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Author Topic: Best starting point, K or F2?  (Read 2442 times)

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Offline nodrog

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Best starting point, K or F2?
« on: January 17, 2015, 03:00:13 PM »
Hello there people,
I am thinking of building a new classic racing sidecar and am thinking I will probably use a CB750 engine. What would be the best engine to start with, a K or an F2? the F2 has the bigger valves but I have heard the heads are more fragile than the K's. Also is there a high compression (like 12.5.1) 836 kit available for the F2? I have only found 10.1:1 kits. Sorry if these are dumb questions, but I currently race a #$%*ty old Beemer and don't really know much about the Hondas.
cheers.
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Offline bwaller

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Re: Best starting point, K or F2?
« Reply #1 on: January 17, 2015, 04:02:18 PM »
You'd have to change valves and do a seat grind anyway, I'd suggest using a K model and installing larger valves in that head. There are a ton of go-fast options available including better than OEM primary chains. Consider undercutting the gearbox too especially with the extra weight of the chair. It's not a cheap proposition, but it sounds like fun already.  Good Luck.
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Offline MRieck

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Re: Best starting point, K or F2?
« Reply #2 on: January 17, 2015, 05:47:57 PM »
Quote from: bwaller on January 17, 2015, 04:02:18 PM
You'd have to change valves and do a seat grind anyway, I'd suggest using a K model and installing larger valves in that head. There are a ton of go-fast options available including better than OEM primary chains. Consider undercutting the gearbox too especially with the extra weight of the chair. It's not a cheap proposition, but it sounds like fun already.  Good Luck.
Brent is right....start with the K.
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Offline Old Scrambler

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Re: Best starting point, K or F2?
« Reply #3 on: January 17, 2015, 07:28:53 PM »
If your plan is to start with a stock frame............I would source a CB750A frame so you retain the original strength but will be able to remove the head IN THE FRAME for any motor work. Search for BEAR on this site...............he has a winning chair in Australia but no longer trusts himself to compete. BIG power.
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Offline nodrog

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Re: Best starting point, K or F2?
« Reply #4 on: January 17, 2015, 10:52:26 PM »
Thanks for the quick replies. Do the K heads fit the F motors?
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JWExperience

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Re: Best starting point, K or F2?
« Reply #5 on: January 17, 2015, 11:35:42 PM »
They may work with the f0-f1 but definately don't swap with the later f bikes. Different oil routings. The early motors were closer to the k's from what I've read but I would also get more info from more experienced guys on here. It's on this site too, shouldn't take too long to find it in the search.
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Offline bear

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Re: Best starting point, K or F2?
« Reply #6 on: January 18, 2015, 01:25:59 AM »
Correct me if I'm wrong but you blokes are restricted to 836cc?
If that's the case go with a K.
On another note, I have a mate that has just retired and will have his outfit up for sale shortly.
If you would like some details PM me.
It's a good bit of gear.

Cheers,
Brian
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Offline bear

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Re: Best starting point, K or F2?
« Reply #7 on: January 18, 2015, 01:35:42 AM »
Quote from: Old Scrambler on January 17, 2015, 07:28:53 PM
If your plan is to start with a stock frame............I would source a CB750A frame so you retain the original strength but will be able to remove the head IN THE FRAME for any motor work. Search for BEAR on this site...............he has a winning chair in Australia but no longer trusts himself to compete. BIG power.

No A's south of the equator Dennis. ;)

Cheers,
Brian
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Offline nodrog

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Re: Best starting point, K or F2?
« Reply #8 on: January 18, 2015, 10:56:36 PM »
Quote from: bear on January 18, 2015, 01:25:59 AM
Correct me if I'm wrong but you blokes are restricted to 836cc?
If that's the case go with a K.
On another note, I have a mate that has just retired and will have his outfit up for sale shortly.
If you would like some details PM me.
It's a good bit of gear.

Cheers,
Brian

Na there is no 836cc restriction, I think that's the UK. Our current classic rules are non Japanese but we are currently changing that. I would just be looking to go to 836cc at this stage, I was impressed with how fast Terry Gays rig was when he brought it over.

I'll flick you a PM.

cheers
Gordie
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Offline bear

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Re: Best starting point, K or F2?
« Reply #9 on: January 20, 2015, 06:01:01 PM »
That's the one, he's a regular top three finisher over here. ;)

Cheers,
Brian
« Last Edit: January 20, 2015, 06:03:49 PM by bear »
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Offline nodrog

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Re: Best starting point, K or F2?
« Reply #10 on: January 20, 2015, 08:42:53 PM »
Quote from: bear on January 20, 2015, 06:01:01 PM
That's the one, he's a regular top three finisher over here. ;)

Cheers,
Brian

cheers mate, have PM'd you.
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Offline bear

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Re: Best starting point, K or F2?
« Reply #11 on: January 21, 2015, 11:27:40 AM »
I'd love to see that little yellow "Jelly Bean" head across the Tasman, It's been annoying the piss out of me for years. ;D

Cheers,
Brian
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Offline kmb69

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Re: Best starting point, K or F2?
« Reply #12 on: January 21, 2015, 01:01:13 PM »
Come on Brian, tell us how you really feel about it?  ??? :-\ ;)
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Offline nodrog

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Re: Best starting point, K or F2?
« Reply #13 on: January 24, 2015, 08:06:23 PM »
Quote from: bear on January 21, 2015, 11:27:40 AM
I'd love to see that little yellow "Jelly Bean" head across the Tasman, It's been annoying the piss out of me for years. ;D

Cheers,
Brian

I'm trying to help you out, but it seems Terry's a bit slow on the email front. The suspense is killing me.
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Offline bear

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Re: Best starting point, K or F2?
« Reply #14 on: January 27, 2015, 03:52:54 PM »
He's a bit of a Ludite I'm afraid.
I'll poke him with a stick for you.
I wouldn't be surprised if he is having second thoughts.
He has put a lot of work and development into that bike and it' a credit to him.
A genuine 100hp at the rear wheel from an 836 is not to be sneezed at.

Cheers,
Brian.
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