Topic: 750 combustion chamber cc's

[Don R]

  I did a search on stock combustion chamber CC's and got mixed results but here's what I found, there were a lot of F answers mixed between years.
  300 heads are found at 22/23cc
  Auto 392?  head 23CC a little different chamber shape?
 392 heads 24cc   75/76F and A.
 405? heads 26cc  77/78K but is also listed as 392 in parts fische
 410 heads 28cc.  77/78F 

  There's not a lot of consensus between potential 392 candidates. I always thought a 77/78 K had a bigger chamber.
 

[scottly]

The K7 (and maybe the K8?) used the same 392/24cc head as the early F. Supposedly, the K8 head had a different tunnel for the cam chain, and used a different valve cover and gasket??

[newday777]

The K7 (and maybe the K8?) used the same 392/24cc head as the early F. Supposedly, the K8 head had a different tunnel for the cam chain, and used a different valve cover and gasket??

The valve cover has a different part number but the gasket is the same.

[Don R]

 There's a lot of mixed information out there but when I look at the parts lists for example, the 392 head shows up everywhere that I thought it was used in spite of other information I've read.
 I had wondered if there was a combustion chamber size between the 300 and 410, it appears to be just the 392 which may be a tad bigger. I had read somewhere there was a  26cc head that I thought might be useful to make a decent compression ratio for a turbocharged engine.

[PeWe]

My 392 head has 23.6/23.7cc chambers after the port job, I asked for that volume so chambers must have been smaller.

New guides, Kibblewhite 33.5/28.5 valves and springs.  392 printed upside down.


It is not milled. A very little off to get a scratch free surface for MLS gasket.
I think height is 72.25mm

Bought it on eBay UK. I think it was written as CB750 A head as first model in the description. But who knows.
That seller imports containers of parts and bikes from USA.

The drilled dents is my work for MLS rivets.

[MRieck]

 Early heads had more of a "bathtub" shape which produce a smaller chamber. Later heads were more true hemispherical which improves deshrouding. I recently acquired a sandcast head and there is a notable amount of extra material in that head.....it would work well with 70 to 72mm flat top pistons if you want more compression without a lot of milling. It would benefit from a nice intake deshrouding cut but that's about it. That sandcast head also has quite a bit of rotary tool clean up in the bowl areas.....you don't see that in later stuff.
  That sandcast head I have is for sale too. It is in excellent condition with no corrosion of the guides, seats or exhaust ports. It is being bead blasted and would be perfect for a nice restoration.

[PeWe]

Stock K6 (300) head restored with new guides and not much used CycleX ex valves.

[Tracksnblades1]

My 392 head has 23.6/23.7cc chambers after the port job, I asked for that volume so chambers must have been smaller.

New guides, Kibblewhite 33.5/28.5 valves and springs.  392 printed upside down.


It is not milled. A very little off to get a scratch free surface for MLS gasket.
I think height is 72.25mm

Bought it on eBay UK. I think it was written as CB750 A head as first model in the description. But who knows.
That seller imports containers of parts and bikes from USA.

The drilled dents is my work for MLS rivets.

PeWe,

Is the drill work for “extra clearance” or “required for clearance” for proper head torque without the rivet interfering or becoming captive..?

[PeWe]

My 392 head has 23.6/23.7cc chambers after the port job, I asked for that volume so chambers must have been smaller.

New guides, Kibblewhite 33.5/28.5 valves and springs.  392 printed upside down.


It is not milled. A very little off to get a scratch free surface for MLS gasket.
I think height is 72.25mm

Bought it on eBay UK. I think it was written as CB750 A head as first model in the description. But who knows.
That seller imports containers of parts and bikes from USA.

The drilled dents is my work for MLS rivets.

PeWe,

Is the drill work for “extra clearance” or “required for clearance” for proper head torque without the rivet interfering or becoming captive..?

The MLS rivets will cause problem if the rivets will interfere with the mating surface.
I have hammered them flat but the dents ensure space for them so the head can be tightened and gasket will seal.
My K6 stock head (ported( and cylinder (then 836cc) had a mating surface where rivets are. Noticed that when I used MLS for the first time.
Gasket did not seal when I started to tighten a little. Huge gap. Apart and drilled the dents where the rivets had made marks. Hammered the rivets too.
MLS for 65mm bore has same place for rivets as a 72mm MLS gasket.

My billet block's design avoid the rivets. The mating surface has the same shape as the gasket, not more.

[Don R]

 I hammered the rivets on my 836, I remember afterwards worrying about the layers needing to float a little to compress correctly.