get a bespoke unit made and likely a forging or machined from billet. Possibly also derived from welding two crankshaft together if they are welding compatible steel.

Irony there is that the original Honda 250-6 is a push together crank. Apparently they went so far towards small construction that each successive crank pin going in from the outside steps up in size as it has to transmit more torque to the centre location drive train, with the rods bearings etc following in size.  Pretty exotic in design, even now.

Offline AshimotoK0

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Re: Bomber crank refurb
« Reply #6 on: March 03, 2021, 05:01:31 PM »
This is how he designed and built his RC374 6-Cyl replica crank. Genius!

https://www.youtube.com/watch?v=J1cQ098eqF8&t=450s
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

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Re: Bomber crank refurb
« Reply #7 on: March 03, 2021, 05:15:45 PM »
Ooh, that is clever. I thought the original crank  cases (and by default, the bearings) are plain, but hadn't seen how he did that effectively converting to roller bearings.

Very clever chap, but needs to grind his lathe tools better to improve first run finished surfaces  ;D

Offline Johnwebley

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Re: Bomber crank refurb
« Reply #8 on: March 03, 2021, 05:16:09 PM »
This is how he designed and built his RC374 6-Cyl replica crank. Genius!

https://www.youtube.com/watch?v=J1cQ098eqF8&t=450s
Nearly all available on YouTube.

He does use Yamaha engines.

I love his relaxed style.

And his addiction to cup cakes.

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Re: Bomber crank refurb
« Reply #9 on: March 03, 2021, 05:33:23 PM »
Notice he pinned the journals too, to prevent them rotating under torque load.

The original Honda apparently can't be loaded at to low an rpm to reduce the risk of twisting them out of phase, with the rev counter staring at something like 8000rpm ! And useable range above 14000rpm.

Offline Bryanj

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Re: Bomber crank refurb
« Reply #10 on: March 03, 2021, 10:13:56 PM »
There was a time when Z 1000 cranks were welded if going racing, actual seen a Z1000 with 3 pistons level and 1 at top

Offline philward

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Re: Bomber crank refurb
« Reply #11 on: March 04, 2021, 10:30:07 AM »
There was a time when Z 1000 cranks were welded if going racing, actual seen a Z1000 with 3 pistons level and 1 at top

The timing must have been a little out on that Bryan!
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Offline Bryanj

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Re: Bomber crank refurb
« Reply #12 on: March 04, 2021, 04:24:05 PM »
It actualy drove in with a "missfire" mate

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Re: Bomber crank refurb
« Reply #13 on: March 04, 2021, 05:47:30 PM »
He's done a beautiful job on that crank Ash, a real credit to him.

We forgot that in our ramblings  :) it does look particularly good work Ash.

Offline Spitfire

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Re: Bomber crank refurb
« Reply #14 on: March 04, 2021, 07:03:48 PM »
Those videos kept me amused (and amazed) for quite some time, what fantastic work and he does sound so casual about it all.

Cheers

Dennis
1976 CB750F

1977 CB750F2 In bits

1964 BSA A65R In bits

 

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