BIRCO Commando Head

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phillyskip

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While recently repairing my 750 Commando that swallowed a single carb interior manifold bolt I noticed that my cylinder head has BIRCO stamped on it. My head also has a "C" stamped on the center top of the rocker area. It doesn't have the typical identification markings over the right hand rocker area.

I'm guessing my bike has an aftermarket head,and if so, are they any good compared to a stock 73 750 head? Thanks,PhillySkip
 
Birco is the foundry ( should be on your cylinder too) that made them. "C" in the middle for Combat. OEM Combat head.
 
phillyskip said:
I noticed that my cylinder head has BIRCO stamped on it. My head also has a "C" stamped on the center top of the rocker area. It doesn't have the typical identification markings over the right hand rocker area.
Click to expand...

A Combat head doesn't normally have the "RH" number stamp.

http://atlanticgreen.com/nhth.htm

If your Commando is a '73 then it may not be the original head, but who knows?
 
Thanks much for your help. This poses another set of issues. With a "Combat" head what head gasket should I be using for normal road work? I have been using a flame ring type. BTW the serial numbers on the engine cases indicate my bike started as a 73.
 
Normal flame ring gasket is fine. You'll need to re-torque frequently in the beginning.
 
batrider said:
Normal flame ring gasket is fine. You'll need to re-torque frequently in the beginning.
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You're right there! I was amazed at how loose the head bolts got.

I've since been told a trick is to torque them up 5lbs over standard and that allows for the natural crushing that takes place.

I have not tried it though!
 
L.A.B. said:
phillyskip said:
I noticed that my cylinder head has BIRCO stamped on it. My head also has a "C" stamped on the center top of the rocker area. It doesn't have the typical identification markings over the right hand rocker area.
Click to expand...

A Combat head doesn't normally have the "RH" number stamp.

http://atlanticgreen.com/nhth.htm

If your Commando is a '73 then it may not be the original head, but who knows?
Click to expand...

Anyone know what the 'RH' designation stands for, if anything?
 
Fast Eddie said:
batrider said:
Normal flame ring gasket is fine. You'll need to re-torque frequently in the beginning.
Click to expand...

You're right there! I was amazed at how loose the head bolts got.

I've since been told a trick is to torque them up 5lbs over standard and that allows for the natural crushing that takes place.

I have not tried it though!
Click to expand...

Funny you should mention that.
I had a flame ring blow out within the first hundred miles. I had torqued to spec.
So next one I started out 5 pounds over and when I went to retorque it didn't need any more than was already there.
Been about 4,000 miles since with no problem.
 
phillyskip said:
Thanks much for your help. This poses another set of issues. With a "Combat" head what head gasket should I be using for normal road work? I have been using a flame ring type. BTW the serial numbers on the engine cases indicate my bike started as a 73.
Click to expand...

The Combat head was a standard one with 0.040" machined off to raise the compression to 10/1 from the standard 9/1.
In conjunction with larger 32mm carbs and ports and hotter 2S cam it gave what the factory claimed 65hp at 6,500 rpm.
Since your bike is a 73 and Combats were only made in 72 if your engine serial number matches the gearbox the head although a Combat probably won't have the 2S cam ment to optimize its potential. But for regular spirited riding the standard cam is very good whereas the 2S gives its performance at rpms most won't want to use for regular riding.

If concern for pinging at 10/1 or maybe even fear of blowing head gaskets you have an option to put a compression plate under the barrel to lower it.
I got an aluminum one from OldBritts for my Combat that I believe was 0.024".
However the PO may have already done that so look very closely at the base of your barrel and you may be able to see it.
 
Would not recommend the 5 ft-lbs over the torque limits especially for the 5/16" small studs in the front. This last head job I was pretty religious about it and retorqued at 5, 20, 50, 100, 500 and 1000 miles. It didn't need much of anything at 1000 miles. (It can be done with the tank on too.)

There is no need to detune a Combat IMO. My head gasket has never "blown" but I did have a head oil leak when the bike was a few months old. If it had been retorqued I don't think it would have happened.

Russ
 
phillyskip said:
Thanks much for your help. BTW the serial numbers on the engine cases indicate my bike started as a 73.
Click to expand...
So your serial number begins with 22XXXX? Does the bike have the deep black instrument cups and large square taillight?
 
My bike is a late 72 by the serial number and build date. However, the title says it is a 73. I don't think it was unusual that a bike that was left over and sold during the next model year ended up being titled a year later.
 
htown16 said:
My bike is a late 72 by the serial number and build date. However, the title says it is a 73. I don't think it was unusual that a bike that was left over and sold during the next model year ended up being titled a year later.
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You are correct about left over models getting titled the following year. So if it's a late '72 it may or may not have a double S camshaft from the factory. If the combat head was original it would have come with this cam. If it has a standard cam, I recommend from experience to use the spacer to lower compression.

Other than the BSA, I like your stable of machines. Used to be BMW R100RS as second bike in the 80's. I'm seeing a few of us with XL1200R now. One of the club members asked me if I was going to trade off the Commando in favor of the Sportster. No, but it is fun from a raw power standpoint.
 
A Combat cam is the 2S type.

The SS type cam started back in the early 1960s with the SS dommies,
and continued on - as the standard cam - into the Commando series.

hopethishelps.
 
My bike's frame ,engine,and gearbox number is 212387. but titled as a 73. I suspect that my head and "S" cam are not standard but I don't know enough about Nortons to say.
 
phillyskip said:
My bike's frame ,engine,and gearbox number is 212387. but titled as a 73. I suspect that my head and "S" cam are not standard but I don't know enough about Nortons to say.
Click to expand...

Combat 2S camshafts are supposed to be stamped 'SS' (not to be confused with the SS camshaft).
According to the NOC figures, '1972' production ran from 200001 - 216000 however, according to Roy Bacon's Norton Twin Restoration book, '1973' begins at 212278.
 
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