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Cast iron head #757902
12/02/18 11:20 pm
12/02/18 11:20 pm
Joined: Dec 2013
Posts: 360
Australia
C
Charlieboy Offline OP
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Charlieboy  Offline OP
BritBike Forum member
C

Joined: Dec 2013
Posts: 360
Australia
G'day all,
Just wondering if an M20 head can be fitted to an M21 ?
My M21 has an alloy head with a few broken fins and I have a cast iron M20 head in good nick ... I'm thinking that the Cast Iron head would would make for a quieter engine too ..

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Re: Cast iron head [Re: Charlieboy] #757911
12/03/18 12:03 am
12/03/18 12:03 am
Joined: Aug 2014
Posts: 1,851
OZ
Triless Offline
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Triless  Offline
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Joined: Aug 2014
Posts: 1,851
OZ
Charley, after 1938 the M20 and M21 had the same 82mm bore, and I have seen headgaskets for both under the same P/N, so I'd say from '38 on the heads are interchangeable !

Re: Cast iron head [Re: Charlieboy] #757916
12/03/18 12:36 am
12/03/18 12:36 am
Joined: Dec 2013
Posts: 360
Australia
C
Charlieboy Offline OP
BritBike Forum member
Charlieboy  Offline OP
BritBike Forum member
C

Joined: Dec 2013
Posts: 360
Australia
Cheers mate ... thanks for that .. hope all's well for you down there

Re: Cast iron head [Re: Charlieboy] #757919
12/03/18 1:34 am
12/03/18 1:34 am
Joined: Oct 2007
Posts: 1,562
Auckland NZ
Ignoramus Online content
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Ignoramus  Online Content
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Joined: Oct 2007
Posts: 1,562
Auckland NZ
the m21 has a longer stroke than the m20 to get the bigger cc..........heads should be a straight change , but the iron head will run a little hotter , something you might want to consider in Australia


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: Cast iron head [Re: Charlieboy] #757938
12/03/18 8:56 am
12/03/18 8:56 am
Joined: Dec 2013
Posts: 360
Australia
C
Charlieboy Offline OP
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Charlieboy  Offline OP
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C

Joined: Dec 2013
Posts: 360
Australia
Thanks Ignoramus ( I'm sure you're not wink ) ...yes, running hotter is something to consider and I have thought about it ...
I'm not at all fond of Summer and neither are my Bikes ...

Re: Cast iron head [Re: Charlieboy] #758085
12/04/18 10:25 am
12/04/18 10:25 am
Joined: May 2004
Posts: 4,017
Sydney Australia
B
BSA_WM20 Offline
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BSA_WM20  Offline
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Joined: May 2004
Posts: 4,017
Sydney Australia
Yep if you are running the std carb, do not turn the engine off unless you are going to be there for an hour or more.
The head gets hot enough to boil off fuel making them next to impossible to start hot.


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Trevor
Re: Cast iron head [Re: Charlieboy] #758088
12/04/18 10:52 am
12/04/18 10:52 am
Joined: Dec 2004
Posts: 9,965
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,965
Scotland
Its a side valve, so no rockers or valves in the head to be either quieter or noisier, get a better alloy head.


Moderated by  Allan Gill, Jon W. Whitley 

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