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Author Topic: CB 750 BIG BORE 836cc  (Read 958 times)

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Offline olasek18_18@o2.pl

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CB 750 BIG BORE 836cc
« on: November 29, 2018, 07:51:49 AM »
Hi everyone
I want to re-drill my CB 750 on 836cc,
Should I change the camshaft, valves, or carburetors?

IS it possible to align it without changes in the cylinder head?

Any suggestions?

Thank You Guys
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Offline Prospect

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Re: CB 750 BIG BORE 836cc
« Reply #1 on: November 29, 2018, 07:57:27 AM »
Hi 

Yes, you can bore out the cylinders to 836cc without changing the rest of the engine or carburetors.  Make sure a good reputable shop does the boring and get the clearance correct. 
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1971 CB750K1
1972 CB750K1
1975 CB400F
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Offline madmtnmotors

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Re: CB 750 BIG BORE 836cc
« Reply #2 on: November 29, 2018, 09:06:40 AM »
It depends. The 836 pistons up to a 10.25 CR (Compression Ratio) should be okay but if you up the game to 12.25 CR then you will want to check valve to piston clearances carefully (good practice even at 10.25 CR). At the 12+ CR I would recommend stronger rods as well.
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Offline PeWe

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Re: CB 750 BIG BORE 836cc
« Reply #3 on: November 29, 2018, 09:41:09 AM »
The higher CR 10.25/10.5-1 need a cam with more overlap than stock, right? This reduce the dynamic compression less hot and risk for pinging
Porting the head is recommended when refurbish the valves and seats.  Use stock valves if they are OK. Mild cam as webcam 41 can use stock springs.
More fun with next step of cam and stronger springs.
My 836 with 80-83 rwhp (depending on cam) ran fine with stock rods.
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