CCing a 2 stroke head

[best]

Just took some picts so thought I'd share:
Just pulled the head on the right off Triplecrowns Blaster, and want to know the CC because it was filed the last time it was installed.

Gathered my tools, not shown is the frosty adult beverage.
Syringe is from the drugstore. They gave me a bunch for free actually. 10cc
The head gasket surface is smeared with a bit of grease and the plate pressed against it.

Head smeared with grease. Notice the odd burn pattern? signs of unbalanced transfer ports.

Plate on, ready to add water:

10cc of water, had to add it twice

There are two ways to do this, either fill it just up to the bottom of the spark plug threads:

Or right to the top of the spark plug threads:

And subtract the difference that fills the threads:

Hardly put a dent in that frosty adult beverage!
That is a reflection of my canoe in the hood of my jeep incidentally...

So to re-cap:
Grease the gasket face, put the plate on
add water up to the bottom of the spark plug threads, there is your measurement.
In case you couldn't see it very well, add more water to the top of the spark plug threads, take measurement
Now take the plate off and dump out the water, flip the head over, plug the top of the sparkplug hole with a greased quarter.
Hill the sparkplug threads with water and take measurement. Subtract thread volume from filled volume. Compare.

Steve

 

[blasterBruce]

Great Write up Best , Lets people know how to do it the simple way First !!

 

[blasterfreek30]

good stuff best...lets sticky this

 

[sporty982000]

Very nice write up. thank You.


Sporty

 

[Surfrjag]

Does this change with different deck heights? How does that work?

 

[best]

Does this change with different deck heights? How does that work?

Deck height of the head or of the cylinder?
Deck height on the head refers to how deep the quench/squish area is sunk in.
Different head deck heights, or decking the head, will drastically affect CC volume.
You compression will change with different cylinder deck heights, but your head volume will not.


It is a bit of a juggle to get the right (0.030"-0.040") squish and the right (150-180) compression.
Typical squish is double or triple those figures so the head needs to come down a lot, but if the head volume starts getting much smaller than 18-20cc, you may not be able to run pump fuel. Neil and I left a fair amount of metal still on the deck of our rechambered heads so that we could progressively file them down to find where maximum usable compression is. We started around 23-25cc on most of the heads and are around 20cc on most of the rechambered heads now.

We did not have so much luck with the stock head, getting detonation when it was lowered 0.040", so be careful out there in Blasterland...

 

[sicivicdude]

Deck height of the head or of the cylinder?
Deck height on the head refers to how deep the quench/squish area is sunk in.
Different head deck heights, or decking the head, will drastically affect CC volume.
You compression will change with different cylinder deck heights, but your head volume will not.


It is a bit of a juggle to get the right (0.030"-0.040") squish and the right (150-180) compression.
Typical squish is double or triple those figures so the head needs to come down a lot, but if the head volume starts getting much smaller than 18-20cc, you may not be able to run pump fuel. Neil and I left a fair amount of metal still on the deck of our rechambered heads so that we could progressively file them down to find where maximum usable compression is. We started around 23-25cc on most of the heads and are around 20cc on most of the rechambered heads now.

We did not have so much luck with the stock head, getting detonation when it was lowered 0.040", so be careful out there in Blasterland...

I'm pretty sure Surfrjag is referring to when someone runs a stroker crank without a spacer plate.

The answer in that situation is a little different. CC'ing the head becomes rather difficult and the method described above ^^^^^^ doesn't work as well for comparing the head volume to one another. The thing to do then is to smear grease around the piston to seal the crown to the cylinder and test the head volume "in situ". You need to turn the motor over to TDC, carefully apply the grease and then assemble the engine nearly completely. Fill the spark plug hole up to the bottom of the hole using a marked syringe (or burette if you have one... ). Once you're done, you remove the head and clean everything off well before continuing on.

Obviously, this is a messy affair and only necessary when comparing heads on the same engine.... comparing two head volumes on two different engines is a exercise in futility as the exhaust port duration comes into play on corrected compression ratio more than head volume (to a certain extent).

This is where combustion chamber design programs come into play. They are the virtual "measuring tool". Basically you can design a head and as long as you can hit the "target" shape, you'll already have the volume figures. Obviously this works much better during the build phase (not so well after the fact)!

 

[B S]

Nice write up...