Need cylinder head volume help

[Pork Chop]

Hi guys,

I am about to get my xs250 head machined to match the xs400 jugs & piston I just got. I am hoping that some one has the head off their engine or have one lying around that they can measure the volume of the head compression chamber (not sure if that is the right term for it).

I did a basic calculation on engine capacity based on the haynes manual & I am a bit confused.
Bore = 69mm
Stroke = 54mm
Jug volume = 112cc per cylinder
Total jug volume = 224cc
Engine capacity = 392cc
This leaves about 166cc total head volume or 84cc per cylinder

I would really appreciate you guys input on this as I don't want to screw up this part of the build.

Thanks in advance.

Pork Chop

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[Pork Chop]

I just realised my calculations are wrong. I probably shouldn't try & do high school level maths at 6am.

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[xschris]

Ok I filled a chamber and got 22cc That is with the plug and valves in it. I see your block is the square type. Mine are not. I know some models have different compression ratios than others. I would think It would be cheaper to use a 400 head and rocker box than trying to make a 250 work. I have a empty 79 head and matching box bead blasted and ready for guts. But the shipping is like $100

 

[Pork Chop]

Thanks for doing that Chris. 22cc sounds about right based on 400cc with 9.2:1 compression ratio. The 250cc is 9.6:1 so the head volume is only 13cc. Not sure what to do next - I might open up the 250cc jugs and have a look and a think and probably call a head machine shop.

Yeah, shipping stuff to Australia is a bit pricey - shipping the cylinder jugs was $85 and they had to travel over 9,000 miles to get here.!

 

[xschris]

The head I did was 9.3:1 fyi

 

[drewpy]

Thanks for doing that Chris. 22cc sounds about right based on 400cc with 9.2:1 compression ratio. The 250cc is 9.6:1 so the head volume is only 13cc. Not sure what to do next - I might open up the 250cc jugs and have a look and a think and probably call a head machine shop.

if you get a 400 head gasket that will give you something to base the milling on!

 

[Pork Chop]

Good idea Drewpy. I already have a xs400 gasket kit that I got from japan for $35 so I will use that.

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