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Author Topic: Which 836 kit do I have?  (Read 1849 times)

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Offline karmasevo

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Which 836 kit do I have?
« on: June 07, 2011, 12:31:00 PM »
First I apologize but I am a bit of a newb. Been buying new bikes my whole life and finally decided to start building my own stuff. I bought a 1974 CB750 last week. Has an 836 kit in it and runs awesome!. Issue is that the guy I bought it from did not do the 836 kit. It was the guy before him. He has no idea what pistons were used and therefore what compression ratio the pistons are. what is the easiest way for me to figure out the compression ratio of the engine as it sits. I want to do head work, lighten the crank, ect. But would like to know where I am starting from. Thanks in advance for the help.
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Offline Sam Green Racing

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Re: Which 836 kit do I have?
« Reply #1 on: June 08, 2011, 03:54:09 AM »
Welcome Karma, you won't really know till you pull it down. If it runs well on pump gas, chances are the pistons are around 10 to 1.
Post some pictures of them plus any markings that might be on them.

Sam. ;)
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Offline turboguzzi

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Re: Which 836 kit do I have?
« Reply #2 on: June 08, 2011, 07:19:06 AM »
Quote from: SamCB750A on June 08, 2011, 03:54:09 AM
Welcome Karma, you won't really know till you pull it down. If it runs well on pump gas, chances are the pistons are around 10 to 1.
Post some pictures of them plus any markings that might be on them.

Sam. ;)
"untill you pull it down"?
Sam, from you, the HiPo master? :)

Place piston nr 4 at TDC, valves closed, lean the bike pretty far on it side (rest on an old matress or something soft and thick), take a burret to measure the quantity of oil needed to fill the combustion chamber till the plugs thread.  ((836/4)+CC volume) /CC volume = CR

TG
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Offline Sam Green Racing

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Re: Which 836 kit do I have?
« Reply #3 on: June 08, 2011, 08:47:14 AM »
Ever so sorry Yossef, I'm tired and didn't read it properley :-[. Thought he wanted to know the comp of the pistons. ::)

Sam. ;)
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C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
CB92
RS 175. sprint/land speed bike
JMR Racing CB750A street ET drag bike

Offline karmasevo

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Re: Which 836 kit do I have?
« Reply #4 on: June 09, 2011, 12:43:37 PM »
Quote from: SamCB750A on June 08, 2011, 08:47:14 AM
Ever so sorry Yossef, I'm tired and didn't read it properley :-[. Thought he wanted to know the comp of the pistons. ::)

Sam. ;)


Wow, That doesn't sound tough at all. Thanks a ton!
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Offline Tintop

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Re: Which 836 kit do I have?
« Reply #5 on: June 09, 2011, 04:42:14 PM »
Easy yes, but make sure you get the oil back out before you try turning it over.  Otherwise you will get a hydraulic lock, and bent parts.
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Offline turboguzzi

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Re: Which 836 kit do I have?
« Reply #6 on: June 10, 2011, 05:45:10 AM »
Quote from: karmasevo on June 09, 2011, 12:43:37 PM
Quote from: SamCB750A on June 08, 2011, 08:47:14 AM
Ever so sorry Yossef, I'm tired and didn't read it properley :-[. Thought he wanted to know the comp of the pistons. ::)

Sam. ;)


Wow, That doesn't sound tough at all. Thanks a ton!

now that you are wiser, do some search on "measuring compression ratio" and sure, dont forget to suck the oil out from that piston!!!

Have a look at pics of the underside of a 750's head to understand better which way to tilt the whole bike so you trap the least amount air while you are measuring
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Offline karmasevo

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Re: Which 836 kit do I have?
« Reply #7 on: July 05, 2011, 02:01:10 PM »
will do thanks a lot to both of you. Sorry it took me so long to respond. I just got back into country a couple of days ago. Thanks again!
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