C R Head Skim

[fatstig1 0]

good day to everyone.

the question ?

can the experts, on the forum, put me out of my misery (lol) with the answer to this problem.

how much needs to be skimmed off the cyl head of an standard xu5ja,in order to increase the cr to 11:1 ?

using a payen gasket with 1.2mm compressed height.

engine balanced,dizzy set .

know how to get cr,just dont know how to calculate the amount of material that needs to be skimmed off in order to reduce the cc in the

combustion chamber.

thanks in advance.

[2052NV 24]

Mate this is a "how long is a piece of string question"

 

What you need to do is calculate ACCURATELY the compression ratio of your engine by using this method.

 

https://www.oldbritts.com/calc_cr.html

 

You must do a CC measurement of the combustion chamber as no one knows if the head has been skimmed before or who has done what in the past etc etc. Then using the calculations work out what the CC of the combustion chmaber needs to be to achieve 11.1 compression. It sound a bit scary but its really not very hard

 

If you dont have the tools dont fret the engine shop that was going to skim your head will no doubt be able to work this out for you.

 

Cheers

[fatstig1 0]

yes,thanks for that,robert.

i know that i have to reduce the combustion chamber by 5cc to get to the cr that i need.

i was hoping that someone had been through this process,and knew the correct measurement needed for a decrease in chamber volume per cc,ie; 1 thou =0.5cc.

 

the only alternative i see is, to skim then measure,skim and measure,etc.

thanks.

[petert 589]

Can't answer directly, but the maximum amount you can take off is 2mm. Don't forget to elongate the engine mount.

[jdt 6]

std head 34.5cc 0.75mm off head = 3.5cc 2mm = 9.33cc 1mm =3.75cc

 

Some info I have recorded, not guaranteed to be 100% accurate but not far away.

Buy a burette and you can measure your own cc

Sunken valves (from seats being recut and valves being refaced) make a huge difference so you really need to measure your own cc

Edited July 23, 2014 by jdt