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#305494 - 03/29/10 9:45 pm Combustion chamber volumes  
Joined: Feb 2008
Posts: 23
British Bike Guy Offline
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British Bike Guy  Offline
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Posts: 23
atlanta, ga
What is the consensus for the combustion chamber volume on the average unadulterated (not milled) cylinder head for a:
750 Norton Commando Head (not combat)?
850 Norton Commando Head?

Sorry one more.
On a stock bike with stock pistons.
How far out from the deck is a 750 stock cast piston??
How far down from the deck is an 850 stock cast piston??

Thanks all
Mark

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#306126 - 04/02/10 1:01 pm Re: Combustion chamber volumes [Re: British Bike Guy]  
Joined: Feb 2008
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British Bike Guy Offline
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British Bike Guy  Offline
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atlanta, ga
With all of the Norton hot rods out there, can any of the guru types help me out with this.

Mark

#306155 - 04/02/10 4:37 pm Re: Combustion chamber volumes [Re: British Bike Guy]  
Joined: Dec 2004
Posts: 8,893
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,893
Scotland
The NOC Commando Service Notes covers all the permentations of heads (there's a lot of variations not just std and combat) and Compression Ratios, you can work backwards from the swept volumes.

http://archives.jampot.dk/Book/Workshop_manuals/Norton_750cc_Service_Notes.pdf

PS its Easter so things are a bit slow.

#306188 - 04/02/10 7:44 pm Re: Combustion chamber volumes [Re: British Bike Guy]  
Joined: Nov 2009
Posts: 2,049
Peter R Online content
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Peter R  Online Content

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Posts: 2,049
Netherlands
For a stock 750 Commando (CR 9:1)the calculated combustion chamber volume works out as 46.5 cc.
For a stock 850 emgine (CR 8.5:1) this will be 55.2 cc

As stated by the above posting, there are several variations.
The only reliable way to verify the combustion chamber volume is by holding the engine in a position with the spark plug hole uppermost, and pour liquid in the cylinderhead with a burette.

Sorry I do not know the answer to the second part of your question.


Peter.
1974 Commando 850
1972 Trident T150T
1961 Goldie DBD34
1969 Benelli 250 sport special
#306237 - 04/03/10 1:28 am Re: Combustion chamber volumes [Re: Peter R]  
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dave - NV Offline
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dave - NV  Offline
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Elko, Nevada USA
If you are doing accurate calcs of chamber volume for compresh, with the head off the engine, you must measure. Make a plexi cover for the head that's sealed with grease on the edges with a hole in the middle and fill the chamber with water.
I use a low cost 60cc medical syringe vs a messy/expensive burett to acurately measure the water needed to fill the chamber.

The largest variable to deal with when calculating static compression is accurately measuring the volume of your piston crown. I have a proven accurate procedure used by engine builders for many years. I will Email a copy. Ask.

Last edited by dave - NV; 04/03/10 1:33 am.

dave - NV
#307165 - 04/08/10 2:42 pm Re: Combustion chamber volumes [Re: dave - NV]  
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Posts: 1,253
Dave Comeau Offline
Crew Chief
Dave Comeau  Offline

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Joined: Aug 2001
Posts: 1,253
Hamilton, Mass. USA
Doing these heads is a pain, since I have to pull the head studs to get the domed acrylic disc to seat over the chamber.
The 850 measured 50cc almost on the money. This RH10 head might not be a full depth chamber.
The 68-70 06-0380 750 is original but had a little carbon in the chamber and on the valves and also read 50CC.
You may get further variation on top of that due to different valve head profiles.


dynodave
BSA 3 1961-1963
Ducati 3 1992-2002
Norton many 1951-1975
87 Serv-Equip 100HP MC brake dynamometer,

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