B12 dot head and cams but what carbs?

[wraith]

11 hours ago, MeanBean49 said:

If that was the case why wouldnt the OEM make the head like that in the 1st place?

Because the bandit (first post at the top) was a down tuned motor not a race motor  and if we all just put only OME items made for that bike or experience named bits for that model on are bikes there would not be a OSS it would be SOC instead 

OSS thinking outside of the box 

[Duckndive]

1 hour ago, clivegto said:

What is going on with those inlets on the top one ?

The top ones been skimmed 

[clivegto]

5 minutes ago, Duckndive said:

The top ones been skimmed 

Look closer no rubber inlets for carbs is what I see.

[Duckndive]

4 minutes ago, clivegto said:

Look closer no rubber inlets for carbs is what I see.

Yes I noticed that but it was not the question  or was it

Edited January 30, 2019 by Duckndive

[Sandman]

56 minutes ago, MeanBean49 said:

Yeah, i said they had same valve size earlier. 750 and 1100 dont have the same bore size though.

The projected area of the combustion chamber for the DOT head and the skimmed 1100 head are almost identical, so what you are writing do not make sense to me.

[Oilyspanner]

I think this has gone off topic !   A dot head will work well, or a skimmed 1157 head will work well. The dot head on a B12 engine works nicely as has been said   - quite a few dot heads have a crack/cracks in the inlet/exhaust divider, this is very rare in 1052/1127/1157 heads, it's thicker on the big bikes heads. If you bump up the comp. a touch on the 1157 head it'll give  similar results to a dot head - the dot head has slightly raised inlet floor too, it helps open up the circumference of the inlet valve a touch. If you skim the head the check the piston to valve clearance and squish clearances, there's more scope on the big engine's head - as has been said, be very careful if you're thinking about skimming the dot head.

I recognise that head with the revised inlet tracts and exhaust spigots, it had larger valves and a shit load of port work done on it  the port floor was epoxied too - it was a drag bike's head - not much in common with a standard head. . . . 

You don't want sharp edges in the chamber or on piston crown, I think Dunc meant not to have a big radius on the edge of the squish area, just smooth the edge. Some valve de-shrouding reaps rewards too, it makes the most of the valve's size.

I'm only a keen amateur who wishes he had some of the machining and welding skills of some of the other members on here !

Keep us up to date though 

[dupersunc]

I modified the combustion chambers on my dot head to suit the 79mm bore. basically I opened up the chamber around the valves to allow them to flow better. the larger bore allows you to do this. Doing this retained the large squish area , but reduced the cr slightly(though still more than a stock 1157), which may be a good thing if you go for  after market pistons.

Best of both worlds.

 

Edited January 31, 2019 by dupersunc

[Svsam]

So 36 carbs are good for now until I want to chase big power. Thanks for everyone's input. Interesting reading about the dot head cons. But I think it's a good start. 

I also read somewhere that I'll need to put the 750 oil pan and pick up on the b12 engineer it to fit the 750 frame, is this correct? 

 

Thanks again

(this forum is awesome!)

[Captain Chaos]

oil pan + pick-up swap is done for exhaust header clearance (if needed), not to fit a certain frame.

[zulishanti]

Sorry to resurrect but wanted to add info for people researching this like I was.

The diagram bean drew is exaggerated, makes sense, but is also biased toward the case of using the bandit head over the dot.

I am looking at both cylinder heads as I type. It's impossible to capture in pictures but easier to measure and post. The B12 combustion chamber offsets into the bore by about 2mm all around. The difference between the dot and B12 chamber diameters are about 4mm so you can say the dot offset will be 4mm around.

The pros and cons of a squish band around the bore (versus a squish pad like between the intake and exhaust valves) is another story. Neither the Bandit nor the dot heads line up perfectly with the bore.

On the other hand, if you take the Bandit head and skim it, the diameter will get smaller. The only way it wouldn't would be to imply that there is a section of the chamber where the walls are vertical, which doesn't exist.

The major difference between the chambers is as mentioned, the depth. Skimming the bandit head will obviously make it shallower but it will also shrink the diameter leading to enlargement of the squish band, NOT what was drawn in the illustration.

Aside from that data, as far as I know having a squish "band" is not a bad thing at all. How much of a band is something that I haven't looked much into.

Just wanted to clear that whole thing up as I have both heads sitting in front of me.

Edited April 19, 2022 by zulishanti
Better verbage to clarify intent of language